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Disturbance history and historical stand dynamics of a seasonal tropical forest in western Thailand
Ecological Monographs
Abstract
Disturbances influence forest dynamics across a range of spatial and temporal scales. In tropical forests most studies have focused on disturbances occurring at small spatial and temporal scales (i.e., gap dynamics). This is primarily due to the difficulty of reconstructing long‐term disturbance histories of forests in which most tree species lack annual growth rings. Consequently, the role of past disturbances in tropical forests is poorly understood. We used a combination of direct and indirect methods to reconstruct the historical disturbance regime and stand development patterns in mature and regenerating seasonal dry evergreen forest (SDEF) in the Huai Kha Khaeng Wildlife Sanctuary in western Thailand. Direct estimates of long‐term establishment and growth patterns were obtained from 12 tree species that form annual growth rings as a consequence of the region's strong intra‐annual rainfall seasonality. Indirect estimates of establishment patterns were obtained from analyses of stand structure and individual tree architecture and application of age‐estimation models to 10 dominant canopy‐tree species using demographic data from a large‐scale, permanent forest‐dynamics plot.
The combination of direct and indirect methodologies revealed a complex disturbance history in the seasonal evergreen forest over the past 250 years. In the mid‐1800s, 200–300 ha of forest were destroyed by a catastrophic disturbance, which led to the synchronous establishment of many of the trees that presently dominate the forest canopy. Since then widespread disturbances of variable intensity have occurred at least three times (1910s, 1940s, and 1960s). These disturbances created discrete temporal pulses of establishment in small to large gaps in the forest matrix across several square kilometers. Background mortality and gap formation were evident in every decade since 1790, but these varied in intensity and frequency.
The SDEF retains a distinct structural and floristic legacy from the catastrophic disturbance of the mid‐1800s. The single‐age cohort that established after the disturbance has developed a complex three‐dimensional structure as a consequence of differences in interspecific growth patterns of the canopy‐tree species and subsequent disturbances of moderate and low intensity. While no single methodological approach provided a complete picture of the disturbance history and stand development patterns of the seasonal evergreen forest, taken together they offered new insights into the long‐term dynamics of a primary tropical forest. In particular, the study highlighted the role of disturbance at multiple spatial and temporal scales and varying intensities in determining the structure and composition of a complex, species‐rich tropical forest and raises important questions about the role of rare, catastrophic events on tropical forest dynamics.
... Trees were sampled in a 50-ha forest plot (15º40′ N, 99º10′ E) in the Huai Kha Khaeng Wildlife Sanctuary in west-central Thailand, at an altitude of approximately 600 m a.s.l. (Baker, Bunyavejchewin, Oliver, & Ashton, 2005). Mean annual rainfall is approximately 1,500 mm with a dry season between November and April. ...
... Five tree species were selected that were reported to form annual growth rings and dominate the forest community by basal area or frequency (Baker et al., 2005) (Nock et al., 2009). Afzelia, Melia and Toona are deciduous, Chukrasia is brevi-deciduous, and Neolitsea is evergreen (Williams, Bunyavejchewin, & Baker, 2008). ...
... Afzelia, Melia and Toona are deciduous, Chukrasia is brevi-deciduous, and Neolitsea is evergreen (Williams, Bunyavejchewin, & Baker, 2008). Afzelia, Melia and Toona are categorised as shade intolerant pioneer species, Chukrasia from shade intolerance to moderately tolerant, and Neolitsea as shade tolerant (Baker et al., 2005). ...
1. Wood serves for mechanical support, water transport and storage. These functions are provided for by different cells with a large variation in wood anatomy among species but also within individual trees. The latter often reflects ontogenetic adjustments , related to tree size or age, which can be studied by looking at patterns of radial variation in wood. 2. We quantified radial variation in wood density (WD) and wood anatomy and ask how ontogenetic changes of wood functions are controlled in five canopy tree species in western Thailand. We ask if there are trade-offs between these main functions of wood, how ontogenetic trends are linked to differences in growth trajectories and shade tolerance among tree species and if wood properties are mainly controlled by tree age or by size. 3. In all species studied, vessel fraction, vessel size, theoretical hydraulic conductivity (K h) and fibre wall thickness significantly increased with tree diameter. While the ray fraction also increased in all species except Neolitsea, axial parenchyma changed significantly only in Afzelia, the species with by far the largest axial parenchyma fraction. The average WD and K h reflect the phenology, with deciduous and shade-intolerant Toona and Melia having low WD and high K h , and shade-tolerant brevi-deciduous Chukrasia and evergreen Neolitsea having higher WD and low K h. Deciduous Afzelia, however, had the lowest K h and second-highest WD. The radial gradients in WD and K h also reflect within-species differences in growth rates during ontogeny. 4. The relationship between WD and its underlying anatomical components varied substantially among species. Modulating fibre wall thickness and vessel size enables growing trees to increase water transport capacity and mechanical strength at the same time. Across species, tree diameter had a stronger effect than age on all parameters except for fibres. 5. Given the very substantial within-tree size-related variation in wood traits, tree size is an essential parameter to include in comparative studies on the functional ecology of wood. Analysing ontogenetic changes in wood can advance our understanding of the different ecological strategies of trees.
... Growth ring boundaries are distinct and characterized by a marginal parenchyma band (Vlam et al., 2014b) ( Fig. 2.1C). Annual growth-ring formation has been confirmed by a cambial wounding experiments (Baker et al., 2005) and previous tree-ring studies (Vlam et al., 2014b). ...
... Approximately 80 % of our sampled trees were synchronized successfully and the derived chronology contains a strong common signal (mean EPS = 0.87). Furthermore, growth ring formation in our species has been confirmed to be annual by a cambial wounding experiment in a seasonally dry evergreen and mixed deciduous forest in Thailand (Baker et al., 2005) with a similar climate seasonality as in our study site. Distinct climate seasonality with a marked dry season (monthly rainfall < 100 mm) for at least five months triggers the formation of annual growth rings in tropical deciduous and semi deciduous trees (Gentry, 1995;Graham and Dilcher, 1995;Worbes, 1999;Pucha Cofrep et al., 2015). ...
... The remote location for sampling and the scattered distribution of the C. tabularis, the length of the borer and our sampling strategy might have constrained the age of the collected trees. Notwithstanding the absence of a concrete record of maximum age, Baker et al. (2005) reported some individuals of C. tabularis that established between 1880 and 1890 in a seasonal tropical forest in Western ...
Increasing atmospheric CO2 and subsequent changes in climate have been recognized as the drivers of changes in forest dynamics across the major forest ecosystems around the world. Tropical forests which play a critical role in the global biogeochemical cycles and livelihood subsistence of millions of people have been affected by global change phenomena. Several large scale studies have already provided evidence that forest structure, composition, above- and below-ground biomass and carbon storage of tropical forests have changed in tropical regions due to global environmental changes. Yet, tree growth and physiological processes and their driving forces and mechanisms in different tropical forest ecosystems are not yet adequately understood. Particularly, tree growth at the individual and at the species level and physiological responses of moist tropical forest species are strongly understudied but an utmost important field of research in a global change context. In this thesis, we studied growth and physiological responses of South Asian tropical forest trees to elevated CO2 and climate change using a combination of approaches, including dendroclimatology, stable isotope analysis and modelling. We focused our research on three species from two nature reserves of Bangladesh. We tested whether ring-width chronologies within a site and between sites contain common environmental signals and if climate sensitivity of tropical moist forest trees has increased over time. Furthermore, we modelled tree radial growth responses until the end of the current century for different representative concentration pathways (RCPs). We also tested if drought resilience differs between ecologically contrasting tree species and explored the long-term trends in tree growth and stable carbon isotope based physiological parameters including intrinsic water-use efficiency (iWUE). Finally, we disentangled the relative contributions of climatic variables and atmospheric CO2 in explaining iWUE variability in three tropical moist forest tree species. Statistical parameters like the expressed population signal (EPS) and other chronology statistics of the individual site chronologies and a regional chronology and a strong synchronization between the site chronologies of the three species provide strong evidence of a strong common climate forcing. Climate-growth analysis revealed that temperatures in the early growing season (March-April) strongly negatively affected radial growth in our studied species. Tree radial growth was also negatively influenced by October precipitation and Niño 3.4 region sea surface temperature (SST) anomalies. The inverse relationship between tree radial growth with temperatures in the early and later growing season is most likely linked to the higher evapotranspiration outside of the main monsoon season. An increase in temperature particularly during the hot and dry pre-monsoon season (early growing season) further increases water stress, resulting in tree growth decline. We found that radial growth sensitivity to climate was higher in the recent decades (1986-2015) than the period 1950-1985, likely because trees actively responded to higher temperatures, increasing frequency of droughts, and a prolonged dry season in the recent decades. During previous droughts, tree growth was reduced by 44-56 % depending on the drought events and species. Based on the climate-growth relationships, tree radial growth was predicted to decline by nearly 20 % under RCP 8.5, irrespective of the tree functional type. Growth resilience to drought also differed between species. Tree hydraulic behavior, shade tolerance and radial growth of two years before and after the drought years were found to be linked with tree drought tolerance. A synthesis of published data on long-term trends in tree growth and carbon isotope based physiological parameters across the tropics revealed a general increasing trend in intercellular CO2 concentration (Ci) and intrinsic water-use efficiency (iWUE), while carbon isotope discrimination (Δ13C) remained nearly constant. However, increasing iWUE did not stimulate tree growth in the tropics, probably because negative impacts of changing climate on tree growth have overridden the small positive impacts of rising atmospheric CO2, which was also reflected in our study species. In our study sites, inter-annual variability in iWUE was triggered mainly by temperature variations, whereas long-term iWUE trends were shaped by the elevated atmospheric CO2 concentration. Our findings provide strong evidence that dendrochronology can be successfully applied in South Asian tropical moist forest trees to answer a variety of ecological and physiological questions in a global change context. Tree growth and the associated ecophysiological processes and mechanisms should be in the focus of future research because the carbon sequestration potential of tropical forests is increasingly at risk due to reduced tree growth across the tropics.
... Studies scaling from the individual to the community can also help us build models and describe underlying mechanisms of succession and recovery Meiners et al., 2015). Turnover dynamics research has found idiosyncratic transient conditions between communities (Baker et al., 2005;Barlow et al., 2016;Ding et al., 2012;Osazuwapeters et al., 2015) and that coexistence of many forest types within a succession sequence can be ascribed to the differences in disturbance regimes (King, 2003;Sheil, 2001). Furthermore, natural vegetation succession has been found to occur both spontaneously and with artificial measures after the disturbance is removed, which tends to increase the carbon sequestration ability of secondary forests and lead ecosystems to new equilibrium states (King, 2003;Osazuwapeters et al., 2015). ...
... The succession and recovery dynamics of secondary forests have been a focus of debate in restoration ecology (Baker et al., 2005;Huang et al., 2015). Disturbance events can cause changes in forest light, nutrient, and water conditions, and therefore affect plant recruitment, growth, and mortality. ...
An important indicator of forest dynamics is the forest community turnover rate, which was defined as the relative change in a variable of interest (e.g., basal area or stem abundance) to its maximum or total in the community over a certain period. Community turnover dynamics in part explain the community assembly process and give insights for understanding forest ecosystem functions. Here, we assessed how anthropogenic disturbances (shifting cultivation, clear cutting) affect turnover relative to old growth forests in a tropical lowland rainforest. Using two censuses over 5 years of twelve 1-ha forest dynamics plots (FDPs), we compared turnover dynamics of woody plant, then analyzed the influencing factors. We found that community turnover dynamics of FDPs that experienced shifting cultivation were significantly higher than those experienced clear cutting or no disturbance, but little difference between clear cutting and no disturbance. Stem mortality and relative growth rates were the highest contributors to stem and basal area turnover dynamics of woody plants, respectively. Both stem and turnover dynamics of woody plants were more consistent by the dynamics of trees (DBH≥5 cm). Canopy openness, as the most important drivers, was positively correlated with turnover rates, while soil available potassium and elevation were negatively correlated with turnover rates. We highlight the long-term impacts of major anthropogenic disturbances on tropical natural forests. Different conservation and restoration strategies should be adopted for tropical natural forests experienced different disturbance types.
... For tropical dendrochronology, if there was a "previously held view" that tropical trees were unreliable, a novel understanding has given way to the insight that, with effort, some species can be "successfully crossdated and used" (e.g., Baker et al., 2005;Buckley et al., 1995Buckley et al., , 2005Buckley et al., , 2007aBuckley et al., , 2007bBuckley et al., , 2010Buckley et al., , 2014Buckley et al., , 2016D'Arrigo et al., 1997D'Arrigo et al., , 2011Pumijumnong et al., 1995;Pumijumnong & Wanyaphet, 2006;Pumijumnong & Eckstein, 2011;Sano et al., 2009Sano et al., , 2012Stahle et al., 2011Stahle et al., , 2012Therrell et al., 2006;Zuidema et al., 2013, as cited in Buckley et al., 2016. According to Buckley et al. (2016), "the most robust Southeast Asian records have been developed from the Fokienia hodginsii of the family Cupressaceae." ...
... This proved to be a crucial step for all ensuing analyses due to the complex ring anatomy and growth irregularities that made crossdating difficult in these cores. The absolute dating of growth rings in trees is arguably the most important step in dendrochronology (Baker et al., 2005). In the case study where locally absent rings and "false" rings are minimal, the error might be marginally consequential to ensuing climate analyses). ...
Dendrochronology deals with the time and dating of special events on tree rings. Today, dendrochronology has become an increasingly important study field given its broad and multidisciplinary nature based on the studies of dating, verification, and reconstruction of past climate and environmental events as well as the study of tree growth patterns and archaeological restoration. This paper is based on a combination of methods of which the Dating of Trees—Tree Assessment for Heritage (TreeAH) is a key one before giving some suggestions on how to better promote eco-tourism areas in the way that can help preserve traditional cultural values, develop tourism, and promote the conservation of forests simultaneously. In particular, the study takes place in the case of Tay Giang District in Quang Nam Province, Vietnam (where have Fokienia Hodginsii (local name is Po-mu)) to understand the relationship between dendrochronology for labeling heritage trees there and the development of eco-tourism in the direction of "Green Tourism" toward sustainable economic development in Tay Giang, Quang Nam. A total of 40 Fokienia hodginsii trees in the Fokienia hodginsii forest population have been date. Those trees have the longest and shortest ages, equivalent to 675 and 123 years (as of 2021). Weighted linear/nonlinear methods were applied for modeling regressions of tree-ring age and diameter. Then, we have labeled more than 700 trees as heritage trees in the area based on this relationship equation. Based on study finding, we suggest to do Fokienia hodginsii forest-based eco-tourism as an effective way to foster green tourism as well as economic development in the study area.KeywordsDendrochronologyTree ringsHeritage treesGreen tourismVietnam
... We used a two-parameter Weibull function to numerically describe forest plot diameter distributions. A two-parameter Weibull distribution function is the most widely applied function for modelling tree size distributions (Baker et al., 2005;Zhang et al., 2001). The two parameters of the Weibull function are shape and scale. ...
... First, we pooled data from all plots experiencing low to moderate, high, or very high-severity disturbances prior to fitting a Weibull function to those disturbance category pools. Second, to evaluate the influence of disturbances on the shape of forest plot diameter distributions, we fit a two-parameter Weibull function to observed diameter distribution (Baker et al., 2005;Coomes and Allen, 2007) using the 'WeibullR' package in R (R Core Team 2019). We visually analyzed differences in DBH distribution shapes across stands and landscapes prior to analyzing variability among regions with a Dunn test using the "FSA" package in R. ...
Natural disturbances strongly influence forest structural dynamics, and subsequently stand structural heterogeneity, biomass, and forest functioning. The impact of disturbance legacies on current forest structure can greatly influence how we interpret drivers of forest dynamics. However, without clear insight into forest history, many studies default to coarse assumptions about forest structure, for example, whether forests are even or unevenly aged. The aim of this study was to analyze the effects of past disturbances on the current diameter distributions of Norway spruce (Picea abies (L.) Karst.)-dominated landscapes throughout the Carpathian Mountains. Our dendroecological dataset comprises tree cores from 339 plots (7,845 total tree cores), nested within 28 primary forest stands, known to vary greatly in the severity of historical disturbances. Our analyses revealed that historical disturbances had a strong and significant effect on the current diameter distribution shapes at the plot level. We demonstrated that mixed-severity disturbance regimes were more frequent and create a complex pattern of diameter distributions at the plot and stand scale. Here, we show that high severity disturbance was associated with unimodal diameter distributions, while low and moderate severity was associated with the reverse J-shaped distribution. This is a result of complex disturbance patterns, with structural biological legacies. Our results will have important management implication in the context of tree size heterogeneity, biomass storage, and productivity as influenced by natural disturbances. Lastly, these results demonstrate that structural changes may arise as consequences of changing disturbance regime associated with global change.
... For instance, Johnson and Dearden (2009) found that fire introduced into SEDF resulted in a transition to MDF or DDF, whereas work undertaken by Bunyavejchewin (2009) andBaker et al. (2008) showed that SEDF was resilient to fire introduced into the system during the 1982e1983 and 1997e1998 El Niño events. This appears to hold true over longer time periods, with Baker et al. (2005) demonstrating SEDF resilience to pulses of disturbance in the 19th and 20th century. To date, there has been limited research that explicitly examines the response of forest to changing hydroclimatic conditions in mainland south-east Asia. ...
... The pollen record from Yeak Mai indicates that in edaphically drier settings, rapidly regenerating, secondary forest taxa (Cannabaceae/Euphorbiaceae) e i.e. those facilitating recovery e are critical for forest maintenance when the landscape is subject to moderate, consistent fire activity, and moderate levels of hydroclimatic stress. The role of pioneer gap recruitment in facilitating post-disturbance forest recovery within SEDF and MDF has been established over shorter time scales (decades to centuries) in Baker et al. (2005) and Baker and Bunyavejchewin (2017). However, when these stressors are amplified (as is the case for Yeak Mai between 2240 and 1700 cal yrs BP), recovery and resistance traits associated with DDF forest taxa (as interpreted from the increase in DDF/MDF surface pollen signatures e i.e. heightened AP:NAP, and stability of Terminalia and Dipterocarpus across this time zone) become important for maintaining forest resilience (Fig. 7). ...
