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A probabilistic spatial model was created based on empirical data to examine the influence of different fire regimes on stand
structure of lodgepole pine (Pinus contorta var. latifolia) forests across a >500,000-ha landscape in Yellowstone National Park, Wyoming, USA. We asked how variation in the frequency
of large fire events affects (1) the mean...
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... 1895-1990 fire history dataset was used to estimate the frequency of fires in the smaller size classes ( <10,000 ha). Estimating the average size and frequency of very large (>10,000 ha), infrequent fire events (e.g., 1988) from a cen- tury-long database is not possible, so we relied on a longer-term (500-year) fire history dataset for this estimate (Table 1; Romme and Despain 1989;Tinker et al. 2003). This dataset is a con- tiguous 130,000 ha map of stand ages recovering from historical stand-replacing fires, which is a standard method of characterizing fire history in subalpine forests (Romme andDespain 1989, Johnson andGutsell 1994). ...
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... this dataset, we identified at least 3 very large fire events during the last 500 years on the subalpine pla- teaus (1988, ~1740, ~1700). These very large fires occurred about every 167 years on average or with a 0.006 probability of occurrence each year (Table 1). The mean size of these three fires was calculated by taking the proportion of the study area where the ~1740 and ~1700 fire events were recorded and multiplying this by the extent of the subalpine plateaus. ...
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... then averaged these numbers with the size of the 1988 fires which occurred across the extent of the plateaus. From this calculation, the average size of 'very large fires' historically was 141,000 ha (Table 1). ...
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... among fire scenarios is based on differences in the frequency of occurrence of very large fires (Table 1), which is the key determinant of area burned and therefore the age and spatial structure of subalpine forest landscapes. A sce- nario in which the frequency of very large fire occurrence is twice that of the nominal scenario (0.012) is referred to as '2HRV'. ...
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... simulation year, the number of fires in each fire-size class is selected based on defined proba- bilities of occurrence for the specified fire regime scenario (Table 1). For each fire, the area to burn is selected from a negative exponential distribu- tion, where the mean reflects the average pro- portion of the subalpine plateaus burned in the historical record from the appropriate fire-size class (Table 1). ...
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... simulation year, the number of fires in each fire-size class is selected based on defined proba- bilities of occurrence for the specified fire regime scenario (Table 1). For each fire, the area to burn is selected from a negative exponential distribu- tion, where the mean reflects the average pro- portion of the subalpine plateaus burned in the historical record from the appropriate fire-size class (Table 1). Fires initiate on the landscape according to probabilities of burning calculated for each cell. ...
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Disturbance and succession have long been of interest in ecology, but how landscape patterns of ecosystem structure and function evolve following large disturbances is poorly understood. After nearly 25 years, lodgepole pine (Pinus contorta var. latifolia) forests that regenerated after the 1988 Yellowstone Fires (Wyoming, USA) offer a prime opport...
Citations
... Extreme, large-scale weather-related disturbances such as hurricanes, massive floods, and severe temperatures can cause immediate loss of genetic diversity by abruptly decreasing the number, size, or extent of populations (Banks et al., 2013). Impacts on diversity are expected to be most severe when disturbances exceed historic ranges of variability (Schoennagel et al., 2006), amplify consequences of chronic environmental stressors (e.g., Manent et al., 2020), or are recurrent (Kollars et al., 2021;Schrey et al., 2016). Predictions of increased frequency and magnitude of disturbances (Dale et al., 2001;McPhillips et al., 2018;Michener et al., 1997;Ummenhofer & Meehl, 2017) suggest we could be poised for broad-scale reductions in genetic diversity in many species. ...
