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Dynamic Structure of Wave-Regenerated Abies Balsamea Forests in the North- Eastern United States
Journal of Ecology
Abstract
Many high-altitude forests of balsam fir (Abies balsamea (L.) Mill.) in the north-eastern United States are characterized by `wave regeneration', a peculiar type of disturbance pattern in which trees continually die off at the front edge of a `wave' and are replaced by vigorous regeneration. This apparently takes place because when an opening occurs in the forest, the canopies of the trees at the leeward edge of the opening, exposed to the prevailing wind, die from a combination of loss of branches and needles in winter due to heavy rime accumulations, death of needles due to winter desiccation, and decreased primary productivity due to cooling of needles in summer. This exposes the trees behind them, which die in turn, and so a `wave' of dying trees moves through the forest. The direction of motion of the waves appears to be controlled by the prevailing wind, while the speed which varies from 1 to 3 m yr-1 is determined by the degree of exposure to the wind. Wave-regenerated forests are fairly common in the north-east, having been observed in the mountains of New York, New Hampshire and Maine. Very similar forests have been described in Japan. The growth pattern of this forest is basically cyclical. Regeneration waves tend to follow each other at approximately sixty year intervals, so the average stand developing after a wave has passed lasts about sixty years before another wave comes through and begins the regeneration process again. Because of the regularity of this process, all stages of degeneration and regeneration are present in the forest at all times; moreover, degenerative changes in one part of the forest are typically balanced by regenerative changes elsewhere, so the composition of the forest as a whole remains relatively constant with time. The ecosystem is thus in what might be termed a steady-state.
... Due to the complexity of integrating fine and broad spatial-temporal scales in ecosystem processes (Carpenter and Turner 2000), most studies investigating the effects of global environmental change in forest regeneration tend to consider broader-scale factors (Petrie and others 2016 and references therein; Maré chaux and others 2021) and while often neglecting microsite variables such as substrate type (McCarthy 2001). Compared to much better studied fine-scale effects of forest gaps on light, microclimate, nutrient cycling, microclimate, and forest regeneration (for example, Sprugel 1976;Prescott 2002;Abd Latif and Blackburn 2010;Muscolo and others 2014), the effects of substrate type on tree seedlings are less well understood. Yet, substrate can influence moisture and nutrient availability (Oleskog and Sahlé n 2000;Mori and others 2004), exposure to pollutants (Delach and Kimmerer 2002), and ultimately tree seedling survivorship (Cornett and others 1998;Mori and others 2004) and abundance (Simard and others 1998;Mori and others 2004). ...
... To improve the understanding of the complex effects of the moss layer on forest regeneration under changing environmental conditions, we studied moss-tree seedling interactions in high-elevation balsam fir (Abies balsamea (L.) Mill.) dominated forests in northeastern United States that are particularly sensitive to both changing climate (Wason and others 2017a) and deposition of mercury (Gerson and others 2017). Importantly, these high-elevation forests are characterized by fir wave regeneration dynamics that consist of alternating contrasting canopy environments-elongated gaps and closed canopies (fir waves)-formed by wind and ice abrasion in mountains in northeastern United States and around the world (Bekker and Malanson 2008;Sprugel 1976). These distinct canopy environments interact with both atmospheric deposition of mercury (higher under forest canopies where litter with mercury accumulates; Hanson and others 1995;Blackwell and others 2014) and climate-change-induced heat and drought stress (higher in gaps where solar radiation is higher; Will and others 2013). ...
... Details of the study area were previously described in Berdugo and Dovciak (2019) and elsewhere (for example, Battles and others 2003;others 2017b, 2021). Briefly, Whiteface Mountain is an isolated massif with the summit at 1,485 m above sea level (asl) and well-developed elevational climatic and vegetation zones whose ecology has been extensively studied over the past half century (for example , Sprugel 1976;Battles and others 2003;Aleksic and others 2009;Wason and others 2017b). The vegetation of the area belongs to the Adirondack-New England Highlands ecosystem province (Bailey 2014) and is representative of regional forest communities with northern hardwood forests occurring below 800 m asl, spruce-fir forests between 800 and 1300 m asl, and alpine communities above 1350 m asl (Battles and others 2003). ...
The persistence of future forests depends on the success of tree seedlings which are experiencing increasing physiological stress from changing climate and air pollution. Although the moss layer can serve as an important substrate for tree seedlings, its potential for reducing environmental stress and enhancing the establishment of seedlings remains poorly understood. We tested if the moss layer decreased environmental stress and increased the abundance of balsam fir seedlings dominant in high-elevation forests of northeastern United States that are sensitive to changing climate and mercury deposition. We surveyed balsam fir seedling density by substrate (moss, litter, other) on 120 quadrats (1 × 1 m) in two contrasting canopy environments (in gaps and under canopies), measured seedling stress, and quantified mercury content in seedlings and substrates. We observed that, in both canopy environments, tree seedlings established on moss exhibited (i) increased density, (ii) decreased physiological stress, and (iii) higher potential to recruit into larger size classes, compared to seedlings established in litter. Regardless of canopy environment, seedling foliar mercury levels did not correspond to substrate mercury despite large differences in substrate mercury concentrations (relative to moss, litter concentrations were ~ 4-times greater and soil concentrations were ~ 6-times greater), likely reflecting the dominance of foliar over root uptake of mercury. Because the moss layer appeared to mitigate seedling drought stress, and to increase seedling establishment and recruitment compared to other substrates, these microsite effects should be considered in models predicting forest regeneration and dynamics under increased drought stress associated with the ongoing climate warming.
... High-elevation conifer forests represent an ideal model system to test GPH and G S PH for bryophyte communities because bryophytes are abundant and forest dynamics is driven by fir waves that form a mosaic of distinct environments including canopy gaps of different sizes, gap edges, and surrounding forest canopy (Sprugel, 1976). Fir waves are characteristic of high-elevation forests dominated by fir (Abies Mill.) ...
... Fir waves are characteristic of high-elevation forests dominated by fir (Abies Mill.) where waves of tree mortality due to ice and wind damage result in elongated canopy gaps that vary considerably in size (with gap widths measured in tens and lengths in hundreds of meters; Sprugel, 1976;Bekker & Malanson, 2008). Canopy openness follows steep gradients between open gap center and adjacent forest canopy over short distances (e.g., 60 m; Sprugel, 1976) where the surrounding forest canopy mediates environmental and biological conditions (cf. ...
... where waves of tree mortality due to ice and wind damage result in elongated canopy gaps that vary considerably in size (with gap widths measured in tens and lengths in hundreds of meters; Sprugel, 1976;Bekker & Malanson, 2008). Canopy openness follows steep gradients between open gap center and adjacent forest canopy over short distances (e.g., 60 m; Sprugel, 1976) where the surrounding forest canopy mediates environmental and biological conditions (cf. Wright, Coates, & Bartemucci, 1998;Kern et al., 2013). ...
Aims
Bryophytes can cover three quarters of the ground surface, play key ecological functions, and increase biodiversity in mesic high‐elevation conifer forests of the temperate zone. Forest gaps affect species coexistence (and ecosystem functions) as suggested by the gap and gap‐size partitioning hypotheses (GPH, GSPH). Here we test these hypotheses in the context of high‐elevation forest bryophyte communities and their functional attributes.
Study Site
Spruce–fir forests on Whiteface Mountain, NY, USA.
Methods
We characterized canopy openness, microclimate, forest floor substrates, vascular vegetation cover, and moss layer (cover, common species, and functional attributes) in three canopy openness environments (gap, gap edge, forest canopy) across 20 gaps (fir waves) (n = 60); the functional attributes were based on 16 morphologic, reproductive, and ecological bryophyte plant functional traits (PFTs). We tested GPH and GSPH relative to bryophyte community metrics (cover, composition), traits, and trait functional sensitivity (functional dispersion; FDis) using indicator species analysis, ordination, and regression.
Results
Canopy openness drove gradients in ground‐level temperature, substrate abundance and heterogeneity (beta diversity), and understory vascular vegetation cover. The GPH was consistent with (a) the abundance patterns of forest canopy indicator species (Dicranum fuscescens, Hypnum imponens, and Tetraphis pellucida), and (b) FDis based on three PFTs (growth form, fertility, and acidity), both increasing with canopy cover. We did not find support for GPH in the remaining species or traits, or for GSPH in general; gap width (12–44 m) was not related to environmental or bryophyte community gradients.
Conclusions
The observed lack of variation in most bryophyte metrics across canopy environments suggests high resistance of the bryophyte layer to natural canopy gaps in high‐elevation forests. However, responses of forest canopy indicator species suggest that canopy mortality, potentially increased by changing climate or insect pests, may cause declines in some forest canopy species and consequently in the functional diversity of bryophyte communities.
... Одновременной сменыпоколений, сопровождающейся массовыми вывалами, не происхо-] дит. В чистых пихтовых горных лесах возможно «волновое» ; восстановление лесов [203], которое наблюдается на верхней гра-' нице леса в горах штата Нью-Йорк (США). Вывал одной или группы бальзамических пихт приводит к оголению крон окружаю-] щих их деревьев, что ведет к гибели пихт на подветренной стороне! ...
... Так, цикл развития еловых лесов в средней и южной тайге составляет 200-380 лет [29, 46, 88]. Пихто-еловые леса имеют цикл развития 120-170 лет [66,109,144], иногда около 300 лет [111], а в горных условиях -60 лет" [203]. Тем не менее массовые ветровалы -относительно редкое явление. ...
... Через десятки лет эти деревья вырастают и закрывают просвет в древесном пологе, изменив освещенность нижних ярусов растительности и увеличив конкуренцию с ними за элементы минерального питания и воду. Такая фитоциклическая 170 домутация в пределах фитоценоза характерна для всех разновозрастных лесов [135,144,177,203,211]. Каждый этап демутации пространственно образует парцеллу в БГЦ. ...
