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Fire History and Climate Change in Giant Sequoia Groves
Abstract
Fire scars in giant sequoia [Sequoiadendron giganteum (Lindley) Buchholz] were used to reconstruct the spatial and temporal pattern of surface fires that burned episodically through
five groves during the past 2000 years. Comparisons with independent dendroclimatic reconstructions indicate that regionally
synchronous fire occurrence was inversely related to yearly fluctuations in precipitation and directly related to decadal-to-centennial
variations in temperature. Frequent small fires occurred during a warm period from about A.D. 1000 to 1300, and less frequent
but more widespread fires occurred during cooler periods from about A.D. 500 to 1000 and after A.D. 1300. Regionally synchronous
fire histories demonstrate the importance of climate in maintaining nonequilibrium conditions.
... fires (e.g., Swetnam 1993), there is also abundant evidence that Native Californians regularly used fire to manage the landscape and its affiliated resources. Fires were deliberately set to burn off woody understory taxa and conifer seedlings, which increased the amount of seasonal forage for large prey animals like mule deer, expanded productive grasslands (small grass seeds were critical to human subsistence in the region), and increased the productivity of patches of important foodstuffs like geophytes and fruiting plants (Stewart 1955;Bean and Lawton 1973;Lewis 1973;M. ...
... For example, pollen regionally indicates an opening forest canopy during low regional fire frequencies ca. 1600 -1650 C.E. and 1850 -2000 C.E. (Swetnam 1993;Swetnam et al. 2009 lor et. al (2016), sedimentary charcoal at Markwood Meadow increases ca. ...
... Thin colored line indicates pollen-derived VRI datapoints. Regional fire frequency study indicated by dotted (high frequency) or hashed (low frequency) overlay (Swetnam 1993;Swetnam et al. 2009). Vertical dashed lines indicate broad climatic time periods. ...
Background
Understanding pre-1850s fire history and its effect on forest structure can provide insights useful for fire managers in developing plans to moderate fire hazards in the face of forecasted climate change. While climate clearly plays a substantial role in California wildfires, traditional use of fire by Indigenous people also affected fire history and forest structure in the Sierra Nevada. Disentangling the effects of human versus climatically-induced fire on Sierran forests from paleoecological records has historically proved challenging, but here we use pollen-based forest structure reconstructions and comparative paleoclimatic-vegetation response modeling to identify periods of human impact over the last 1300 years at Markwood Meadow, Sierra National Forest.
Results
We find strong evidence for anthropogenic fires at Markwood Meadow ca. 1550 – 1750 C.E., contemporaneous with archaeological evidence for fundamental shifts in Indigenous lifeways. When we compare our findings to five other paleoecological sites in the central and southern Sierra Nevada, we find evidence for contemporaneous anthropogenic effects on forest structure across a broad swath of cismontane central California. This is significant because it implies that late 19th and early twentieth century forest structure – the structure that land managers most often seek to emulate – was in part the result anthropogenic fire and precolonial resource management.
Conclusion
We consequently suggest that modern management strategies consider (1) further incorporating traditional ecological knowledge fire practices in consultation with local tribal groups, and (2) using pollen-based reconstructions to track how forest composition compares to pre-1850 C.E. conditions rather than the novel forest states encountered in the late 20th and early twenty-first centuries. These strategies could help mitigate the effects of forecast climate change and associated megafires on forests and on socio-ecological systems in a more comprehensive manner.
... Current groves are often found in "microclimatic refugia"-locations with su cient late summer soil moisture (Rundel, 1972) coupled with a short historical re return interval. Indeed, dendrochronological reconstructions of re histories in S. giganteum groves demonstrate a positive relationship between re frequency and grove health (Swetnam, 1993;Stephenson and Demetry, 1995;McGraw, 2000;Stephenson, 2000;Carroll et al., 2014). Accordingly, reintroduction of re to S. giganteum groves has been recommended across their distribution, and applied with varying degrees of success (Kilgore and Biswell, 1971; Meyer and Safford, 2011;Parsons, 1993). ...
