Explore the vast range of titles available.

Predicting future ecosystem dynamics depends critically on an improved understanding of how disturbances and climate change have driven long-term ecological changes in the past. Here we assembled a dataset of >100,000 tree species lists from the 19th century across a broad region (>130,000km 2 ) in temperate eastern Canada, as well as recent forest inventories, to test the effects of changes in anthropogenic disturbance, temperature and moisture on forest dynamics. We evaluate changes in forest composition using four indices quantifying the affinities of co-occurring tree species with temperature, drought, light and disturbance. Land-use driven shifts favouring more disturbance-adapted tree species are far stronger than any effects ascribable to climate change, although the responses of species to disturbance are correlated with their expected responses to climate change. As such, anthropogenic and natural disturbances are expected to have large direct effects on forests and also indirect effects via altered responses to future climate change. Separating anthropogenic and climatic impacts on forest compositions can be challenging due to a lack of data. Here the authors look at forest compositional changes in eastern Canada since the 19th century and find land use has most strongly shaped communities towards disturbance-adapted species.

Forest anthropogenic and natural stand-replacing disturbances are increasing worldwide due to global change. Many uncertainties regarding the regeneration and growth of these young forests remain within the context of changing climate. In this study, we investigate the effects of climate, tree species composition, and other landscape-scale environmental variables upon boreal forest regrowth following clearcut logging in eastern Canada. Our main objective was to predict the effects of future climate changes upon post-logging forest height regrowth at a subcontinental scale using high spatial resolution remote sensing data. We modeled forest canopy height (estimated from airborne laser scanning [LiDAR] data over 20 m resolution virtual plots) as a function of time elapsed since the last clearcut along with climate (i.e. temperature and moisture), tree species composition, and other environmental variables (e.g. topography and soil hydrology). Once trained and validated with ∼240 000 plots, the model that was developed in this study was used to predict potential post-logging canopy height regrowth at 20 m resolution across a 240 000 km 2 area following scenarios depicting a range of projected changes in temperature and moisture across the region for 2041–2070. Our results predict an overall beneficial, but limited effect of projected climate changes upon forest regrowth rates in our study area. Stimulatory effects of projected climate change were more pronounced for conifer forests, with growth rates increasing between +5% and +50% over the study area, while mixed and broadleaved forests recorded changes that mostly ranged from −5% to +35%. Predicted increased regrowth rates were mainly associated with increased temperature, while changes in climate moisture had a minor effect. We conclude that such growth gains could partially compensate for the inevitable increase in natural disturbances but should not allow any increase in harvested volumes.

There is a pressing need for a better understanding of changing forest fire regimes worldwide, especially to separate the relative effects of potential drivers that control burned areas. Here we present a meta-analysis of the impacts of climate fluctuation and Euro-Canadian settlement on burned areas from 1850 to 1990 in a large zone (>100 000 km2) in northern temperate and boreal forests of eastern Canada. Using Cox regression models, we tested for potential statistical relationships between historical burned areas in 12 large landscapes (reconstructed with dendrochronological data) with climate reconstructions, changes in the Euro-Canadian population, and active suppression (all reconstructed at the decadal scale). Our results revealed a dominant impact of climate fluctuations on forest burned areas, with the driest decades showing fire hazards between 5 to 15 times higher than the average decades. Comparatively, the Euro-Canadian settlement had a much weaker effect, having increased burned areas significantly only during less fire-prone climate conditions. During periods of fire-prone climate, burned areas were maximum independent of fluctuations in Euro-Canadian populations. Moreover, the development of active fire suppression did not appear to reduce burned areas. These results suggest that a potential increase in climate moisture deficit and drought may trigger unprecedented burned areas and extreme fire events no matter the effects of anthropogenic ignition or suppression.

Forest fires are a key driver of boreal landscape dynamics and are expected to increase with climate change in the coming decades. A profound understanding of the effects of fire upon boreal forest dynamics is thus critically needed for our ability to manage these ecosystems and conserve their services. In the present study, we investigate the long-term post-fire forest dynamics in the southern boreal forests of western Quebec using historical aerial photographs from the 1930s, alongside with modern aerial photographs from the 1990s. We quantify the changes in forest cover classes (i.e., conifers, mixed and broadleaved) for 16 study sites that were burned between 1940 and 1970. We then analyzed how interactions between pre-fire forest composition, site characteristics and a fire severity weather index (FSWI) affected the probability of changes in forest cover. In the 1930s, half of the cover of sampled sites were coniferous while the other half were broadleaved or mixed. Between the 1930s and the 1990s, 41% of the areas maintained their initial cover while 59% changed. The lowest probability of changes was found with initial coniferous cover and well drained till deposits. Moreover, an important proportion of 1930s broadleaved/mixed cover transitioned to conifers in the 1990s, which was mainly associated with high FSWI and well-drained deposits. Overall, our results highlight a relatively high resistance and resilience of southern boreal coniferous forests to fire, which suggest that future increase in fire frequency may not necessarily result in a drastic loss of conifers.