In summer 2011, Tropical storms Lee and Irene caused an estimated 90% decline of the submersed aquatic plant Vallisneria americana Michx. (Hydrocharitaceae) in the Hudson River of New York (USA). To understand the genetic impact of such large‐scale demographic losses, we compared diversity at 10 microsatellite loci in 135 samples collected from five sites just before the storms with 239 shoots collected from nine sites 4 years after. Although 80% of beds sampled in 2011 lacked V. americana in 2015, we found similar genotypic and genetic diversity and effective population sizes in pre‐storm versus post‐storm sites. These similarities suggest that despite local extirpations concentrated at the upstream end of the sampling area, V. americana was regionally resistant to genetic losses. Similar geographically based structure among sites in both sampling periods suggested that cryptic local refugia at previously occupied sites facilitated re‐expansion after the storms. However, this apparent resistance to disturbance may lead to a false sense of security. Low effective population sizes and high clonality in both time periods suggest that V. americana beds were already small and had high frequency of asexual reproduction before the storms. Dispersal was not sufficient to recolonize more isolated sites that had been extirpated. Chronic low diversity and reliance on asexual reproduction for persistence can be risky when more frequent and intense storms are paired with ongoing anthropogenic stressors. Monitoring genetic diversity along with extent and abundance of V. americana will give a more complete picture of long‐term potential for resilience.
... In addition, high-severity fires alter the forest species composition and stand age [62]. As a consequence, there has been an increase in the proportion of young forest stands [63,64]. There is a significant effect on SOC stock dynamics from the stand age, especially in the surface layer (0-20 cm) [65]. ...
Soil organic carbon (SOC) is an important component of the ecosystem carbon pool, and fire is one of the important disturbances in forest ecosystems. With global warming, there has been a gradual increase in boreal forest fires, which has a nonnegligible impact on the SOC dynamics in forests. The CENTURY model was employed in our study to simulate the changes in SOC stocks in boreal forests of the Great Xing’an Mountains, China under different fire severity conditions. Fire severity was represented by the metric of difference normalized burn ratio (dNBR) derived from 30-m Landsat-8 imageries. Changes in forest SOC stocks following fire disturbance were predicted under four future Representative Concentration Pathway (RCP) scenarios (RCP2.6, RCP4.5, RCP6.0, and RCP8.5). We found that the CENTURY model had good results in simulating the SOC stocks in the postfire of China’s boreal forests. Forest SOC dynamics responded differently to fire severities and the larger SOC loss was associated with increasing fire severity. Importantly, a feedback mechanism was found between climate change and SOC stocks, which reduces SOC stocks with increasing temperatures. High-severity forest fires tended to cause serious damage to the SOC pool and delay forest SOC recovery time; after such events, forest SOC stocks cannot be fully recovered to the prefire levels (6.74% loss). In addition, higher CO2 emissions and warmer temperatures significantly affected the recovery of SOC stocks after fire disturbance, resulting in larger SOC losses. Overall, we projected losses of 10.14%, 12.06%, 12.41%, and 15.70% of SOC stocks after high-severity fires in four RCP scenarios, respectively. Our findings emphasize the importance of fire disturbance and climate change on future dynamics of SOC stocks in China’s boreal forests, providing a scientific basis for future boreal forest management and fire management.
... In situ obligate seeders (represented by serotinous pines here) were most affected by shortening of fire rotation, but their equilibrium density peaked at intermediate fire rotations. Other studies have also found that an intermediate fire rotation benefits serotinous trees, as propagule release following fires more than compensates for fire induced mortality (Schoennagel et al., 2006). However, we found an abrupt decline in density as fire rotation declined. ...
Disturbances are ubiquitous in ecological systems, and species have evolved a range of strategies to resist or rebound following disturbance. Understanding how the presence and complementarity of regeneration traits will affect community responses to disturbance is increasingly urgent as disturbance regimes shift beyond their historical ranges of variability. We define “disturbance niche” as a species' fitness across a range of disturbance sizes and frequencies that can reflect the fundamental or realized niche, that is, whether the species occurs alone or with other species. We developed a model of intermediate complexity (i.e., a Goldilocks model) to infer the disturbance niche. We parameterized the model for subalpine forests in Yellowstone National Park (USA) adapted to infrequent stand‐replacing fires and included the three major tree‐regeneration strategies: (1) obligate seeders that rely on ex situ seeding into burned areas (non‐serotinous lodgepole pine, Pinus contorta var. latifola), (2) obligate seeders that depend on in situ seedbanks (serotinous lodgepole pine, Pinus contorta var. latifola), and (3) species that can resprout from surviving roots following fire (quaking aspen, Populus tremuloides). Our results showed which regeneration strategies increase or decrease in prevalence as fire rotation declines. Non‐serotinous pines were extirpated when fire rotation was below 50 years in a monoculture and 100 years in a mixed forest; serotinous pines were extirpated when fire rotation was below 20 years; and aspen was extirpated when fire rotation fell below 6 years. The fundamental and realized disturbance niches pinpointed the key mechanisms limiting regeneration for each strategy, namely, increasing fire size for non‐serotinous pine (ex situ seeders), decreasing fire frequency for serotinous pine (in situ seeders), and interspecific competition for aspen (resprouters). In a mixed forest, the three regeneration strategies were complementary and each dominated at different combinations of fire size and frequency. Consequently, diversity of regeneration strategies enhanced forest resilience to declining fire rotations. Despite its simplicity, our Goldilocks model produced realistic dynamics and could be readily adapted to other disturbance‐prone ecosystems to explore the generality of these results. The disturbance niche is a key concept for anticipating community resilience to changing disturbance regimes.