Скворцова Е. Б., Уланова Н. Г., Басевич В. Ф. Экологическая роль ветро-валов.-М.: Лесн. пром-сть, 1983.-192 с.
Рассмотрено одно из важнейших явлений в жизни леса: вывал деревьев под действием ветра и других факторов. Освещено влияние ветровалов на почвенно-растительныи покров леса, на лесовозобновление. Раскрыты причины ветровала, скорость разрушения валежа, эволюция почвы и растительности на месте вываленного дерева. Впервые предложена методика датирования ветровального микрорельефа, рассмотрены методы диагностики ветровальных, нарушений почвы. На основе хронологического подхода исследовано изменение размеров и формы ветровального микрорельефа. Включенные в книгу материалы полезны в методическом отношении при детальном картировании лесных почв. Для научных работников лесного хозяйства. Полезна геоботаникам, почво-ведам, биологам, а также преподавателям, аспирантам и студентам лесохозяй-ственных вузов. Табл. 36, ил. 42, библиогр.-214 названий. Рецензенты: д-р биол. наук Л. О. Карпачевский (МГУ) и д-р биол. наук Л. П. Рысин (АН СССР).
... The majority of older-aged forest in New England is at high elevation, whereas forest management and historical legacies of agricultural conversion strongly influence the characteristics of lowland forest (Publicover and Kimball 2011;Ducey et al. 2013). Harsh climate at high elevation also contributes to structurally complex forest (Sprugel 1976). Combined, these dynamics may influence space use and resource selection by martens, given that they often have large or shifting home ranges in landscapes that contain managed forest (Thompson and Colgan 1987;Thompson and Harestad 1994;O'Doherty et al. 1997;Fuller and Harrison 2005), minimize early regenerating forest (<30 years) within home ranges (Katnik 1992;Chapin et al. 1998;Potvin et al. 2000;Cheveau et al. 2013), and prefer forested stands with complex structure (e.g., coarse woody debris (CWD) and >30% canopy cover; Potvin et al. 2000;Payer and Harrison 2003;Bull et al. 2005;Godbout and Ouellet 2008), especially during winter (Fuller and Harrison 2005). ...
... High-elevation forest (>823 m; New Hampshire Wildlife Action Plan 2005) was dominated by uncut red spruce (Picea rubens Sarg.), balsam fir (Abies balsamea (L.) Mill.), yellow birch (Betula alleghaniensis Britton), white birch (Betula papyrifera Marshall), and sugar maple (Acer saccharum Marsh.), and interspersed with spruce-fir waves (Sprugel 1976) along ridgelines (950-1060 m). The majority of forest along mountain flanks below 823 m was primarily hardwood composed of yellow birch, sugar maple, American beech (Fagus grandifolia Ehrh.), red maple (Acer rubrum L.), aspen (species of the genus Populus L.), white birch, red spruce, and balsam fir. ...
The threats that affect a species often vary within its geographic range. Wood Turtles (Glyptemys insculpta (Le Conte, 1830), formerly Clemmys insculpta (Le Conte, 1830)) are a species of concern due to widespread decline from anthropogenic threats. We studied two populations of Wood Turtles from June to September 2019 and 2020 to evaluate how landscape features and vegetative structure influenced space and habitat use and to identify potential risks in the remote, northern parts of its range. We hypothesized that space use would vary due to regional, landscape, and sex-specific differences. Turtles at the conifer-dominated site with higher road density had significantly smaller home ranges than the site with expansive and contiguous floodplains (7.25 ± 1.92 ha and 26.28 ± 6.77 ha, respectively). Females moved farther away from rivers than males (136.00 ± 23.68 m and 69.18 ± 34.81 m, respectively) and made the longest single-event movements. However, movements by males were significantly longer (34.65 ± 1.91 m) than females (23.99 ± 1.03 m) and followed rivers. At finer spatial scales, we found that turtles selected activity areas with complex vegetative structure and a more open canopy. Our study indicates that populations in contiguous forest could be critical to the conservation of Wood Turtles and we discuss management recommendations to reduce potential mortality risks in the northern part of its range.
... Following the initial wave of vegetation research, Whiteface continued to be a key research location for vegetation and forest dynamics in parallel with other work in the neighboring Green (Siccama 1974) and White Mountains (Leak 1975, Reiners andLang 1979). For example, fir-waves were first identified and described on Whiteface (Sprugel 1976, Sprugel andBormann 1981 phenomenon (Bekker and Malanson 2008) describing a migrating pattern of tree mortality and regeneration common in mountain forests dominated by Abies spp. As small canopy gaps open in the forest, exposed trees become more susceptible to mortality from the prevailing wind direction (Holroyd 1970) leading to a migrating front of mortality followed by a wave of regeneration (Fig. 4). ...
... As small canopy gaps open in the forest, exposed trees become more susceptible to mortality from the prevailing wind direction (Holroyd 1970) leading to a migrating front of mortality followed by a wave of regeneration (Fig. 4). Fir-waves have been reported to move 1-3 m per year and are an example of the dynamic nature of natural forest communities (Sprugel 1976), and recent research on Whiteface has elaborated on the importance of the moss layer in fir-wave regeneration in these high-elevation forests (Berdugo and Dovciak 2020). ...
Research at sentinel research sites focuses on long-term ecological monitoring related to global environmental changes. Despite the value of sentinel research sites during the Anthropocene, the factors that drive their development, success, and sustainability are not clear. Here we study the history of Whiteface Mountain, NY—a sentinel research site in global environmental change research. We review the origins of Whiteface Mountain as a research site, its contributions to forest ecosystem science, and the factors that contributed to the location’s development, success, and sustainability. We identified 6 key characteristics that contributed to the success of Whiteface Mountain as a sentinel research site: (a) accumulation of high-quality long-term data, (b) features representative of a broad area, (c) availability of appropriate infrastructure and staffing, (d) sustained governmental and community support, (e) active communication and outreach programs, and (f) dedicated leadership. These characteristics provide a roadmap for the successful development and sustainable operation of sentinel research sites in global environmental change research.
... Wave-regeneration is often observed in subalpine fir forests on slopes facing prevailing winds in several global regions, including Japan and northeastern North America (Iwaki and Totsuka 1959, Sprugel 1976, Boyce 1988, Kohyama 1988). Their landscapes are characterized by visible strips of dead trees between living stands, with a sequential arrangement between from smaller-to larger-sized trees down the slope. ...
... Many studies have described the stand structure and dynamic features of wave-regenerated forests (e.g. Okubo 1933, Oshima et al. 1958, Sprugel 1976, Tadaki et al. 1977, Kohyama and Fujita 1981, Kimura 1982, Ugawa et al. 2007. Without catastrophic disturbance such as severe blowdown, strips of new dead trees were observed year by year at the edges of mature stands in the windward direction. ...
Understanding post-disturbance reforestation processes could make a valuable contribution towards predicting the impacts of future changes in disturbance regimes on forest ecosystems. In this study, we aimed to estimate biomass dynamics in a wave-regenerated fir forest following blowdown. Three research forest stands at different developmental stages (young, intermediate, and mature; 19, 36, and 59 years-old, respectively) were established in a wave-regenerated Abies forest on Mt. Shimagare in central Japan, where a severe large-scale windthrow event occurred during a typhoon landfall in 1959 (Typhoon "Vera"). For each stand, above-and below-ground biomass was estimated using tree census data measured repeatedly from 2001 to 2008 and size-mass allometric equations developed based on the sample trees' data. Growth patterns were also examined by tree ring analysis. The estimated biomass was the lowest in the young stand, but reached a similar level in both intermediate and mature stands. During the research period, mean height and estimated mass of trees were increasing in all sites but plot biomass were not increasing in the mature site because of mortalities of canopy trees. In the intermediate stand, tree ring analysis showed that post-typhoon seedlings could grow fast and thus a similar biomass accumulated to that in the mature stand, where trees originated from advanced seedlings that existed in high density prior to the disturbance. Compared to mature wave-regenerated fir forest without disturbance, mature forest in this study had lower biomass and the onset of mortality started earlier. These results suggest that typhoon disturbance affect subsequent forest structures and biomass accumulation.
... Clearcut logging generally creates large patches of similar aged trees and, with sustained yield management objectives, tends to normalize the age and vertical structure of forest landscapes. On the other hand, natural disturbances, particularly on high elevation sites, tend to create small and scattered patches of forest regrowth, creating lots of variability in forest structure at small scale (<4 ha; Lambert et al., 2017;Sprugel, 1976;Reiners and Lang, 1979). This can provide a greater availability of smaller patches of suitable habitat (COSEWIC, 2009). ...
... At high elevation sites, this might have excluded older forest stands with high stem density, due to harsh climate and small-size natural disturbances, which could provide additional habitat suitable for BITH (Ruel, 2000). Third, we may have underestimated the impacts of natural disturbances related to wind such as windthrow and fir waves (sensu Sprugel, 1976) which can also favor the creation of suitable BITH habitat. Finally, SBW outbreaks were simulated at their highest severity; this might have contributed to create more regenerating balsam fir stands, and hence potential BITH habitat, then would be expected under a less severe SBW outbreak regime. ...
