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Beguin, Julien; Côté, Steeve D.; Vellend, Mark — 2022-04-18 <p class="MsoNormal"><span style="font-family:'Times New Roman';font-size:12 , 0000pt;">Large herbivores can exert top-down control on terrestrial plant communities, but the magnitude, direction, and scale-dependency of their impacts remain equivocal, especially in temperate and boreal forests, where multiple disturbances often interact. Using a unique, long-term and replicated landscape experiment, we assessed the influence of a high density of white-tailed deer (</span><em><span style="font-family:'Times New Roman';font-size:12 , 0000pt;">Odocoileus virginianus</span></em><span style="font-family:'Times New Roman';font-size:12 , 0000pt;">) on the spatiotemporal dynamics of diversity, composition, and successional trajectories of understorey plant assemblages in recently logged boreal forests. This experiment provided a rare opportunity to test </span><span style="font-family:'Times New Roman';font-size:12 , 0000pt;">whether deer herbivory represents a direct filter on plant communities or if it mainly acts to suppress dominant plants which, in turn, release other plant species from strong negative plant-plant interactions. These two hypotheses make different predictions about changes in community composition, alpha and beta diversity in different</span><span style="font-family:'Times New Roman';font-size:12 , 0000pt;"> vegetation layers and at different spatial scales. Our results showed that deer had strong effects on plant community composition and successional trajectories, but the resulting impacts on plant alpha and beta diversity patterns were markedly scale-dependent in both time and space. Responses of tree and non-tree vegetation layers were strongly asymmetric. Deer acted both as a direct filter and as a suppressor of dominant plant species during early forest succession, but the magnitude of both processes was specific to tree and non-tree vegetation layers. Although our data supported the </span><span style="font-family:'Times New Roman';font-size:12 , 0000pt;">ungulate-driven </span><span style="font-family:'Times New Roman';font-size:12 , 0000pt;">homogenization hypothesis, </span><span style="font-family:'Times New Roman';font-size:12 , 0000pt;">compositional shifts and changes of alpha diversity were poor predictors of beta diversity loss.</span><span style="font-family:'Times New Roman';font-size:12 , 0000pt;"> Our findings underscore the importance of long-term studies in revealing non-linear temporal community trends, and they challenge managers to prioritize particular community properties and scales of interest, given contrasting trends of composition, alpha, and beta diversity across spatial scales.</span></p>

Leander Oh, Klara; Cromsigt, Joris PGM; te Beest, Mariska; Austrheim, Gunnar; Beguin, Julien; Churski, Marcin; Côté, Steeve D.; Kolstad, Anders L.; Kuijper, Dries P. J.; Kuiters, A. T. (Loek); Larkin, Jeffery L.; Parker Larkin, Halie A.; Perea, Ramón; Jensen, Linda K.; Ramirez, J. Ignacio; Siipilehto, Jouni; Slim, Pieter A.; Tremblay, Jean-Pierre; De Vriendt, Laurent; Vuorinen, Kataraiina Elsa Maria — 2024-09-03 Herbivores shape the environment and ecosystem functions by interacting with vegetation, including modulating the carbon cycling through changing vegetation structure and composition. The strength and rate of these effects can depend on herbivore density and forage availability. In Europe and North America, populations of several species of deer (Cervidae) have increased in number and expanded in distribution, raising questions about how current deer populations affect carbon stocks and sequestration in temperate and boreal forests. Using a meta-analysis of 17 deer exclusion datasets from 12 different publications drawn systematically from online academic databases, we assessed the effect of deer exclusion on aboveground tree carbon stocks within the lower forest strata (≤3m) in temperate and boreal forests in Europe and North America. We found that deer exclusion may indeed affect aboveground carbon stocks within the lower forest strata, but these effects were highly variable in direction and strength and not consistent across exclosure studies or scenarios. Furthermore, the inclusion of species-specific wood densities and carbon conversion factors in carbon stock calculations, rather than estimating carbon stocks using genus-specific or generic values, had a minimal influence on the estimates of deer exclusion effects on aboveground carbon stocks. This study highlights the complex relationship between deer and carbon cycling across temperate and boreal forests. Disentangling the mechanisms behind woody plant responses to deer exclusion is key to improving our understanding of wildlife-carbon relations. Future research should include long-term effects of deer on higher forest strata, such as canopy trees, and on non-tree components, such as herbaceous vegetation and shrubs. This knowledge will be important for promoting carbon sequestration and storage, improving the conservation of temperate and boreal forests in the face of increasing deer populations, and applying conservation and mitigation efforts where they are needed most. https://creativecommons.org/licenses/by/4.0/legalcode