Authors: Steve Vissault, Matthew Talluto, Isabelle Boulangeat, Dominique Gravel
Affiliation (all authors): Département de biologie, chimie et géographie, Univiversité du Québec à Rimouski, 300 Allée des Ursulines, Rimouski,QC G5L 3A1, Canada.
A majority of studies on ecotones, which are transitional areas expected to be particularly sensitive to climate change, focus on the transition between forest and non-forest ecosystems. However, little attention has been given to evaluate the dynamics between two forest ecosytems such as the temporate-boreal ecotone. The equilibrium distribution of the two forest types is largely related to climate at the continental scale, and it is therefore expected that temperate trees will expand northward in the coming decades. However, the observed distribution of the two forests in the ecotone area is patchy and highly variable, suggesting that they may coexist as alternative stable states under the same climatic conditions at the landscape scale. We hypothesize that a positive plant-soil feedback may operate, as both types of forest stands change the seedbed conditions in a way that favours their own regeneration. If this hypothesis is correct, the initial composition of patches would influence the migration of temperate tree species. Otherwise, the patchiness might be the result of transient dynamics. We explore these hypotheses using a state and transition model of landscape dynamics, parameterized on an extensive database of 160,000 forest plots widely distributed along a latitudinal gradient in the east of America. We found that the observed transitions between the different states successfully predicted the location of the ecotone. We also found, despite the absence of alternative stable states, a significant variability in landscape composition at the transition between temperate and boreal forests suggesting that some part of the landscape is currently transient, creating the patchy structure that we observe. These results emphasize the role of disturbances such as fire or logging which maintain a high proportion of transcient forests. This model predicts not only the equilibrium state but also the transitions and delay to reach the equilibrium forest composition, which is of prime importance for forest mangement.
303 Words
Keywords: Climate change, Temperate forest, Boreal forest, Equilibrium, Ecotone, States and transitions model, Resilience.