With climate change, natural resource managers are faced with the challenging task of planning the conservation of habitat for threatened species. Classified as "threatened" under the Species at Risk Act in Canada, the Bicknell's Thrush (Catharus Bicknelli - BITH) is a migratory bird whose range is highly restricted. Bioclimatic models project more than 50% loss of suitable habitat - high elevation dense balsam fir (Abies balsamea) forests - in the northeastern USA by 2050 due to climate change. We used BITH as a case study to demonstrate the value of forest landscape models (e.g., LANDIS-II) to support decision- making on conservation of habitat of threatened species. We modeled the impacts of for- est management and natural disturbances, as well as climate-induced changes, on forest stand and landscape structure. Under RCP climate forcing scenarios 2.6, 4.5 and 8.5, simulations projected significant changes in dominant tree species biomass, from coniferous to broadleaved deciduous, implying important losses of mature balsam fir forest. Climate change was projected to have severe effects with major changes projected to occur after 2080 and losses of more than half of BITH suitable habitat by 2100 for “worst-case” climate change scenarios. This contrasts with results from bioclimatic models which do not capture the expected lags in vegetation responses to changing climate. Our results also suggest that innovative forest management strategies could help maintain BITH habitat abundance under RCP 2.6 and RCP 4.5 climate forcing. Such results can provide guidance for considering effective long-term conservation of habitat for threatened species in a changing world.
... Recent commentators have gone so far as to describe the abandonment of the classical notion of a regional climax by modern ecologists (Pickett 1976) or cite the notion of climax as having been a "rather oppressive influence on the minds of many ecologists" (Sprugel 1976). On the other hand, White (1979), while acknowledging the problematic nature of the term "climax," did not advocate its complete abandonment. ...
... When released after years of suppression, such seedlings respond vigorously and often grow at rates equal to that of seedlings that did not experience suppression (Hatcher 1960;Logan 1969;Crossley 1976;Hatcher 1964;Herring 1977;Seidel 1977Seidel , 1980Ferguson and Adams 1980;Alexander 1987;Tucker et al. 1987;Antos et al. 2000). Fir species may thus be considered small gap specialists, but not in an obligate sense, for fir will grow rapidly and vigorously in large patches created after removal of the parent canopy as a result of clearcutting (Vincent 1956;Hughes 1964), insect outbreaks (Vincent 1962;Fye and Thomas 1963;Bakuzis and Hansen 1965), windthrow (Kimura et al. 1986), stand attrition and breakup (Baskerville 1965), and wind-induced wave forests in high-altitude fir forests (Iwaki and Totsuka 1959;Sprugel 1976). ...
Small-scale gap disturbance in forests is reviewed. Caused by the death of individual or multiple trees with subsequent fall from the canopy, gaps have been extensively studied in temperate deciduous and tropical forests for the past 20 years. This review considers much of this research with a view to assessing the importance of gap disturbance in boreal forests. Because of the ubiquity of large-scale, stand-initiating disturbances such as landscape-level fires, epidemic insect outbreaks, and periodic extensive windthrow events, gap processes in boreal forests have received little attention. Research in the Scandinavian and Russian boreal forest, as well as in high-altitude boreal "outliers" found in Japan and the United States, is showing that gap disturbance determines forest structure and processes to a greater extent than previously assumed. Boreal forests dominated by the shade-tolerant fir (Abies) - spruce (Picea) complex are particularly well-adapted to the development of long-term, old-growth continuity in the absence of large-scale disturbance.
... Montane boreal forests in the northeastern United States represent unique climate and mature forests (Sprugel 1976, Dingman 1981, Cogbill 1996 that support locally threatened carnivores such as American marten (Martes americana; Sir en et al. 2016b) and Canada lynx (Hoving et al. 2005). Despite their importance to threatened wildlife, these forests are undergoing increased wind farm development. ...
... Elevation in the study area ranged from 619-1,056 m with high-elevation forest (>823 m; New Hampshire Wildlife Action Plan 2015) characterized by red spruce (Picea rubens) and balsam fir (Abies balsamea) stands, interspersed with paper birch (Betula papyrifera) inclusions and regenerating spruce-fir waves (Sprugel 1976) at the highest elevations. The terrain was gradual in the valleys with slopes ranging from 0-108, with steeper slopes at mid-to high-elevation (11-528); cliff bands and steep ravines were common along the shoulder of the mountain ridgelines ( Fig. 1). ...
Wind power development is regarded as a clean energy source. Efforts to mitigate climate change, however, may degrade habitat and compromise wildlife. During winter 2011–2012, we examined the potential influence of a wind farm on a community of carnivores in the New England-Acadian Forest, northern New Hampshire, United States, with a focus on American martens (Martes americana), a mid-to late-successional forest species adapted for snow. We counted marten, red fox (Vulpes fulva), and coyote (Canis latrans) tracks and measured snowpack along roads, and snowmobile and hiking trails to determine the relative influence of wind farms on space use for each species. We observed all species at high-elevations (>823 m), although use frequency varied by road or trail type. As expected, we detected martens most often at high elevations along hiking trails and least often along wind farm roads. We observed the opposite pattern for red foxes and coyotes. Additionally, there was a higher probability of observing canids when snow depth increased and a lower probability when penetrability increased. Although our results indicate spatial partitioning, the edge habitat and compacted snow created by wind farm roads increased access for canids to high-elevation forest. In addition to habitat loss and fragmentation, these conditions may increase competition for martens and lower population viability. Future wind development should minimize disturbance of rare habitats, especially those considered climate refugia. Ó 2017 The Wildlife Society.
... Jirisan decreased by approximately 18%, from 262 ha in 1981 to 216 ha in 2007 (Kim and Lee 2013). Species belonging to the section Balsamea in the genus Abies, including Korean fir, have a regenerative mechanism that utilizes the changed conditions after dieback or decline due to a mass mortality event (Iwaki and Totsuka 1959;Sprugel 1976;Kohyama 1982Kohyama , 1984Diaci et al. 2011). ...
Although climate change-related concerns have long been raised regarding the sudden dieback of Korean fir ( Abies koreana ), the event’s etiology and subsequent ecosystem processes must be explained. Our study aims to clarify the continuity or transience of mass mortality events within the coarse woody debris (CWD) structure and, if transient, to identify the climatic conditions (1974–2021) that could be responsible for the massive dying phenomena in Korean fir populations. On average, precipitation during the non-growing season (November–April as winter) constituted 18.5% relative to the growth period; in the winter of 1999, it was 4.8% due to an abnormal drought event. The dead stems occurred evenly across all size classes. In the CWD structure, the density and biomass of the dead fir individuals peaked in decay classes II or III. The size distribution of the retained fir was inverse-J shaped across the entire altitudinal range. The abnormal winter drought event, causing root damage by soil frost and heaving, may be one of the factors that increased Korean fir mortality across the entire stem size range. Despite transient cohort senescence, the retained Korean fir individuals transmitted drought-resistant traits into the regional pool following the drought event.
... This sinusoidal pattern may have been due to negative edge effects on vegetation growth at intermediate distances that were ameliorated at further distances, thus following a pat-tern more similar to natural variations associated with gap dynamics (McCarthy 2001;Seymour et al. 2002). Greater density and growth along the forest edge may, in fact, create wave patterns in forest structure into the interior forest (Sprugal 1976;Robertson 1991;Taylor and MacLean 2007). Our design did not allow us to examine whether these secondary increases were once again reduced at further distances. ...
Deforestation causes forest fragmentation and associated edge effects. The boreal forest of Alberta, Canada has undergone substantial fragmentation via the creation of seismic lines, roads, and wellpads for resource exploration and extraction, but their associated edge effects have not been fully assessed, particularly for the latter two footprint types. We examined how these disturbances influence forest composition and structure along anthropogenic forest edges in the oil sands region of northeastern Alberta. We then used generalized linear models to test distance to edge responses in tree and shrub density given treatment (disturbance) type and forest canopy composition. Our results indicate the presence of edge effects, even along narrow seismic lines. Tree and shrub density and tree basal area were greater at the forest edge, being two times greater at 1 m from the forest edge relative to intermediate interior forest distances (∼30 m). Variations in tree basal area, tree density, and shrub and sapling density were best explained by interactions between disturbance type, distance from the forest edge, and % conifer composition. This study demonstrates that anthropogenic disturbances from energy exploration in the boreal forests cause changes in tree and shrub density (structure), and this effect is most pronounced in deciduous-dominated forests.
... The transitions between adjacent zones are gradual and are not welldefined. Within each zone there are important secondary patterns that result from variations in soil texture, soil moisture, microclimate, slope, aspect, and disturbance history (Braun 1950, DiNunzio 1972, Heimberger 1934, Holway et al. 1969, Kudish 1975, 1981, Nicholson et al. 1979, Reiners and Lang 1979, Scott and Holway 1969, Sprugel 1976, Young 1934. For a more detailed description of vegetation see Jackson (1990). ...
... Cloud-droplet and rime-ice deposition are not recorded by standard rain gauges but occur in significant amounts at high elevations in northeastern mountains (Schlesinger and Reiners, 1974). Lovett et al. (1982) estimate that such deposition may increase effective precipitation those observed in mountainous regions of northeastern North America (Bray, 1915;Braun, 1950;Costing and Billings, 1951;McIntosh and Hurley, 1964;Holway et al., 1969;Scott and Holway, 1969;Bormann et al., 1970;DiNunzio, 1972;McIntosh, 1972;Siccama, 1974;Sprugel, 1976;Reiners and Lang, 1979). ...
... Other typical cases of line demarcations within vegetation landscapes exist, too. Among many others, let us cite wave regeneration lines in north-eastern US spruce forests (Sprugel, 1976), and banded or patchy vegetation patterns in semi-arid environments (Ludwig et al. , 1999;Sileshi et al. , 2010). In all cases so far reported in the absence of any ecological barriers a keystone species (Paine, 1969) or a keystone functional group (Ortiz et al. , 2013) is in play, interacting with the biotic or abiotic environment and modifying it to the advantage of some species and to the disadvantage of some others. ...