... Yellowstone Lake is the largest North American high-elevation (above 2.1 km) lake by area. Yellowstone National Park is largely dominated by sub-alpine fir landscapes, with the most abundant habitats consisting of lodgepole pine (Pinus contorta, 64.0% of area) due to fire history and soil conditions [45], followed by non-forested landscapes (13.4%), whitebark pine (Pinus albicaulis, 12.8%), Douglas fir (Pseudotsuga menziesii, 6.0%), Engelmann spruce and sub-alpine fir (Picea engelmannii and Abies lasiocarpa, 3.2%), aspen (Populus tremuloides, 0.2%), and krummholz (various species of stunted trees near tree line, 0.1%) ( Figure 2) [37,42,[45][46][47]. The distribution of vegetation types in the park generally follows an elevational gradient, with aspen at the lowest elevations and krummholz at the highest elevations ( Figure 2). ...
The study’s objective was to quantify the responses of vegetation greenness and productivity to climate variability and change across complex topographic, climatic, and ecological gradients in Yellowstone National Park through the use of remotely sensed data. The climate change signal in Yellowstone was pronounced, including substantial warming, an abrupt decline in snowpack, and more frequent droughts. While phenological studies are increasing in Yellowstone, the near absence of long-term and continuous ground-based phenological measurements motivated the study’s application of remotely sensed data to aid in identifying ecological vulnerabilities and guide resource management in light of on ongoing environmental change. Correlation, time-series, and empirical orthogonal function analyses for 1982–2015 focused on Daymet data and vegetation indices (VIs) from the Advanced Very High-Resolution Radiometer (AVHRR) and Moderate Resolution Imaging Spectroradiometer (MODIS). The study’s key questions address unique time scales. First, what are the dominant meteorological drivers of variability in vegetation greenness on seasonal to interannual time scales? Key results include: (1) Green-up is the most elevation- and climate-sensitive phenological stage, with La Niña-induced cool, wet conditions or an anomalously deep snowpack delaying the green-up wave. (2) Drought measures were the dominant contributors towards phenological variability, as winter–spring drought corresponded to enhanced April–June greening and spring–summer drought corresponded to reduced August–September greening. Second, how have patterns of productivity changed in response to climate change and disturbances? Key results include: (1) The park predominantly exhibited positive productivity trends, associated with lodgepole pine re-establishment and growth following the 1988 fires. (2) Landscapes which were undisturbed by the 1988 fires showed no apparent sign of warming-induced greening. This study motivates a systematic investigation of remote-sensing data across western parks to identify ecological vulnerabilities and support the development of climate change vulnerability assessments and adaptation strategies.
... Our study suggests substantial resilience of lodgepole pine stands to projected warming; non-forest states rarely occurred in the simulation with the combinations of factors considered here, although tree density could change substantially in the future (e.g., Schoennagel et al. 2006). In part, this may reflect our conservative definition of regeneration failure (< 50 stems/ha at postfire year 30) relative to the prolific regeneration capacity of lodgepole pine and its ability to produce cones at a young age ). ...
