Changes In Forest Composition Research Articles

Status of ash forests and regeneration a decade after first detection of emerald ash borer infestation in New York state

In many forest stands, persistence of mature ash (Fraxinus spp.) and the ability of regenerating ash to reach maturity is likely to influence future forest composition and ecosystem structure. Seedlings and saplings are often too small to be infested by the initial wave of invasive emerald ash borer (EAB), Agrilus planipennis Fairmaire, and low release numbers and a lagged response of introduced biological control agents in outbreak EAB populations make quick protection of mature trees unpredictable but may provide protection for the next generation of ash. This study reports current composition and status of historically ash-dominated forest stands in eastern and western New York a decade after first EAB detection and nine years after release of parasitoid wasps for biological control. Monitored trees exhibited an increasingly binary status over the study period with the death of almost all trees that initially showed signs of decline, leaving only healthy individuals with full canopies alive. Near complete mortality of mature trees was observed in eastern New York, whereas a substantial number of mature trees persisted in western New York. There was little change in numbers of ash seedlings (<2.5 cm DBH) or saplings (≥2.5 cm DBH and < 10 cm DBH) between 2014 and 2021 in either region; however, density of the tallest seedlings (>1 m in height) increased significantly in eastern New York. Changes in overstory forest composition were mostly explained by loss of mature ash. These results provide hope for regenerating ash to grow into existing canopy gaps with the protection provided by continued presence of biological control agents.

Contrasting impacts of climate change on protection forests of the Italian Alps

Protection forests play a key role in protecting settlements, people, and infrastructures from gravitational hazards such as rockfalls and avalanches in mountain areas. Rapid climate change is challenging the role of protection forests by altering their dynamics, structure, and composition. Information on local- and regional-scale impacts of climate change on protection forests is critical for planning adaptations in forest management. We used a model of forest dynamics (ForClim) to assess the succession of mountain forests in the Eastern Alps and their protective effects under future climate change scenarios. We investigated eleven representative forest sites along an elevational gradient across multiple locations within an administrative region, covering wide differences in tree species structure, composition, altitude, and exposition. We evaluated protective performance against rockfall and avalanches using numerical indices (i.e., linker functions) quantifying the degree of protection from metrics of simulated forest structure and composition. Our findings reveal that climate warming has a contrasting impact on protective effects in mountain forests of the Eastern Alps. Climate change is likely to not affect negatively all protection forest stands but its impact depends on site and stand conditions. Impacts were highly contingent to the magnitude of climate warming, with increasing criticality under the most severe climate projections. Forests in lower-montane elevations and those located in dry continental valleys showed drastic changes in forest structure and composition due to drought-induced mortality while subalpine forests mostly profited from rising temperatures and a longer vegetation period. Overall, avalanche protection will likely be negatively affected by climate change, while the ability of forests to maintain rockfall protection depends on the severity of expected climate change and their vulnerability due to elevation and topography, with most subalpine forests less prone to loosing protective effects. Proactive measures in management should be taken in the near future to avoid losses of protective effects in the case of severe climate change in the Alps. Given the heterogeneous impact of climate warming, such adaptations can be aided by model-based projections and high local resolution studies to identify forest stand types that might require management priority for maintaining protective effects in the future.

Calibrating a process-based simulation model for the Acadian forest region

Climate change is projected to have profound impacts on Canada’s Acadian Forest Region (AFR). However, large uncertainties arising from climate change and increasing disturbance activity pose challenges for forest management decisions. Process-based (mechanistic) simulation models offer a means by which vulnerabilities and different management strategies can be tested under multiple climate and disturbance regimes. However, applying these complex models can be dauting, especially for novice modelers and forest practitioners; nonetheless, this complexity is increasingly necessary to more realistically project changes in forest growth and composition, ecosystem services, biodiversity, disturbance regimes, and the spread of forest pests. Here, we present a methodology for calibrating and validating iLand (v1.1.1), a landscape-scale, process-based forest model that offers a novel approach for assessing the feedback between individual trees and their environment (ecosystem processes, climate, and disturbance). For the first time, 18 tree species were parameterized and calibrated for the AFR and model performance was evaluated against independent field observations at the tree population and stand level. iLand was able to accurately emulate the dynamics of individual tree species populations as well as the succession of mixed-species forest stands across a range of soil conditions and is now ready to be used to simulate future forest dynamics of the AFR. We also discuss calibration method selection and the potential impacts of model and project structure in relation to our project. As the accessibility and usability of process-based forests models increases, our work provides a unique case study for forest managers looking to expand their toolbox.