... In this vein, the re-introduction of prescribed re has been shown to increase forest resilience to drought stress by reducing competition for surviving trees (Harrod et al., 2008;van Mantgem et al., 2016). Reproduction in S. giganteum is re-dependent (Hartesveldt et al., 1975); re opens the serotinous cones and allows dispersal while simultaneously creating colonizable canopy gaps and bare mineral soil (Harvey et al., 1980;Weatherspoon, 1990;Swetnam et al., 1991;Swetnam, 1993 Shellhammer, 2006). However, post-re regeneration in temperate coniferous forests is highly spatially variable; seedling density and growth depend not only on re severity and distance to a seed source, but also microhabitat (Stevens-Rumann and Morgan, 2019). ...
Background
As fire regimes change under a warming climate, ideal tree seedling recruitment locations and conditions are important to understand for forest management and restoration. In forests adapted to frequent, low-intensity fire, reintroduction of fire is often the preferred or recommended management approach. Little work, however, has explored the interacting roles of local-scale microhabitat and fire severity in determining post-fire recruitment. Here we use a back burn applied to a giant sequoia (Sequoiadendron giganteum [Lindl.] Buchholz) grove in Yosemite National Park, California, to ask how sub-meter microhabitat variation influences seedling establishment and growth following fire.
Results
Post-fire S. giganteum seedling establishment was greatest in microhabitats with lower burn severity, higher post-fire sequoia litter, higher moss cover, and higher presence of sequoia cones.
Conclusion
These results indicate the importance of burn severity coupled with propagule pressure and post-fire surface organic matter in defining the seedling regeneration niche. These attributes should be incorporated in future fire management and seedling recruitment plans.
... The apparent success of S. giganteum in the UK has also raised interest in their utility as commercial and amenity trees that may be resilient to the changing climate and environment, particularly rainfall, soil moisture and fire, as they are in their natural range [14,15]. The research arm of the UK's Forestry Commission, Forest Research, has investigated the viability of S. giganteum as a climate-and disease-resilient species for diversifying UK commercial forestry [16]. ...
... In addition to environmental factors, the growth response of the UK giant sequoia is directly affected by management actions. Conversely, fire is the main factor affecting competition in the native range of the species [6,15]. The grand house to which Havering avenue led was demolished in 1925 [57], with the land becoming the property of the local council, which has allowed native woodland to grow up around the giant sequoias (see figure 2). ...
Giant sequoias (Sequoiadendron giganteum) are some of the UK’s largest trees, despite only being introduced in the mid-nineteenth century. There are an estimated half a million giant sequoias and closely related coastal redwoods (Sequoia sempervirens) in the UK. Given the recent interest in planting more trees, partly due to their carbon sequestration potential and also their undoubted public appeal, an understanding of their growth capability is important. However, little is known about their growth and carbon uptake under UK conditions. Here, we focus on S. giganteum and use three-dimensional terrestrial laser scanning to perform detailed structural measurements of 97 individuals at three sites covering a range of different conditions, to estimate aboveground biomass (AGB) and annual biomass accumulation rates. We show that UK-grown S. giganteum can sequester carbon at a rate of 85 kg yr⁻¹, varying with climate, management and age. We develop new UK-specific allometric models for S. giganteum that fit the observed AGB with r ² > 0.93 and bias < 2% and can be used to estimate S. giganteum biomass more generally. This study provides the first estimate of the growth and carbon sequestration of UK open-grown S. giganteum and provides a baseline for estimating their longer-term carbon sequestration capacity.
... We used Superposed Epoch Analysis (SEA) to assess the influence of climatic conditions in previous years and the year of fire occurrence (Swetnam 1993). The six fire seasons with the largest (1986-1987, 1993-1994, 2000-2001, 2003-2004, 2013-2014, 2017-2018) and smallest (1991-1992, 1996-1997, 2004-2005, 2011-2012, 2014-2015, 2015-2016) burned areas were selected for analysis. ...