Environmental change is accelerating in the 21st century, but how multiple drivers may interact to alter forest resilience remains uncertain. In forests affected by large high-severity disturbances, tree regeneration is a resilience linchpin that shapes successional trajectories for decades. We modeled stands of two widespread western US conifers, Douglas-fir (Pseudotsuga menziesii var. glauca) and lodgepole pine (Pinus contorta var. latifolia), in Yellowstone National Park (Wyoming, USA) to ask: (1) What combinations of distance to seed source, fire return interval and warming-drying conditions cause postfire tree-regeneration failure? (2) If postfire tree regeneration was successful, how does early tree density differ under future climate relative to historical climate? We conducted a stand-level (1 ha) factorial simulation experiment using the individual-based forest process model iLand to identify combinations of fire return interval (11 to 100 years), distance to seed source (50 to 1000 m), and climate (historical, mid-21st century, late-21st century) where trees failed to regenerate by 30-years postfire. If regeneration was successful, we compared stand densities between climate periods. Simulated postfire regeneration were surprisingly resilient to changing climate and fire drivers. Douglas-fir regeneration failed more frequently (55%) than lodgepole pine (28% and 16% for non-serotinous and serotinous stands, respectively). Distance to seed source was an important driver of regeneration failure for Douglas-fir and non-serotinous lodgepole pine; regeneration never failed when stands were 50 m from a seed source and nearly always failed when stands were 1 km away. Regeneration of serotinous lodgepole pine only failed when fire return intervals were ≤ 20 years and stands were far (1 km) from a seed source. Warming climate increased regeneration success for Douglas-fir but did not affect lodgepole pine. If regeneration was successful, postfire density varied with climate. Douglas-fir and serotinous lodgepole pine regeneration density both increased under 21st-century climate but in response to different climate variables (growing season length vs cold limitation). Results suggest that given a warmer future with larger and more frequent fires, a greater number of stands that fail to regenerate after fires combined with increasing density in stands where regeneration is successful could produce a more coarse-grained forest landscape. This article is protected by copyright. All rights reserved.
... complete tree death) are common in subalpine lodgepole pine forests during periods of severe fire weather (Romme 1982;Lotan et al. 1985;Bessie and Johnson 1995;Schoennagel et al. 2004). Greater frequency and severity of drought over the next century are projected to reduce fire intervals and shift the forest mosaic towards a greater abundance of young forests (Schoennagel et al. 2006;Westerling et al. 2011). Stand replacing fires temporarily reduce fuel biomass and continuity, especially fine dead fuels and live canopy fuels , and initiate a period of reduced burn probability as fuels reaccumulate. ...
... [2] What are the relative contributions of fuel loads, fuel moisture and wind on simulated fire behaviour? YNP is the premiere landscape for such a study because human intervention on fire regimes and forest dynamics have been minimal, substantial reductions in future fire intervals have been projected (Schoennagel et al. 2006;Westerling et al. 2011) and the scale of the 1988 fires represents the anticipated magnitude of mega-disturbances under projected climate conditions (Running 2006). ...
Early-seral forests are expanding throughout western North America as fire frequency and annual area burned increase, yet fire behaviour in young postfire forests is poorly understood. We simulated fire behaviour in 24-year-old lodgepole pine (Pinus contorta var. latifolia) stands in Yellowstone National Park, Wyoming, United States using operational models parameterised with empirical fuel characteristics, 50-99% fuel moisture conditions, and 1-60kmhr-1 open winds to address two questions: [1] How does fireline intensity, and crown fire initiation and spread vary among young, lodgepole pine stands? [2] What are the contributions of fuels, moisture and wind on fire behaviour? Sensitivity analysis indicated the greatest contributors to output variance were stand structure mediated wind attenuation, shrub fuel loads and 1000-h fuel moisture for fireline intensity; crown base height for crown fire initiation; and crown bulk density and 1-h fuel moisture for crown fire spread. Simulation results predicted crown fire (e.g. passive, conditional or active types) in over 90% of stands at 50th percentile moisture conditions and wind speeds greater than 3kmhr⁻¹. We conclude that dense canopy characteristics heighten crown fire potential in young, postfire lodgepole pine forests even under less than extreme wind and fuel moisture conditions.