Vegetation dynamics and land-use change at the Neolithic lakeshore settlement site of Ploča Mičov Grad, Lake Ohrid, North Macedonia

Detailed knowledge about the interactions between vegetation, climate and land use during the Mesolithic and Neolithic, at the transition from foraging to farming, is still scarce in the Balkans. Here we present a palaeoecological study combining pollen, spores and charcoal found in sedimentary cores from Lake Ohrid, Ploča Mičov Grad, North Macedonia, with a particular focus on the vegetation dynamics during the Late Glacial-Holocene and the Mesolithic-Neolithic transitions. Our record begins at ca. 13,500 cal bp (11,550 cal bc) when partially open vegetation, consisting mainly of Pinus, Abies and deciduous Quercus tree stands grew on the hilly flanks of the bay of Ploča. From 12,650 cal bp (cal 10,700 bc), herbs dominated the record until the onset of the Holocene (ca. 11,700 cal bp; 9750 cal bc), when increasing temperatures led to the establishment of pine-deciduous oak forests including Alnus, Fraxinus ornus, Tilia, Ulmus and Abies. These forests persisted until 7,500 cal bp (cal 5550 bc), when deforestation started due to Neolithic land use. This first phase of Neolithic activities in the Ploča Mičov Grad area precedes the earliest archaeological structures so far recorded by almost 1,000 years. Our data suggest two phases of human land use between 7,500 and 6,300 cal bp (5550–4350 cal bc), when high values of Cerealia type pollen and other cultural indicators indicate intense arable and pastoral farming activities. Once human activities decreased, forests were able to re-establish quickly (within 100–250 years), although the composition changed with disturbance-adapted Ostrya type (mostly Ostrya carpinifolia) and Fagus becoming more important. We conclude that forests were resilient to early human disturbance, despite intensive land use and logging activities gradually leading to forest composition changes. Many of these composition changes can still be seen today, suggesting the legacy of Neolithic farmers is still present in today’s landscape.

Future climate change effects on US forest composition may offset benefits of reduced atmospheric deposition of N and S.

Climate change and atmospheric deposition of nitrogen (N) and sulfur (S) are important drivers of forest demography. Here we apply previously derived growth and survival responses for 94 tree species, representing >90% of the contiguous US forest basal area, to project how changes in mean annual temperature, precipitation, and N and S deposition from 20 different future scenarios may affect forest composition to 2100. We find that under the low climate change scenario (RCP 4.5), reductions in aboveground tree biomass from higher temperatures are roughly offset by increases in aboveground tree biomass from reductions in N and S deposition. However, under the higher climate change scenario (RCP 8.5) the decreases from climate change overwhelm increases from reductions in N and S deposition. These broad trends underlie wide variation among species. We found averaged across temperature scenarios the relative abundance of 60 species were projected to decrease more than 5% and 20 species were projected to increase more than 5%; and reductions of N and S deposition led to a decrease for 13 species and an increase for 40 species. This suggests large shifts in the composition of US forests in the future. Negative climate effects were mostly from elevated temperature and were not offset by scenarios with wetter conditions. We found that by 2100 an estimated 1 billion trees under the RCP 4.5 scenario and 20 billion trees under the RCP 8.5 scenario may be pushed outside the temperature record upon which these relationships were derived. These results may not fully capture future changes in forest composition as several other factors were not included. Overall efforts to reduce atmospheric deposition of N and S will likely be insufficient to overcome climate change impacts on forest demography across much of the United States unless we adhere to the low climate change scenario.

