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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