Background Natural and anthropogenic wildfires burn large areas of arid and semi-arid forests with significant socioeconomic and environmental impacts. Fire regimes are controlled by climate, vegetation type, and anthropo-genic factors such as ignition sources and human-induced disturbances. Projections of climate and land-use change suggest that these controlling factors will change, altering fire regimes in the near future. In the southern Central Monte, Mendoza, Argentina, the factors that modulate the fire temporal and spatial variability are poorly understood. We reconstructed the fire history of southeast of Mendoza from 1984 to 2023 and investigated the relationships between fire extent and climate variability at seasonal and interannual scales. Burned areas were determined using Google Earth Engine by processing Landsat 5-TM, Landsat 7-ETM+ , and Landsat 8-OLI-TIRS sensor imagery. Results The region exhibited high spatial and temporal variability in fire occurrence, being a mosaic of areas with different fire histories and recovery times. Between 1985 and 2023, fire recurrence ranged from sites unburned to sites with up to 14 fires. The occurrence of large fires was strongly favored by a combination of a year with abundant spring-early summer precipitation, which favors fuel accumulation, followed by a year of low spring-early summer precipitation. Precipitation and burnt area showed a very pronounced 6-7 year cycle, suggesting a dominant climatic control on fire occurrence. Conclusions Fire distribution in southeastern Mendoza forests is not homogeneous, resulting in a mosaic of patches with different fire histories. This heterogeneity may be related to vegetation patterns and land use. The temporal variability of fires is strongly influenced by climate variability, which would promote fuel production and subsequent drying. Large fires are concentrated in periods of high interannual precipitation variability. Climate change scenarios predict an increase in temperature and precipitation variability in the region, suggesting future changes in fire dynamics. Our results contribute to the development of fire guidelines for southeastern Mendoza forests, focusing on periods of wet years followed by dry years that favor fire occurrence and spread.
... The closing canopy signal in the VRI between 1625 and 1750 does not correspond with reported charcoal, which indicates five events during this period. Anderson and Stillick note that the charcoal reconstruction corresponds well with regional fire scar studies (Swetnam, 1993;Swetnam et al., 2009), further supporting my argument that charcoal likely reflects climate and does not necessarily capture established cultural burning. Therefore, both pollen-based methods find evidence for cultural burning from 1550 to 1800. ...
Paleoecology and paleolandscape modeling have the potential to differentiate cultural burning from climatic fires, improving interpretations of past fire histories and vegetation resource management practices. People have conducted variations of traditional fire management to increase terrestrial resources for hundreds of millennia, commonly in fire-prone areas where vegetation is adapted to frequent fire events. Over time, these cultural fires influenced regrowth and led to an anthropogenically-modified landscape. For some non-agrarian, semi-nomadic societies, such as the pre-Colonial groups within what is now known as California, identifying anthropogenic landscapes is difficult because of a lack of domesticated plant remains in the environmental record to indicate where human impacts occurred. This paper uses case studies from the central and southern Sierra Nevada range in California to explore the potential of paleoecology, specifically pollen and sedimentary charcoal, and spatially-explicit paleolandscape modeling to identify and distinguish periods of cultural burning in mountainous forests to improve archaeological interpretations of human-fire dynamics. Specifically, I use climate-vegetation dynamics and cluster analysis to look at temporal relationships of change between sites. These case studies are ideal because (1) the region is naturally fire-prone, (2) study sites are typically well-dated and analyzed at a sub-centennial resolution, (3) study sites are associated with archaeological sites, and (4) indigenous groups were proto-agricultural, balanophagy societies known to practice cultural burning. These case study sites show a strong potential to identify periods of cultural burning that help better inform archaeological interpretations and show synchronous evidence for cultural burning during the Little Ice Age (1250-1850). Furthermore, these studies provide better dated timelines of human influence at each site than nearby archaeological studies, indicating that in certain locales, paleoecological studies with high temporal resolutions could be used to inform the timing of archaeological activities and shifts.