Effects of forest structural and compositional change on forest microclimates across a gradient of disturbance severity

Forest structural diversity and community composition are key in regulating forest microclimates. When disturbance affects structural diversity or composition, forest microclimates may be altered due to changes in soil temperature, soil water content, and light availability. It is unclear however which structural or compositional components, when changed or to what extent, result in microclimatic change. To address this question, we used data from a large scale, manipulative stem-girdling experiment in northern, lower Michigan—the Forest Resilience and Threshold Experiment (FoRTE). FoRTE follows a factorial design with multiple levels of disturbance severity (0, 45, 65, 85%) based on targeted reductions in gross leaf area index via stem-girdling induced mortality. These disturbance severity treatments are applied in two ways: either as top-down (largest trees are killed) or bottom-up (small to medium trees killed) treatments. We examined how multiple components of structural diversity and community composition changed as a product of disturbance severity and type, and then tested for resulting effects on forest microclimates (light availability, soil temperature, and soil water), using a multivariate, Random Forest framework. We found that measures of community composition (species richness, species evenness, and Shannon-Wiener Diversity Index) and stand structure (basal area, standard deviation of DBH, tree size diversity) declined more following disturbance than did measures of canopy cover, heterogeneity, arrangement, or height. However, when changes in each variable from pre- to post-disturbance, measured as log change, were employed in a multivariate, Random Forest regression framework, structural diversity measures of heterogeneity (rugosity, top rugosity), cover (canopy cover), and arrangement (porosity) were the most influential variables, but with differences among bottom-up and top-down treatments We found that the death of large trees from disturbance impacts soil temperature, water, and light environments more substantially and uniformly across disturbance gradients than does the death of smaller trees. Our results have implications for both statistical and process-based modeling of forest disturbance.

Alder stands promote N-cycling but not leaf litter mass loss in Mediterranean streams flowing through pine plantations

During the last century, the abandonment of traditional dryland farming and pastures in the Mediterranean basin promoted the development of ambitious afforestation programs causing a drastic transformation of the landscape. Afforestation programs were usually accomplished without considering the potential ecological impacts on the recipient ecosystems. Forest streams rely on terrestrial organic detritus, so their functioning and conservation status can be altered by changes in riparian forest biodiversity and composition. However, the influences of conifer plantations in particular on stream functioning are still unclear, possibly because the presence of multiple species in plantations or the presence of other species in the riparian zones of streams may act as buffers of such effects. Here, by means of a field experiment, we assessed whether the presence of black alder in the riparian zone and/or as leaf litter within the stream may mitigate the impacts exerted by pine plantations on stream ecosystem functioning. We found (i) that streams were functionally similar but differed in water N concentrations; (ii) no differences in litter mas loss between riparian types, but higher total litter mass loss of those mixtures containing alder leaf litter; and (iii) higher N losses (or lower N gains) for all litter types in streams without riparian alder. These results demonstrate that microbial decomposers can use either stream water N or litter N, and that detritivores can feed simultaneously on resources of contrasting quality to balance their diet. Our study underscores the effect of even low-density riparian cover of alder promoting microbial nutrient cycling by moderate increases of water N concentrations. We suggest thinning of pine plantations combined with planting of native deciduous species as alder to alleviate the effects of pine plantations on Mediterranean streams.

Impacts of Myrtle Rust Induced Tree Mortality on Species and Functional Richness within Seedling Communities of a Wet Sclerophyll Forest in Eastern Australia.

Austropuccinia psidii is an introduced plant pathogen known to have caused significant declines in populations of several Australian native Myrtaceae species. However, limited research has focused on the impacts of the pathogen on plant communities in the aftermath of its invasion. This study investigated the relationship between disease impact level, plant species diversity, and functional richness in seedling communities in a wet sclerophyll forest in southeast Queensland. A clear shift was found from early colonizer Myrtaceae species in the mid- and understory to a more diverse non-Myrtaceae seedling community indicative of secondary succession. Comparisons of key Myrtaceae species and the seedling community suggest that there may also be a shift towards species that produce drupes and larger seeds, and overall, a current reduction in fruit availability due to the dramatic loss of previously dominant species. Seedling diversity showed no significant correlation with tree mortality, possibly due to favorable rainfall conditions during the study period. The more subtle changes in forest composition, such as changes in fruit type and availability due to myrtle rust, however, could affect the visitation of local bird species in the short term and certainly reduce the store of early colonizing native shrub and tree species.