Communities are shaped by the activity of ecosystem engineers, which modify their environment to their benefit and that of subordinate species within their functional domain. Communities are defined as embedded assemblages of interactions, from cells to landscapes. They are threatened by present-day global changes which trigger the invasive nature of ecological engineers, with cascading effects. This perspective paper starts with a definition of ecosystem engineers and functional domains in the frame of developments in community ecology. Then I show that the concepts of ecosystem engineer and functional domain explain (i) most of the observed cases of community boundaries, and (ii) the passage from small-scale interactions among individuals to community-wide processes of dynamics and stability. I will further show that ecological engineering exists at various scales, from viruses to landscapes, functional domains being embedded in a flexible manner. At last, I will show that threats posed by global changes to communities are mainly mediated by their negative or positive effects on ecosystem engineers.
... The third pattern of wind-caused trees cluster ("tree waves" or "mortality waves") was observed in the northeastern US mountain forest formed by Abies balsamea (L.) Mill. where winds caused trees mortality by mechanical root damage (Sprugel 1976;Reiners and Lang 1979). ...
We hypothesize that in mountain windy habitat trees formed clusters (hedges) as adaptive structures for seedlings’ rooting, survival, and tress’ upslope migration. We studied hedges formed by Siberian pine (Pinus sibirica du Tour) and larch (Larix sibirica Ledeb.) within the treeline ecotone in southern Siberian Mountains, investigated hedges formation, evolution, habitat amelioration, and analyzed tree’s growth index (GI) dependence on the eco-climate variables (air temperature, precipitation, soil moisture, wind speed) and relief features (elevation, aspect, slope steepness, and terrain curvature). We conducted a ground survey, measured biometrical parameters of trees and hedges, determined species composition and tree physiognomy, soil types and nutrient contents, and sampled wood cores and applied dendrochronology for trees’ GI analysis. With high-resolution satellite scenes for hedge detection and upslope migration, we found that winter winds and soil moisture are the main constraints of trees’ settlement and growth. Hedge formation always links with wind-sheltered microtopography features (boulders, local depressions or felled trees). Once the first tree is established, a positive feedback is aroused that facilitates seedling rooting and in-hedge habitat amelioration. Trees form a streamlined dense “common crown” that mitigates adverse winter wind influence. Hedges always orient along the prevailing winds, and trees’ uphill migration occurs by seedlings establishment within the leeward hedge side. Hedge growth facilitates soil formation and fertilization. The concentration of nutrients (K, P, N and S) within hedges exceeds the background by 1.5–5.5 times. Hedge extension leads to increased snow accumulation that mitigates the influence of desiccation and snow abrasion and mitigates seasonal water stress. In the extremely harsh windy habitat, in-hedge trees present in mat, prostrate or krummholz forms. With warming, tree stems and even twigs turn upright. Notably that GI dependence on the wind speed is insignificant until prostrated trees get turning upright. Since that, the negative correlation between GI and wind speed is arisen with subsequent decrease since hedges form streamlined crown. Hedge growth also leads to a “phytofield” formation (i.e., grasses, lichen, moss and small bushes growth) around the hedges that, in its turn, encourages seedling rooting which is about triple more efficient than outside the phytofield. Larch, in comparison with Siberian pine, is less often formed hedges. GI of both species is stimulated by warmer air temperature in the beginning of the growth season. Meanwhile, larch GI has stronger response to elevated temperatures and less dependent on soil moisture. This indicates larch is a potential substitute of Siberian pine in a warmer and dryer climate. Hedges in warming climate evolve into closed stands due to both in-hedge tree growth and filling gaps between hedges by different tree species.
... Additionally, unlike other boreal species such as black spruce that produce seedbanks that can exist in the canopy for sev- eral years and disperse following a fire, balsam fir does not produce a persistent seed bank, so seed dispersal is dependent upon living trees (Houle and Payette 1991). The seed dispersal strategy of balsam fir is also negatively affected by fire; it undergoes wave regeneration, in which seedlings establish close to the parent tree (Sprugel 1976). Consequently, balsam fir rarely colonizes areas affected by stand-replacing fires as easily as species with a higher seed dispersal range, such as trembling aspen (Populus tremuloides Michx.) and paper birch (Betula papyrifera Marsh.) ...
Balsam fir (Abies balsamea) is one of the most abundant softwood species in eastern Canada but is projected to be adversely affected by climate change. Balsam fir decline could occur due to a combination of reduced germination and regeneration, lower growth and competitive ability, and higher rates of mortality. However, tree regeneration represents one of the most vulnerable stages to climate-induced stress. In this paper, we synthesize potential and observed effects of climate change on balsam fir regeneration. Recent studies have shown no detrimental effects of increased temperatures on either germination or seedling growth of balsam fir, but clear deleterious effects of decreased water availability. Balsam fir seeds require 28–60 days of cold stratification to become germinable, and such conditions should still be met under climate change across most of the species’ range. Sampling along a north-south climatic gradient throughout the Acadian Forest Region of eastern Canada indicated effects are complex and do not suggest a clear decline under warmer, drier conditions for the species. Thus, effects of global warming on balsam fir may be more gradual than projected in modeling studies and occur primarily via reduced competitive ability and/or higher mortality in overstory trees, rather than regeneration failure.
... For instance inhibition may represent the spread of agents such as pathogens or predators from one population to the next, resulting in suppressed local populations as the respective wave passes. Theoretical expectations of travelling waves have been supported by empirical evidence from a variety of fields, all of which can be considered to have such activator-inhibitor relationships; for example herbivore-plant, predator-prey, parasite-host (Berthier et al., 2014;Bierman et al., 2006;Johnson et al., 2004;Lambin et al., 1998;Mackinnon et al., 2001;Moss et al., 2000), susceptible-recovered, (Cummings et al., 2004;Grenfell et al., 2001), death and regeneration (Sprugel, 1976) and cellular biochemistry (Bailles et al., 2019;Müller et al., 1998). Within such systems, the cumulative impact of both activator and inhibitor gives rise to the overall cyclic pattern. ...
The dynamics of cyclic populations distributed in space result from the relative strength of synchronising influences and the limited dispersal of destabilising factors (activators and inhibitors), known to cause multi‐annual population cycles. However, while each of these have been well studied in isolation, there is limited empirical evidence of how the processes of synchronisation and activation–inhibition act together, largely owing to the scarcity of datasets with sufficient spatial and temporal scale and resolution. We assessed a variety of models that could be underlying the spatio‐temporal pattern, designed to capture both theoretical and empirical understandings of travelling waves using large‐scale (>35,000 km²), multi‐year (2011–2017) field monitoring data on abundances of common vole (Microtus arvalis), a cyclic agricultural rodent pest. We found most support for a pattern formed from the summation of two radial travelling waves with contrasting speeds that together describe population growth rates across the region.
... The third pattern of wind-caused trees cluster ("tree waves" or "mortality waves") was observed in the northeastern US mountain forest formed by Abies balsamea (L.) Mill. where winds caused trees mortality by mechanical root damage (Sprugel 1976;Reiners and Lang 1979). ...
Birch (Betula tortuosa) is one of the treeline forming species within the Siberian Mountains. We analysed the area dynamics of birch stands and the upslope climb of birch treeline based on the Landsat time series scenes and on-ground data. We found that since the warming onset (1970th) birch area increased by 10%, birch stands and treeline boundary were moving upslope with a rate of 1.4 m/yr and 4.0 m/yr. Birch upslope shift correlated with air temperatures at the beginning (May-June) and the end (August-October) of the growth period. Meanwhile, no correlation was found between birch upslope migration and precipitation. Winds negatively influenced both birch area growth and birch upslope climb during spring, fall, and wintertime. In the windy habitats, birch, together with larch and Siberian pine, formed clusters (hedges) which mitigated the influence of adverse winds. These clusters are the adaptive pattern for trees’ upslope climb within windward slopes. The other adaptation to the harsh alpine ecotone habitat is non-leaf (bark) photosynthesis which supports tree survival. Thereby, Betula tortuosa upslope climb depends on the wind impact and warming in spring and fall that extended growth period. With ongoing warming and observed wind speed decrease on the background of sufficient precipitation, it is expected to further birch advance into alpine tundra in the Siberian Mountains.
... Other typical cases of line demarcations within vegetation landscapes exist, too. Among many others, let us cite wind-induced wave regeneration lines along slopes in Japanese (Iwaki & Totsuka, 1959) and US (Sprugel, 1976) coniferous forests, or banded or patchy vegetation patterns in semiarid environments (Ludwig et al., 1999;Sileshi et al., 2010). In all cases so far reported in the absence of any ecological barriers a keystone species (Paine, 1969) or a keystone functional group (Ortiz et al., 2013) is in play, interacting with the biotic or abiotic environment and modifying it to the advantage of some species and to the disadvantage of some others. ...
Communities are shaped by the activity of ecosystem engineers, which modify their environment to their benefit and that of subordinate species within their functional domain. Communities are defined as embedded assemblages of interactions, from cells to landscapes. They are threatened by present‐day global changes which trigger the invasive nature of ecological engineers, with cascading effects. This perspective paper starts with a definition of ecosystem engineers and functional domains in the frame of developments in community ecology. Then I show that the concepts of ecosystem engineer and functional domain explain (i) most of the observed cases of community boundaries, and (ii) the passage from small‐scale interactions among individuals to community‐wide processes of dynamics and stability. I will further show that ecological engineering exists at various scales, from viruses to landscapes, functional domains being embedded in a flexible manner. At last, I will show that threats posed by global changes to communities are mainly mediated by their negative or positive effects on ecosystem engineers.
... Other typical cases of line demarcations within vegetation landscapes exist, too. Among many 173 others, let us cite wind-induced wave regeneration lines along slopes in Japanese (Iwaki & Totsuka, 174 1959) and US (Sprugel, 1976) coniferous forests, or banded or patchy vegetation patterns in semi-arid 175 environments (Ludwig et al., 1999;Sileshi et al., 2010). In all cases so far reported in the absence of 176 any ecological barriers a keystone species (Paine, 1969) or a keystone functional group (Ortiz et al.,177 2013) is in play, interacting with the biotic or abiotic environment and modifying it to the advantage of 178 some species and to the disadvantage of some others. ...