... Understanding the spatial differences in overstory AGB at two points in time across a landscape has various applications in forest management policies such as fuel classification, fire spread prediction, and post-disturbance vegetation changes [34][35][36]. Such information can improve our understanding of how trees and forests respond and will continue to respond towards changes in disturbance regimes [37] and help silviculturists design restoration treatments that move forests towards more resilient conditions similar to reference conditions. ...
Restoring current ponderosa pine (Pinus ponderosa Dougl. Ex P. and C. Laws)-dominated forests (also known as “dry forests”) to spatially resilient stand structures requires an adequate understanding of the overstory spatial variation of forests least impacted by Euro-American settlers (also known as “reference conditions”) and how much contemporary forests (2016) deviate from reference conditions. Because of increased tree density, dry forests are more spatially homogeneous in contemporary conditions compared to reference conditions, forests minimally impacted by Euro-American settlers. Little information is available that can be used by managers to accurately depict the spatial variation of reference conditions and the differences between reference and contemporary conditions. Especially, forest managers need this information as they are continuously designing management treatments to promote contemporary dry forest resiliency against fire, disease, and insects. To fill this knowledge gap, our study utilized field inventory data from reference conditions (1934) along with light detection and ranging and ground-truthing data from contemporary conditions (2016) associated with various research units of Blacks Mountain Experimental Forest, California, USA. Our results showed that in reference conditions, above-ground biomass—a component of overstory stand structure—was more spatially heterogeneous compared to contemporary forests. Based on semivariogram analyses, the 1934 conditions exhibited spatial variation at a spatial scale < 50 m and showed spatial autocorrelation at shorter ranges (150–200 m) compared to those observed in contemporary conditions (>250 m). In contemporary conditions, prescribed burn with high structural diversity treatment enhanced spatial heterogeneity as indicated by a greater number of peaks in the correlograms compared to the low structural diversity treatment. High structural diversity treatment units exhibited small patches of above-ground biomass at shorter ranges (~120 to 440 m) compared to the low structural diversity treatment units (~165 to 599 m). Understanding how spatial variation in contemporary conditions deviates from reference conditions and identifying specific management treatments that can be used to restore spatial variation observed in reference conditions will help managers to promote spatial variation in stand structure that has been resilient to wildfire, insects, and disease.
... In recent years, the urbanization process in Zhejiang province has been speeding up. With the increase in the frequency of natural hazards, it is prone to natural hazards and highly vulnerable to climate change, rapid industrial development and urbanization 26 . ...
Household adaption to natural hazards has been critical in disaster prevention and mitigation in disaster-prone regions. However, the adaption of urban household to natural hazards is not yet fully understood, especially in the subtropical forested region of Southeast China. In this study, we investigated the urban household adaption to natural hazards in the forested region of southeastern China by using a multinomial logistic regression model to analyze 763 urban household questionnaire responses from 6 districts in Hangzhou City, Zhejiang province. The results indicated that (1) from high to low, the top 6 natural hazards deeply concerned by urban household of Hangzhou City were typhoon, rainstorm, lightning, flood, low temperature disaster and snow disaster and (2) gender, length of family residence, disaster awareness and household satisfaction all significantly influenced the urban household adaption to natural hazards. This study suggested that Government should improve channels for disaster publicity, strengthen community management and promote social emergency construction in future decades.
Disturbance ecology is an expansive topic complicated by the reality that it is a scientific discipline that also directly engages the general public, who regularly witness and are affected personally by these events. In this chapter, we begin with some basic but necessary definitions and then sample an enormous literature to highlight a series of fundamental lessons about disturbances and disturbance regimes. These lessons include: whether disturbances are “inside” or “outside” the system, the roles of interacting factors and indirect effects, positive feedback in disturbance regimes, and persistent disturbance legacies. Above all, the lessons underscore the role of disturbances as profound agents of pattern over a range of spatial and temporal scales. We adopt a model template for understanding disturbances that is useful because it is expressed in terms that are general without being vague, and specific without being idiosyncratic to a particular type of disturbance. We then revisit the Sierran case study from the previous chapters, to layer a fire regime onto the forest process and the physical template of this landscape. Finally, we consider the characteristic scaling of disturbance regimes in space and time, as a prelude to a more formal exploration of ecological scale in the next chapter.