UAVs for monitoring responses of regenerating forests under increasing climate change-driven droughts - a review

The impact of climate change-driven droughts on regenerating forests is poorly understood due to the complexities involved in regeneration processes and the difficulties in measuring the relevant parameters with sufficient spatial and temporal resolution in a timely manner. Drought increases tree mortality in both undisturbed and disturbed forests and may influence forest regeneration dynamics from seed germination to the recruitment, growth, and survival of tree seedlings. Seedlings and small saplings may be more susceptible to changes in water availability than larger individuals due to their shallower roots that may be unable to reach the deeper, moist soil layers, and due to uneven competition with adult trees for soil moisture. The potential range shifts and local extinction of drought-sensitive species can also result in changes in forest species community composition and diversity loss at different scales. There is a need for precise and low-cost monitoring systems that facilitate better capturing of the complexities of such processes for restoration measures. The objective of this paper is to study the use of UAVs (Unmanned Aerial Vehicles) for monitoring responses of regenerating forests under increasing climate change-driven droughts. UAVs have several advantages over traditional field-based monitoring techniques and flexibility in selecting the required spatiotemporal resolution over other remote sensing methods, making them a promising tool for monitoring forest recovery. Although further research is required to ensure the accuracy and effectiveness of UAV-facilitated measures for monitoring forest regeneration, UAVs possess great potential in forest management in the event of increasing occurrences of climate-change driven droughts.

THE KEY SECTION OF THE VALDAIAN PEAT BOG AS A SOURCE OF PALEOECOLOGICAL AND PALEOCLIMATIC INFORMATION

A paleoclimatic reconstruction of the last 14 ka years was carried out based on the results of GPR sounding, spore-pollen analysis and radiocarbon dating of a peat section (7 m) located in a model bog of the Valdaisky National Park (Novgorod Region). Peat accumulation rates varied from 0.075 mm per year during the Late Glacial to 0.15–1.15 mm per year during the Boreal stage (when the levels of the Valdaian lakes dropped 10 m) and 4.25 mm/year in recent centuries. Numerous cycles of Holocene warming/cooling events were within ±1–2°C compared to the current ones and were accompanied by moderate fluctuations in annual precipitation (±25–50 mm). The greatest amount of forest compositional change took place during the Atlantic period, when spruce–broad-leaved forests and oak forests dominated. In the last two millennia, the vegetation dynamics of the region were mainly influenced by agricultural activity.

Replicate Studies Separated by 40 Years Reveal Changes in the Altitudinal Stratification of Montane Passalid Beetle Species (Passalidae) in Mesoamerica

Two patterns are apparent in the altitudinal distribution of Neotropical passalid beetles: (a) species that occur only in lowland forest habitats but have broad geographic distributions, and (b) montane endemic species with relatively limited distributions. The transition zone between these distributions in upper Mesoamerica occurs, on average, at approximately 1500 m above sea level (a.s.l.). We studied the altitudinal stratification of passalid beetle communities living on two volcanoes in Guatemala (Atitlan and Santa Maria), revisiting a study conducted in 1981 by MacVean and Schuster. We collected passalid beetles at the same study sites and compared the community composition along the altitudinal gradient. We collected all but one of the species reported by MacVean and Schuster and found three additional species. We observed two key differences in the passalid communities observed in 1981 versus the present: (a) for the Atitlan site, the species’ turnover line from lowland to montane species shifted from 1600 to 1800 m a.s.l.; and (b) in both volcanoes, we collected passalid beetles well above 2700 m a.s.l., which was the upper limit at which they were found in 1981. Both observations are consistent with a shift of the passalid beetle community to higher elevations, perhaps in response to changes in local climate/habitat conditions, including increased temperatures and changes in forest composition.