Communities are shaped by the activity of ecosystem engineers, which modify their environment to their benefit and that of subordinate species within their functional domain. Communities are defined as embedded assemblages of interactions, from cells to landscapes. They are threatened by present-day global changes which trigger the invasive nature of ecological engineers, with cascading effects. This perspective paper starts with a definition of ecosystem engineers and functional domains in the frame of developments in community ecology. Then I show that the concepts of ecosystem engineer and functional domain explain (i) most of the observed cases of community boundaries, and (ii) the passage from small-scale interactions among individuals to community-wide processes of dynamics and stability. I will further show that ecological engineering exists at various scales, from viruses to landscapes, functional domains being embedded in a flexible manner. At last, I will show that threats posed by global changes to communities are mainly mediated by their negative or positive effects on ecosystem engineers.
... Studies of the feedback loop between ecological pattern and process, a central theme of landscape ecology, can benefit from the study of visually striking vegetation patterns. For example, the phenomena of ''fir waves'' (e.g., Oshima et al., 1958;Sprugel, 1976;Reiners and Lang, 1979), and ''ribbon forest'' (e.g., Billings, 1969;Holtmeier, 1982;Butler et al., 2003) in subalpine environments, and ''tiger bush'' (e.g., White, 1969White, , 1970Tongway et al., 2001) in arid and semiarid environments illustrate the importance of interactions between vegetation patterns and various climatic, hydrologic, and geomorphic processes. Ecotones, transition areas between adjacent ecological systems, provide another focus for the study of patternprocess interactions, as the systems and the abiotic and biotic factors influencing them interact at multiple scales to form unique characteristics over space and time (Wiens et al., 1985;Holland, 1988;Gosz and Sharpe, 1989;Gosz, 1991). ...
The development and maintenance of several types of visually striking vegetation patterns are controlled by positive feedback between pattern and process. These patterns are particularly common at ecotones, where the influence of positive feedback may affect the position and dynamics of the boundary between the adjacent biotic communities. In this study, I use dendrochronology to examine the role of feedback between existing trees and the establishment and survival of seedlings in the advancement of linear, finger-like strips of subalpine forest in Glacier National Park, Montana. A general upslope, windward to leeward pattern of older trees followed by progressively younger trees was evident in all sample transects, although in some cases this pattern repeated several times along the length of a transect, with each repetition originating leeward of boulders. Overall advancement rates varied from 0.28 to 0.62 m yr⁻¹. The oldest trees established in the early to mid-1700s, but establishment and advancement increased rapidly after 1850, and peaked in the early 1900s. In addition, almost all seedlings established within 5 m downwind of existing trees between 1700 and 1850, while establishment beyond this distance was common after 1850. These patterns suggest that existing trees facilitate leeward seedling establishment and survival, by depositing wind-blown snow. These seedlings in turn modify their leeward environment, thus allowing forest advancement in a linear pattern. Feedback was critical for the survival of seedlings before 1800, and strongly controlled advancement between about 1800 and 1850, but appears to have had little effect on establishment patterns since that time. The importance of feedback between pattern and process may change over time and space as a result of changes in climatic conditions or biotic surroundings.
... Disturbance loops. Several examples of cyclic succession have been published, in systems such as heathlands (Watt 1947, Bokdam 2001, coniferous forests (Sprugel 1976), alpine tundra (McPhail and Kirkpatrick 2016), intertidal habitats (Benincà et al. 2015), and oceanic island forests (Mueller-Dombois et al. 2013). Less attention has been paid to the cyclic disturbances associated with those same systems, perhaps because the time lags involved (table 1) make their interactions less obvious. ...
Global change has been accompanied by recent increases in the frequency and intensity of various ecological disturbances (e.g., fires, floods, cyclones), both natural and anthropogenic in origin. Because these disturbances often interact, their cumulative and synergistic effects can result in unforeseen consequences, such as insect outbreaks, crop failure, and progressive ecosystem degradation. We consider the roles of biological legacies, thresholds, and lag effects responsible for the distinctive impacts of interacting disturbances. We propose a hierarchical classification that distinguishes the patterns and implications associated with random co-occurrences, individual links, and multiple links among disturbances that cascade in chains or networks. Disturbance-promoting interactions apparently prevail over disturbance-inhibiting ones. Complex and exogenous disturbance cascades are less predictable than simple and endogenous links because of their dependency on adjacent or synchronous events. These distinctions help define regional disturbance regimes and can have implications for natural selection, risk assessment, and options for management intervention.
... Finally, physical mortality agents including crushing and some forms of wind-related mortality (e.g., wind waves) may be regarded as distance-dependent as probability of mortality is positively related to the proximity to a falling tree (Das et al. 2008) or the edge of a gap (Taylor 1990). Patches of wind-related mortality are often associated with root-and stem-rot (Sprugel 1976), and their spatial structure is therefore additionally influenced by the distribution and spread of saprophytic decay fungi. Physical mortality agents that operate at broader spatial scales, such as wind, ice, and snow storms, are most strongly determined by environmental heterogeneity (Rebertus et al. 1997) and the spatial variability in the intensity of the weather event (Pasher and King 2006). ...
Abstract Background tree mortality is a complex process that requires large sample sizes and long timescales to disentangle the suite of ecological factors that collectively contribute to tree stress, decline, and eventual mortality. Tree mortality associated with acute disturbance events, in contrast, is conspicuous and frequently studied, but there remains a lack of research regarding the role of background mortality processes in mediating the severity and delayed effects of disturbance. We conducted an empirical study by measuring the rates, causes, and spatial pattern of mortality annually among 32,989 individual trees within a large forest demography plot in the Sierra Nevada. We characterized the relationships between background mortality, compound disturbances (fire and drought), and forest spatial structure, and we integrated our findings with a synthesis of the existing literature from around the world to develop a conceptual framework describing the spatio‐temporal signatures of background and disturbance‐related tree mortality. The interactive effects of fire, drought, and background mortality processes altered the rate, spatial structuring, and ecological consequences of mortality. Before fire, spatially non‐random mortality was only evident among small (1
... The results of these simulations were used to identify regions within the S and T parameter space that suggested qualitatively different dynamics based on quantitative patterns in the mean and variance of the proportion of the landscape occupied by the mature successional stage [sensu 30]. These regions represent the range of observed or theoretically predicted dynamics, including steady state dynamics [34,35], stable dynamics with repeating recovery sequences characterized by low or high response fluctuations [36,37], and unstable dynamics [38]. The definition of each region is as follows: region A, where the landscape is relatively undisturbed, the mature stage is dominant (> 50% of the landscape) and variance is low (< 5), indicating equilibrium dynamics; region B, where disturbance is more frequent, the mature stage is dominant and variance is low (5-10), indicating stable dynamics with low variance; region D, where disturbance is still more frequent, the mature stage is < 50% of the landscape and variance is low (5-10), indicating stable dynamics with low variance; and regions C and E, where coverage of the mature stage fluctuates substantially producing high (10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) or very high (> 20) variance, respectively, indicating stable dynamics with high variance; and region F, where disturbances are both frequent and large, producing low variance (< 5) and unstable dynamics, as the mature stage is no longer dominant over the duration of the simulation. ...
Altered ecosystem variability is an important ecological response to disturbance yet understanding of how various attributes of disturbance regimes affect ecosystem variability is limited. To improve the framework for understanding the disturbance regime attributes that affect ecosystem variability, we examine how the introduction of stochasticity to disturbance parameters (frequency, severity and extent) alters simulated recovery when compared to deterministic outcomes from a spatially explicit simulation model. We also examine the agreement between results from empirical studies and deterministic and stochastic configurations of the model. We find that stochasticity in disturbance frequency and spatial extent leads to the greatest increase in the variance of simulated dynamics, although stochastic severity also contributes to departures from the deterministic case. The incorporation of stochasticity in disturbance attributes improves agreement between empirical and simulated responses, with 71% of empirical responses correctly classified by stochastic configurations of the model as compared to 47% using the purely deterministic model. By comparison, only 2% of empirical responses were correctly classified by the deterministic model and misclassified by stochastic configurations of the model. These results indicate that stochasticity in the attributes of a disturbance regime alters the patterns and classification of ecosystem variability, suggesting altered recovery dynamics. Incorporating stochastic disturbance processes into models may thus be critical for anticipating the ecological resilience of ecosystems.
... Seagrass shoots sometimes are arranged in rows (Fonseca et al., 2007) that can create anisotropic gaps in the canopy, and random arrangements of shoots can also create gaps in grass beds. Canopy gaps in terrestrial systems have long been recognized as local regions of higher light intensity and as initiation points of disturbance propagation (e.g., Sprugel, 1976;Veblen, 1985;Iwasa et al., 1991), and similar effects have been postulated for seagrasses (Fonseca et al., 1983;Valentine et al., 1994). Folkard (2011) studied how gaps within an array of flexible vegetation introduce flow into the canopy and described the likely role of gaps on various depositional process. ...