The vegetation composition of northeastern North American forests has significantly changed since pre-settlement times, with a marked reduction in conifer-dominated stands, taxonomic and functional diversity. These changes have been attributed to fire regime shifts, logging, and climate change. In this study, we disentangled the individual effects of these drivers on the forest composition in southwestern Quebec from 1830 to 2000 by conducting retrospective modelling using the LANDIS-II forest landscape model. The model was run based on pre-settlement forest composition and fire history reconstructions, historical timber harvest records, and climate reanalysis data. We compared counterfactual scenarios excluding individual factors to a baseline historical scenario. Our results indicated that timber harvesting had the greatest impact on forest dynamics over the past centuries. In the absence of timber harvesting, pre-settlement species abundances were largely maintained, preserving key functional traits like fire and shade tolerance that contribute to ecosystem resilience. Increased fire activity during the settlement period contributed to the increase of early-successional aspen (Populus tremuloides), but timber harvesting played the dominant role. Fire exclusion had no influence on vegetation composition, suggesting mesophication unfolds over longer timescales than those captured in this study. Climate change, characterized by modest increases in temperature and precipitation, had a minor effect on vegetation shifts, as increased precipitation might have mitigated the adverse effects of rising temperatures. However, future climate change is projected to become a more significant driver of forest composition. These findings underscore the importance of forest restoration and continued research on past forest dynamics to better understand current and future changes. The online version contains supplementary material available at 10.1007/s10980-025-02043-x.

ContextKnowledge of how environmental gradients generate changes in community composition across forest landscapes (β-diversity) represents a critical issue in the era of global change, which exerts especially powerful impacts by shifting disturbance regimes.ObjectivesWe analyzed the response of tree communities to increased disturbance rates that were linked to European settlement at the temperate-boreal interface of eastern Canada. We tested whether disturbance has led to spatial homogenization or heterogenization, and to decoupling or strengthening of community-environment relationships.MethodsWe used a reconstruction of pre-industrial tree communities based on historical land survey records (1854–1935), together with modern data, to assess changes in tree β-diversity patterns. Then, β-diversity was partitioned into fractions explained by spatial (dbMEM) and environmental variables (latitude, elevation, slope, drainage and surface deposits) in order to assess changes in spatial structures and community-environment relationships.ResultsIn pre-industrial times, environmental variables explained only a small proportion of β-diversity since dominant taxa were present across the range of environmental gradients, whereas habitat specialists were very rare. Between pre-industrial and modern times, our analysis highlights an increase in β-diversity and the proportion of β-diversity that was explained by environmental variables. Increased disturbance rates have favored early-successional habitat specialist taxa and reduced the habitat breadth of pre-industrial generalists, thereby increasing the strength of community-environment relationships.ConclusionsOur results support that disturbance can alter the strength of community-environment relationships and also suggest that functional traits of species within the regional pool could predict whether or not disturbance alters such relationships.

QUESTIONS: What were the pre‐industrial forest landscape composition patterns? Which factors had structured the pre‐industrial landscape patterns? How have pre‐industrial landscape patterns and post‐industrial disturbances controlled composition changes? LOCATION: An area of 4175 km² at the temperate–boreal forest interface of southwest Quebec, Canada. METHODS: Reconstruction of the pre‐industrial composition is based on an original early land survey data set (1874–1935). Composition changes were computed by comparing historical data with modern forest inventories. Landscape‐scale patterns and composition changes were assessed through spatially constrained clustering analysis. RESULTS: Pre‐industrial forest composition was structured across the landscape by the combination of environmental gradients (topography, deposits, drainage, etc.) and recurrence of fire. Frequency and intensity of fires were most likely the main drivers of forest dynamics and composition across the landscape. Black spruce (Picea mariana) and balsam fir (Abies balsamea) dominated hilly areas affected by former fires; aspen (Populus tremuloides) dominated lowlands following recent fire. White cedar (Thuja occidentatlis) and pines (Pinus spp.) dominated areas probably affected by small surface fires. New disturbance regimes that were subsequently incurred by human activities have shifted the pre‐industrial landscape mosaic and have led to the current landscapes. Composition changes included a replacement of conifers by early successional species within settled or burned areas, and the maintenance of conifers and an increase in cedar dominance in areas affected by partial disturbance. CONCLUSIONS: Post‐industrial composition changes must be perceived as complex interactions between pre‐industrial landscape patterns and natural and human disturbances. Such land‐use legacies could be important drivers of future landscape change and should be investigated and considered when predicting future climate‐induced ecological changes.