Holocene fire regimes, fire‐related plant functional types, and climate in south‐coastal British Columbia forests

AbstractPaleoecological records of past fire events and forest composition provide long‐term ecological context for modern changes in fire regimes and forest dynamics. Here, we use pollen and contiguous macroscopic charcoal analyses of lake sediments from Pender Island, British Columbia, Canada to reconstruct changes in fire regimes over the last 10,000 years and investigate how these interact with changes in climate and forest composition with a focus on fire‐related plant functional types. The relatively warm and dry early Holocene was characterized by high charcoal accumulation rates, fire episodes of moderate severity, and a mean fire return interval of 100 ± 27 years. Forests at the time were open‐canopy Pseudotsuga menziesii forests with abundant fire endurer taxa (e.g., Pteridium aquilinum) that have a competitive advantage in regimes of frequent fire. Fire continued to occur every ~100 years, on average, during the establishment of Quercus garryana savanna communities; however, a decrease in charcoal peak magnitudes suggests the fire regime shifted to one characterized by smaller and/or lower intensity surface fires. As temperature and moisture deficits decreased in the mid‐ and late Holocene (i.e., after ~6000 calendar years before present), mean fire return intervals lengthened to 176 ± 54 years and increased variability in charcoal peak magnitudes suggests a mixed fire regime of low‐moderate‐intensity fires combined with infrequent crown or stand‐replacing fires. Relatively stable and moderate climate, longer fire return intervals, and mixed‐severity fires allowed P. menziesii (a fire resister) to dominate closed‐canopy forests and for fire avoiders to gradually become more common forest constituents. Millennial‐scale climate change has acted as the dominant driver of changes in both fire regimes and forest composition over the last 10,000 years; however, changes in fire‐related plant functional types highlight the important role that interactions between vegetation and fire play in long‐term fire regimes and forest dynamics.

Old forest structural development drives complexity of nest webs in a naturally disturbed boreal mixedwood forest landscape

Structural complexity generated by forest development processes and tree species compositional changes provide key habitat features for vertebrate communities that rely upon tree size and decay processes for foraging, denning or nesting. Complexity of forest structure in old stands could not only be key for harboring increased taxonomic species diversity but also greater functional diversity through more complexity in networks of tree cavity dependent species. Using a nest web approach that hierarchically links cavity-bearing trees with cavity formation agents (natural decay processes and avian excavators) and cavity users (non-excavator species), we compared network characteristics of nest webs along a time since fire gradient in a naturally disturbed boreal mixedwood forest landscape in eastern North America. Since 2003, twelve 24 to 40 ha plots ranging from 61 to more than 245 years after fire were surveyed at the Lake Duparquet Research and Teaching Forest in Abitibi, Quebec, Canada to detect active nesting, and denning cavities. We found that network complexity both in terms of number of vertebrate species and number of interactions among species, increased along the age gradient and was significantly higher in the older stands than predicted by chance. Whereas cavity-nesting communities in old forests used a higher diversity of tree species over a wide range of decay stages, trembling aspen remained a key cavity-bearing tree throughout the age gradient. Woodpeckers were the main cavity formation agents whereas less than 1% of cavities originated from natural decay. The structural development of older forests is thus a driver for functional diversity in cavity-using vertebrate communities through higher interaction richness in nest webs, among cavity-bearing trees, excavators and non-excavating users. The pivotal contribution of the entire gradient of old forest cover types to the overall complexity of nest webs in the boreal mixedwood zone is also a key for the resilience of the cavity-using vertebrate community to natural disturbances. We discuss how such resilience may be compromised by even-aged industrial timber harvesting with short rotations that shifts the age structure of boreal landscapes toward regenerating and young pole forests whereas old forest cover types become below their historical range of variability.

Amazon windthrow disturbances are likely to increase with storm frequency under global warming

Forest mortality caused by convective storms (windthrow) is a major disturbance in the Amazon. However, the linkage between windthrows at the surface and convective storms in the atmosphere remains unclear. In addition, the current Earth system models (ESMs) lack mechanistic links between convective wind events and tree mortality. Here we find an empirical relationship that maps convective available potential energy, which is well simulated by ESMs, to the spatial pattern of large windthrow events. This relationship builds connections between strong convective storms and forest dynamics in the Amazon. Based on the relationship, our model projects a 51 ± 20% increase in the area favorable to extreme storms, and a 43 ± 17% increase in windthrow density within the Amazon by the end of this century under the high-emission scenario (SSP 585). These results indicate significant changes in tropical forest composition and carbon cycle dynamics under climate change.

