by Claire Morin | 10 April 2020
Published in Forest ecology and management 442: 96-104. doi: 10.1016/j.foreco.2019.03.040
From a forest management stand point, it is crucial to know which ecological processes are most likely to drive changes in tree species distributions and abundance under warming climate conditions. In this study, we simulated forest dynamics in a 703,580 km2 territory that straddles the boreal and temperate broadleaved forest biomes in the province of Québec (Canada), under a RCP 8.5 climate change scenario. The objective was to evaluate how future forest composition is sensitive to variation in four potential drivers: fire regimes, harvesting regimes, the capacity of tree species to persist under warmer climate conditions, and species capabilities for long-distance colonization. The results indicate that forest composition in 2100 is most sensitive to variation in the parameters controlling species persistence when conditions become warmer or dryer than the conditions found in their current range. Concretely, this points to avenues of research to improve the accuracy of our predictions regarding the impacts of climate change on forest composition. For instance, we should further investigate the underlying ecological (competition) or physiological (drought stresses) processes that influence tree species persistence at the receding edge of their current distributions.
by Audrey Verreault | 10 April 2020
Published in Landscape Ecology 34: 159-174
Context: Forest landscapes at the boreal–temperate ecotone have been extensively altered. Reducing the gap between current and presettlement forest conditions through ecosystem-based forest management (EBFM) is thought to enhance ecological integrity. However, climate change may interfere with this goal and make these targets unrealistic.
Objectives: We evaluated the impacts of climate change on the ability of EBFM to reduce discrepancies between current and presettlement forest conditions in southeastern Canada.
Methods: We used early-land-survey data as well as projections from a forest landscape model (LANDISII) under four climate change scenarios and four management scenarios to evaluate future discrepancies between presettlement forest conditions and future forest landscapes.
Results: By triggering swift declines in most latesuccession boreal conifer species biomass, climate change would greatly reduce the ability of forest management to reduce the gap with presettlement forest composition, especially under severe anthropogenic climate forcing. Scenarios assuming extensive clearcutting also favor aggressive competitor species that have already increased with high historical harvest levels (e.g., poplars, maples).
Conclusions: EBFM would still be the ‘‘less bad’’ forest harvesting strategy in order to mitigate composition discrepancies with the presettlement forests, though it is likely to fail under severe climate forcing. In this latter case, one might thus question the relevancy of using presettlement forest composition as a target for restoring degraded forest landscapes. As such, we advocate that managers should relax the centrality of the reference condition and focus on functional restoration rather than aiming at reducing the gaps with presettlement forest composition per se.
by Audrey Verreault | 10 April 2020
Published in Nature Communications 10: 1265. doi:10.1038/s41467-019-09265-z
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 (>130,000km2) 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.
by Audrey Verreault | 10 April 2020
Published in Journal of Applied Ecology 56(3): 758-768
It has recently been reported that changing precipitation patterns increase tree mortality and reduce biomass accumulation in northern temperate and boreal forests. Functional diversity can mitigate the impacts of climate extremes in different types of ecosystems, but few studies have focused on tree functional diversity in forest ecosystems. It is critical to identify functional traits that could help anticipate the impact of drought on tree mortality, and how these affect above-ground tree biomass productivity at the ecosystem level.
We tested how three functional traits (ratio of dry leaf mass per unit area [LMA], xylem pressure at which 50% of stem xylem conductivity is lost through cavitation [Ψ50] and leaf area to sapwood ratio) influence severe drought impacts on stand mortality and productivity. We used structural equation modelling to compare the effect of a latent variable composed of these three traits between plots that had suffered drought and plots that had not, on the mortality and productivity of northern temperate and boreal forests of Québec, Canada.
A latent variable composed of LMA and Ψ50 significantly explained drought-induced tree mortality, but did not explain stand productivity response to severe drought. Therefore, even if these traits relate to the ability of species to survive drought (drought tolerance) at the tree level, they did not affect the maintenance of plant productivity during drought events (drought resistance) at the stand scale. We hypothesize that the effect of tree mortality on productivity was likely compensated by the formation of canopy openings that stimulate the growth of surviving trees.
Synthesis and applications. Our results show that mitigation of water loss and xylem resistance to cavitation contribute similarly to severe drought tolerance in trees within northern temperate and boreal forests. Therefore, including drought-resistant trees in fine-scale mixtures might mitigate the impacts of drought on forest productivity due to the survivors’ response to released resources.
by Marie-Claude Boileau | 3 February 2020
More than 80 fish species are found in the freshwater and brackish waters of the St. Lawrence River and evaluation of the status of these fish stocks is complex. In order to paint a current picture of our understanding of the fish communities and aquatic habitats of the St. Lawrence, and to judge the evolution of these elements over the last 25 years, different status indicators were used: (1) Index of Biotic Integrity, (2) status of the stock of certain species subject to recreational and commercial fishing, (3) status of species under threat, (4) coastal zone fish biodiversity index and (5) relative abundance index for submerged aquatic vegetation. Analysis of these indicators highlights what are sometimes very different findings between species and sectors. Several rapid changes that have arisen during the last two decades in the characteristics of aquatic habitats and in the structure of fish communities testify to an evolving ecosystem that is tending to degrade in certain sectors. Over the years, several exploited fish stocks have seen periods of decline. While certain species have been able to re-establish themselves thanks to restrictive management measures, others have been slow to recover due to several factors other than pressures from fishing.