... The dominant species in our study area is lodgepole pine, which typically has serotinous cones needing high temperatures to trigger and release the seeds. This fire-dependent characteristic allows for post-fire tree regeneration soon after fires (Turner et al., 1997), but the abundance of serotinous cones can vary with fire regimes and pre-fire seed density (Schoennagel et al., 2006). Lodegpole pine start seed production at an early age, approximately 5–10 years (Burns and Honkala, 1990). ...
The pine forests in the southern portion of the Rocky Mountains are a heterogeneous mosaic of disturbance and recovery. The most extensive and intensive stress and mortality are received from human activity, fire, and mountain pine beetles (MPB; Dendroctonus ponderosae). Understanding disturbance interactions and disturbance-succession pathways are crucial for adapting management strategies to mitigate their impacts and anticipate future ecosystem change. Driven by this goal, we assessed the forest disturbance and recovery history in the Southern Rocky Mountains Ecoregion using a 13-year time series of Landsat image stacks. An automated classification workflow that integrates temporal segmentation techniques and a random forest classifier was used to examine disturbance patterns. To enhance efficiency in selecting representative samples at the ecoregion scale, a new sampling strategy that takes advantage of the scene-overlap among adjacent Landsat images was designed. The segment-based assessment revealed that the overall accuracy for all 14 scenes varied from 73.6% to 92.5%, with a mean of 83.1%. A design-based inference indicated the average producer’s and user’s accuracies for MPB mortality were 85.4% and 82.5% respectively. We found that burn severity was largely unrelated to the severity of pre-fire beetle outbreaks in this region, where the severity of post-fire beetle outbreaks generally decreased in relation to burn severity. Approximately half the clear-cut and burned areas were in various stages of recovery, but the regeneration rate was much slower for MPB-disturbed sites. Pre-fire beetle outbreaks and subsequent fire produced positive compound effects on seedling reestablishment in this ecoregion. Taken together, these results emphasize that although multiple disturbances do play a role in the resilience mechanism of the serotinous lodgepole pine, the overall recovery could be slow due to the vast area of beetle mortality.
... Observed and projected increases in wildland fire extent and frequency have raised concern among scientists and forest managers regarding the consequences of escalating wildland fire activity (Flannigan et al. 2000, Scholze et al. 2006, Westerling et al. 2006, Krawchuk et al. 2009, Moritz et al. 2012, Stephens et al. 2013, Parks et al. 2015. Extreme fire seasons have become more common over the last three decades and have had major social and ecological consequences including loss of human life and infrastructure, escalating costs of fire prevention and suppression, changes in ecosystem services (e.g., water, timber, carbon storage, and recreation resources), and increasing extents of young forests (Schoennagel et al. 2006, Stephens et al. 2013. In subalpine forests across western North America, large fires historically burned during rare periods of extreme weather (Romme 1982, Lotan et al. 1985, Bessie and Johnson 1995, Schoennagel et al. 2004). ...
... In subalpine forests across western North America, large fires historically burned during rare periods of extreme weather (Romme 1982, Lotan et al. 1985, Bessie and Johnson 1995, Schoennagel et al. 2004). Projections of more frequent severe fire weather over a longer fire seasons suggest that a new wildland fire issue may emerge-the potential for extensive reburning of young forests (Schoennagel et al. 2006, Parks et al. 2015, Harvey et al. 2016). ...