Climate and fire drivers of forest composition and openness in the Changbai Mountains since the Late Glacial

Ongoing climate changes have a direct impact on forest growth; they also affect natural fire regimes, with further implications for forest composition. Understanding of how these will affect forests on decadal-to-centennial timescales is limited. Here we use reconstructions of past vegetation, fire regimes and climate during the Holocene to examine the relative importance of changes in climate and fire regimes for the abundance of key tree species in northeastern China. We reconstructed vegetation changes and fire regimes based on pollen and charcoal records from Gushantun peatland. We then used generalized linear modelling to investigate the impact of reconstructed changes in summer temperature, annual precipitation, background levels of fire, fire frequency and fire magnitude to identify the drivers of decadal-to-centennial changes in forest openness and composition. Changes in climate and fire regimes have independent impacts on the abundance of the key tree taxa. Climate variables are generally more important than fire variables in determining the abundance of individual taxa. Precipitation is the only determinant of forest openness, but summer temperature is more important than precipitation for individual tree taxa with warmer summers causing a decrease in cold-tolerant conifers and an increase in warmth-demanding broadleaved trees. Both background level and fire frequency have negative relationships with the abundance of most tree taxa; only Pinus increases as fire frequency increases. The magnitude of individual fires does not have a significant impact on species abundance on this timescale. Both climate and fire regime characteristics must be considered to understand changes in forest composition on the decadal-to-centennial timescale. There are differences, both in sign and magnitude, in the response of individual tree species to individual drivers.

Eight decades of compositional change in a managed northern hardwood landscape

We analyzed over 8 decades of change in forest composition (represented by species proportion of basal area) and size class from more than 400 permanent plots located on the Bartlett Experimental Forest in the White Mountains of New Hampshire. These data represent one of the longest-term landscape-scale records of forest change based on permanent plots in North America. We analyzed the plots based on elevation class, land type indicating assumed successional direction (grouped into coniferous and deciduous), and inventory period within managed and unmanaged portions of the forest. An ongoing shift from small- to large-diameter stems is clear across all species, in response to the overall aging of the forest following exploitative harvesting in the 19th century. Major compositional changes include a continuing decline in shade-intolerant species (paper birch and aspen), along with the mid-tolerant yellow birch. An increase in red maple abundance through the early 1990s has leveled off or reversed. Among shade-tolerant species, increases in beech and red spruce were largely consistent with assumed land type on unmanaged plots, but heavy marking against diseased beech on managed plots restricted increase of that species. Sugar maple declined in abundance except where silvicultural intervention helped maintain it. By contrast, eastern hemlock showed a continuing expansion at all elevations below 600 m. The data continue to show little or no evidence of upward migration of species, despite evidence of recent regional change in climate. However, the BEF is poised for substantial changes when emerald ash borer and hemlock woolly adelgid, both of which are known to infest nearby areas, do arrive.

High‐severity burned area and proportion exceed historic conditions in Sierra Nevada, California, and adjacent ranges

AbstractAlthough fire is a fundamental ecological process in western North American forests, climate warming and accumulating forest fuels due to fire suppression have led to wildfires that burn at high severity across larger fractions of their footprint than were historically typical. These trends have spiked upwards in recent years and are particularly pronounced in the Sierra Nevada–Southern Cascades ecoregion of California, USA, and neighboring states. We assessed annual area burned (AAB) and percentage of area burned at high and low‐to‐moderate severity for seven major forest types in this region from 1984 to 2020. We compared values for this period against estimates for the pre‐Euro‐American settlement (EAS) period prior to 1850 and against a previous study of trends from 1984 to 2009. Our results show that the total average AAB remained below pre‐EAS levels, but that gap is decreasing (i.e., ~14% of pre‐EAS for 1984–2009, but 39% for 2010–2020 [including ~150% in 2020]). Although the average AAB has remained low compared with pre‐EAS, both the average annual area burned at high severity (AAHS) and the percentage of wildfire area burned at high severity have increased rapidly. The percentage of area burned at high severity, which was already above pre‐EAS average for the 1984–2009 period, has continued to rise for five of seven forest types. Notably, between 2010 and 2020, the average AAHS exceeded the pre‐EAS average for the first time on record. By contrast, the percentage of area that burned at low‐to‐moderate severity decreased, particularly in the lower elevation oak and mixed conifer forest types. These findings underline how forests historically adapted to frequent low‐to‐moderate severity fire are being reshaped by novel proportions and extents of high‐severity burning. The shift toward a high‐severity‐dominated fire regime is associated with ecological disruptions, including changes in forest structure, species composition, carbon storage, wildlife habitat, ecosystem services, and resilience. Our results underscore the importance of finding a better balance between the current management focus on fire suppression and one that puts greater emphasis on proactive fuel reduction and increased forest resilience to climate change and ecological disturbance.