Warning: This article contains terms, descriptions, and opinions used for historical context that may be culturally sensitive for some readers.Background: Understanding drivers of boreal forest dynamics supports adaptation strategies in the context of climate change.Aims: We aimed to understand how burn rates varied since the early 1700s in North American boreal forests.Methods: We used 16 fire-history study sites distributed across such forests and investigated variation in burn rates for the historical period spanning 1700–1990. These were benchmarked against recent burn rates estimated for the modern period spanning 1980–2020 using various data sources.Key results: Burn rates during the historical period for most sites showed a declining trend, particularly during the early to mid 1900s. Compared to the historical period, the modern period showed less variable and lower burn rates across sites. Mean burn rates during the modern period presented divergent trends among eastern versus northwestern sites, with increasing trends in mean burn rates in most northwestern North American sites.Conclusions: The synchronicity of trends suggests that large spatial patterns of atmospheric conditions drove burn rates in addition to regional changes in land use like fire exclusion and suppression.Implications: Low burn rates in eastern Canadian boreal forests may continue unless climate change overrides the capacity to suppress fire.

Context The vegetation composition of northeastern North American forests has significantly changed since pre-settlement times, with a marked reduction in conifer-dominated stands, taxonomic and functional diversity. These changes have been attributed to fire regime shifts, logging, and climate change. Methods In this study, we disentangled the individual effects of these drivers on the forest composition in southwestern Quebec from 1830 to 2000 by conducting retrospective modelling using the LANDIS-II forest landscape model. The model was run based on pre-settlement forest composition and fire history reconstructions, historical timber harvest records, and climate reanalysis data. We compared counterfactual scenarios excluding individual factors to a baseline historical scenario. Results and Conclusions Our results indicated that timber harvesting had the greatest impact on forest dynamics over the past centuries. In the absence of timber harvesting, pre-settlement species abundances were largely maintained, preserving key functional traits like fire and shade tolerance that contribute to ecosystem resilience. Increased fire activity during the settlement period contributed to the increase of early-successional aspen (Populus tremuloides), but timber harvesting played the dominant role. Fire exclusion had no influence on vegetation composition, suggesting mesophication unfolds over longer timescales than those captured in this study. Climate change, characterized by modest increases in temperature and precipitation, had a minor effect on vegetation shifts, as increased precipitation might have mitigated the adverse effects of rising temperatures. However, future climate change is projected to become a more significant driver of forest composition. These findings underscore the importance of forest restoration and continued research on past forest dynamics to better understand current and future changes.

With steep climatic gradients over short distances, montane ecosystems provide exceptional opportunities to study ecological responses to climate and other environmental changes. Here we present a summary and synthesis of 10 years of research on this theme in a protected area in southern Québec, Canada (Parc National du Mont Mégantic), with ecological conditions closely similar to the northern Appalachians. During the ∼150 years since European settlement, anthropogenic disturbance has reduced the abundance of certain taxa (e.g., Picea [spruce]), while favoring other taxa that thrive during succession (e.g., Betula [birch], Acer [maple]). In more recent decades, climate warming (∼0.21 °C per decade) appears to have prompted upward elevational range shifts for many plant species, although such responses lag behind changes in climate itself. Experimental studies with seeds and seedlings of Acer saccharum (Sugar Maple) suggest that upward range expansion might be constrained by non-climatic factors such as belowground properties and seed predators, while escape from insect herbivores might actually accelerate range expansion. Similar studies with understory plants have not revealed clear evidence of non-climatic constraints on range limits, although some preliminary data presented here suggest a possible role of a lack of microsites with rich, moist soil at high elevation. Current studies focus on the lower elevational range limits of species restricted to mountaintops, such as certain lichens. Vegetation and flowering phenology are also sensitive to climate, and we have found that earlier springs are associated with decreased potential gene flow across populations at different elevations; ongoing studies will determine how differential sensitivity of herbs vs. trees might influence the duration of a high light period in spring in the understory. Overall, we have found clear signals of plant responses to long-term anthropogenic disturbances and recent climatic warming, but considerable uncertainty remains about how climatic and non-climatic factors will interact to determine the future of this montane ecosystem.