Tropical forests are the most biodiverse terrestrial ecosystems on earth, yet are particularly susceptible to future climatic and human-induced change. Identifying tipping points at which tropical ecosystems will reorganise is therefore an important research goal. Limited research within the seasonally dry tropical forests of south-east Asia means that much uncertainty exists around the resilience of these systems to future global change. This is a critical research gap because these forests should – given their physiognomic attributes, current bioclimatic envelope and the range of stressors – be very sensitive to a stable-state shift to savanna. Here we adopt a palaeoecological approach to examine the interaction between key drivers of change (decreased precipitation and heightened fire activity) and forest response over ∼4700 years though interrogation of sediment-based proxies from volcanic crater lakes within north-east Cambodia – in the core range of southeast Asia’s tropical dry forests. Our results suggest that rapidly regenerating, secondary forest taxa are important for maintaining a forested state when the landscape is subject to moderate fire and climatic disturbance. However, when these stressors are amplified, recovery and resistance traits associated with key deciduous dipterocarp forest taxa appear critical for forest stability. Notably, shifts from more closed, seasonal evergreen forest formations to more open secondary/deciduous dipterocarp formations appear reversible when the stressors are removed, suggesting that these transitions are not analogous with the difficult-to-reverse, forest-to-savanna stable state shifts that occur elsewhere in Neotropical and Afrotropical settings. Our results indicate that the resilience of south-east Asian forests to climatic forcing appears contingent on the maintenance of secondary forest, deciduous forest, and seasonal evergreen dry forest mosaics across the ecoregion. This has implications for the conservation and wise-use of mainland south-east Asia’s lowland dry forests.
... Tropical forests, in contrast, are extremely diverse, have relatively short histories of observation, and few tree species with annual growth rings for dendroecological analyses. This has severely constrained even the most basic understanding of the role of fire disturbances on tropical forests (Baker et al., 2005, Zuidema et al., 2013. In this study we used direct observations of mortality in a large-scale, long-term forest dynamics plot that experienced a fire to estimate both fine-grained spatial variability in disturbance intensity and species-specific differences in susceptibility to fire. ...
... However, only a small area of the plot experienced all three fires, so the average fire return interval will be considerably longer across most of the plot. In one of the only reconstructions of disturbance history from a tropical forest, Baker et al. (2005) working in and around the HKK plot found evidence of four moderate disturbance events during the period 1890-1985. These were consistent with the directly observed mortality patterns associated with the 1998 ENSO-driven fires and imply a firereturn interval over the 20th Century of ∼23 years. ...
Increasing temperatures and human activity are likely to reduce fire return intervals in the seasonal tropics. Anticipating how more frequent fires may alter forest community structure and composition requires understanding how fire intensity and species‐specific responses to fires interact to drive fire‐induced mortality for large numbers of species. We developed an analytical framework to estimate unobserved fire intensities and species‐ and size‐specific susceptibility to fire using observed mortality data.
We used census data from a 50‐ha forest dynamics plot in western Thailand to better understand species and community responses to a fire that burned ∼60% of the plot in 2005. Trees species, size and status (live, dead) were censused just before the fire (2004) and again 5 years later (2009). We jointly estimated a map of relative fire intensity and species‐specific size‐dependent background and fire‐induced mortality. We then calculated the time required for individuals of each species to reach a fire‐safe size threshold (the age at which the fire‐induced mortality probability was <50%). To better understand community‐level responses to fire, we compared results among different species groups (canopy status, forest‐type association).
Our model‐derived map of fire intensity closely matched the field survey taken in the days after the fire. On average, individuals growing at the 95th percentile growth rate for most species groups required ∼5 years to reach their species’ fire‐safe size threshold, while individuals growing at the median growth rate required ∼17 years (assuming growth <1 cm diameter at breast height was similar to growth >1 cm). However, understorey species associated with the seasonal evergreen forest took 1.8 times longer than average to reach their fire‐safe size threshold, with one species requiring up to 190 years.
Synthesis. Our approach provided insights into spatial patterning of fire intensity in a seasonal tropical forest and species‐ and size‐specific susceptibility to fire‐induced mortality. Our results suggest increasing fire frequency will have the greatest impact on slow‐growing understorey species of the evergreen forest. In addition, our model accurately predicts the growing dominance of a fast‐growing understorey species, Croton roxburghii; Euphorbiaceae, common to evergreen and deciduous forests that can reach its fire‐safe size threshold in 1.3 years.
... Asimismo, la información sobre los regímenes de incendios pasados puede ser una referencia útil para comprender las características, los patrones y las características de la estructura forestal actuales y futuros del régimen de incendios. Los cambios en la estructura de un bosque y, en consecuencia, en su dinámica pueden ser examinados mediante técnicas dendrocronológicas que nos permiten documentar fechas de establecimiento y mortalidad de los individuos, los patrones de crecimiento radial y la frecuencia y magnitud de los disturbios (Fritts & Swetnam, 1989;Baker et al.,2005;Amoroso et al.,2017). Las técnicas dendrocronológicas permiten inferir patrones y procesos por períodos más prolongados que los resultantes de estudios regulares de monitoreo ecológico y con una resolución precisa a escala anual. ...
... Even trees established in the canopy can undergo sudden changes in growth when they benefit from intensified management (Caetano Andrade et al. 2019). This reveals the enormous potential that this species has for investigating forest disturbances, as has been done by Baker et al. (2005), linked not only to human management, but to other factors such as extreme weather events (i.e., floods, droughts), and blowdowns that occur stochastically in the Amazon (Marra et al. 2014). In addition, disturbances related to severe climate conditions showed a remarkable reduction in diameter growth for a Brazil Nut population in Central Amazonia in the 1860s (Caetano- Andrade et al. 2019), which might be the result of pluriannual drought conditions, shown by tree-ring based reconstruction of precipitation (Granato-Souza et al. 2019, 2020. ...
The Brazil Nut tree ( Bertholletia excelsa , Lecythidaceae) is a species of considerable historical, economic and ecological importance in South America. Radiocarbon dating indicates some individuals can live from hundreds to more than 1000 years, which means they have the potential to reconstruct deep time growth patterns and their relationship to anthropogenic management or climate change from pre-colonial to present times. However, age estimates vary considerably amongst trees dated with different methods (i.e. tree-ring analysis, radiocarbon-dating, and repeated diameter measurements). Here we analyze living Brazil Nut trees growing in four distinct regions across the Brazilian Amazon using two dating methods: tree-ring counting and radiocarbon dating. Our results show that the congruence between the two methods varies amongst regions, and the highest congruence is found at the site of Tefé, Amazonas. This region features archaeological sites with anthropogenic Terra Preta soils, and is known for its long-term human forest management. This management likely enhanced light and nutrient availability, which possibly enabled the trees to grow at higher rates and form annual rings. Our findings highlight the need for better understanding of the growth of Brazil Nut trees for ecological research, but also the potential of dendrochronology for exploring climate change and human-forest interactions in the Amazon Basin.
... pnas.org forest and savanna, higher δ 13 C in the combined lowland and upland records within the range of seasonal forest (SI Appendix, Fig. S2), in combination with the lack of widespread grassland signatures evident in regional pollen records, probably reflects expansion of seasonally dry forest in the lowlands and, potentially, the encroachment of some seasonal elements into the montane zone (Fig. 6). This interpretation aligns with shorter-term ecolog ical (57,58) and late-MIS 2 and Holocene palaeoecological obser vations (32,54) demonstrating the role of seasonally dry tropical forest in supporting forest recovery and resistance to drier climates and fire. Our interpretation of a MIS 2 seasonal forest corridor in the lowlands reflects the original, more tempered classifications of savanna corridor vegetation (9,12) and underscores the impor tance of incorporating mixed vegetation types into analyses of palaeoenvironmental δ 13 C in Asia and the global tropics. ...
The dominant paradigm is that large tracts of Southeast Asia’s lowland rainforests were replaced with a “savanna corridor” during the cooler, more seasonal climates of the Last Glacial Maximum (LGM) (23,000 to 19,000 y ago). This interpretation has implications for understanding the resilience of Asia’s tropical forests to projected climate change, implying a vulnerability to “savannization”. A savanna corridor is also an important foundation for archaeological interpretations of how humans moved through and settled insular Southeast Asia and Australia. Yet an up-to-date, multiproxy, and empirical examination of the palaeoecological evidence for this corridor is lacking. We conducted qualitative and statistical analyses of 59 palaeoecological records across Southeast Asia to test the evidence for LGM savannization and clarify the relationships between methods, biogeography, and ecological change in the region from the start of Late Glacial Period (119,000 y ago) to the present. The pollen records typically show montane forest persistence during the LGM, while δ13C biomarker proxies indicate the expansion of C4-rich grasslands. We reconcile this discrepancy by hypothesizing the expansion of montane forest in the uplands and replacement of rainforest with seasonally dry tropical forest in the lowlands. We also find that smooth forest transitions between 34,000 and 2,000 y
ago point to the capacity of Southeast Asia’s ecosystems both to resist and recover from climate stressors, suggesting resilience to savannization. Finally, the timing of ecological change observed in our combined datasets indicates an ‘early’ onset of the LGM in Southeast Asia from ~30,000 y ago.
... The difference between the two simulations reflected the net effect of historical Ca increase on tree growth in our model. Historical disturbance events such as storm and fire can also shape the sampling distribution and growth patterns in tree rings (Baker et al., 2005;Vlam et al., 2017) and model simulations. However, the exact timing and magnitude of those disturbances were unknown and thus could not be included in model simulations and we used a constant disturbance rate of 0.5% ...
The strength and persistence of the tropical carbon sink hinges on the long‐term responses of woody growth to climatic variations and increasing CO 2 . However, the sensitivity of tropical woody growth to these environmental changes is poorly understood, leading to large uncertainties in growth predictions. Here, we used tree ring records from a Southeast Asian tropical forest to constrain ED2.2‐hydro, a terrestrial biosphere model with explicit vegetation demography. Specifically, we assessed individual‐level woody growth responses to historical climate variability and increases in atmospheric CO 2 (C a ). When forced with historical C a , ED2.2‐hydro reproduced the magnitude of increases in intercellular CO 2 concentration (a major determinant of photosynthesis) estimated from tree ring carbon isotope records. In contrast, simulated growth trends were considerably larger than those obtained from tree rings, suggesting that woody biomass production efficiency (WBPE = woody biomass production:gross primary productivity) was overestimated by the model. The estimated WBPE decline under increasing C a based on model‐data discrepancy was comparable to or stronger than (depending on tree species and size) the observed WBPE changes from a multi‐year mature‐forest CO 2 fertilization experiment. In addition, we found that ED2.2‐hydro generally overestimated climatic sensitivity of woody growth, especially for late‐successional plant functional types. The model‐data discrepancy in growth sensitivity to climate was likely caused by underestimating WBPE in hot and dry years due to commonly used model assumptions on carbon use efficiency and allocation. To our knowledge, this is the first study to constrain model predictions of individual tree‐level growth sensitivity to C a and climate against tropical tree‐ring data. Our results suggest that improving model processes related to WBPE is crucial to obtain better predictions of tropical forest responses to droughts and increasing C a . More accurate parameterization of WBPE will likely reduce the stimulation of woody growth by C a rise predicted by biosphere models.
... Ecologists have long recognized that disturbances and recovery processes overlap in both spatial and temporal dimensions [6] and [7]. Accordingly it might not be possible to identify clearly the nature of vegetation response to particular disturbance regimes, even if we have access to paleoecological data and historical information on land use and disturbance events [8]. ...
-Sudanese natural forests have become an easy alternative source of income to the majority of rural population, especially in the Blue Nile state, where the presence of such forests and better transportation facilities provide good encouragement. The main reasons contributing to the severe impact on the natural forests are partly due to the general economic instability in the country which could partly be related to poor returns from agricultural activities and to fluctuating weather conditions. Accordingly, and in their attempts to seek for alternative source of income, people have added to their traditional demands of house hold forest products an additional demand of charcoal mass production. Such new demand put additional impacts on these types of forests and drastically disturbs their natural dynamics. This paper aims to assess the diversity and dynamics of tree species in these natural forests and investigate the possible disturbing factors influencing forest regeneration, recovery and dynamics. The study was conducted in El Nour natural Forest reserve of the Blue Nile state, Sudan. The specific objectives were to quantify the changes in species composition and structure, assess the potential causal factors so as to maintain sustainable forest productivity. Our results have indicated that the dynamic and succession of the forest species are positively favour less than 40 % of the total species native to the forest, while the majority are struggling to survive the next few years before complete disappearance from the forest. Acacia seyal followed by Balanites aegyptiaca in the northern part of the forest, and Combretum hartmannianum in the middle of the forest were found to be the pioneer species although are heavily cut for production of firewood and charcoal. The major forces driving the disturbance of the mother trees in the forest were found to be illicit felling, while those influencing natural regeneration were overgrazing and the lengthy dry season before the next rains. Weak forest management system and lack of official wills to acknowledge and support the needed fundamental reforms were found to play their role. Moreover, the concerned local communities lack economic and other incentives to play an active role in the *Correponding author conservation or sustainable utilisation of the forest due to lack of or insecure user rights and privileges.
... The construction of such models usually relies on forest inventory data or panel data extracted from tree rings. Analysis of tree species growth patterns based on tree ring series provides important insights into their ecology and dynamics, such as information on growth rates and long-term growth changes (Baker et al. 2005 As a widely planted arti cial tree species on the Tibetan Plateau, Pinus tabuliformis often appears in the form of pure pine forests and plays an important role in mitigating climate change (Niu et al. 2022). At present, little scienti c and systematic empirical research has been conducted on the carbon sequestration effects of the near-natural transformation of pure coniferous forests on the Tibetan Plateau. ...
Many qualitative studies have found that mixed conifer–broadleaf forests provide higher ecological benefits than monoculture forests, and the demand for mixed forests is increasing. However, the carbon sequestration benefits of artificial mixed forests remain unclear. In particular, considering specific growth characteristics of plantation trees and capturing the dynamic changes in carbon sequestration over time are necessary. Using 456 tree disks for dendrochronological analyses, we established a dynamic growth model for the carbon stock of Pinus tabuliformis under three afforestation modes in the eastern Tibetan Plateau. Based on the fundamental growth model, nonlinear fixed-effect (NLFE) models with specific parameter combination constraints were established to improve model stability. Compared with other models, the NLFE model based on the Weibull equation, which uses the model parameters n and z as classification parameters, was the optimal model. This model was used to evaluate the potential contribution of afforestation modes to the growth of carbon stock in individual P. tabuliformis trees over 100 years and to predict the carbon sequestration benefits of mixed and pure forests. Conifer–broadleaf forests can bring lower initial returns but higher long-term returns than the other two afforestation modes, and such forests can store more carbon. In addition, this study provides a feasible method for establishing a carbon stock growth model with minimal sample damage as well as evaluation methods and basis for large-scale pure forest transformation and management strategies.
... The changes in gap disturbance patterns are related to features that act both at coarser (e.g., forest age) and finer scales (e.g., slope) [76]. However, some studies suggest that dissimilarities between the gap disturbance and gap size frequency distribution within a forest may be encountered [79][80][81][82][83]. Concerning the distribution of gap fillers with altitude, we obtained a weak correlation, like the findings of [84], which state that altitude did not influence gap fillers. ...
The interest to assess the relationship between forest gap characteristics and topography features has been growing in the last decades. However, such an approach has not been studied in undisturbed mixed sessile oak-beech old-growth forests. Therefore, the present study carried out in one of the best-preserved sessile oak-beech old-growth forests in Europe, aims to assess the influence of topographic features (slope, altitude and aspect) on (i) some characteristics of canopies and expanded gaps (surface, diameter and perimeter) and (ii) the proportion of beech and sessile oak as bordering trees, gap fillers and gap makers. Through a complete gap survey on an area of 32 ha, 321 gaps were identified and mapped. The largest gaps and also the highest gap frequency (140) was found in the slope class (15.1-20°), while the gap frequency increased with altitude, with 99 gaps being recorded at 601-650 m a.s.l. The size and perimeter of the canopy and expanded gaps, as well as the number of gap makers, were negatively related to the slope and altitude. The expanded gap to canopy gap size ratio decreased with the slope and was positively related to the altitude, while a significant negative decrease in gap filler density with altitude was encountered. The sessile oak participation ratio as bordering trees forming the gap increased not only with the altitude but also with the slope. The topography plays an important role in the formation of gaps as well as in the characteristics of the future stand. This study provides valuable insights into the relationship between canopy gap characteristics and topography, which is useful information for forest owners that pursue the design of forest management toward nature-based solutions.
... The evaluation of disturbance patterns and successional development in forests is commonly done through tree-size distributions, based on the diameter of the stem at 1.3 m (d) or total height (h) (Goff and West, 1975;Lorimer and Krug, 1983;Donoso et al., 1985;Baker et al., 2005;Zenner, 2005;Müller-Landau et al., 2006;Coomes and Allen, 2007;Wang et al., 2009). Moreover, foresters and forest ecologists have used the diameter/age distribution in a stand to reflect its general structural attributes, such as cohort structure and vertical/horizontal complexity (Tyrrell and Crow, 1994;Zenner, 2005;Fajardo and Alaback, 2005;Soto et al., 2010;Esse et al., 2021). ...