Efforts to delineate the influence of atmospheric variability on regional wildfire activity have previously been complicated by the stochastic occurrence of ignition and large fire events, particularly for Southern California, where anthropogenic modulation of the fire regime is extensive. Traditional metrics of wildfire activity inherently contain this stochasticity, likely weakening regional fire–climate relationships. To resolve this complication, we first develop a new method of quantifying regional wildfire activity that aims to more clearly capture the atmospheric fire regime component by aggregating four metrics of fire activity into an annual index value, the Annual Fire Severity Index (AFSI), for the 27-year period of 1992–2018. We then decompose the AFSI into trend and oscillatory components using singular spectrum analysis (SSA) and relate each component to a set of five climate predictors known to modulate macroscale fire activity in Southern California. These include the Atlantic Multidecadal Oscillation (AMO), Pacific Decadal Oscillation (PDO), El Niño–Southern Oscillation (ENSO), and Santa Ana wind (SAW) events, and marine layer frequency. The results indicate that SSA effectively isolates the individual influence of each predictor on AFSI quantified by generally moderate fire–climate correlations, |r|>0.4, over the full study period, and |r|>0.5 over select 13–15-year periods. A transition between weaker and stronger fire–climate relationships for each of the oscillatory PC–predictor pairs is centered around the mid-2000s, suggesting a significant shift in fire–climate variability at this time. Our approach of aggregating and decomposing a fire activity index yields a straightforward methodology to identify the individual influence of climatic predictors on macroscale fire activity even in fire regimes heavily modified by anthropogenic influence.
An independently developed tree ring chronology for bristlecone pine in
the White Mountains, California, provides a basis for testing the
accuracy of dendrochronological calibration of the radiocarbon time
scale. Several lines of evidence show that the growth rings in this
species are true annual rings. Internal evidence and cross-chronology
comparison indicate that there is no error in calendar dates assigned to
wood specimens for comparative radiocarbon analysis, at least back to
3535 B.C.
Temporal patterning of disturbance may play an important role in determining the effects of disturbance on species diversity. To describe this temporal patterning, a 'phasing parameter' is developed, and mechanisms by which this parameter affects the relative abundances of fugitive and competitively dominant species are discussed.-from Author Dept Ecology & Evolutionary Biology, Northwestern University, Evanston, Illinois 60201, U.S.A.
The authors begin by outlining the role of the dendrochronologists both in the field and in the laboratory. The basic principles of tree-ring dating are then explained in detail, followed by a guide to the collection of archaeological and modern specimens from the field. The final section deals with the laboratory techniques used: the preliminary processing and preparation of archaeological and modern specimens; the process of dating specimens; and finally the compilation of a master chronology.
Data on the years in which fires burned, on fire frequency, and on intensity and areal extent of fires were gathered from 935 scars on 220 stumps of mixed conifer forest species in an 1800ha-study area in the Sierra Nevada, California, USA. Before 1875, fires scarred clusters of living trees every 9 yr on west-facing slopes at Redwood Mountain and every 16 yr on east-facing slopes. Mean fire-free intervals between 1700 and 1875 varied by habitat phase from 5 yr in ponderosa pine on a dry ridge to 15-18 yr in more moist sites with white fir. For most 1-ha sites, the maximum time without fire was 14-28 yr. From 1700 to 1875, fires of various sizes were found every 2-3 yr somewhere in a given drainage (not necessarily the same site) and every 5-9 yr in 3to 16-ha sites. This compares with fires every 8-18 yr in 1-ha clusters and every 11-39 yr on individual trees. Scar records of pre-1700 fires suggest intervals fairly comparable to those from 1700 to 1875. Evidence of fires diminished greatly after Indian burning was eliminated in the early 1870's, and such fire records became almost nonexistent after 1900, when fire suppression became more effective. Most of the pre-1875 fires were small and of low intensity. Even the larger fires were usually confined to 1 slope or 1 drainage area. The short mean intervals between fires suggest that pre-1875 mixed conifer forests did not usually have heavy accumulations of litter or dense thickets of understory trees. Instead, small-acreage, low-intensity surface fires must have consumed accumulated litter at frequent intervals and at the same time killed most of the conifer regeneration which had become established since previous fires. Such frequent fires would have led to an intricate mosaic of age classes and vegetation subtypes which, in turn, insured that a subsequent fire would not burn large areas with great intensity. Intense fires which moved from crown to crown were absent in the study area for the past 400 to 2000 yr. If frequency of lightning ignition of fires over the past 50 yr is typical, ignitions by Indians must have augmented lightning-caused fires to yield the pre-1865 frequency of fires in the Sierra mixed conifer forest. Since 1900, the lack of frequent, low-intensity fires has resulted in a major increase in understory forest and fuels.