Water flow through seagrass beds transports nutrients, affects sediment stability and chemistry, and imposes hydrodynamic forces on shoots that alter canopy configuration. Past studies done under diverse conditions yielded conflicting results about the effects of shoot density on flow through seagrass bed canopies. We used eelgrass, Zostera marina, to study how the density of flexible shoots affect the hydrodynamics of seagrass beds in unidirectional water flow. By exposing randomly-arranged shoots of uniform length to current velocities controlled in a flume, the effects of shoot density and distance downstream from the bed edge could be determined without confounding factors. Comparison of velocity profiles within beds to those upstream of beds showed that flow was slower in the beds. However, shoot density, downstream distance, and current velocity did not affect the percent reduction in flow velocity in a bed. Turbulence enhances mixing of substances carried in the water. Here, turbulence intensity (index of the importance of turbulent velocity fluctuations relative to average current velocity) was lower when ambient flow was faster, but was not affected by shoot density or downstream position, Drag (hydrodynamic force on a shoot that bends it over in the flow direction) provides another measure of how the canopy affects flow experienced by a shoot. Drag was not affected by current velocity, shoot density, or downstream position in the bed. Gaps between shoots can enhance light and flow penetration into the canopy, but when shoots are bent over by flow, they can cover gaps. Faster ambient currents caused greater gap closure, which at each current speed was greater for high shoot densities. Thus, canopy gap closure did not correlate with percent flow reduction in grass beds or with drag on individual shoots, both of which were independent of shoot density and ambient current velocity. Since changing shoot density does not affect the flow in a grass bed exposed to a given ambient current, our results are inconsistent with the hypothesis that the high shoot densities observed in grass beds in habitats exposed to rapid flow are due to a direct, adaptive response of the grass to the flow environment.
... With infrequent fires, balsam fir established beyond the treeline in favorable microsites, and persists near its thermal limit by means of clonal layering. Balsam fir is not a common treeline species in Canada; its presence in krummholz form is more consistent with Appalachian mountain ranges (e.g., Reiners and Lang 1979;Sprugel 1976) and along the Labrador coast (Hustich 1953). Eastern larch had the lowest altitudinal limit with all but one stem found below 625 m a.s.l.-the approximate Mealy Mountains tree-form line. ...
Cone and seed production at the forest-tundra ecotone, or treeline, depend on species-specific tolerances to limiting abiotic and biotic factors. As range expansion via seed dispersal is needed to keep pace with climate change, reproductive limitations act as a bottleneck for treeline advance. The treeline in the Mealy Mountains, central Labrador, was comprised of four codominant species: black spruce (Picea mariana [Mill.] B.S.P.), white spruce (Picea glauca [Moench] Voss), eastern larch (Larix laricina [Du Roi] K. Koch), and balsam fir (Abies balsamea [L.] Mill.). Conifer stem surveys from three treeline zones (forest, forest-tundra transition, krummholz) were used to assess patterns of altitudinal distributions, tree densities, and cone production to provide insight into overall reproductive potential. The altitudinal limit of the spruce species was 39 m a.s.l. higher than the altitudinal limit of black spruce cone production. Black spruce had the highest densities of cone-bearing trees across treeline with eastern larch values being comparable in the forest-tundra transition zone, although overall cone production was low and highly variable in all species. Compared to the other treeline species, black spruce has the greatest reproductive potential for upslope advance.
... Furthermore, sequential community dynamics termed "wave regeneration" or "fir waves" have been observed in some subalpine Abies forests (Iwaki and Totsuka 1959), similar to those in Abies balsamea (L.) Mill. in the northeastern part of the United States (e.g. Sprugel 1976Sprugel , 1984Moloney 1986;Silvertown and Dodd 1999). A fir-wave results in a sequential wavelike arrangement of cohorts (e.g. ...
To determine the change in nutrient absorption capacity with stand development, we aimed to clarify the changes in fine root characteristics with stand development and stand characteristics. Stand characteristics (stand age, maximum tree height, tree density and basal area) and fine root characteristics were examined in three fir-wave stands that aged sequentially along the slope in a subalpine Abies forest in central Japan. The biomass, length, surface area and N content of fine roots did not change, but the specific root length (SRL) decreased with stand development, i.e. distance from the upper side of each transect. On the other hand, we observed an increase in fine root biomass with stand characteristics, i.e. maximum tree height and basal area of the Abies community, while a decrease in SRL was also observed. These changes resulted in an increase in surface area and N content of fine roots. However, the surface area of absorptive roots that were <0.5 mm in diameter did not change with stand characteristics. Thus, we suggest that the nutrient absorption capacity of the subalpine Abies community increased with aboveground biomass from the viewpoint of comprehensive activity of fine roots, but not from the viewpoint of fine root morphology. We further confirmed that the ratios of surface area and N content of fine roots to basal area decreased with stand development. Future research is needed to understand the actual effect of surface area and N content of fine roots on the maintenance of aboveground organs.
... Bicknell's Thrush nesting habitat quality seems to be mostly driven by elevation and associated vegetation dynamics (e.g., wind throw, fir waves sensu Sprugel 1976) in both the northeastern United States (Lambert et al. 2005, Hale 2006) and in Québec (Aubry et al. 2016). In Vermont, in mostly protected areas, occupancy of high-elevation habitat approaches 100% (Frey et al. 2012). ...
In North America, several migratory bird species inhabiting boreal and eastern forests are declining. Habitat loss is frequently cited as a limiting factor. We estimated occupancy of suitable nesting habitat by Bicknell's Thrush (Catharus bicknelli), a forest dwelling threatened species, in the Laurentian Highlands of Québec. Forests in this region are shaped by intensive forestry activities and natural disturbances. The species was found primarily in stands of about 20 years or more, with higher occupancy in older stands on hilltops where recent forestry activities and natural perturbations have been much less prevalent. Bicknell's Thrush occupancy was significantly associated with high elevations in landscapes with relatively low amounts of precommercial thinning. Occupancy and multivariate niche approaches indicated that a large extent of potential habitat (> 80%) was unoccupied by breeding Bicknell's Thrushes. We conclude that maintaining sufficient amounts of suitable breeding habitat in this exploited forest landscape remains important to enable the species' recovery, but that an increase in its numbers may not materialize without further measures unrelated to availability of breeding habitat.
... It is possible that the high abundance of Balsam Fir at some transects was related to the regeneration pattern of Balsam Fir. Wave regeneration comes about when Balsam Fir trees at the edge of a forest gap that are exposed to the prevailing wind die due to a variety of exposure-related causes (Sprugel 1976). In time, the Balsam Fir trees behind these trees also die, creating a spreading band (or wave) of dead trees, and bands of young, regenerating trees as well. ...
We collected water samples from upstream and downstream sites over 3 years on 18 study streams in the Adirondacks, NY, and conducted analysis via ANOVA for the presence of road-salt runoff, as measured by chloride ion content. Streams crossed by state roads received more road-salt runoff than streams crossed by county roads, as shown by higher mean chloride loads across different sampling years (P ≤ 0.01). The chloride load in streams was not reliably higher downstream from a road as opposed to upstream from a road for either state or county roads but varied in different sampling years (P < 0.001-P > 0.05). We collected a total of 1259 nymphs of Ephemeroptera, Plecoptera, and Trichoptera during water sampling. High levels of road-salt runoff were not associated with lower levels of Plecoptera or Trichoptera. Neither numbers of individuals nor numbers of genera of Ephemeroptera, Plecoptera, or Trichoptera collected per month showed any pattern when regressed on stream-chloride level. However, we detected no Ephemeroptera above a relatively high level of road-salt runoff (154 mg/L chloride ion). We employed the point-centered quarter method to assess forest composition on 10 transects above and below state roads. We conducted further analysis on trees in the lowest quartile of circumference in each transect as a representation of tree-species recruitment. Mean chloride-ion content of study streams, indicating adjacent forest exposure to road-salt runoff, was associated with greater recruitment of Abies balsamea (Balsam Fir), and lower Shannon-Weiner diversity. At the highest chloride levels, there was almost no recruitment of any species but Balsam Fir. Soil-cation analysis and linear regression, however, did not indicate concomitant depletion of plant nutrients, and therefore, we did not confirm the cause of the apparent relationship between higher road-salt runoff and higher Balsam Fir recruitment.
... Quantifying the impacts of climate change, climate variability, and disturbances on forest dynamics ultimately requires estimating recruitment dates, and thus tree age. Field-based methods such as node or bud-scar counts are commonly used to provide approximate tree ages, and they have the advantage of being efficient and non-destructive (Dovčiak et al., 2005;Haire and McGarigal, 2010;Harvey et al., 2016;Millar et al., 2004;Sprugel, 1976;Urza and Sibold, 2013). However, node and bud-scar counts are only proxies for true tree age (Urza and Sibold, 2013). ...
Accurately aging trees is critical for understanding tree demography and tree responses to environmental change. Given the proliferation of studies aimed at understanding the effects of climate and disturbance on forest ecosystems, it is important to understand the tradeoffs between field-based age estimates and precise dendrochronological techniques. We assessed the accuracy of age estimates from node counts in the field against precise tree-ring counts at the root-shoot boundary, in 1279 ponderosa pine and 1268 Douglas-fir seedlings sampled from across three study regions in the western U.S. We also assessed the accuracy of age estimates from bud-scar counts in the field against node counts and precise tree-ring counts in a subset of 757 seedlings from the Northern Rockies. Node counts systematically underestimated ring counts by an average of 4.1 years, with bias increasing with tree age. At annual, ±1-, ±2-, and ±5-yr precision, the accuracy of node counts was 5%, 15%, 29%, and 74% across all regions and species, respectively. Similar results were found for bud scars. Given the magnitude of the bias between field-based methods and ring counts, it is critical to select appropriate aging methods, based on the precision required to answer specific ecological questions. To improve the accuracy of field-based age estimates in these species, we provide a tool for correcting for the bias when precise dendrochronological aging is not feasible.
... Previously, old-growth forests were regarded as a stable climax community (Cajander, 1926;Odum, 1969;Weaver & Clements, 1938). Sernander (1936) and (Watt, 1947) emphasized disturbance as an important process in old-growth forest; however, it was not until the 1970s that this view was widely accepted (Borman & Likens, 1979;Heinselman, 1970;van der Maarel, 1996;Sprugel, 1976). ...