Climate is a critical variable in determining the productivity and structural complexity of forest ecosystems. Under similar temperature regimes and other site conditions, precipitation becomes fundamental for forest regeneration and growth, and eventually for the development of structural complexity and patterns in forest productivity. Empirical quantification for this expected response to varying precipitation is needed, especially to provide conservation and management strategies under current and future climate change impacts. To address this need, we evaluated the effects of varying annual precipitation regimes (dry, mesic, and humid sites; all with similar temperature regimes) on three key forest attributes and processes; 1) size and age structure, 2) tree spatial point patterns, and 3) forest stand productivity based on the normalized difference vegetation index (NDVI), in three old-growth lenga (Nothofagus pumilio) forests in western Patagonia. Tree-size and age structure were irregular in the humid and mesic sites, and regular (unimodal) in the dry site (based on Weibull probability function). The relationship between tree diameter and age was strongest in the humid site (r² = 0.86), and weakest in the dry site (r² = 0.36). Forest stand productivity was significantly higher in the humid site (mean NDVI = 0.73, vs. 0.68 and 0.63 in the mesic and dry sites, respectively). Univariate spatial-point patterns showed that the humid site had the strongest clumped pattern for live trees along all distances analyzed (i.e., 20 m), while the dry site had a fully random pattern for live and dead trees along all distances analyzed. Collectively, these results illustrate different challenges for silviculture in these forests: 1) The multi-aged structure, plus clumped spatial patterns of small trees (following partial overstory disturbance) in the humid and mesic sites, reflect a gap-based regeneration mode, which consequently suggests the feasibility of implementing uneven-aged silviculture in these sites; 2) Dry sites, close to the forest-steppe ecotone (dry, cool and windy) may require a focus on silviculture for adaptation to cope with expected declines in precipitation and to potentially avoid the loss of these ecosystems to woodlands; 3) Dieback of larger trees in mesic sites (presumably due to xylem cavitation) is a reflection of climate change impacts and a warning to implement strategies that may adapt these forests to new climate conditions (transition to dry condition). Consideration of the great variation in structure and productivity in Patagonian lenga forests due to differences in precipitation regimes, is urgently needed to guide the development of site-specific management approaches for this forest type, particularly given expected future declines in precipitation.
... Deciduous forests can be found throughout the tropics, including continental Southeast Asia [1,2]. Unlike other tropical forests, these deciduous forests have a distinct and long dry period (5-6 months) almost every year [3]. ...
Forage plants, as primary producers, play an essential role in maintaining populations of large herbivores. The availability and quality of these forage plants can affect the health and viability of these animals. Seasonally dry forests of Huai Kha Khaeng Wildlife Sanctuary and Huai Thab Salao-Huai Rabum Non-Hunting Area are recognized as one of the largest contiguous pieces of forests in mainland Southeast Asia and serve as a home to many large herbivore species, particularly banteng (Bos javanicus birmanicus). However, our understanding of forage plants and their dynamics is still limited. Therefore, the current study was undertaken to understand the dynamics of forage plants, prescribed burning effects, and the associated environmental factors. During 2018–2019, the results showed that the highest forage availability was in June after the prescribed burns at 156.2–252.6 kg ha−1 and the lowest in February before the burning at 16.8–39.8 kg ha−1. Environmental factors that impacted the forage availability include canopy cover, tree density, tree basal area, soil bulk density, soil pH, and topography. However, the impacts of these factors varied among the studied plant life forms, suggesting the importance of active habitat management through prescribed burns and stand improvement to maintain sufficient forage for large herbivores in the future.
... Ecologists have long recognized that disturbances and recovery processes overlap in both spatial and temporal dimensions [6] and [7]. Accordingly it might not be possible to identify clearly the nature of vegetation response to particular disturbance regimes, even if we have access to paleoecological data and historical information on land use and disturbance events [8]. ...
-Sudanese natural forests have become an easy alternative source of income to the majority of rural population, especially in the Blue Nile state, where the presence of such forests and better transportation facilities provide good encouragement. The main reasons contributing to the severe impact on the natural forests are partly due to the general economic instability in the country which could partly be related to poor returns from agricultural activities and to fluctuating weather conditions. Accordingly, and in their attempts to seek for alternative source of income, people have added to their traditional demands of house hold forest products an additional demand of charcoal mass production. Such new demand put additional impacts on these types of forests and drastically disturbs their natural dynamics. This paper aims to assess the diversity and dynamics of tree species in these natural forests and investigate the possible disturbing factors influencing forest regeneration, recovery and dynamics. The study was conducted in El Nour natural Forest reserve of the Blue Nile state, Sudan. The specific objectives were to quantify the changes in species composition and structure, assess the potential causal factors so as to maintain sustainable forest productivity. Our results have indicated that the dynamic and succession of the forest species are positively favour less than 40 % of the total species native to the forest, while the majority are struggling to survive the next few years before complete disappearance from the forest. Acacia seyal followed by Balanites aegyptiaca in the northern part of the forest, and Combretum hartmannianum in the middle of the forest were found to be the pioneer species although are heavily cut for production of firewood and charcoal. The major forces driving the disturbance of the mother trees in the forest were found to be illicit felling, while those influencing natural regeneration were overgrazing and the lengthy dry season before the next rains. Weak forest management system and lack of official wills to acknowledge and support the needed fundamental reforms were found to play their role. Moreover, the concerned local communities lack economic and other incentives to play an active role in the *Correponding author conservation or sustainable utilisation of the forest due to lack of or insecure user rights and privileges.
... Konkret helfen dabei, wie in den gemäßigten Breiten, verschiedene gewonnene Proxydaten aus den Zuwachsringen, wie Zuwachsringbreite, Holzdichtemessungen oder Signaturen stabiler Isotope von Kohlenstoff oder Sauerstoff, um Rückschlüsse auf Wachstumsverhalten (Worbes, 1999b;Brienen und Zuidema, 2006), lokale Störungseinflüsse (Baker at al., 2005;Vlam et al., 2014), Zusammenhänge mit klimatologischen Parametern (Brienen und Zuidema, 2005;Schollaen et al., 2013) oder Zirkulationsmuster (Brienen et al., 2012a) zu erhalten. ...
Age and radial growth rate are key data on understanding some aspects of tropical forest dynamics and ecology. In species that produce annual tree rings, tree-ring analysis allows the most precise estimate of these two parameters. The present study assessed the age and radial growth rate of three Hymenaea species inhabiting four of the six biomes found in Brazil. Out of these four biomes, two harbor the largest rainforests in South America, the Amazon Forest on the west and the Atlantic Forest in the east. The Cerrado biome is an open and seasonally drier vegetation found between them and the Pantanal is a wetland in the west. The H. courbaril species inhabits almost the entire Neotropical lowlands while H. parvifolia and H. stigonocarpa are restricted to the Amazon and Cerrado biomes, respectively. To investigate these species dynamics within different biomes, age and radial growth rate were calculated for 217 trees through tree-ring analyses. The oldest H. courbaril and. H. parvifolia trees were 316 and 371 years old, respectively, while H. stigonocarpa trees were considerably younger, up to 144 years old. Hymenaea courbaril trees showed the widest variation in average growth rate, from 1.00 to 6.63 mm per year, while the other two species showed a narrower variation from 0.89 to 2.81 mm per year. The studied populations presented distinct trends in the lifetime growth pattern that seems to be related to the biome of provenance. Overall, trees from the Amazon forest showed a trend of increasing growth rate up to about 100 years followed by a decreasing of it, while trees growing in the Pantanal and Atlantic forest showed only decreasing growth rates. In the Cerrado, trees showed a constant pattern of growth rate up to 50 years followed by a clear decline. It is important to highlight that different species of Hymenaea showed similar growth trends within the same biome. In larger trees, the average growth rate is lower in the Cerrado, which is characterized by deeper water tables and more dystrophic soils while the growth rates in the Amazon and Atlantic Forests are 60% and 79% higher, respectively. This study represents one of the most comprehensive datasets of trees age and growth rate of tropical congeneric species under such large geographical range. A tropical tree-ring study is presented using 36 specimens of Cariniana estrellensis from the Mata Atlantica Biome within the State of São Paulo: Caetetus and Carlos Botelho. We aimed to assess the suitability of this species for chronology building, as well as for dendroclimatological studies, with the help of its lifetime growth trajectories. Cariniana estrellensis forms visible tree rings with a dense sequence of parenchyma bands at the end of the latewood, followed by a relatively distant sequence of parenchyma bands in the subsequent early wood of a tree ring. However, it was impossible to establish a chronology, solely by tree-ring width measurements and crossdating, for a number of reasons, including sequences of problematic wood anatomy, abundance of wedging rings and probably missing rings. Therefore, building a robust chronology for this species requires a multi-parameter approach, however, no experience is currently available. Therefore, to reveal possible climate-growth relationships for Cariniana estrellensis at both sites, we tested to correlation analyses of microclimatic conditions with tree growth and investigated patterns of lifetime growth trajectories. Annual precipitation is over 1300 mm at both sites, with the dry season primarily between June and August. Both sites showed clear differences in their microclimatic regime and topography. Overall, light availability is the most likely crucial factor for the studied species. A significantly lower photosynthetic active radiation and daily photoperiod was found at Carlos Botelho by the strong influence of orographic rainfall, foggy conditions and shade caused by the adjacent mountain chain. Consequently, trees at this site generally showed a lower average annual growth rate as compared to the Caetetus site with differences between juvenile and mature growth phases remaining nearly constant throughout their lives. In contrast, trees from Caetetus had less consistent growth phases, with increased growth after the juvenile growth phase. Thus, it can be concluded that dendroclimatological studies using growth characteristics have the potential to clarify the generally complex stand dynamics of Cariniana estrellensis. However, the development of tree-ring chronologies, based on tree-ring width analyses of cores or discs is nearly impossible. Deforestation in tropical regions is raising fragmentation to alarming levels. Not only does it lead to losses of forest area, but also the abiotic and biotic changes on forest edge areas alter the development of the remaining trees. We aimed to assess the impacts of forest fragmentation on the growth of tropical emergent trees. We sampled the endangered species Aspidosperma polyneuron (Apocynaceae) at forest edge and interior in the highly fragmented Brazilian Atlantic Forest. We obtained increment cores of each tree along with data about tree and surrounding canopy heights, plus their current levels of liana infestation. We used tree-ring analyses to estimate age and growth rate of trees. Sampled trees and surrounding canopy were taller at the forest interior than at the edge, even though both sampled populations have similar ages. Overall, trees at forest interior show a lifetime growth pattern common to shade-tolerant species, with a peak of growth rate at 120 years. Indeed, all sampled trees exhibited this pattern before fragmentation. However, trees at forest edge presented constantly slow growth rates for all diameter classes after the fragmentation event. The strong presence of lianas at forest edge prevents trees from experiencing the expected growth releases throughout their lifetime, probably by keeping the leaves of A. polyneuron under shaded conditions. Therefore, the management of lianas at the forest edge is likely the most effective procedure to ensure the growth of emergent trees, guarantying their role on forests structure, carbon storage, and ecosystem functioning.
... Secondly, long-term observations of fire activity in tropical forests are rare. And, thirdly, unlike their temperate counterparts few tropical species have annual growth rings to enable reconstruction of historical disturbance events (but see Baker, et al. [13]) and their impact on community structure [14]. ...
The effects of forest fires on tree recruitment dynamics in tropical forests is important for predicting forest dynamics and ecosystem function in Southeast Asia. To our knowledge, no studies have examined the effects of fire intensity on community-level recruitment patterns in tropical forests due to the rarity of long-term observation datasets in fire-impacted tropical forests and the difficulty of quantifying fire intensity. We addressed two questions: (1) is tree recruitment among species affected by fire intensity? and if so, (2) are there specific plant functional traits associated with these responses? We used data from a long-term forest dynamics plot at the Huai Kha Khaeng (HKK) Wildlife Sanctuary in Thailand. The HKK plot occurs in a strongly seasonal tropical environment and has experienced several fires since its establishment in 1994. We found 46 tree species (52% of the 89 species analysed) showed evidence of reduced recruitment rates with increasing fire intensities during the most recent fire in 2005. Tree species in this flammable landscape have various leaf and wood functional traits associated with fire. Spatial and temporal variability in fire activity may lead to alterations in long-term taxonomic and functional composition of the forest due to selection on fire-related traits.
... Establishing taper equations for tree species in the tropics is a complex exercise, which may explain the limited amount of research to date that has focused on this topic. Tropical forests contain species with irregular stem forms [22], for example, buttresses [23,24]. As a result, predicting the diameter at any height along the stem, and subsequently merchantable volume, is challenging [25]. ...
Taper functions are important tools for forest description, modelling, assessment, and management. A large number of studies have been conducted to develop and improve taper functions ; however, few review studies have been dedicated to addressing their development and parameters. This review summarises the development of taper functions by considering their parameterisation, geographic and species-specific limitations, and applications. This study showed that there has been an increase in the number of studies of taper function and contemporary methods have been developed for the establishment of these functions. The reviewed studies also show that taper functions have been developed from simple equations in the early 1900s to complex functions in modern times. Early taper functions included polynomial, sigmoid, principal component analysis (PCA), and linear mixed functions, while contemporary machine learning (ML) approaches include artificial neural network (ANN) and random forest (RF). Further analysis of the published literature also shows that most of the studies of taper functions have been carried out in Europe and the Americas, meaning most taper equations are not specifically applicable to tropical tree species. Developing well-conditioned taper functions requires reducing the variation due to species, measurement techniques, and climatic conditions, among other factors. The information presented in this study is important for understanding and developing taper functions. Future studies can focus on developing better taper functions by incorporating emerging remote sensing and geospatial datasets, and using contemporary statistical approaches such as ANN and RF.
... Retrospective analyses of preserved growth rings of living trees provide information on tree ages and growth rates over the course of their life span. These analyses can be applied across the large multidisciplinary and interdisciplinary field of ecology, geosciences, archaeology and forest sciences, addressing ecologically guided logging systems (Schöngart, 2008;Andrade et al., 2019), dynamics of tropical forests (Baker et al., 2005;Vlam et al., 2017), relationships between tree growth and climatic variations at different scales (Brienen et al., 2010;Schöngart et al., 2004), tree response to anthropogenic disturbance in pre-colonial and contemporary times (Caetano- Andrade et al., 2019;Resende et al., 2020) and detailed, annual reconstruction of climatic parameters for pre-instrumental periods (Granato-Souza et al., 2019). While once thought impossible in the tropics, a growing literature of tropical dendrochronology is demonstrating the wide variation in ages and diametric growth patterns between individual trees, species, ecosystems and biomes (Brienen et al., 2016;Schöngart et al., 2017). ...
Incremental coring of trees is the key method used in non-destructive dendrochronological sampling. Despite the advances in developing such methods, the sampling of large, high-density trees still poses a challenge in remote tropical forests. Manually operated incremental drills, while easy to transport across difficult terrain, limit sample size and can often get damaged in the sampling process, especially when trees have wood densities above 0.8 g/cm³. Here, we discuss the existing available alternatives and present an up-to-date incremental coring system composed of a borer coupled to a hand-held drilling machine and a support attached to the tree which can collect incremental cores of 1.5 mm in diameter and over 1.0 m in length. The support ensures stability for the drill throughout the sampling process. This system is relatively lightweight and portable, offering field flexibility and suitability for sampling in remote locations. It provides a core sample of an appropriate diameter and amount for carrying out ring-width measurements, stable isotope and radiocarbon analyses on some of the large, older trees which are now being found in the tropics. We expect that this methodology will broaden the possibilities in the now-blossoming sub-field of tropical dendrochronology.
... However, it is important to recognize that variability in tree age with respect to other biometrics (e.g., DBH) has not yet been studied, and we currently lack a definitive understanding of the age distributions of the forests at Ituri. Hubau et al. [72] and Baker et al. [73] reveal that age distributions within stratified tropical forests are not always what they seem. This represents a potentially fruitful area of research, in that recharacterization of uneven-aged stands into even-aged stands would necessitate a reframing of Gilbertiodendron's developmental dynamics and persistence. ...
Patterns of structural change associated with monodominant tropical forest complexes have remained enigmatic for decades. Here, we extend previous efforts in presenting a longitudinal, local-scale analysis of forest dynamics in central Africa. Using four 10-ha census plots measured across three time periods (959,312 stems ≥1 cm DBH), we analyzed changes in a number of biometrical attributes for four distinct forest types capturing the developmental gradient from mixed species forest to Gilbertiodendron dewevrei-dominated forest. We modeled above-ground biomass (AGB), basal area (BA), and stem density across all species, and diameter at breast height (DBH), recruitment, and mortality for Gilbertiodendron dewevrei. We hypothesized that trends in these attributes are consistent with a slow spread of Gilbertiodendron dewevrei into adjacent mixed species forest. We identified statistically significant increases in AGB and BA across sites and positive, though nonsignificant, increases in AGB and BA for most forest types. DBH and relative recruitment increased significantly for Gilbertiodendron dewevrei stems, while relative mortality did not. When looking from mixed species to transitional to monodominant forest types, we found a statistically significant pattern of developmental aggradation and net expansion of monodominant forest. We do not attribute this to atmospheric forcing but to a combination of (a) landscape-scale recovery or response to widespread disturbance (primarily historical fires), (b) Gilbertiodendron dewevrei’s ectomycorrhizal association, and (c) Gilbertiodendron dewevrei’s exceptional stress tolerance traits.
... In addition, to better characterize the variability of the shapes of the observed structures and to make possible comparisons between structures, an adjustment to the theoretical Weibull distribution based on the maximum likelihood method was applied. This simple and flexible distribution fits perfectly both positive and negative skewed distributions, as well as normal ones (Lorimer and Krug, 1983;Baker et al., 2005). Its probability density function, f is expressed by the formula: ...