A successional process model has been adapted for use with species from ponderosa pine/Douglas-fir (Pinus ponderosa var. ponderosa)/(Pseudotsuga menziesii var. glacua) forests of the inland Northwest. Its design allows modification for application to other forest types. This model, FIRESUM, simulates tree establishment, growth, and mortality, along with live and dead fuel accumulation, fire behavior, and fuel reduction on a 400-m² plot. The modeling contains algorithms for influences on tree establishment and growth including temperature, water stress, light tolerance, and site quality. The model was used to predict 200 yr of forest succession for five different disturbance regimes. This allowed comparison of patterns of basal area by species, of duff and fuel accumulation, and of fire intensities among the following scenarios: (1) no fires (fire suppression), (2) consistent fire intervals of 10, 20, and 50 yr, and (3) a natural fire regime of variable intervals reconstructed from fire scarred trees. These five scenarios resulted in a differential survival of species determining dominance in the understory and eventually in the overstory. A test of the model showed predictions to be within 19% of field observations, and a sensitivity analysis of FIRESUM showed parameters associated with the growth algorithm to be most critical for predicting successional trends.
Aboriginal Indian occupance of Sequoia National Park began about 1000 A. D. Periodic burning to aid in food gathering and lightning-caused fires led to the development of a vegetation cover considered to be “natural.'’In the 1860s, a period of resource exploitation began, as sheepherders drove their flocks throughout the area and set fires to increase forage. With the establishment of the Park in 1890, the federal government initiated a protectionist resource management policy; steps were taken to prevent and suppress all fires. Increased forest densities and fire dangers led to disagreement on this policy. In the 1960s, experiments were begun with controlled burning and natural fire zones; these led to the development of a management policy based on the natural functioning of ecosystems.
Two primary goals of landscape ecologists are to (1) evaluate changes in ecological pattern and process on natural landscapes through time and (2) determine the ecological consequences of transforming natural land-scapes to cultural ones. Paleoecological techniques can be used to reconstruct past landscapes and their changes through time; use of paleoecological methods of investigation in combination with geomorphic and paleoethnobiological data, historical records, and shorter-term ecological data sets makes it possible to integrate long-term ecological pattern and process on a nested series of temporal and spatial scales. ‘Natural experiments’ of the past can be used to test alternative hypotheses about the relative influences of environmental change, biological interactions, and human activities in structuring biotic communities within landscape mosaics.
On the absolute time scale of the Quaternary Period, spanning the past 1.8 million years, current distributional ranges of the biota have taken shape and modern biotic communities have assembled. Quaternary environmental changes have influenced the development of natural landscapes over time scales of centuries to hundreds of thousands of years; human cultural evolution has resulted in the transformation of much of the biosphere from natural to cultural landscapes over the past 5,000 years. The Quaternary extends to and includes the present and the immediate future. Knowledge of landscape changes on a Quaternary time scale is essential to landscape ecologists who wish to have a context for predicting future trends on local, regional, and global scales.