Stand dynamics and the gap initiation prior to gap formation are not well-understood because of its long-term nature and the scarcity of late-successional stands. Reconstruction of such disturbance is normally based on historical records and dendroecological methods. We investigated gap initiation and formation at the fine-scale stand level in the old-growth reserve of Karlshaugen in Norway. Given its long-term conservation history, and thorough mapping in permanent marked plots with spatially referenced trees, it provides an opportunity to present stand development before, during, and after gap formation. Late-successional decline in biomass was recorded after more than 50 years of close to steady state. Gaps in the canopy were mainly created by large old trees that had been killed by spruce bark beetles. Snapping by wind was the main reason for treefall. Long-term dominance of Norway spruce excluded downy birch and Scots pine from the stand. Comparisons of the forest floor soil properties between the gap and nongap area showed significantly higher concentrations of plant available Ca within the gap area. Plant root simulator (PRS™) probes showed significantly higher supply rates for Ca and Mg, but significantly lower K for the gap compared to the nongap area. Soil water from the gap area had significantly higher C:N ratios compared to the nongap area. Fine-scale variation with increasing distance to logs indicated that CWD is important for leaking of DOC and Ca. Our long-term study from Karlshaugen documents gap dynamics after more than 50 years of steady state and a multiscale disturbance regime in an old-growth forest. The observed disturbance dynamic caused higher aboveground and belowground heterogeneity in plots, coarse woody debris, and nutrients. Our study of the nutrient levels of the forest floor suggest that natural gaps of old-growth forest provide a long-lasting biogeochemical feedback system particularly with respect to Ca and probably also N. Norway spruce trees near the gap edge responded with high plasticity to reduced competition, showing the importance of the edge zone as hot spots for establishing heterogeneity, but also the potential for carbon sequestration in old-growth forest.
Populations along geographical range limits are often exposed to unsuitable climate and low resource availability relative to core populations. As such, there has been a renewed focus on understanding the factors that determine range limits to better predict how species will respond to global change. Using recent theory on range limits and classical understanding of density dependence, we evaluated the influence of resource availability on the snowshoe hare Lepus americanus along its trailing range edge. We estimated variation in population density, habitat use, survival, and parasite loads to test the Great Escape Hypothesis (GEH), i.e. that density dependence determines, in part, a species' persistence along trailing edges. We found that variability in resource availability affected density and population fluctuations and led to trade‐offs in survival for snowshoe hare populations in the northeastern USA. Hares living in resource‐limited environments had lower and less variable population density, yet higher survival and lower parasitism compared to populations living in resource‐rich environments. We suggest that density‐dependent dynamics, elicited by resource availability, provide hares a unique survival advantage and partly explain persistence along their trailing edge. We hypothesize that this low‐density escape from predation and parasitism occurs for other prey species along trailing edges, but the extent to which it occurs is likely conditional on the quality of matrix habitat. Our work indicates that biotic factors play an important role in shaping species' trailing edges and more detailed examination of non‐climatic factors is warranted to better inform conservation and management decisions.
The boreal zone, the Zonobiome VIII, begins where the climate becomes too unfavourable for the hardwood-deciduous species, i.e. where the summers become too short and the winters too long. It can be recognised in the climate diagram by the fact that the duration of time with daily means above 10 °C falls below 120 days and the cold season lasts more than six months, thus only 3–4 thermal months of vegetation are exhibited. The Northern boundary of ZB VIII against the Arctic is where about only 30 days with daily means above 10 °C and a cold season of 8 months are typical for the climate. The vegetation are often oceanic birch forests or continental coniferous forests (taiga), but often water-saturated mires and bogs may prevail.
The contribution of sapling banks to the coexistence of species with different shade tolerance under the “wave regeneration” regime has not been researched extensively. This study first assessed spatial and temporal variations in the relative dominance of two Abies species, Abies veitchii and Abies mariesii, with different shade tolerance in a wave‐regenerated forest. Second, we present the age structure and its spatial variation in young Abies stands (sapling stage) to exhibit the prevalence and variability of regeneration from sapling banks (defined as trees established 10 years before canopy opening). The relative dominance of A. mariesii, the more shade‐tolerant species, compared to that of A. veitchii, did not change over a period of 10 years, irrespective of stand developmental stages, indicating the importance of initial dominance in determining the local species composition. The tree ages at the sapling stage were significantly higher for A. mariesii than for A. veitchii. Approximately, 30% of all trees were likely to arise from a sapling bank, and 86% of them were A. mariesii. Age structure significantly varied between 5 × 5 m quadrats; some quadrats were dominated by A. mariesii originating from sapling banks, while others were dominated by A. veitchii that were established at the time of canopy opening. These results indicate that regeneration from sapling banks contributes to the dominance of A. mariesii and that the spatial variation in the abundance of trees originating from sapling banks is essential for the coexistence of A. mariesii with A. veitchii. Relative basal area of two Abies species did not change over a period of 10 years irrespective of stand developmental stage in spite of the difference in shade tolerance between the two species.
p>The overall aim of this work was to assess the importance of topographic complexity in structuring rocky shore communities. In order to achieve this the distributions of intertidal species were related to physically and biologically generated features of the habitat. In addition manipulative experiments were used to gain a more complete understanding of the processes in operation. Initially a review of the methods and indices used to measure habitat complexity was made. Three methods were compared using field trials: stereophotography, profile gauges and lengths of chain contoured over the substratum. Chains were the most efficient method to use, followed by stereophotography and profile gauges respectively. The results derived from the chain method and profile gauges were directly related, but stereophotography results were not comparable. Stereophotography, correlations between topographic features and the distribution of the overlying biota. This led to the development of an automated technique that directly linked these parameters. The strongest correlations between topographic features and biological distributions were typically observed for algal species. The influence of complexity, however, varied across a number of scales depending on the species examined. however, offered the additional benefit of allowing direct Both physical and biological complexity was demonstrated to have an important role in structuring rocky shore communities. Details of the recruitment of algae and sessile invertebrates to substrata of varying complexity were first examined. In order to achieve this the topography of the substratum was manipulated by the use of concrete blocks cast with differing surface features. The succession of intertidal communities was also observed on mussel beds. The recruitment of algae did not appear to be related to the complexity of the physical substratum, but was affected by biologically generated complexity. In contrast the settlement of barnacles was influenced by both habitat types. The distribution of mobile invertebrates in relation to topographic structures was highly variable; crevices therefore represented temporary habitats and refuges for these organisms. The shelter provided by both mussel beds and the physical properties of macroalgal canopy also influenced the distribution of such species. Results regarding species number and diversity on the concrete blocks were not consistent with the commonly held view that increased habitat complexity leads to increased richness and diversity. The movement patterns of intertidal predators were examined via the use of underwater camera technology. Biologically generated complexity was investigated in mussel beds in North Cornwall. Factorial manipulations of grazers and mussels were studied to examine their respective roles within a community. Predation and grazing pressure were influenced by both physical and biological structures. As a consequence the distribution of prey species were in part determined by the complexity of the habitat. Spatial and temporal scales of the structure and dynamics of mussel mosaics was also investigated. Habitat complexity was observed to have an impact on a number of community structuring processes. The generalities of these results and the requirements for future research are discussed throughout the thesis.</p
Aims: Understanding the processes driving forest dynamics requires considering that species within communities do not respond in a coordinated manner to external factors. We argue that temporal turnover in species composition results from contrasting differences in species life history and functional strategies (demography and seed and wood traits) that might simultaneously promote stability and dynamism by operating on distinct subsets of species. Specifically, fast taxonomic turnover should be promoted by species that take advantage of sporadically available resources, while forest stability should be promoted by species with conservative and stress‐tolerant life histories.
Location: Northeastern USA.
Methods: We combine demographic information (survival, recruitment) over a 14‐year period from temperate tree communities in the northeastern United States with trait information on species seed mass and wood density as a proxy for their reproductive and resource acquisition strategies, to evaluate the differential contribution of species with contrasting ecological strategies (low vs high seed mass/wood density) to rates of compositional turnover in temperate forests.
Results: The apparent dynamism of US forests is mostly driven by high mortality and low recruitment of small‐seeded species and by high mortality and recruitment of low wood density species. Simultaneously, species with the opposite traits, i.e., high seed mass and wood density, contribute more to stability. Our findings suggest that forests dynamics in the northeastern United States are the outcome of opposing contributions of life history and plant traits that simultaneously promote forest stability and rapid taxonomic turnover by operating differentially across tree species.
Conclusions: Small‐seeded and low wood density species promote faster forest turnover than species with the opposite traits. Not accounting for these functional differences in community‐level analyses is likely to mask the complex dynamics of temperate forests. This study demonstrates the importance of studying forest composition and structure under a dynamic scope that accounts for differences in functional strategies across species.
Analyses of soil water and groundwater samples from a high-elevation coniferous ecosystem in New England indicate that sulfate anions supply 76 percent of the electrical charge balance in the leaching solution. This result implies that atmospheric inputs of sulfuric acid provide the dominant source of both H ⁺ for cation replacement and mobile anions for cation transport in subalpine soils of the northeastern region affected by acid precipitation. In soils of relatively unpolluted regions, carbonic and organic acids dominate the leaching processes.
Canopy openness is an important forest characteristic related to understory light environment and productivity. Although many methods exist to estimate canopy openness, comparisons of their performance tend to focus on relatively narrow ranges of canopy conditions and forest types. To address this gap, we compared two popular approaches for estimating canopy openness, traditional spherical densiometer and modern smartphone hemispherical photography, across a large range of canopy conditions (from closed canopy to large gaps) and forest types (from low-elevation broadleaf to high-elevation conifer forests) across four states in the northeastern United States. We took 988 field canopy openness measurements (494 per instrument) and compared them across canopy conditions using linear regression and t-tests. The extensive replication allowed us to quantify differences between the methods that may otherwise go unnoticed. Relative to the densiometer, smartphone photography overestimated low canopy openness (<10%) but it underestimated higher canopy openness (>10%), regardless of forest type.