The present study was carried out in the municipality of Tibiri where assisted natural regeneration is the method adapted by agriculture to maintain trees for various reasons. The general objective of this study is to characterize the floristic diversity and the structure of the woody stand resulting from assisted natural regeneration. The methodology adopted for this study consisted of inventories of woody species and regenerations in crop fields by placing plots of 50m x 50m during the crop season. Thus twenty (20) plots were placed in the agrosystems according to homogeneity following an equidistance of 300m. The floristic survey made it possible to identify 19 species divided into 9 families of which the most represented are the Fabaceae (72%). The most represented species are P. reticulatum (30%), F. albida (17%) and P. africana (14%). These species also have the highest IVI values. The distribution of individuals by diameter class shows an "inverted J" shape with the shape parameter c = 1.959 (1 <C <3.6), characteristic of populations with a predominance of young or small diameter individuals. The total regeneration density is 2648 stems / ha, grouped into eleven (11) species showing good regeneration and dominated by G. senegalensis representing 61.93% of the density of the inventoried species followed by P. reticulatum (14 , 80%). ANR is a practice that contributes to improving the woody biodiversity of the fields where it is practiced. It is not only an alternative to greening the environment, but also provides several products and services to populations.
... For example, small-scale events, like gap dynamics, can enhance the growth of suppressed seedlings or recruitment of light-demanding species, contributing to the maintenance of forest composition and structure (McCarthy, 2001;Runkle, 1982;Yamamoto, 1992). Over longer temporal scales, climatic shifts and/or disturbances may provide occasional periods that facilitate tree recruitment and impart a legacy in forest communities centuries after their occurrence (Baker et al., 2005;Brown & Wu, 2005;Hoffmann et al., 2020;Pederson et al., 2014;Vlam et al., 2014). Understanding the effects of temporal variation in seedling vital rates on the seedling-to-sapling transition will help evaluate the importance of the seedling stage for the entire tree life history. ...
Experimental and observational studies on seedling dynamics posit mechanisms that can influence forest diversity, structure and function. However, high mortality and slow growth of seedlings make it difficult to evaluate the importance of this life‐history filter to total tree life history. Quantifying the duration and transition of the seedling phase would help us understand this ‘black box’ in tree population biology.
We used a 16‐year dataset of comprehensive seedling‐to‐sapling demography from a subtropical rainforest to construct population models that capture temporal demographic fluctuations for eight major tree species. We used data‐driven demographic models and simulations to estimate the transition ratios from newly recruited seedlings to saplings of 2‐m height and the time taken to attain 2‐m height for a newly recruited seedling conditional on its survival.
Projections among species estimated that as few as 57 to more than 40,000 seedlings (with a median of 2,087) were required to make a single 2‐m high sapling. Furthermore, it would take 22–200 years (with a median of 47) for a newly recruited seedling to become a 2‐m high sapling. We found that temporal variation in demographic rates could greatly reduce the number of seedlings per established sapling, but not passage times (PTs). We also identified the importance of consistently fast growth rates for seedlings to escape the high mortality of early stages.
Synthesis. Our findings demonstrate that high mortality in the very early seedling stage severely limits the probability that a newly recruited seedling will transition to the sapling stage. Although the PTs vary, we found this to be true across species with a range of life‐history strategies. Only seedlings with consistently fast growth rates are expected to pass through this life‐history filter. Findings from seedling studies should consider how short‐term studies of seedling demography might capture the rare exceptional individuals and exceptional conditions that might define the dynamics of this seedling bottleneck.
... The evaluation of disturbance patterns and successional development in forests is commonly done through tree-size distributions, based on the diameter of the stem at 1.3 m (d) or total height (h) (Goff and West, 1975;Lorimer and Krug, 1983;Donoso et al., 1985;Baker et al., 2005;Zenner, 2005;Müller-Landau et al., 2006;Coomes and Allen, 2007;Wang et al., 2009). Moreover, foresters and forest ecologists have used the diameter/age distribution in a stand to reflect its general structural attributes, such as cohort structure and vertical/horizontal complexity (Tyrrell and Crow, 1994;Zenner, 2005;Fajardo and Alaback, 2005;Soto et al., 2010;Esse et al., 2021). ...
Forest understories are essential to plant diversity and ecosystem functioning. However, studies about changes in understory patterns as affected by varying precipitation are scarce. Pure Nothofagus pumilio (common name: lenga) forests dominate the eastern side of the Andes mountains in Patagonia across an ample range of precipitation (~1500-500 mm). By studying the same forest type, in the same developmental stage (old-growth), we aimed to isolate the effects of precipitation upon these N. pumilio ecosystems, particularly for the understory. Three sites were selected with annual average precipitations of ~1000 mm (humid), ~800 mm (mesic), and 600 mm (dry), with a distance of 30 km between the humid and the dry sites, and only 18 km between the mesic and the dry sites. In each site, we established three 40 × 40 m plots in 4 blocks, and 30 1 m 2 regeneration subplots within each plot. In each subplot we measured vascular plant cover, richness and diversity (alpha and beta), litter cover and coarse woody debris, plus several abiotic variables. We analyzed the data with mixed analysis of variance, differences of understory plant communities through blocked distance-based multivariate analysis of variance, and visualized the groups (sites) with non-metric multidimensional scaling. Indicator species at each site were identified through blocked species indicator analysis. The dry site differed significantly compared to the humid and mesic sites, with the lowest understory cover (4 vs. 82-78%), plant richness (15 vs. 25-26 species), and Simpson diversity index (0.05 vs. 0.66-0.64). Beta turnover diversity was higher between the dry site with either the humid and the mesic sites (βt = 0.613 and 0.561, respectively), which in turn had more species in common (βt = 0.115). An increase in exposed mineral soil, soil water content, and leaf area index occurred from dry to humid sites, and vice versa for transmitted radiation and litter cover. All sites had different indicator species, but with indicator values increasing from dry to humid sites. The dramatic impoverishment of the plant community once precipitation drops within the range of 800 and 600 mm per year in Northern Patagonia sets a warning to the potential effects of climate change upon N. pumilio-dominated forest ecosystems and their plant diversity. Some forest management and potential adaptation strategies are proposed.
... We selected four tree species for this study (Magnolia champaca, Chukrasia tablularis, Lagerstroemia speciosa, and Toona ciliata) based on their growth-ring boundary distinctness (Fig. 2) and their wide distribution in the tropics (Islam et al., 2018a). Annual growth ring formation of these species were proved in some earlier studies (Baker et al., 2005;Heinrich et al., 2009;Rahman et al., 2019Rahman et al., , 2018Vlam et al., 2014). Another species selection criterion is that they represent a broad range plant functional guild from strong light demanding to shade tolerant, semi-deciduous to deciduous and diffuse porous to semi-ring porous or ring porous. ...
Tropical forests have been focused for mitigating climate change impact through carbon sequestration in plant biomass under clean development mechanism (CDM). Since trees represent more than 98% of the above ground plant biomass, variation in tree growth rate drives carbon dynamics in tropical forests. By using tree-ring analysis, trait-based measurements, and field observations, we aimed at understanding the drivers of growth rate variation in four South Asian tropical moist forest tree species varying in plant functional types. Principal component analysis (PCA) revealed that mainly demographic and wood traits represented the first axis explaining 37% of the variance, whereas the second axis was represented by the leaf traits. Stem growth rate (DI) showed a nonlinear negative relation with competition index (CI) and the ratio of crown surface area to basal area (CBR) in three out of four tree species (p < 0.001) except Lagerstroemia speciosa which showed no significant relationship with any of the studied variables. DI was linearly positively related with light interception index (LI) and the ratio of sapwood area to heartwood area (SHR) in the shade intolerant Magnolia champaca and Toona ciliata (p < 0.001). Sap wood area (SA) had a strong positive effect on DI in the three species (p < 0.001). Taking tree size as a random factor and thus accounting for ontogenetic effects on tree growth, linear mixed effect modelling revealed that CI, SA and SHR are the best predictors of DI in M. champaca (AIC = 25.81, R2m = 0.81) and T. ciliata (AIC = 62.95, R2m = 0.61). In C. tabularis, CI, SA and CBR included in the best model predicting DI (AIC = 94.62, R2m = 0.55). Variance partitioning analysis showed that the highest pure effect was observed in C. tabularis contributed by CI (12 %), while the highest joint effect was found in M. champaca contributed by CI, SA and SHR (40 %). Our analyses suggest that competition by neighbouring trees especially for soil moisture and the amount of active xylem portion are the main drivers of tree growth in moist tropical forests. Since tree growth rates regulate forest carbon dynamics, the insights into the growth drivers of the four selected species revealed by the study have important implications for forest/plantation management with a focus on carbon storage under CDM.
... Species-level studies across many ForestGEO FDPs have demonstrated differential sensitivity to drought (e.g., Condit et al., 1995;Engelbrecht et al., 2007;Itoh et al., 2012;Zuleta et al., 2017). On century time scales, dendrochronological studies provide increasing evidence that current community composition of some ForestGEO FDPs reflects historical disturbance events (e.g., Baker et al., 2005). Despite these cases, in many forests there is no obvious S.J. Davies et al. factor driving differential abundance changes among species . ...
ForestGEO is a network of scientists and long-term forest dynamics plots (FDPs) spanning the Earth's major forest types. ForestGEO's mission is to advance understanding of the diversity and dynamics of forests and to strengthen global capacity for forest science research. ForestGEO is unique among forest plot networks in its large-scale plot dimensions, censusing of all stems >1 cm in diameter, inclusion of tropical, temperate and boreal forests, and investigation of additional biotic (e.g., arthropods) and abiotic (e.g., soils) drivers, which together provide a holistic view of forest functioning. The 71 FDPs in 27 countries include approximately 7.33 million living trees and about 12,000 species, representing 20% of the world's known tree diversity. With >1300 published papers, ForestGEO researchers have made significant contributions in two fundamental areas: species coexistence and diversity, and ecosystem functioning. Specifically, defining the major biotic and abiotic controls on the distribution and coexistence of species and functional types and on variation in species' demography has led to improved understanding of how the multiple dimensions of forest diversity are structured across space and time and how this diversity relates to the processes controlling the role of forests in the Earth system. Nevertheless, knowledge gaps remain that impede our ability to predict how forest diversity and function will respond to climate change and other stressors. Meeting these global research challenges requires major advances in standardizing taxonomy of tropical species, resolving the main drivers of forest dynamics, and integrating plot-based ground and remote sensing observations to scale up estimates of forest diversity and function, coupled with improved predictive models. However, they cannot be met without greater financial commitment to sustain the long-term research of ForestGEO and other forest plot networks, greatly expanded scientific capacity across the world's forested nations, and increased collaboration and integration among research networks and disciplines addressing forest science.
... Species-level studies across many ForestGEO FDPs have demonstrated differential sensitivity to drought (e.g., Condit et al., 1995;Engelbrecht et al., 2007;Itoh et al., 2012;Zuleta et al., 2017). On century time scales, dendrochronological studies provide increasing evidence that current community composition of some ForestGEO FDPs reflects historical disturbance events (e.g., Baker et al., 2005). Despite these cases, in many forests there is no obvious S.J. Davies et al. factor driving differential abundance changes among species . ...
ForestGEO is a network of scientists and long-term forest dynamics plots (FDPs) spanning the Earth's major forest types. ForestGEO's mission is to advance understanding of the diversity and dynamics of forests and to strengthen global capacity for forest science research. ForestGEO is unique among forest plot networks in its large-scale plot dimensions, censusing of all stems ≥1 cm in diameter, inclusion of tropical, temperate and boreal forests, and investigation of additional biotic (e.g., arthropods) and abiotic (e.g., soils) drivers, which together provide a holistic view of forest functioning. The 71 FDPs in 27 countries include approximately 7.33 million living trees and about 12,000 species, representing 20% of the world's known tree diversity. With >1300 published papers, ForestGEO researchers have made significant contributions in two fundamental areas: species coexistence and diversity, and ecosystem functioning. Specifically, defining the major biotic and abiotic controls on the distribution and coexistence of species and functional types and on variation in species' demography has led to improved understanding of how the multiple dimensions of forest diversity are structured across space and time and how this diversity relates to the processes controlling the role of forests in the Earth system. Nevertheless, knowledge gaps remain that impede our ability to predict how forest diversity and function will respond to climate change and other stressors. Meeting these global research challenges requires major advances in standardizing taxonomy of tropical species, resolving the main drivers of forest dynamics, and integrating plot-based ground and remote sensing observations to scale up estimates of forest diversity and function, coupled with improved predictive models. However, they cannot be met without greater financial commitment to sustain the long-term research of ForestGEO and other forest plot networks, greatly expanded scientific capacity across the world's forested nations, and increased collaboration and integration among research networks and disciplines addressing forest science.
... Tree-ring studies revealed, by retrospective analyses, information on the species' ecology and allow the detection of past disturbances, caused by abiotic (e.g. fires, severe droughts, floods) or biotic (inter-tree competition) events (Schweingruber, 1988;Cook & Kairiukstis, 1990;Baker et al., 2005;Speer, 2010;Assahira et al., 2017). ...
The long‐lived tree species Eschweilera tenuifolia (O. Berg) Miers is characteristic of oligotrophic Amazonian black‐water floodplain forests (igapó), seasonally inundated up to 10 months per year, often forming monodominant stands. We investigated E. tenuifolia' growth and mortality patterns in undisturbed (Jaú National Park ‐ JNP) and disturbed igapós (Uatumã Sustainable Development Reserve ‐ USDR, downstream of the Balbina hydroelectric dam).
We analysed age–diameter relationships, basal area increment (BAI) through 5‐cm diameter classes, growth changes and growth ratios preceding death, BAI clustering, BAI ratio, and dated the individual year of death (¹⁴C). Growth and mortality patterns were then related to climatic or anthropogenic disturbances.
Results were similar for both populations for estimated maximum ages (JNP, 466 yr; USDR, 498 yr, except for one USDR tree with an estimated age of 820 yr) and slightly different for mean diameter increment (JNP: 2.04 mm; USDR: 2.28 mm). Living trees from JNP showed altered growth post‐1975 and sparse tree mortality occurred at various times, possibly induced by extreme hydroclimatic events. In contrast with the JNP, abrupt growth changes and massive mortality occurred in the USDR after the dam construction began (1983).
Even more than 30 yr after dam construction, flood‐pulse alteration continues to affect both growth and mortality of E. tenuifolia. Besides its vulnerability to anthropogenic disturbances, this species is also susceptible to long‐lasting dry and wet periods induced by climatic events, the combination of both processes may cause its local and regional extinction.
... Changes in the structure of a forest, and consequently in its dynamics, can be examined through dendrochronological techniques that enable us to document the dates of establishment and mortality of individuals, the patterns of radial growth and the frequency and magnitude of disturbances related to forest ecosystems (Fritts and Swetnam 1989, Baker et al. 2005Amoroso et al. 2017a, b;among others). Overall, the dendrochronological techniques allow inferring patterns and processes for longer periods than those resulting from regular ecological monitoring studies and with a precise resolution on annual scale. ...
The study of forest dynamics over large temporal and spatial scales has widely benefited from dendrochronological techniques. Patagonia is home to several long-lived tree species (Austrocedrus chilensis, Araucaria araucana, Fitzroya cupressoides, Nothofagus dombeyi and N. pumilio) with well-defined tree rings suitable for reconstructing tree establishment, mortality, spatio-temporal growth patterns and disturbance regimes with annual resolution. The first dendrochronological studies in the region date back to the 1950s and had a strong emphasis on hydroclimatology. It was not until the last few decades that studies using dendroecological techniques began to emerge. In this chapter, we review the experience gained by the tree-ring lab at IANIGLA (CONICET, Mendoza, Argentina) and colleagues from other institutions over the past 30 years applying dendroecological techniques to understand the role of climate and disturbances (insect outbreaks, snow avalanches, windblows, fires and decline) on forest dynamics. For each case, we summarized the process, and the dendrocronological methods used. In this way, it was possible to detect those gaps of knowledge that still can be explored using dendroecological methods in the Patagonian forests of Argentina.
... Once chronologies for tree growth have been established, joint analysis of multiple individuals can be used to analyze recruitment patterns in a tropical forest stand [28,29], growth patterns of individual trees [25,30], biomass productivity [31], and forest dynamics [32,33] in a given region at a high level of temporal constraint. These parameters can then be related to external factors, including human activities. ...
After the ice caps, tropical forests are globally the most threatened terrestrial environments. Modern trees are not just witnesses to growing contemporary threats but also legacies of past human activity. Here, we review the use of dendrochronology, radiocarbon analysis, stable isotope analysis, and DNA analysis to examine ancient tree management. These methods exploit the fact that living trees record information on environmental and anthropogenic selective forces during their own and past generations of growth, making trees living archaeological 'sites'. The applicability of these methods across prehistoric, historic, and industrial periods means they have the potential to detect evolving anthropogenic threats and can be used to set conservation priorities in rapidly vanishing environments.
... More than half of the TDF (54.2%) is located within South America and 45.8% is distributed among North and Central America, Africa, Eurasia, Australasia and Southeast Asia (Miles et al., 2006). TDF was defined by Baker et al. (2005) as areas within the tropics where there is a drought (<30 mm of rain per month for at least four months) during the low sun period, and a rainy season of several months duration with more than 100 mm of monthly rainfall when the sun is highest in the sky. While other tropical forests tend to have at least one period of lowered water availability in a year, tropical dry forests (TDFs) experience both prolonged and severe dry season. ...
Data and information are required to manage a renewable natural resource (such as forest) sustainably. This information is largely obtained through forest inventories. Forest inventory is very important in forest management since it provides the data for planning, monitoring, evaluation, research, growth and yield, biodiversity, and timber sale. Inadequate and/or irregular forest inventory has resulted to paucity of data on which forest management decisions can be based. This study aimed at enlightening conservationists, ecologists, environmentalists, and forest managers on the need to carryout diversity assessment and inventory of flora and fauna resources within their forest ecosystems. This will help to ensure sustainable yield and prevent the extinction of economic trees and endangered animal species in the tropical dry forests. The study therefore recommended that inventory should be carryout among the tropical dry forests at regular intervals.
