Species composition determines resistance to drought in dry forests of the Great Lakes – St. Lawrence forest region of central Ontario

Abstract

Question: Predicted changes in the frequency of short-term drought events raise concerns about potential effects of climate change on forest ecosystems. Few experiments have investigated the effects of tree species richness and composition in forest assemblages exposed to drought, and general conclusions for these systems are currently lacking. We tested the hypothesis that different species richness and composition affects community-level stability during a severe short-term drought event across a gradient of tree species assemblages typical of temperate forest ecosystems on dry substrates.Location: Great Lakes -St. Lawrence forest region, central Ontario, Canada. Methods:The study assemblages spanned a gradient of 15 different combinations of species richness and composition of four tree species. The drought occurred in 2005 and was characterized by high growing season temperature and low precipitation. Plots (n = 63) representing replicate assemblages were selected to collect increment cores (n = 1193) and examine growth responses to past drought at the community and population levels. Cross-dated tree ring measurements were used to reconstruct basal area increment (BAI) and calculate indices of resistance, resilience and productivity over the drought period. We used hierarchical analysis of variance models to estimate the effects of species richness and composition on drought responses. Results:We identified a significant effect of species composition on community-level resistance and productivity. White pine (Pinus strobus) abundance was associated with lower community resistance and white birch (Betula papyrifera) abundance with higher resistance. Assemblages with greater productivity were often characterized by the high abundance of trembling aspen (Populus tremuloides). There was no overall effect of the assemblage gradient on the population-level stability; however, red pine (Pinus resinosa) productivity was higher in combination with trembling aspen and white birch. Conclusion:Our study demonstrated that species richness had no effect on the community-level stability of growth during a drought in temperate forests on dry substrates. Instead, there were important compositional effects that determine some aspects of stability during drought events. If pine forests were managed to maintain a component of deciduous species, the capacity to dampen the community-level effects of more frequent drought would increase.

Seasonal variability of forest sensitivity to heat and drought stresses: A synthesis based on carbon fluxes from North American forest ecosystems

“…Comparisons between managed forests and their counterpart natural forests also revealed that their response to the same extreme event could be opposite (van Gorsel et al, ; Zald & Dunn, ). Other studies have indicated that resistance of forests to climate extremes is determined by the species composition and stand density (Arthur & Dech, ; Giuggiola, Bugmann, Zingg, Dobbertin, & Rigling, ). Natural forests with lower density, higher structural complexity, and more understory tend to be more resilient to climate anomalies.…”

Effect of the 2022 summer drought across forest types in Europe

“…The spread of drought, as the total sum of areas across z-scores, exhibited different patterns in different years, leading to varied responses of different forest types to the climatic anomalies. Impact of drought on forests can vary largely depending on the forest type, tree species, and factors that are controlled by species composition, and past exposure to extreme conditions (Arthur and Dech 2016;Chen et al 2022). Our analysis showed that conditions in summer 2022 reduced vegetation functioning across DBFs the most, as it was indicated by declined SIF signals (Figure 5).…”

Heat and drought impact on carbon exchange in an age-sequence of temperate pine forests

“…Our findings agree with other studies (e.g., Irvine et al 2002 ; Yang et al 2010 ; Gao et al 2017 ; Chen et al 2020b ; Duffy et al 2021 ) and further imply that mature forests are more resilient to drought stresses. It is also likely that long-term forest management activities, such as selective thinning, may have increased the forest’s resilience to drought by reducing stand density (Giuggiola et al 2013 ) or by introducing more drought resistant secondary deciduous species (Arthur and Dech 2016 ). Our results imply that the more frequent climate extremes in the future may have a profound impact on forest carbon sink in managed temperate forests, as the most productive middle aged forest are the most sensitive to heat and drought stresses.…”