Study Implications
We compared two popular ways of measuring canopy openness (smartphone hemispherical photography and spherical densiometer) across a large range of forest structures encountered in the northeastern United States. We found that, when carefully applied, the traditional spherical densiometer can characterize canopy openness across diverse canopy conditions (including closed canopies) as effectively as modern smartphone canopy photography. Although smartphone photography reduced field measurement time and complexity, it was more susceptible to weather than the densiometer. Although selection of the right method depends on study objectives, we provide a calibration for these two popular methods across diverse canopies.
Irreversibility can be either physical or economic in origin. For example, the extinction of a species is physically irreversible. On the other hand, contamination of lake‐bottom sediments by mercury is not physically irreversible (the mercury and/or sediments can be physically removed), but the cost is so high that it can be said to be economically irreversible. This paper argues that economic irreversibility associated with environmental change is much more common than typically discussed in the economics literature. The source of the problem is the inherent complexity of ecological relationships. The paper discusses the origin and policy importance of these indirect irreversibilities.
In forest ecosystems, canopy openness affects understory light availability, plant growth, and tree species recruitment, thus shaping future forest composition, structure, and functional diversity. Foresters must correctly and quickly measure canopy openness to meet their management objectives. To help guide the selection of an appropriate method for measuring canopy openness, we compared three common techniques that vary in cost, complexity, and time required for measurements and data processing: smartphone-based hemispherical photography, spherical densiometer measurements, and direct measurements of solar radiation (using AccuPAR ceptometer). We measured canopy openness using these three methods on 28 permanent forest health monitoring plots in pine-oak forests of the Central Pine Barrens of Long Island in New York State. By analysis of variance and regression analyses, we found the three methods (particularly densiometer and hemispherical photographs) yielded broadly equivalent and strongly positively correlated descriptions of canopy openness. The direct measurements of solar radiation seemed to have a greater potential to detect subtle variation in forest understory light. Forest managers may sufficiently characterize canopy openness using quick and cheap methods (e.g., spherical densiometers) and avoid larger costs of devices for direct light measurements (e.g., ceptometers) and the larger data-processing times of hemispherical photography.
Die eigentliche boreale Zone (► Abb. J-49), das Zonobiom VIII beginnt dort, wo das Klima für die Hartholz-Laubholzarten zu ungünstig wird, das heißt, wo die Sommer zu kurz und die Winter zu lang werden. Im Klimadiagramm erkennt man es daran, dass die Dauer der Zeit mit Tagesmitteln über 10 °C unter 120 Tage sinkt und die kalte Jahreszeit über sechs Monate dauert (◘ Abb. K-1). Diese Zone ist auf der Karte der Ökoklimate (► Abb. A-50) als kaltgemäßigte Region mit 3-4 thermischen Vegetationsmonaten gekennzeichnet und trotz der einheitlichen Vegetationsbedeckung nach den Humiditätsstufen in vier Kategorien unterteilt. Die Nordgrenze der borealen Zone gegen die Arktis liegt dort, wo etwa nur 30 Tage mit Tagesmitteln über 10 °C und eine kalte Jahreszeit von acht Monaten für das Klima typisch sind.
Satellite imagery was used to model the distribution and abundance of Bicknell's Thrush (Catharus bicknelli) in the White Mountains of New Hampshire. Image-derived data for live softwood shrub density, standing dead-tree basal area, distance to nearest fir-shrub cover type, along with a digital elevation model and point-count data, were used to supply regressor estimates in a multivariate logistic habitat model that was constructed from field vegetation sampling and point-count data. Spatially explicit predictions of probability of Bicknell's Thrush presence were made for each 28.5 × 28.5 m-pixel covering 70,000 ha. A model validation procedure using observations independent from model calibration revealed no difference (P > 0.05) between modeled and observed estimates of Bicknell's Thrush presence within probability deciles 0 to <0.1, 0.1 to <0.2, 0.2 to <0.3, 0.3 to <0.4, 0.5 to <0.6, and 0.6 to <0.7 with respective densities (40 ha−1) of 0.5, 1.6, 2.8, 4.1, 7.3, and 9.4. Transforming probabilities into relative abundance produced an estimated 4,900 Bicknell's Thrushes across the study area. Habitats supporting the highest density of Bicknell's Thrushes were predicted to be at the uppermost elevations. However, abundance estimates decreased even as density increased, owing to decreasing amounts of habitat area with increasing elevation, and suggested that lower-elevation, low-density habitats may support a significant fraction of Bicknell's Thrushes.
Utilisation de l'Imagerie Satellitaire afin de Modéliser la Distribution et l'Abondance de Catharus bicknelli dans les White Mountains du New Hampshire
The altitudinal distributions of members of the genus Pinus were studied on mountain ranges in the western United States and Mexico. The community of pines on each mountainside consists of members of three major groupings - long-needled Diploxylon species, short-needled Diploxylon species and Haploxylon species. Long-needled Diploxylon species form a core sequence of altitudinally replacing species over whose distribution are superimposed sequences of members of one of the other two groups. In the northern mountains ranges Haploxylon species formed this second sequence while in the southern ranges short-neddled Diploxylon species assumed this role. Some morphological characteristics of these species were examined and random associations of species pairs generated using these characteristics. The results suggest that resource partitioning between altitudinally associated species does not occur but rather that a successional situatton exists with long-needled Diploxylon species being replaced by either Haploxylon in the norrhern ranges or short-needled Diploxylon species in the southern ranges.
Premise of the study:
Areas lacking dominant plants, or gaps, can support high diversity and specialist species. Previous chronosequence research in Florida rosemary scrub showed indistinct gap area patterns with fire and the dependence of certain species on gaps. We hypothesized that fire and gap size would affect extinction, colonization, diversity, and vegetation composition.
Methods:
In 2011-12, we revisited gaps first sampled in 2003, recording vascular plant and ground lichen occurrence by species, gap area, and burn history. We analyzed gap, vegetation, and species dynamics using linear mixed models, with Florida rosemary scrub patch as a random factor.
Key results:
Gap areas declined quickly during the first 10 yr postfire and then stabilized. Between 2003 and 2011-12, unburned gaps usually remained extant or split, whereas burned gaps usually merged. Unburned gaps tended to shrink, whereas burned gaps became larger. Species richness was positively related to gap area, fire, and their interaction. Over time, richness declined in unburned gaps and increased in burned gaps. Local extinction and colonization of individual species were related to fire between 2003 and 2011-12. In burned gaps, ground lichens disappeared, but many herbaceous species, including those killed by fire, increased occupancy. Colonization of most species was favored by burning, large gaps, or both.
Conclusions:
In Florida rosemary scrub, fire and increasing gap size increased species richness and many individual species occurrences, reduced local extinctions, and increased colonizations. Therefore, land management activities that encourage the creation and maintenance of large gaps will promote biodiversity in this system.
Boreal Forest forms a continuous belt across northern North America and covers much of Alaska, southern Canada, and New England. Fingers of Boreal Forest extend down western mountain ranges and Appalachians. Boreal Forest is largest biome in North America and, with its counterpart in Eurasia, forms largest in the world. Despite its great size, the biome is remarkably uniform in its physiognomy, a result of a canopy dominated by relatively few species of spruce and other conifers. Thus, northern coniferous forest often is used to describe Boreal Forest. The wide band of Boreal Forest occupies a formerly glaciated region that bears tell-tale scars of glacial moraines, cold lakes, and rivers. Unlike most types of forests Boreal Forest lacks a layered structure, a feature of its limited diversity and uniform physiognomy. Based on climate, the separation of Tundra from Boreal Forest seems closely associated with summertime location of Arctic air mass.
The synecology of tree species was studied in a mature second-growth forest in the Hubbard Brook ecosystem. The forest, on a 13-ha undisturbed watershed ecosystem covering a 245-m range of elevation, has a basal area of about 23 m^2ha^-^1. Dominance is shared by Acer saccharum, Fagus grandifolia, and Betula alleghaniensis. Direct gradient analysis and regression analysis indicated a strong response in both stand and species characteristics to an elevational complex gradient. Basal area per hectare, basal area per tree, deciduousness, and canopy height decreased with increasing elevation, whereas density, evergreenness, and species diversity increased. A lower rate of net primary productivity is correlated with higher elevations. Gradient analyses indicated that no two tree species have identical patterns of importance values over the elevational complex gradient. Sugar maple shows a decreasing trend; balsam fir, paper birch, and mountain ash show increasing trends. Beech, red spruce, mountain maple, and striped maple show intermediate patterns. Seedlings and saplings respond to the elevational gradient as do larger trees; however, the behavior of trees, seedlings, and saplings of the same species is clearly different. The Hubbard Brook ecosystem is located in relation to the vegetational zonation systems of earlier authors. The only generally agreed upon vegetational boundary, ca. 760 m (2,500 ft), is accounted for by a steepened rate of environmental change in the vicinity of that elevation. Various lines of evidence indicate that the present second-growth forest at Hubbard Brook approximates old-age mature northern hardwood forest. Therefore, the biogeochemical, productivity, and ecological data obtained from this study are representative of a mature ecosystem in dynamic balance with regional and local controlling factors, i.e., climate, geology, and topography.
The losses of dissolved Ca, Na, Mg and K have been determined for six small watersheds in New Hampshire during the period 1963–1967. From the rate at which Ca and Na are lost, the steady-state chemical weathering rate is calculated at 800 kg of bedrock-till per hectare per year. Under podzol weathering conditions, a major part of the K and Mg released by the breakdown of primary minerals is apparently retained in pedogenic clays.