... Tree-ring studies revealed, by retrospective analyses, information on the species' ecology and allow the detection of past disturbances, caused by abiotic (e.g. fires, severe droughts, floods) or biotic (inter-tree competition) events (Schweingruber, 1988;Cook & Kairiukstis, 1990;Baker et al., 2005;Speer, 2010;Assahira et al., 2017). ...
The long-living tree species Eschweilera tenuifolia (O. Berg) Miers (Lecythidaceae) is characteristic to oligotrophic floodplain forests (igapo) influenced by a regular and predictable flood-pulse. This species preferentially occurs at macrohabitats flooded up to 10 months per year forming monodominant stands. We aimed to analyze the growth and mortality patterns of this species under pristine conditions (Jau National Park-JNP) and in an impacted igapo (Uatuma Sustainable Development Reserve-USDR) where the downstream flood-pulse disturbance occasioned by the Balbina hydroelectric plant caused massive mortality of this species. Using a total of 91 trees (62 living and 29 dead) at the USDR and 52 (31 living and 21 dead) from JNP, we analyzed age-diameter relationships, mean passage time through 5-cm diameter classes, growth change patterns, growth ratios, clustering of mean diameter increment (MDI), and dated the year of death from each individual using radiocarbon (14C) analysis. Growth and mortality patterns were then related to climatic or anthropogenic disturbances. Our results show similar structural parameters for both studied populations regarding the estimated maximum ages of 466 years (JNP) and 498 years (USDR) and MDI, except for one single tree at the USDR with an estimated age of 820 yrs. Living trees from JNP showed distinctly altered growth after 1975, probably related to consecutive years of high annual minimum water levels. Tree mortality in the JNP occurred during different periods, probably induced by extreme hydroclimatic events. At the USDR changes in growth and mortality patterns occurred after 1983, when the Balbina dam construction started. Despite being one of the best flood-adapted tree species, E. tenuifolia seems to be sensitive to both, long-lasting dry and wet periods induced by climatic or anthropogenic disturbances or resulting synergies among both. Even more than 30 years after the start of disturbances at the USDR, the flood-pulse alteration continues affecting both mortality and growth of this species which can potentially cause regional extinction.
... Effects of the long-term interaction of climatic and environmental conditions, regeneration patterns, resource competition, and interference factors on plant populations have an important impact on plant population structure, which is reflected in 2 ways: morphological structure (size and height) and age structure (Coomes et al. 2003;Webster et al. 2005;Wang et al. 2009). Thus, morphological and age structures are key factors for assessing the effects of interference on the plant population (Baker et al. 2005;Coomes and Allen 2007). Biomass is a major indicator of the production capacity of bamboo for the giant panda, and it is usually used to evaluate the impact of panda foraging on the sustainability of bamboo (Zhou et al. 2012). ...
To understand the defense mechanism of Arundinaria spanostachya clonal populations in response to grazing by giant pandas, dynamic variations in A. spanostachya clonal population structure and biomass allocation in a wild giant panda habitat at the Liziping Nature Reserve were evaluated, as well as whether the clonal populations would be continuously used by the wild giant pandas. The population density of each age-class in the grazed and control plots after grazing (2014a and 2015a) was similar to that before grazing (2013a). The effects of grazing on the size-class and height-class structures were relatively lower. Before and after grazing, the perennial individuals showed the highest total biomass, followed by the biennial and annual individuals, and the maximum dry matter content in each module was found in the culm, followed by the branch and leaf. The dry matter content of A. spanostachya individuals increased as the age class increased, whereas the total water content decreased. The maximum water content allocation in the modules was observed in the culm, and no significant differences were found between the shoot and leaf. Thus, foraging by the wild giant pandas had no impact on the size-class and height-class structures and biomass allocation of A. spanostachya clonal populations, and the clonal populations have established an adaptive mechanism against grazing by giant pandas. After grazing, the A. spanostachya clonal populations showed greater self-adjustment ability to restore the status to that before grazing and, thus, continuously supply food for the giant pandas. Further management intervention of A. spanostachya clonal populations after the foraging of wild giant pandas is not needed, which has implications for understanding the impact of co-evolutionary mechanisms between giant panda and its staple bamboo species.
... However, igapó species growth slower than várzea species because of the oligotrophic conditions of soil and water (Worbes 1997, Da Fonseca Júnior et al. 2009, Rosa et al. 2017. By using tree-rings analysis, it is possible to understand the ecology of trees as well as to detect disturbance events in the past, such as extreme temperatures, rainfall, fires, insect attacks, severe droughts, floods, among others factors , Baker et al. 2005 In the Amazon region, severe droughts and floods are not a recent phenomenon, they have also been registered in the past ( ...
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Tipo do documento: Tese
Título: Alterações no pulso de inundação: como reagem os igapós da Amazônia Central?
Autor: Resende, Angélica Faria de
Primeiro orientador: Schöngart, Jochen
Primeiro coorientador: Silva, Thiago S. F.
Segundo coorientador: Trumbore, Susan
Resumo: Os igapós de águas pretas são cobertos por florestas alagadas por águas ácidas e pobres em nutrientes, que ocorrem às margens de grandes rios como o Rio Negro, Rio Uatumã e outros da Bacia Amazônica, perfazendo mais de 140,000 km2. Naturalmente, esses ambientes possuem uma fase de águas altas (fase aquática) e uma fase de águas baixas (fase terrestre), caracterizando um pulso de inundação monomodal e previsível, o que permitiu a especialização e dependência da flora a condições semiaquáticas. Este trabalho buscou compreender como os igapós de duas sub-bacias na Amazônia Central se comportam em condições normais; sob influência de eventos hidro climáticos extremos que aumentaram drasticamente nas últimas três décadas (Rio Jaú, afluente do Rio Negro) e em condições severas de alteração no pulso de inundação (Rio Uatumã, afluente do Rio Amazonas) induzidas pela hidrelétrica de Balbina instalada nos anos 80. Para tal, a jusante do Rio Uatumã, no capítulo 1 mapeamos e classificamos os igapós para identificar áreas onde houve a mortalidade massiva de árvores e onde a mortalidade ainda está ocorrendo. O mapeamento foi feito com 56 imagens de radar de abertura sintética (ALOS/PALSAR) adquiridas em diferentes níveis de inundação entre 2006 e 2011. A classificação pelo algoritmo supervisionado (Random Forests) apresentou acurácia geral de 87,2%. Foi observada a mortalidade de 12% da floresta de igapó após os primeiros 43 km a jusante, ao longo de um trecho de 80 km. Com base nas imagens e dados hidrológicos, detectamos que 29% dos remanescentes de igapó vivos podem estar atualmente sofrendo mortalidade. Os resultados indicaram que principalmente as topografias baixas caracterizadas por macro-habitats dominadas pela espécie arbórea Eschweilera tenuifolia (O. Berg) Miers (Lecythidaceae) foram os mais impactados. Para estudar em mais detalhe a ecologia desta espécie arbórea os capítulos 2 e 3, comparam os macro-habitats nas duas áreas de estudo, visando compreender como e quando os distúrbios no pulso de inundação afetaram as populações desta espécie, altamente adaptada às condições de inundações prolongadas de até 10 meses por ano em média. Nos igapós do Rio Uatumã, coletamos discos de 30 árvores mortas e bastões de madeira (duas amostras por árvore retirados com trado dendrocronológico) de 62 indivíduos vivos. Em florestas de igapó adjacentes ao Rio Jaú, coletamos 21 discos de indivíduos mortos e bastões de madeira de 31 indivíduos vivos. O segundo capítulo aborda as relações entre crescimento arbóreo e fatores climáticos em ambientes naturais (Parque Nacional do Jaú - PNJ) e perturbados (Reserva de Desenvolvimento Sustentável do Uatumã - RDSU). Para isso foram construídas cronologias de anéis de crescimento em cada sítio de estudo que apresentam estatísticas robustas para os períodos 1927-1999 (PNJ) e 1920-2006 (RDSU). As cronologias foram relacionadas com parâmetros regionais de hidrologia (nível mensal da água) e clima (precipitação mensal) e com anomalias de temperaturas superficiais do mar (TSM) do Pacífico Equatorial e Atlântico Tropical. Os resultados sugerem fortes mudanças nas respostas das árvores de Eschweilera tenuifolia à intensificação do ciclo hidrológico, caracterizado pelo aumento da frequência e magnitude de cheias severas no sistema natural (PNJ) e pelo aumento do nível mínimo da água durante o período da operação da barragem de Balbina (RDSU). No PNJ as árvores indicam um aumento nas respostas às anomalias de TSM dos dois oceanos (correlação positiva) em resposta da intensificação do ciclo hidrológico, causada pelo aquecimento do Atlântico Tropical e o simultâneo esfriamento do Pacífico Equatorial resultando na intensificação da circulação de Walker, forte convecção de nuvens e aumento de precipitação nas secções norte e central da Bacia Amazônica. Na RDSU, os impactos das mudanças do regime hidrológico induzidas pela barragem de Balbina resultaram em respostas do crescimento arbóreo opostas ao período pré-barragem. O terceiro capítulo aborda o crescimento arbóreo e a mortalidade da espécie nos dois sítios por meio de análises de séries temporais de incrementos diamétricos e datação com radiocarbono para detectar mudanças nos padrões de crescimento e mortalidade e suas causas. Os resultados mostram que o incremento diamétrico médio (IMD) e a idade média para árvores do PNJ foram 2,04 ± 0,39 mm e 201 ± 103 anos (DAP médio: 43,9 ± 21,7 cm) , respectivamente, enquanto para árvores da RDSU o IMD foi 2,28 ± 0,69 mm e a idade média 213 ± 103 anos (DAP médio: 45,9 ± 24,6 cm). A trajetória de crescimento acumulado entre os dois sítios de estudo foi similar, ao considerarmos um período de 500 anos de modelagem do crescimento. O IMD foi comparado entre os dois sítios de estudo e entre períodos antes e após (a partir de 1982) das mudanças do ciclo hidrológico induzidas por mudanças de clima (PNJ) e UHE (RDSU). O período anterior à construção da usina hidrelétrica (UHE) de Balbina indica que o crescimento das árvores não diferiu entre os dois sítios de estudo. Da mesma forma, o IMD das árvores no PNJ não apresentou diferença entre os períodos antes e depois de 1982. Em contraste, a manipulação do pulso de inundação ocasionada pela operação da UHE resultou na diferenciação do IMD entre as duas áreas e entre os períodos no Rio Uatumã. As árvores do Rio Uatumã morreram cerca de dez anos após o início da construção da barragem enquanto as árvores do Rio Jaú não apresentaram um padrão distinto de mortalidade ao longo da cronologia avaliada. As árvores vivas do Rio Uatumã apresentaram um aumento no incremento entre 1982 e 2000 e um abrupto e forte declínio de IMD após o ano 2000, que perdura até hoje, caracterizando um padrão de supressão de crescimento induzido pelas condições permanentes de inundação que possivelmente resultará em mortalidade. Com isso, concluímos que a alteração do pulso de inundação, causou e continua causando anomalias no crescimento e mortalidade de Eschweilera tenuifolia, mesmo em mais de 30 anos após a perturbação. A espécie é altamente sensível às mudanças na amplitude e duração da inundação que impactam os macro-habitats dominados por ela. A mortalidade massiva de árvores pode levar a perda destes macro-habitats, serviços ecossistêmicos e até a extinção regional da espécie. É necessário que as leis para a instalação e funcionamento de UHEs na Amazônia sejam criteriosamente revisadas com base em estudos feitos em áreas alagáveis a jusante das barragens.
https://bdtd.inpa.gov.br/handle/tede/3143
... For Horsfieldia, we observed in the same time period a sudden release in three out of four randomly sampled discs. This is the consequence of an external influence, very likely the reduction of competition [53]. Locals hinted that the studied forest was partially logged years before with a focus on the most valuable timber species (creaming). ...
Tree growth rings are signs of the seasonality of tree growth and indicate how tree productivity relates to environmental factors. We studied the periodicity of tree growth ring formation in seasonally inundated peatlands of Central Kalimantan (southern Borneo), Indonesia. We collected samples from 47 individuals encompassing 27 tree species. About 40% of these species form distinct growth zones, 30% form indistinct ones, and the others were classified as in between. Radiocarbon age datings of single distinct growth zones (or "rings") of two species showing very distinct rings, Horsfieldia crassifolia and Diospyros evena, confirm annual growth periodicity for the former; the latter forms rings in intervals of more than one year. The differences can be explained with species-specific sensitivity to the variable intensity of dry periods. The anatomical feature behind annual rings in Horsfieldia is the formation of marginal parenchyma bands. Tree ring curves of other investigated species with the same anatomical feature from the site show a good congruence with the curves from H. crassifolia. They can therefore be used as indicator species for growth rate estimations in environments with weak seasonality. The investigated peatland species show low annual growth increments compared to other tropical forests.
The area surveyed is part of the Edwards Plateau physiographic region in central Texas. It is mostly private property and includes isolated riparian and nonriparian deciduous woodlands. We searched for isolated deciduous woodland communities using satellite imagery and drone flights. Deciduous communities found were in deep canyons but not in riparian communities with physical positions similar to some isolated forests present in the southern Appalachian Mountains in North America. Eight communities were selected for ground surveys and had 16 overstory and 30 understory woody species. Surrounding the deciduous communities were Juniperus-Quercus woodlands (juniper-oak). Acer grandidentatum (Aceraceae, bigtooth maple) overstory density was 169 ± 73 plants/ ha (mean ± SD) and basal area was 9.6 ± 4.7 m2/ha, or 43% relative basal area. Quercus muehlenbergii (Fagaceae, chinkapin oak) and Quercus laceyi (Lacey oak) had the second and third highest basal areas at 6.1 ± 6.1 and 4.4 ± 7.4 m2/ha, or 25% and 18% relative basal area. Size-class distributions were examined to determine recruitment. Distributions had many juveniles, few to no saplings, and a few larger trees. Weibull comparisons suggested little or no replacement of adults of the mature deciduous community species. There was a bottleneck with few or no saplings entering the adult population. Recruitment could be highly episodic depending on fire or drought, but browsing pressure by Odocoileus virginianus (white-tailed deer) seems to be the primary cause of lack of recruitment. Lack of recruitment would mean a loss of species and possibly all of these rare deciduous communities in the future.
To better understand fire regimes and their relation to climate in the seasonal tropical forests of continental Southeast Asia, we developed the first multi‐century tree‐ring based fire history chronology for the region. The chronology included 776 fire scars collected at Bidoup NuiBa National Park (BNNP) in the Central Highlands of Vietnam and spans the period 1636–2020. Fires were recorded in 116 years, representing 47% of the years covered by the 249‐year period between the first fire scar (1772) and the last (2020). While only 9% of years within the sampled BNNP forests experienced fires before 1905, 70% recorded fires between 1906 and 1963 and 90% showed evidence of fire after 1963. Fire occurrence was highly correlated with climate indices (wet season Nino 3.4 and dry season regional Palmer Drought Severity Index) during the period 1906–1963, but showed no significant correlation after 1963. Our fire reconstruction from BNNP suggests that the fire regime has shifted from one driven primarily by climate to one in which human activities dominate the occurrence of fire within these seasonal tropical landscapes.
Much hard work with periodic, exciting breakthroughs by academicians, students, and practicing foresters of several generations slowly congealed into what has become “forest stand dynamics.” Repeated applications of “stand reconstruction” techniques led to an understanding that trees invade forests in pulses as growing space becomes available following disturbances, rather than in an all-aged manner. Further studies showed this pattern common in many parts of the world. With increased understanding, research became more focused. Where partial disturbances left large trees, newly regenerating trees were disadvantaged by side shade and crown densification and did not simply grow in small gaps. The new knowledge was amalgamated, taught in mid-career short courses, incorporated into books, and described with additional terminology, some of which has stood the test of time.KeywordsForest historyMixed-species standsMulti-cohort standsStand reconstructionStratification
A castanha-do-Brasil (Bertholletia excelsa Humb. Bonpl., Lecythidaceae) é uma espécie nativa amazônica protegida por lei no Brasil, classificada como vulnerável em termos de risco de extinção, e bastante explorada por extrativistas. O objetivo deste trabalho consistiu em avaliar a diversidade fenotípica de diferentes populações de Bertholletia excelsa por meio da morfometria dos frutos e sementes. Foram avaliados um total de 60 frutos provenientes de três populações localizadas em três áreas do sudeste do Pará: Floresta Nacional do Tapirapé-Aquiri (FLONATA), Floresta Nacional de Carajás (FLONACA) e Fazenda Sousa (FAZENDA). As variáveis mensuradas foram: número de sementes por fruto (NS), peso do fruto (PF), comprimento do fruto (CP), largura do fruto (LF), diâmetro do opérculo (DO), peso da semente (PS), comprimento da semente (CS), largura da semente (LS) e espessura da semente (ES). Elas foram testadas quanto à normalidade (Shapiro-Wilk) e homocedasticidade (Bartlett) e, posteriormente, submetidas a um teste de variância (ANOVA). Foi realizado teste de comparação de média (Tuckey) e análise multivariada (PCA) para avaliar as relações entre as variáveis morfométricas com as diferentes áreas de coleta. As análises evidenciaram a formação de três grupos correspondentes (FLONATA, FLONACA e FAZENDA), sendo que a primeira se destaca por apresentar mensurações médias superiores para a maioria das variáveis testadas e diferir significativamente das outras duas, e que estas não diferem entre si. Tais respostas evidenciam maiores variações fenotípicas em populações que ocorrem em ambientes com condições edafoclimáticas distintas evidenciando a importância de se considerarem os fatores exógenos além dos fatores endógenos.