Escalating wildfire in subalpine forests with stand-replacing fire regimes is increasing the extent of early-seral forests throughout the western US. Post-fire succession generates the fuel for future fires, but little is known about fuel loads and their variability in young post-fire stands. We sampled fuel profiles in 24-year-old post-fire lodgepole pine (Pinus contorta var. latifolia) stands (n=82) that regenerated from the 1988 Yellowstone Fires to answer three questions. (1) How do canopy and surface fuel loads vary within and among young lodgepole pine stands? (2) How do canopy and surface fuels vary with pre- and post-fire lodgepole pine stand structure and environmental conditions? (3) How have surface fuels changed between 8 and 24 years post-fire? Fuel complexes varied tremendously across the landscape despite having regenerated from the same fires. Available canopy fuel loads and canopy bulk density averaged 8.5 Mg ha-1 [range 0.0-46.6] and 0.24 kg m3 [range: 0.0-2.3], respectively, meeting or exceeding levels in mature lodgepole pine forests. Total surface-fuel loads averaged 123 Mg ha-1 [range: 43 - 207], and 88% was in the 1000-hr fuel class. Litter, 1-hr, and 10-hr surface fuel loads were lower than reported for mature lodgepole pine forests, and 1000-hr fuel loads were similar or greater. Among-plot variation was greater in canopy fuels than surface fuels, and within-plot variation was greater than among-plot variation for nearly all fuels. Post-fire lodgepole pine density was the strongest positive predictor of canopy and fine surface fuel loads. Pre-fire successional stage was the best predictor of 100-hr and 1000-hr fuel loads in the post-fire stands and strongly influenced the size and proportion of sound logs (greater when late successional stands had burned) and rotten logs (greater when early successional stands had burned). Our data suggest that 76% of the young post-fire lodgepole pine forests have 1000-hr fuel loads that exceed levels associated with high-severity surface fire potential, and 63% exceed levels associated with active crown fire potential. Fire rotations in Yellowstone National Park are predicted to shorten to a few decades and this prediction cannot be ruled out by a lack of fuels to carry repeated fires. This article is protected by copyright. All rights reserved.
... These characteristics of wildfire can vary greatly by ecosystem . For example, wildfires occur as frequently as once every one to five years in grassland ecosystems to once every 300 years, or longer in some coniferous forests (Turner et al. 2003, Schoennagel et al. 2006). The characteristics of wildfire determine effects on environmental amenities and dis-amenities provisioned to people, such as carbon storage, timber production, and forest aesthetics (Chapin et al. 2003, Gallant et al. 2003, Hunt and Haider 2004, Balshi et al. 2009). ...
... Picea pollen percentages declined, however, after subsequent fire episodes and effective moisture increased. Such brief persistence of high spruce abundance in the forest surrounding Little Windy Hill Pond compares well with simulated variability of forests disturbed on this time scale (Turner et al. 1993, Schoennagel et al. 2006, and indicates that an FIG. 8. A conceptual framework for considering the vegetation effects of different frequencies of disturbances and climatic changes (''perturbations'') in subalpine forests, such as near Little Windy Hill Pond. ...
Paleoecological records indicate that subalpine forests in western North America have been resilient in response to multiple influences, including severe droughts, insect outbreaks, and widely varying fire regimes, over many millennia. One hypothesis for explaining this ecosystem resilience centers on the disruption of forest dynamics by frequent disturbance and climatic variability, and the resulting development of non-steady-state regimes dominated by early-successional conifers with broad climatic tolerances, such as lodgepole pine (Pinus contorta var. latifolia Engelm. ex Wats.). To evaluate this hypothesis, we independently reconstructed the vegetation, fire, and effective-moisture histories of a small, forested watershed at 2890 m elevation in southeastern Wyoming, USA, using sedimentary pollen and charcoal counts in conjunction with sedimentary lake-level indicators. The data indicate that prominent vegetation shifts (from sagebrush steppe to spruce—fir parkland at ca. 10.7 ka and spruce—fir parkland to pine-dominated forest at ca. 8.5 ka [ka stands for thousands of years before the present, defined as AD 1950]) coincided with changes in effective moisture. However, after lodgepole pine forests established at ca. 8.5 ka, similar hydroclimatic changes did not produce detectable vegetation responses. Fire history data show that other aspects of the ecosystem were responsive to changes in effective moisture at centennial timescales with prolonged fire-free episodes coinciding with periods of low effective moisture ca. 7.2—5.6 and 3.7—1.6 ka. Throughout our record, the ratio of ecosystem perturbation time (i.e., fire frequency and changes in effective moisture) to recovery time (assuming 200—600-year successional processes) falls within estimates of the ratio for non-steady state ecosystems. Frequent perturbations, therefore, may have prevented this ecosystem from reaching compositional equilibrium with the varied climatic conditions over the past 8.5 ka. Equilibrium states could have included more abundant spruce (Picea spp.) and fir (Abies spp.) than presently observed based on brief increases in pollen abundances of these taxa during prolonged dry, fire-free intervals. Our results show that, although current climate changes favor widespread disturbance in Rocky Mountain forests, the composition of these ecosystems could be highly resilient and recover through successional dynamics over the next few decades to centuries.