Windthrow characteristics and their regional association with rainfall, soil, and surface elevation in the Amazon

Windthrows (trees uprooted and broken by winds) are common across the Amazon. They range in size from single trees to large gaps that lead to changes in forest dynamics, composition, structure, and carbon balance. Yet, the current understanding of the spatial variability of windthrows is limited. By integrating remote sensing data and geospatial analysis, we present the first study to examine the occurrence, area, and direction of windthrows and the control that environmental variables exert on them across the whole Amazon. Windthrows are more frequent and larger in the northwestern Amazon (Peru and Colombia), with the central Amazon (Brazil) being another hot spot of windthrows. The predominant direction of windthrows is westward. Rainfall, surface elevation, and soil characteristics explain the variability (20%–50%) of windthrows but their effects vary regionally. A better understanding of the spatial dynamics of windthrows will improve understanding of the functioning of Amazon forests.

Mid‐ and long‐term ecological changes after enrichment planting with native tree species in Mexican tropical mountain forests

Ecological restoration is a viable strategy to recover floristic, structural, and functional attributes of the very vulnerable and widely degraded tropical mountain forests. Most restoration efforts in these highly diverse and narrowly distributed systems involve unassisted forest regeneration or enrichment planting with a small number of species, usually those with commercial value and success evaluated after a few years. We assessed changes in soil attributes, forest composition and structure in four sites with plots under unassisted forest regeneration or enrichment planting. The sites are in the limestone massif of the central highlands of Chiapas (Mexico) and share geological, edaphic and climatic conditions, but differ in level of previous disturbance and the time elapsed since the enrichment planting (16–30 years). No changes in soil variables (contents of C, N, P, and K, cation exchange capacity, and pH) were detected. Total density of juveniles was not consistently related to unassisted forest regeneration or enrichment planting but was highest in the two sites that had severe disturbance level. Influence of enrichment planting on forest regeneration depended on the composition and structure of the surrounding stands, and more so when opportunistic trees like pines and other shade‐intolerant species are available. Yet long‐lived shade‐tolerant species, including oaks, which may have synergistic effects during forest recovery, were well represented in sites with original severe disturbance level.

Keystone structures maintain forest function for Canada lynx after large-scale spruce beetle outbreak

Central to species conservation in an era of increased disturbance from climate change is understanding the primary mechanisms that facilitate how forest-dependent species respond to changes in forest structure and composition. Here, we leveraged a natural experiment to investigate how changed forest structure and function pre-spruce-beetle (Dendroctonus rufipennis) and post-beetle disturbance influenced the regional distribution of Canada lynx (Lynx canadensis) at their southern range periphery. We compared the distribution of Canada lynx that were reintroduced into Colorado, USA from 1999–2006 to the current (2015–2017) distribution following a spatial large-scale spruce beetle outbreak from 2007 to 2016. Canada lynx did not substantially alter their distribution following the wide-spread alteration of forest structure and composition following the insect outbreak. We used the Bhattacharyya’s affinity metric to document that core (50% isopleth) and overall population ranges (95% isopleth) overlapped significantly at 50% and 77% respectively. In addition, areas of low and high relative use remained similar after the bark beetle outbreak and mapped onto one another in nearly a 1:1 fashion (Spearman rank correlation = 0.92, p < 0.01). The low impact of forest change on distribution was due to the keystone habitat elements (high horizontal forest cover, snowshoe hares) that remained functional. Thus, our results highlight that conservation scientists should increase their focus to understand the underlying mechanisms that impact wildlife distributions as climate-related disturbances becomes ever more amplified.