This paper presents an assessment of changes in Avicennia marina population along the Egyptian coasts of the Red Sea. A retrospective analysis of the mangrove cover and distribution was carried out. The populations in Sharm El-Bahary and wadi El-Gimal lack at least one or more volume class stages, while all volume classes are represented in the last two populations occurring in wadi Al-Qu’lan and Sharm El-Madfa’a. The relationships
between the individual diameter and canopy volume of A. marina population are simply linear. Strong correlation coefficients are obtained (r2=0.92) for the population of Sharm El-Bahry and the weak correlation coefficients are obtained (r2=0.63) for the population of wadi El-Gimal. On the other hand, the relationships between the individual heights and canopy volume of A. marina population are simply linear. Strong correlation coefficients
are obtained (r2=0.72) for the population of Sharm El-Bahry and the weak correlation coefficients are obtained (r2=0.46) for the population of wadi El-Gimal. All growth performance of A. marina species differ significantly at the four localities except the circumference. The comparison of soil characteristics A. marina populations in the four study localities showed significant variations in all variables except the silt content and SO4.
Typical soil organic carbon (SOC) measurements do not account for the higher SOC concentration adjacent to, inside and under the trunks of large trees, or for the root volume which displaces soil and thereby reduces spatial density of SOC. Any net difference between these two omissions could have a significant impact on carbon accounts for the conversion of a primary forest with large trees to a type of land cover with much smaller trees, or no trees, such as to a secondary forest on short harvest cycles, or to deforested land, respectively. To improve knowledge of carbon stocks in primary forests, for better carbon management and climate change modelling, we sampled SOC and soil bulk density directly under large tree trunks, inside tree trunks, in the humus mounds in the buttress region, and under the humus mounds. The measurements were in primary Eucalyptus regnans mixed-forest. SOC was formulated as a function of depth. Adjacent to the trees, 90% of the total cumulative SOC was estimated to be within ~2.6 m of the mineral soil surface. That SOC was compared with an earlier measurement in the same locality of SOC in-between trees, away from the trunk and buttress. The SOC under large tree trunks was about four times more concentrated than in-between trees. Formulae that link SOC, root volume, and buttress shape, to tree diameter and ground slope were applied to forest stands within 54.4 ha of primary forest. When the under-trunk SOC was tallied with the organic soils associated with the buttress region and in nearly decomposed logs, SOC at the unit-area-level increased by ~7% [95% CI: 3–12%] relative to the in-between-tree SOC alone, and the absolute increase was 21 Mg ha⁻¹ [95% CI: 10–37 Mg ha⁻¹] of SOC. Our results suggest that, at least for land use change that fells mature trees >1 m in diameter, there may have been higher greenhouse gas emissions from past forest attrition than have been inferred. Globally, we identified 50 example tree species, other than E. regnans, that may also have extra SOC at the stand-level in the absence of fire. Additional SOC per hectare was positively correlated with basal area of trees, which increases with the number of large trees in a stand. The maintenance of large trees will help ensure higher levels of forest carbon. The protection of medium-sized trees will be necessary to ensure existence of large trees in the future.
Multidrug resistance (MDR) is regarded as a main obstacle for effective chemotherapy, and P‐glycoprotein (P‐gp)‐mediated drug efflux has been demonstrated to be the key factor responsible for MDR. In this study, a novel pH‐responsive hybrid drug delivery system was developed by conjugating d‐α‐tocopheryl polyethylene glycol 1000 succinate (TPGS), a kind of P‐gp inhibitor, on the surface of laponite nanodisks to overcome MDR. The prepared LM‐TPGS display excellent colloidal stability, a high encapsulation efficiency of doxorubicin (DOX), and a pH‐responsive drug release profile. In vitro experiments verified that LM‐TPGS/DOX could exhibit significantly enhanced therapeutic efficacy in treating DOX‐resistant breast cancer cells (MCF‐7/ADR) through inhibiting the activity of P‐gp‐mediated drug efflux and effectively accumulating DOX within cancer cells. In vivo results revealed that LM‐TPGS/DOX outstandingly suppressed MCF‐7/ADR tumors with low side effects. Therefore, the high drug payload, enhanced inhibition efficacy to drug‐resistant cells, and low side effects make the LM‐TPGS/DOX a promising nanoplatform to reverse MDR for effective chemotherapy.
Background
Estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) immunohistochemistry (IHC) guide the clinical management of breast cancer metastases. Decalcification of bone core needle biopsies (CNBs) can affect IHC. In the current study, the authors sought to define whether fine‐needle aspiration (FNA) would be a better alternative to CNB for reliable IHC.
Methods
Patients with breast cancer metastases to bone that were sampled by both CNB and FNA were selected. ER, PR, and HER2 were performed in FNA cell blocks (FNA‐CBs) and concurrent decalcified CNBs. Discrepancies were classified as minor when there was a difference of up to 30% nuclear staining in IHC for ER and PR between paired samples and as major when a clinically relevant change was observed (ie, positive vs negative). Quantitative reverse transcriptase–polymerase chain reaction of ESR1 messenger RNA levels was performed on FNA/CNB pairs with discrepancies for ER IHC. IHC status of the primary breast carcinoma was recorded.
Results
Concordance rates for ER, PR, and HER2 were 89%, 67%, and 93%, respectively, between FNA‐CB and CNB pairs from 27 patients. Major discrepancies were noted in approximately 11% of FNA/CNB pairs for ER IHC and in 33% of FNA/CNB pairs for PR. ESR1 messenger RNA levels of FNA/CNB matched samples were similar and did not explain the differences in ER IHC expression in the majority of cases. Two of 27 FNA/CNB pairs had different results for HER2 IHC that changed from negative on CNB to equivocal (2+) on FNA‐CB. Both cases had prior HER2 amplification by fluorescence in situ hybridization.
Conclusions
FNA‐CB and CNB appear to constitute acceptable methods for the assessment of ER, PR, and HER2 for clinical decision making.
Background
Much of the reluctance about using cytology specimens rather than histology specimens to assess programmed death ligand 1 (PD‐L1) expression for guiding the use of immune modulating drugs in the management of non–small cell lung cancer (NSCLC) is based on the belief that the alcohol‐based fixatives favored by cytopathologists might reduce the antigenicity of PD‐L1 and lead to artifactually low expression levels and false‐negative reporting. Therefore, this study was performed to determine whether there is any difference in PD‐L1 expression between endobronchial ultrasound (EBUS)–guided aspirates of NSCLC fixed in alcohol‐based fixatives and those fixed in neutral buffered formalin (NBF), the standard laboratory fixative for histology specimens.
Methods
The expression of PD‐L1 was compared in 50 paired EBUS aspirates of NSCLC taken from the same lymph node during the same procedure. One aspirate of each pair was fixed in an alcohol‐based fixative, and the other was fixed in NBF.
Results
In none of the 50 pairs was there any significant difference, qualitative or quantitative, in the strength, pattern, or extent of PD‐L1 expression. In the great majority, the expression was identical, regardless of fixation.
Conclusions
There is no evidence from this study showing that the use of alcohol‐based fixatives has any effect on the expression of PD‐L1 or its interpretation. Notwithstanding the general challenges in accurately assessing such expression in cytology specimens, pathologists should feel able to interpret them with confidence, and clinicians should feel able to rely on the results.
Background
The Paris System for Reporting Urinary Cytology (TPS) defines clear morphologic criteria to classify urinary specimens into 7 diagnostic categories. According to TPS, a nuclear‐to‐cytoplasmic ratio (N:C ratio) >0.7 and hyperchromasia must be observed to render a diagnosis of high‐grade urothelial carcinoma (HGUC). TPS was established using only liquid‐based preparation techniques, and to the authors' knowledge it is unknown whether TPS can be applied using other preparation methods.
Methods
In the current prospective study, voided urine samples from patients with HGUC and negative for HGUC (NHGUC) were prepared using both ThinPrep and cytospin methods. ImageJ image processing software was used to measure the N:C ratio and hyperchromasia. For each patient, the N:C ratio and degree of hyperchromasia of urothelial cells present in both cytopreparations were compared.
Results
A total of 10 HGUC cases and 9 NHGUC cases, represented by a total of 688 cells (mean, 36.7 cells in HGUC cases; and mean, 35.8 cells in NHGUC cases), were evaluated in the current study. An overall comparison of HGUC cells with NHGUC cells demonstrated that HGUC cells had a higher average N:C ratio (0.5465 vs 0.2846) and greater hyperchromasia as measured by the average nuclear pixel gray value (100.8 vs 120.7). The N:C ratio was statistically different in 4 NHGUC cases, demonstrating higher N:C ratios in the ThinPrep preparations. Hyperchromasia was found to be statistically different in 6 cases, 5 of which demonstrated increased hyperchromasia in the ThinPrep specimens.
Conclusions
The morphologic features of HGUC cells appear to be similar in samples prepared using the ThinPrep and cytospin methods, and therefore TPS criteria may be applied successfully in laboratories that use these methods.
In this issue of Cancer Cytopathology, Gargano et al. describe their experience using the Milan System for Reporting Salivary Gland Cytopathology for the diagnosis and grading of a subset of salivary gland tumors with basaloid features. Among salivary gland tumors, this subset of basaloid tumors is considered by many to be the most problematic to classify cytologically.
Background
Basaloid salivary gland neoplasms (BSNs), which include benign primary tumors and primary or metastatic malignancies, show overlapping morphology in fine‐needle aspiration (FNA). The Milan system recommends assigning a grade (low or high) to malignant salivary neoplasms because of the impact on surgical planning. This study investigated cytomorphologic features of BSNs on FNA that would help to favor a high‐grade malignancy over a low‐grade malignancy or a benign tumor.
Methods
Two pathologists performed a double‐blinded cytologic evaluation of FNA cases diagnosed as BSNs that had corresponding surgical resections. The diagnosis made with the Milan system was correlated with the final surgical diagnosis and grade. Cytologic sensitivity, specificity, and predictive values were calculated.
Results
There were 132 BSN FNA cases; cytology slides were available for 77 of 87 patients who had undergone resection. The risk of malignancy for the benign neoplasm (BN), salivary gland neoplasm of uncertain malignant potential (SUMP), suspicious for malignancy (SFM), and malignant categories were 13.6%, 22%, 100%, and 100%, respectively. The sensitivity of the malignant/SFM category was 51.7%; another 37.9% of confirmed malignancies were diagnosed as SUMP. The specificity of the BN category was 86%. Favoring a high‐grade malignancy on FNA had 100% accuracy (5 of 5). Favoring a low‐grade malignancy on FNA had 75% accuracy (6 of 8). The most specific cytomorphologic clues for a high‐grade malignancy were necrotic/apoptotic debris, mitoses, discohesion, and anisonucleosis.
Conclusions
BSNs encompass a broad spectrum of primary and metastatic tumors. Necrotic/apoptotic debris, mitotic activity, discohesion, and significant anisonucleosis, alone or especially in combination, should make a cytopathologist suspect a high‐grade malignancy.
The new environmental conditions imposed by disturbance events often create a mosaic of spots in different successional stages. Our objective was to describe the temporal variation of a semideciduous seasonal forest based on its anthropic disturbance history, verifying possible changes in forest dynamics and structure. We sampled the arboreal vegetation with a diameter at breast height (1.3 m above the ground; DBH) ≥ 5 cm in 15 permanent plots of 20 × 20 m where we performed four inventories (2003, 2005, 2007 and 2015). We observed a density decrease and a basal area increase, which indicates the late successional stage of the analyzed tree community. The phytosociological structure, richness and species diversity of the tree community did not show changes throughout the monitoring. However, the Protium spruceanum predominance may be a response to the environmental changes caused by the mining occurred in the area 250 years ago. The anthropic disturbances enduring influences make this type of work indispensable because it allows the ecological processes understanding, allowing a factual management of the forests by the its effective management and conservation.
Characteristics of diameter distributions in 28 even-aged northern hardwood (Acer-Betula-Tsuga) and upland oak (Quercus spp.) stands were investigated to determine if even-aged stands of shade-tolerant and midtolerant (intermediate) species can be consistently identified without direct age determinations. The diameter distributions of midtolerant species consistently approximated a normal distribution. Those of tolerant species were highly variable, ranging from unimodal to steeply descending in form. Distributions of tolerant species that departed strongly from a unimodal form were those of stands having a large admixture of midtolerant species. Confusion with all-aged stands in such cases can be avoided if classification of age structure is based on the diameter distributions of midtolerant species. Even-aged and all-aged stands can generally be distinguished on the basis of diameter distributions, but even-aged stands cannot be consistently distinguished from multi-aged stands in which young trees are sparse or absent. In such cases, a number of direct age determinations would be necessary.
Duncan, R.P. (1989). An evaluation of errors in tree age estimates based on increment cores in kahikatea (Dacrycarpus dacrydioides). New Zealand Natural Sciences 16: 31-37. Twelve kahikatea (Dacrycarpus dacrydioides) discs were used to assess the likely errors associated with estimating tree age from growth ring counts in increment cores. Two major sources of error were examined: (1) Failure of the increment core to pass through the tree's chronological centre. A geometric model is developed for estimating the distance to the chronological centre in cores where the arcs of the inner rings are visible. The mean percentage error from 84 cores that passed within 50 mm of the chronological centre was ± 35% corresponding to a mean absolute error of ± 21 years. The majority of this error is due to growth rate differences between the missing radius and the measured part of the core. (2) Missing rings. The average age underestimate from 48 cores due to missing rings was 13%. A significant correlation between radius length and age under estimate (r = 0.81) suggests that sampling along the longest radii will reduce this error. The average age underestimate due to missing rings from cores located along the longest radii of the twelve samples was 3%.
A methodology is proposed for developing a disturbance chronology in stands by identifying the probable date of canopy accession for each sample tree. Canopy disturbance intensity is defined as the percentage of sample trees with canopy accession events in each decade. Rotation periods for disturbances of various intensities are calculated from the chronology. The method was evaluated using 893 increment cores from 70 plots in northern hardwood stands of W Upper Michigan. Average disturbance rate for all plots and decades was 5.7-6.9% of land area per decade, with an implied average canopy tree residence time of 145-175 yr. -from Authors
To assess the diversity of tropical tree life histories, a conceptual framework is needed to guide quantitative comparative study of many species. We propose one such framework, which focuses on long-term performance through ontogeny and over the natural range of microsites. For 6 yr we annually evaluated survival, growth, and microsite conditions of six non-pioneer tree species in primary tropical wet forest at the La Selva Biological Station, Costa Rica. The species were: Lecythis ampla, Hymenolobium mesoamericanum, Dipteryx panamensis, Pithecellobium elegans, Hyeronima alchorneoides (all emergents), and Minquartia guianensis (a canopy species). The study was based on long-term measurement of individuals from all post-seedling size classes. Trees were sampled from 150 ha of primary forest spanning several watersheds and soil types. To evaluate individuals' microsites we recorded the number of overtopping crowns, forest phase (gap, building, mature), and crown illumination index (an estimate of the tree's light environment). For comparison, we also evaluated the microsites of three species that have been categorized as pioneers (Cecropia insignis, C. obtusifolia) or high-light demanders (Simarouba amara). For the six species of non-pioneers, mortality rates declined with increasing juvenile size class. As a group, these emergent and canopy trees showed a much lower exponential annual mortality rate (0.44%/yr at >10 cm diameter) than has been found for the La Selva forest as a whole. Growth rates increased with juvenile size class for all six species. As adults (trees >30 cm in diameter), all five emergent species showed substantial annual diameter increments (medians of 5-14 mm/yr). Small saplings and adults of all species had significant year-to-year variation in diameter growth, with much greater growth occurring in the year of lowest rainfall. Passage time analysis suggests that all six species require >150 yr for growth from small saplings to the canopy. Evaluation of all nine species revealed four patterns of microsite occupancy by juveniles. Among the non-pioneers, one species pair (Lecythis and Minquartia: Group A) was associated with low crown illumination and mature-phase forest in all juvenile stages. For two species (Dipteryx and Hymenolobium: Group B) the smallest saplings were in predominantly low-light, mature-forest sites, but crown illumination and association with gap- or building-phase sites increased with juvenile size (Simarouba also showed this pattern). Two species (Pithecellobium and Hyeronima: Group C) were strongly associated with gap or building phase as small juveniles (@<4 cm diameter) and again as subcanopy trees (>10-20 cm diameter), but were predominantly in mature-phase sites at intermediate sizes. Juveniles of the two pioneer species (Cecropia: Group D) showed the highest crown illumination and association with gap or building sites. Among the six non-pioneer species, only one aspect of juvenile performance clearly varied according to microsite group. The smallest saplings (@<1 cm diameter) of Groups B and C showed significant mortality differences across a small gradient in crown illumination; neither of the Group A species showed this pattern. Otherwise, juvenile performance was strikingly similar among the six species. All showed a capacity for growth responses to small increases in light, substantial height and diameter increments at higher light levels, equal ability to survive 4-yr periods of no growth, and very low mortality rates at intermediate-to-large juvenile sizes. Species differed significantly in growth rates, but relative differences shifted with tree size and were unrelated to microsite group. These findings do not support prevailing paradigms concerning trade-offs and correlated suites of traits. For non-pioneer tropical trees, life history classification based on generalized concepts such as gap dependence and shade tolerance is inadequate to describe the complex size-dependent patterns of life history differences and similarities that exist among species.
In an old-growth tropical wet forest at La Selva, Costa Rica, we combined radiocarbon (14C) dating and tree-ring analysis to estimate the ages of large trees of canopy and emergent species spanning a broad range of wood densities and growth rates. We collected samples from the trunks of 29 fallen, dead individuals. We found that all eight sampled species formed visible growth rings, which varied considerably in distinctiveness. For five of the six species for which we combined wood anatomical studies with 14C-dates (ring ages), the analyses demonstrated that growth rings were of annual formation. The oldest tree we found by direct ring counting was a Hymenobbium mesoamericanum Lima (Papilionaceae) specimen, with an age of ca. 530 years at the time of death. All other sampled individuals, including very large trees of slow-growing species, had died at ages between 200 and 300 years. These results show that, even in an everwet tropical rain forest, tree growth of many species can be rhythmic, with an annual periodicity. This study thus raises the possibility of extending tree-ring analyses throughout the tropical forest types lacking a strong dry season or annual flooding. Our findings and similar measurements from other tropical forests indicate that the maximum ages of tropical emergent trees are unlikely to be much greater than 600 years, and that these trees often die earlier from various natural causes.
For most species, a changeable environment creates a situation in which recruitment varies considerably from one breeding season to the next. If adults survive well, an occasional favorable recruitment can sustain population numbers over long periods: gains made in favourable periods are stored in the adult population. Storage is particularly important when the species is at low densities, because then the potential population growth rate is very high if a favorable period occurs. Storage mechanism can lead to coexistence of 2 species in lottery competition for space, as long as generations overlapped and there was sufficient variation in recruitment. This was true even if one species had an average competitive advantage. The storage model also operates when >2 species are competing, when resources renew independently of population sizes, and when not all the resource is used. Species with relatively long lives and high fecundities are most likely to enjoy the benefits of the storage effect. Environments that theoretically elicit these life history characteristics are relatively benign and permanent for established adults, but are such that births and/or juvenile survivorship vary widely. Trees and many marine organisms are examples of species with the proper life histories, and storage may be important in maintaining the high diversity of these communities.-from Authors
There is still limited understanding of the processes underlying forest dy- namics in the world's tropical rain forests, ecosystems of disproportionate importance in terms of global biogeochemistry and biodiversity. Particularly poorly documented are the nature and time scale of upward height growth during regeneration by the tree species in these communities. In this study, we assessed long-term height growth through ontogeny for a diverse group of canopy and emergent tree species in a lowland neotropical rain forest (the La Selva Biological Station, northeastern Costa Rica). Species were evaluated based on annual height measurements of large samples of individuals in all postseedling size classes, over a 16-yr period (.11 000 increments). The study species were seven nonpi- oneers (Minquartia guianensis, Lecythis ampla, Hymenolobium mesoamericanum, Sima- rouba amara, Dipteryx panamensis, Balizia elegans,and Hyeronima alchorneoides ) and two pioneers (Cecropia obtusifoliaand Cecropia insignis). For each species, inherent height growth capacity was estimated as the mean of the five largest annual height increments (from different individuals) in each juvenile size class (from 50 cm tall to 20 cm in diameter). All species showed marked ontogenetic increases in this measure of height growth potential. At all sizes, there were highly significant differences among species in height growth potential. The two Cecropia species consistently showed the highest observed maximum height increments as smaller juveniles (#4 cm in diameter). Among the nonpioneers, Sim- arouba had the highest growth potential across all juvenile sizes. For all species, mean annual height increments in all juvenile size classes were very much lower than the species' potential growth rates and reflected the impacts of frequent periods of zero growth and major height losses from physical damage. Because of the same factors, maximum net height increments declined over increasing measurement intervals (1-15-yr periods). With only one exception (Simarouba amara saplings #1 cm in diameter that survived 10 yr), the annual height growth increments of these species showed no significant temporal au- tocorrelation. For the seven nonpioneer species, we estimated the minimum time required to grow from 50 cm tall saplings to 10 cm diameter trees, based on their greatest net height increments over increasing intervals. Estimated passage times increased from 7-33 yr, when based on maximum 5-yr height increments, to 37-83 yr, when based on maximum net height growth over 15 yr for the six longest studied (nonpioneer) species. Given the erratic height growth trajectories found for these juvenile trees in this 16-yr study, it is clear that much longer term observation is required. Still unknown are the actual growth trajectories that characterize successful regeneration in each of our focal species, how much time successful trees spend as suppressed juveniles, and the number of times they experience and recover from major physical damage.
The sources and origins of forest fires that occurred in the peak fire season of 1998 in the Huay Kha Khaeng Wildlife Sanctuary of Thailand were delineated using single date satellite imagery. It was found that the Landsat Thematic Mapper (TM) data is extremely useful for accurate delineation and demarcation of 'burnt areas' that occurred during the season. An overall classification accuracy of 87.38% was achieved for general land use/land cover categorization and an overall classification accuracy of 88.3% was achieved for 'burnt areas' delineation. The underlying causes of forest fires and fire susceptibility of different forest types of the sanctuary are described. Key management prescriptions to avoid occurrence of future forest fires are suggested. It is recommended to acquire and analyse multiyear and multiseasonal satellite data in order to create a fire history of the area and to capture all forest fire events of the season. It is also recommended to create a GIS database consisting of biophysical and socio-economic variables needed for fire hazard mapping and forest fire simulation.
Examines, in a variety of contexts, a number of theoretical and empirical relationships between disturbance (environmental fluctuations and destructive events, whether predictable and/or cyclical or not) and patch dynamics (where discrete spatial patterns possess internal characteristics and also inter-relate with surrounding patch and non-patch areas). The main sections are on: patch dynamics in nature; adaptations of plants and animals in a patch dynamic setting; and implications of patch dynamics for the organisation of communities and the functioning of ecosystems. A final chapter moves towards a general theory of disturbance. All 21 chapters are abstracted separately. -P.J.Jarvis
In the past three decades tropical rainforests of the Far East have been managed using systems based almost exclusively on cutting cycles. Much recent research concerning this management approach has focused on reducing logging impacts on the residual forest. Evidence from historical records and research suggests that in certain circumstances shelterwood systems and their variants that provide both structural and age-class diversity can be appropriate. We give examples of such systems in India, Sri Lanka, and Malaysia.
This highly acclaimed book, the standard history of Thailand for almost twenty years, has now been completely revised by the author. David K. Wyatt has also added new sections examining the social and economic changes that have transformed the country in the past two decades.
Disturbance is both a major source of temporal and spatial heterogeneity in the structure and dynamics of natural communities and an agent of natural selection in the evolution of life histories. This review emphasises the impact of disturbance on the numerical abundance of populations and on the relative abundance of species in guilds and communities. Disturbance also has an important influence on ecosystem-level processes, eg primary and secondary production, biomass accumulation, energetics, and nutrient cycling. Assemblages of sessile and mobile organisms are subject to disturbance with rather different responses. -from Author
A study was made to determine the rate and extent of border-tree crown expansion into openings cut to obtain reproduction in sawtimber stands of Appalachian hardwoods. Measurements were made on poletimber- and sawtimber-sized trees of red oak and yellow-poplar. A regression was developed for each species, based on the independent variables of tree d.b.h. and the number of years since cutting. Red oak crowns extended farther and grew faster laterally than yellow-poplar crowns. However, the rate of crown encroachment into openings was surprisingly slow for both species.
Charcoal recovered from pits in mixed forest and forest dominated by Gilbertiodendron dewevrei in the Ituri watershed of NE Zaire provide a 4000 year record of vegetation change. 36 tree, shrub and liana species were identified from 1817 charcoal samples; 28 samples were radiocarbon-dated. Guineo-Congolian rain forest was present throughout the period. Cynometra alexandri is common in both the contemporary forest and the charcoal. Two notable changes in forest composition are the absence of G. dewevrei in the charcoal, and the disappearance from the contemporary flora of Lebruniodendron leptanthum, the most frequently identified species in the charcoal. Charcoal distribution and dates indicate that fires were widespread but probably mostly small. Increase in fire frequency in the last two millennia may reflect climate fluctuations and human activity.
Reconstructive studies that use paleoecological, dendroecological, historical and other approaches in order to interpret long-term ecosystem dynamics generate valuable insights for ecologists, conservationists and foresters who are interested in the ecology, protection and management of old-growth forests. In most cases, the historical context provided by these studies reveals a long-term pattern of change that challenges assumptions about the pristine condition of these systems. It is the history of environmental fluctuations, natural disturbance processes, and subtle, often indirect, human impacts that is revealed by reconstructive work that may shape the characteristic structure, composition and ecosystem processes of old-growth forests, and that will provide the greatest challenge to their future conservation and management.
The lack of annual growth rings in the majority of tropical tree species greatly limits our understanding of the long-term dynamics of tropical forests. To address this problem, several methods have been developed to estimate the age of tropical trees from diameter growth data. These past approaches, however, suffer from two major flaws: (1) they assume a deterministic age-size relationship for a tree species, and (2) they have not been verified with independently derived age data. In this paper, I present a new approach that uses diameter growth rates, independent of tree size, that are stratified by crown class to estimate the age of individual trees. Past approaches have assumed that when present-day canopy trees were juveniles they grew at rates similar to conspecifics currently in the understory. In contrast, the crown class model assumes that present-day canopy trees have grown at rates similar to conspecifics in the same crown class, irrespective of size, throughout ontogeny. The crown class model was compared to a periodic annual increment (PAI) model typical of past approaches in mixed oak-hardwood forest in the southern Appalachians, USA. Tree ages were obtained independently from tree cores from three stands of differing age structure. Comparisons between the two models were made for species' population age structures (independent of stands) and stand age structures (independent of species). Age estimation errors for the crown class model were lowest for relatively shade-intolerant species such as yellow poplar (Liriodendron tuliplfera) and chestnut oak (Quercus prinus), but increased with the increasing shade tolerance of the species. The PAI model followed the opposite pattern, providing the most accurate age estimates for shade-tolerant species. These results were consistent with the underlying ecological assumptions of each model. When predicted age distributions for individual stands were compared to the true age distributions, the PAI approach had higher estimation errors than the crown class model in almost every case. In addition, the PAI model had a strong tendency to overestimate tree ages. A mixed model that used crown class age estimates for shade-intolerant species and PAI model age estimates for shade-tolerant species generated the most accurate estimates of stand age distribution. The results of this study suggest new opportunities for the study of long-term dynamics in tropical forests and underscore the importance and utility of validating models with independent data.
A 0.36—ha area in the Harvard Forest, Petersham, Massachusetts, was intensively analyzed to determine its history. Natural and man—caused disturbances of varying magnitudes occurred periodically in the central New England mixed—species stand. Evidence of two hurricanes and a fire prior to 1803 were found. Between 1803 and 1952, 14 natural or man—caused disturbances of various magnitudes occurred in the area. Large disturbances created new age classes, but small disturbances did not. Species arising together after large disturbances formed a distinct vertical stratification, with northern red oak (Quercus rubra L.) arising after several decades to the dominant canopy. Smaller disturbances to the overstory allowed understory trees such as black birch (Betula lenta L.), red maple (Acer rebrum L.), and eastern hemlock (Tsuga canadensis L. Carr.) to emerge to the dominant canopy. The composition of this forest was more the result of allogenic influences rather than autogenic development. See full-text article ...
Radial increment was studied in natural forest trees in East Kalimantan, Indonesia, and in mangrove trees in Thailand and on Iriomote Island (Japan). Nails were driven into the trunk at breast height. Barrier zones fonned in response were located after felling of the tree, and the amount of wood fonned subsequent to nailing was measured. Thanks to the distinctness of the cambial response to nailing, this method appears very effective for measuring radial increment in tropical trees. The following results were obtained: 1. In natural forest trees in East Kalimantan: a) In the Dipterocarpaceae studied the barrier zone fonned after nailing is charac-terised by tangential bands of gum/resin canals. In the two species studied from other families the barrier zone is composed of a tangential band of parenchyma. b) Annual diameter increment in meranti puteh (Shorea spp.) ranges from 1.6-20 mm. c) Radial growth was strongest in the period from August to October, during the dry season as a result of the production of more cells which had moreover a greater radial diameter than the cells fonned during the rainy season. 2. In mangrove trees in Thailand and Japan: a) In mangrove trees in Thailand with a diameter of about 10 cm, average annual radial increment was 13.4 mm in Xylocarpus, 11.6 mm in Bruguiera, 8.4 mm in Rhizophora, and 9.6 mm in Ceriops. b) In the smaller trees on Iriomote Island with dbh of 3-6 cm, annual increment ranged from 3.8 mm in Rhizophora to 5.7 mm in Avicennia.
Some of the first tree-ring chronologies from mainland Southeast Asia have been developed from Thailand, and a significant link between climate and tree growth has been suggested. Four chronologies from two species of pine (Pinus kesiya Royle ex Gordon and Pinus merkusii Jungh. ' de Vriese) from northeastern, lower northern and northwestern Thailand have been constructed: three from P. kesiya and one from P. merkusii. A second P. merkusii chronology is being developed from samples from northwestern Thailand. Preliminary climate modelling demonstrates significant relationships for tree growth with both temperature and precipitation for both species. A significant, direct relationship is revealed with temperature at the beginning of the wet season for Pinus merkusii from Thung Salaeng Luang National Park, along with an inverse relationship with precipitation for the same period. It is also suggested that the month of November (the transitional month from wet to dry season) during the year of growth is most important for Pinus kesiya from Nam Nao National Park, based on significant, direct relationships with both temperature and precipitation. The dendrochronological potential of another species, the long-lived Podocarpus neriifolius, is also discussed.
All trees = or >2.5 cm dbh were censused on a 1.5 ha tract of 60-yr-old Barro Colorado Island, Panama, forest in 1968 and again in 1978 to determine rates of tree mortality, recruitment, dbh increment, and canopy gap formation. Species composition changed very little. The pioneer or gap species Cordia alliodora, Luehea seemanii and Spondias radlkoferi had no recruitment and accounted for most mortality in the larger size classes. Some 90% of all mortality was for stems <10 cm dbh. Total tree density declined 11% (from 3112 to 2781 trees/ha), but basal area increased 22% (from 25.7 to 31.4 m 2/ha). Growth in diameter was highly variable, both among species and among size classes. Trees in the 30-50 cm dbh class had a mean dbh increment of 0.9 cm/yr. Gaps occurred over an area equal to 7.3% of the plot during the 10-yr period, suggesting that about 137 yr would be required for the 1.5 ha plot to be affected by tree falls. -Authors
Charcoal fragments in soils and sediments document Holocene fires in the rain forests of the La Selva Biological Station in the northern Caribbean lowlands of Costa Rica, and in the paramo surrounding Cerro Chirripo in the Cordillera de Talamanca. Radiocarbon determinations on soil charcoal from La Selva and charcoal-rich lake sediment from Chirripo duster at 2430 yr B.P. and at 1110-1180 yr B.P.; dates in each cluster are coeval, suggesting that the rain forest and paramo fires occurred at similar times. Fires at la Selva were likely set by human activity but may have spread into intact rain forest during exceptionally dry periods; fires at Chirripo were set by people or lightning during what may have been lower lake stands. The drought periods suggested by our charcoal samples may have been associated with short-term atmospheric anomalies such as El Nino, or with longer-term shifts in climate.
Mortality rates of 205 tree and shrub species were estimated during two intervals, 1982-1985 and 1985-1990, in two size classes, 1-10 and ≥ 10 cm in diameter, in a 50-ha census plot in tropical moist forest on Barro Colorado Island in Panama. The severe dry season of 1983 was the focus of the study, since prior observations had demonstrated that it caused mortality in the forest. Here we document that forest-wide mortality was ≈ 3%/yr during the drought interval but only 2%/yr during the period afterwards, and that excess mortality during the first interval amounted to 2% of stems in the larger size class and 1% in the smaller. Overall, just under 70% of all species had higher mortality during the first census interval, but not all species were equally affected. Canopy trees had significantly higher mean mortality rates during 1982-1985 than during 1985-1990, but treelets and shrubs showed no or slight differences. This was counter to our prediction that species with short root systems would suffer more from a long drought. Shrubs did, however, have higher mortality rates than trees and treelets during both census intervals. We also evaluated mortality rates for subgroups of species that specialized on different microhabitats in the forest. As we predicted, colonist species (those associated with light gaps) had higher mortality rates than generalist species, 7-10%/yr compared to 2-4%/yr, but only in the smaller size class. Unexpectedly, colonizers had similar mortality rates as non-colonizers in the larger size class. Gap colonizers and generalist species were similarly affected by the drought--both had elevated mortality during 1982-1985. Species whose distributions were associated with moister soils (on the slopes around the island's plateau or in a swamp in the midst of the 50-ha plot) also had elevated mortality during the drought period, but no more so than generalist species. This was counter to our prediction that species from moist microhabitats would suffer more during an extended drought than generalists. Understory treelets that were slope specialists had higher mortality than generalists during both census intervals, but not large trees that were slope specialists. Our conclusions emphasize diversity as well as pattern. Every trend we illustrated had well-documented exceptions: large trees with lower mortality during the drought period, for example. Clearly, accurate predictions about how tropical forests will respond to climatic perturbations will require much detailed information from many species.
The ecological significance of fire is reviewed, particularly in relation to the savanna forest of mainland South East Asia, a community, in which dry season burns occur annually or at least every 2-3 years. It is argued that this tropical deciduous formation is basically an edaphic climax which is well adapted physiognomically, physiologically and phenologically to fire and which in consequence has been gradually spread into the more fire-sensitive adjacent associations, such as tropical semi-evergreen rain forest, by cutting and burning. A careful examination is made of the forest fire environment, of the fuels involved, of the life forms and their adaptive capacity, and of the origins and characteristics of the fires themselves. A case is presented for the prescribed application of fire in this type of habitat and suggestions for appropriate future work are given.
The process of tree mortality has dimensions of intensity, spatial, and temporal scales that reflect the characteristics of endogenic processes (i.e., senescence) and exogenic disturbances (i.e., severity, frequency, duration, spatial scale, and points of interaction with the ecosystem). Tree mortality events expressed as percent of stems or biomass per unit area, range in intensity from background (<5% yr-1) to catastrophic (>5% yr-1), in spatial scale from local to massive, and in temporal scale from gradual to sudden (hours to weeks). Absolute annual rates of background tree mortality (biomass or stem ha-1 yr-1) can vary several fold depending on stand conditions and tend to increase with stem density. The ecological effects of a catastrophic, massive, and sudden tree mortality event contrast with those of background, local, and gradual tree mortality in terms of the direction of succession after the event, community dynamics, nutrient cycling, and possibly selection on trees. When standardized for the return frequency of disturbance events, area, and topography, the ranking of tree mortality events (trees ha-1 century-1) in the Luquillo Experimental Forest is: background > hurricanes > individual tree fall gaps > landslides. Estimates of vegetation turnover rates require long-term and spatial analysis to yield accurate results.
This study describes changes occurring in a stand of Pinus kesiya in hill evergreen forest adjacent to a new settlement of tribal people in the Doi Inthanon mountain region of northern Thailand. These forests are increasingly experiencing chronic human impacts as tribal people are settled permanently at one site by government programs which encourage the cultivation of cash crops in place of opium. Results from age stand structure analysis suggest that two factors, human-set fires and kindling stick harvesting, are now severely affecting the age distribution of Pinus kesiya in the mixed pine and evergreen hardwood forest. /// Cette étude décrit les changements qui ont affecté un peuplement de Pinus kesiya situé dans une forêt sempervirente adjacente à une nouvelle collectivité tribale établie dans la région montagneuse de Doi Inthanon, en Thaïlande septentrionale. Ces forêts sont de plus en plus sujettes à des impacts humains chroniques au fur et à mesure que des collectivités tribales s'établissent en permanence sur certains sites, dans le cadre de programmes gouvernementaux encourageant la culture de denrées commerciales plutôt que de l'opium. Les résultats d'une analyse structurale du peuplement de pins suggèrent que deux facteurs, les feux de forêt allumés par les habitants et la collecte du petit bois de chauffage, affectent énormément la distribution par âge de Pinus kesiya dans la forêt sempervirente mixte de bois durs. /// Diese Studie beschreibt Veränderungen in einem Kiefernwald in der Doi Inthanon Gebirgsregion von Nordthailand, an den eine neue Siedlung mit einheimischen Bewohnern angrenzt. Diese Waldflächen sind mehr und mehr menschlichen Dauerbelastungen ausgesetzt, da die einheimische Bevölkerung durch Regierungsprogramme ermutigt wird, sich an einem Ort fest anzusiedeln, um Gartenfrüchte statt Opium anzubauen. Einige Kiefernstände in diesem Gebiet haben als gleichaltrige Gruppen den bestandszerstörenden Einflüssen widerstanden. Eine Analyse dieser Bestände deutet darauf hin, daß zwei Faktoren die Altersverteilung der "Pinus kesiya" gravierend beeinträchtigen: Von Menschenhand verursachte Feuer und die Feuerholzgewinnung. Versäumte Aufforstung der Kiefernwälder und die geringere Feuerempfindlichkeit von breitblättrigen Arten deuten auf den Trend, daß in der Zukunft Kiefernwälder durch breitblättrige Baumarten ersetzt werden.
References in the literature to the `patchy' distribution of rain-forest tree species, and to the relationship between this phenomenon and the processes of rain-forest regeneration, are examined critically; it is concluded that direct observations on succession, even over a short time-scale, are needed. The vegetation (1775 plants of seventy-six species) in a 40 × 20 m plot of 12-year-old regrowth in an experimental clearing in a virgin subtropical rain forest is recorded in detail and analysed by various numerical techniques. A number of specific and hitherto unanswered questions were extracted from the literature and at least partial answers have been obtained to the following problems: (i) the regeneration of the canopy; (ii) the size and age-class representation of canopy spp.; (iii) continuous v. intermittent regeneration; (iv) the time scale of seedling and sapling mortality during succession; and, in particular, (v) the role of chance in regeneration. It is shown that a patchy structure, with patches of area c. 100-150 m2, has developed, but that the patches differ quantitatively in composition rather than qualitatively. `Spot-wise regeneration' by gravity dispersal of seeds occurs, but experience of this forest type suggests that it is not necessarily followed by a monospecific stand in the same place. It is concluded that, after the pioneer stage culminating in a temporary canopy, further succession is not unidirectional and is probabilistic rather than determinate. The implications of these findings for the interpretation of rain-forest pattern are discussed, and it is concluded that the pattern will be determinate in its response to recognizable environmental discontinuities, but probabilistic within these on a finer scale, thus producing patchiness.
The effect of a category 4 hurricane (Hurricane Hugo, 18 September 1989) on subtropical wet forest in Puerto Rico was examined at stand and species levels with respect to the frequency of tree damage, mortality, and resprouting. Roughly a quarter of the trees suffered some type of damage involving the main stem, and mortality due to the hurricane was 9%. Mortality among trees was primarily due to uprooting and broken stems. Many surviving trees sprouted new branches following the hurricane, indicating that this was an important component of stand recovery following hurricane damage. Patterns of species-specific damage and recovery formed two distinct groups. One group ("pioneers'), represented by three species, suffered a high frequency of stem breakage and mortality during the hurricane and had a low capacity to sprout new branches after being damaged. The remaining species ("nonpioneers') lost many branches during the hurricane, thereby suffering low to moderate stem damage and mortality, and sprouted many new branches following the hurricane. Stem breakage and related species-specific characteristics were significantly correlated with wood density and shade tolerance. Species exhibited few significant size-specific relationships with respect to hurricane damage, mortality, or resprouting, with the exception of branch damage, which often increased as a function of tree size. Nonpioneers dominate early in recovery because of the ability to survive a storm and sprout new branches following the storm, while the immediate impact of a hurricane on the abundance of pioneer species is strongly negative. -from Authors
Gap-phase regeneration of trees was described for the first 5-6 yr of regrowth in 30 treefall gaps (20-705 m^2) in tropical moist forest on Barro Colorado Island, Panama. Trees were classified as pioneers (saplings found only in gaps) or primary species (saplings found in gaps and in the understory of mature forest). In most of the gaps studied, stem densities rose rapidly after gap formation, then levelled off or declined by years 3-6. This pattern was particularly marked in some large gaps (>150 m^2), where pioneers attained high densities, then experienced heavy mortality. Stem density of primary species did not vary with gap size. In large gaps the mean rate of growth in height was greater for pioneers than for primary species, size-class distribution broadened more for pioneers than for primary species, and early recruits of both regeneration types grew faster than later ones. Gap formation fosters regeneration of pioneer and primary species and, in this forest, produces patches that differ markedly in tree population dynamics, species composition, and growth rate.
1 Prior to European settlement, Quercus alba, Castanea dentata, Carya spp. and Pinus strobus dominated Ridge and Valley forests in southern West Virginia. Dendroecological techniques were used to study the disturbance history and successional dynamics of one of the few remaining valley-floor remnants of this primary forest type. 2 The uneven-aged forest is presently dominated by P. strobus, Acer rubrum, Q. alba, Q. rubra and Q. velutina. Quercus alba and P. strobus represented most of the oldest and largest trees in the forest, while Acer, Fagus and Tsuga were the youngest and smallest. Maximum age was 295 years for Q. alba and 231 years for P. strobus. 3 There was continuous recruitment of Q. alba trees from 1700 to 1990. The abundance of P. strobus increased between 1830 and 1900, with a peak in the 1870s associated with releases in radial growth. The subsequent peak recruitment of Q. rubra and Q. velutina from 1880 to 1900 is suggestive of possible facilitation of these species by P. strobus. Following the cessation of Pinus and Quercus recruitment in 1900, Acer, Fagus and Tsuga abundance increased, particularly A. rubrum. 4 Radial growth chronologies across all species and age classes exhibited a series of major or moderate releases at regular intervals (typically every 20-30 years). However, the asynchronous nature of these releases suggests that they were caused by a series of small-scale disturbances, such as fire and wind-throw, each of which had localized impacts within the stand. 5 We believe that Pinus and Quercus were maintained in this stand during the 18th and 19th centuries by periodic disturbance, in particular fire, which would have eliminated later successional species. The lack of Pinus and Quercus recruitment after 1900 and the subsequent increase in Acer, Fagus and Tsuga indicates the transitional nature of this forest in the absence of fire. 6 Coupling of tree-ring chronologies and species establishment dates greatly increased our understanding of the disturbance history and dynamics of this old-growth forest, and we believe this represents an important approach to the study of species life-history attributes and ecological history in general.
Age and size structures, and tree locations were used to identify cohorts of trees that were initiated by flood events. This, along with information on species microsite preferences and spatial patterning, was used to reconstruct the patterns of establishment of the four dominant canopy trees (Dacrycardpus dacrydioides, Dacrydium cupressinum, Prumnopitys ferruginea, Weinmannia racemosa) in response to flood disturbance. The four species coexisted by partitioning establishment site with respect to the amount of overhead cover and the type of forest floor microsite. D. dacrydioides and D. cupressinum established in large gaps but colonized contrasting microsites; D. dacrydioides established mostly on mineral soil while D. cupressinum established on elevated microsites. W. racemosa and P. ferruginea both established on elevated microsites beneath largely intact canopies. However, W. racemosa colonized canopy gaps while P. ferruginea established mostly under closed cover. Disturbance was critical to the maintenance of species diversity because it was the source of much of the environmental variation to which species responded differentially. -from Author
To characterize the disturbance regime of one type of vegetation, study areas in which relatively small-scale disturbance predominates were chosen in several old-growth mesic forests in the eastern United States. Canopy openings covered 9.5% of total land area. New gaps were formed at an average of 1% of total land area per year; old gap area closed at a similar rate primarily by sapling height growth. With increasing gap size, vegetation within gaps increased in woody species diversity, total basal area, and total number of stems. Stems also showed accelerated growth into larger size classes. As gaps aged, stems grew into larger size classes and basal area increased. Species responses to canopy gaps varied. Some species survived and became established in fairly small gaps (50-100 m^2). Although in large gaps (up to 2009 m^2 in the present study) these species usually increased in total number of stems and basal area, they declined in importance relative to species which rarely survived in small gaps but grew rapidly in large gaps. The disturbance regimes in the forests studied favored tolerant species but allowed opportunists to persist at low densities.
Vegetation change following selective logging and major natural disturbance was investigated through the use of stand history reconstruction and population monitoring in an east Texas pine-hardwood forest. High frequencies of release in beech (Fagus grandifolia) and white oak (Quercus alba) occurred after apparently natural disturbances in 1800-1810, 1860-1870, and 1960-1970, and after selective logging beginning @?1910. Pulses of recruitment occurred after all disturbances except the most recent one. Age data suggest that recruitment after the 1910 disturbance was asynchronous among species, with loblolly pine (Pinus taeda) regenerating first, followed sequentially by white oak, red maple (Acer rubrum), and beech. At present, only magnolia (Magnolia grandiflora) is showing significant new recruitment. After the 1910 disturbance, regenerating pines grew rapidly and became dominant in the re-forming overstory. Most hardwoods originating after the 1910 disturbance did not reach the overstory. White oak initially outgrew maple and beech and is presently larger. Over the last 20 yr beech growth has been greater than white oak growth, resulting in a decline in the average size difference between individuals of these species. Presently, mortality rates of understory populations are high for sweetgum, blackgum, and the oaks, and are low for beech and magnolia. These latter two species are also the faster growing. If these trends continue, beech and magnolia will become increasingly predominant in the forest understory and eventually in the overstory as well. Map data show that saplings and small trees are abundant under pine and oak, but not under beech and magnolia. Future disturbance is therefore likely to accelerate succesion to more shade-tolerant species in parts of the forest now dominated by pine and oak, but is most likely to re-initiate new regeneration, including pine and oak, in areas now dominated by beech and magnolia. These results suggest a pattern of cyclical replacement driven by disturbance, a pattern which may help preserve species diversity in southern mesic forests.
From a network of teak chronolo gies in northern Thailand. 75 trees with in one province were evaluated regarding their climatic signal . The raw tree-rin g series revealed a high mean sensitivity of 0.50 and a moderate first-order autocorrelation of 0.48. The first princip al component of the standardi zed data explained 44 % of the total variation in the tree-ring data, indicating a considerable climatic influence on tree growth . The climate-growth relation ship suggested that growth of teak in this study area is mainly controlled by rainfall from April to June. Thus . there is some promise that the whole network of teak chronologies in northern Th ailand can contr ibute to reconstructing climate over at least the last three centuri es.
It is argued that the problem of pattern and scale is the central problem in ecology, unifying population biology and ecosystems science, and marrying basic and applied ecology. Applied challenges, such as the prediction of the ecological causes and consequences of global climate change, require the interfacing of phenomena that occur on very different scales of space, time, and ecological organization. Furthermore, there is no single natural scale at which ecological phenomena should be studied; systems generally show characteristic variability on a range of spatial, temporal, and organizational scales. The observer imposes a perceptual bias, a filter through which the system is viewed. This has fundamental evolutionary significance, since every organism is an "observer" of the environment, and life history adaptations such as dispersal and dormancy alter the perceptual scales of the species, and the observed variability. It likewise has fundamental significance for our own study of ecological systems, since the patterns that are unique to any range of scales will have unique causes and biological consequences. The key to prediction and understanding lies in the elucidation of mechanisms underlying observed patterns. Typically, these mechanisms operate at different scales than those on which the patterns are observed; in some cases, the patterns must be understood as emerging form the collective behaviors of large ensembles of smaller scale units. In other cases, the pattern is imposed by larger scale constraints. Examination of such phenomena requires the study of how pattern and variability change with the scale of description, and the development of laws for simplification, aggregation, and scaling. Examples are given from the marine and terrestrial literatures.
Investigations on growth zones of tropical trees were carried out and published since the beginning of our century.
In tropical regions with severe annual dry seasons or inundation phases trees form annual rings. This is demonstrated for trees from Central Amazonian inundation forests and the Gran Sabana in Venezuela using a combination of several dendrochronological methods (wood anatomy, radiocarbon dating, ring width measurements).
The occurrence of annual rings allows the determination of age and growth rate of trees. The growth rate depends on the growth strategy of the species and the growth conditions. At a given site growth rate shows a weak negative correlation with the specific gravity of the wood of trees from the upper story. Several reported ring width patterns are explained by the vegetation history of different forest stands.
Old-growth forests often have complex, uneven age structures reflecting both the long time elapsed since a major disturbance and the periodic formation of small canopy gaps. I established 12 plots of 0.1 ha in four areas of old growth to describe the stand-scale disturbance regime of forests dominated by eastern hemlock (Tsuga canadensis (L.) Carrière) in northern Adirondack Park, N.Y., U.S.A. I analyzed radial-increment patterns of cores from all canopy trees (398 trees in total) on each plot to determine the date of accession to canopy for each tree. Major growth releases indicated disturbance events that resulted in either gap origin (16% of events) or release from suppression (82% of events). The average decadal rate of disturbance for all plots and decades of the 130-year period from 1850 to 1979 is 4.8–5.4% of current exposed crown area. The average canopy-tree residence time is 184–211 years. The stand-scale disturbance regimes in these Adirondack forests are similar to those of hemlock–hardwood forests in Wisconsin, Michigan, Pennsylvania, and New York. These hemlock-dominated old-growth stands appear to be in quasi-equilibrium when viewed together over 13 decades.Les forêts anciennes ont souvent une structure d'âge complexe et irrégulière qui reflète à la fois la longue période de temps écoulé depuis une perturbation majeure et la formation périodique de petites trouées dans le couvert. Douze placettes de 0,1 ha ont été établies dans quatre zones de forêt ancienne pour décrire le régime de perturbation des forêts dominées par la pruche du Canada (Tsuga canadensis (L.) Carrière) dans le nord du parc des Adirondacks (État de New York, États-Unis). Les patrons de croissance radiale ont été analysés à partir des carottes de tous les arbres du couvert (398 arbres au total) de chaque placette, de façon à déterminer, pour chaque arbre, le moment d'acces sion au couvert. Les regains de croissance les plus importants sont liés à des perturbations qui ont causé soit une trouée (16% des évènements), soit une libération de la suppression (82% des évènements). Le taux moyen décennal de perturbation pour toutes les placettes et les décennies de la période de 130 ans entre 1850 et 1979 est de 4,8 à 5,4% de la surface actuelle des cimes exposées. Le temps de résidence moyen des arbres dans le couvert varie de 184 à 211 ans. Les régimes de perturbation à l'échelle du peuplement dans ces forêts des Adirondacks sont comparables à ceux observés dans les forêts de pruche et de feuillus des états du Wisconsin, du Michigan, de la Pennsylvanie et de New York. Ces peuplements de forêt ancienne dominés par la pruche semblent être proches de l'équilibre lorsqu'ils sont analysés ensemble sur 13 décennies.[Traduit par la Rédaction]
Examines characteristics that affect the ability of trees and shrubs to respond to openings created by natural disturbances, emphasising those traits that determine the kinds of disturbances in which a species is most likely to be successful in reaching reproductive size. Attention focuses on trees of closed forests, particularly the deciduous and mixed conifer-hardwood forests of E North America. Examination of the establishment of woody plants following disturbance includes discussion of seed production and dispersal, seed storage and germination, and seedling establishment. Comments are then made on growth and resource use by woody plants following disturbance. Factors such as patchiness in the patterns of seedling establishment, differences in the timing of establishment, and regrowth of surviving plants following disturbance can all act to reduce the importance of differential growth rates and efficiencies in vegetation regrowth. -P.J.Jarvis
Canopy stratification is one of the oldest concepts in tropical forest ecology. However, there has been considerable debate over the existence and identification of strata. Much of the confusion arises from the differing definitions of strata (i.e. vertical stratification of phytomass, individual crowns, or species) and the methods used to evaluate them (e.g. profile diagrams). In this paper, a quantitative technique for identifying stratification of individual tree crowns in the forest canopy is presented. Strata are identified by comparing sorted tree heights to a moving average of height at the base of the live crown. Height and crown measurements were obtained from 21 published profile diagrams of forests, representing many biogeographic regions and covering a wide variety of forest types. The technique provides an objective measure of canopy strata allowing for a valid comparison of stratification between the different profile diagrams. Neither the original author's estimates of strata nor the number of strata detected by the quantitative technique support the premise that tropical forests have more strata than temperate forests. With the sole exception of a mono-layered European Douglas-fir plantation, all forests in this study had two or three layers.