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Through their foraging and habitat selection, white-tailed deer (Odocoileus virginianus) can have profound effects on forest plant communities that produce persistent legacy effects. To examine the duration of persistence of potential legacy effects, we investigated the long-term consequences of deer herbivory in plant communities following canopy gap creation in a hemlock–northern hardwood forest in the Upper Peninsula of Michigan. Twenty artificial canopy gaps were created during the winter of 2002–03: seven small gaps (50–150 m2), seven medium gaps (151–250 m2), and six large gaps (251–450 m2). Herbaceous layer communities were sampled within arrays of exclosed and nonexclosed sample plots, established within a few years of gap creation, during the summer of 2020 and compared to a previous study conducted in 2007. Eighteen years following canopy gap creation, herbaceous layer communities exhibited both persistent and transient legacies of deer herbivory. Persistent legacies included similarity of small to large gaps compositionally and low abundance of browse-sensitive species outside of exclosures. Transient patterns included initial high graminoid cover and low cover of trees in the ground layer outside of exclosures and differences in diversity between gap size classes. Some emergent patterns were also observed, including declining floristic quality indices over time but sustained high occurrence of a number of species with moderately high coefficients of conservatism on deer access plots, albeit at low abundance. Differential compositional trajectories emerged based on gap-specific tree species colonization patterns. Our results suggest that through differential foraging patch selection and control of woody regeneration, white-tailed deer may alter or reinforce patterns of dominance depending on initial conditions. These interactions may result in context-specific persistent, transient, and emergent dynamics as plant communities recover from canopy disturbance. [ABSTRACT FROM AUTHOR]

Plant–herbivore interactions account for much of the biodiversity observed in an ecosystem. Plants may alter defense expression dependent on the specific herbivore present. Many studies focus on the optimization of these defenses against a single herbivore, but in an ecological context, there may be a myriad of herbivores at any given time. We designed a study to examine defenses employed by swamp white oak (Quercus bicolor) against insects and large mammals. We established six deer exclosures with trees located inside and outside each exclosure. Outside the exclosures, physical constraints only allow deer to feed up to a browseline on trees, whereas insects can potentially access all portions of the tree. Trees inside exclosures were only accessible to insect herbivores. Furthermore, insecticides were applied to half of the exclosures to create insect‐free (i.e., insecticide applied), deer‐free (i.e., inside exclosures), deer‐only (i.e., outside exclosures with insecticide), and herbivore‐free (i.e., inside exclosures with insecticide) environments. This design allowed us to analyze simultaneous defensive responses of individual trees to mammal and insect herbivores. We predicted that because insects represent a continuous threat, plants should invest in fixed concentrations of defenses (e.g., polyphenols, tannins, and condensed tannins), even when deer are absent. When deer are present, plants should increase investment in defenses in tissues that deer have access to. We found that plant defense strategies varied spatially on individual trees. When only insects were present, nutritional constituents (e.g., nitrogen and non‐structural carbohydrates) did not change but antinutritional constituents increased. Contrastingly, when deer were present, both nutritional and antinutritional constituents decreased. We found a decrease in insect functional group diversity when deer were present. Our findings suggest that plants may partition defense strategies depending on the most prominent herbivore pressure. However, changes in insect functional group diversity may result from either changes in plant defense strategy or intraspecific competition among multiple herbivores. Future studies should investigate patterns of chemical heterogeneity displayed by plants in response to diverse herbivore pressures. [ABSTRACT FROM AUTHOR]

Abstract Plant–herbivore interactions account for much of the biodiversity observed in an ecosystem. Plants may alter defense expression dependent on the specific herbivore present. Many studies focus on the optimization of these defenses against a single herbivore, but in an ecological context, there may be a myriad of herbivores at any given time. We designed a study to examine defenses employed by swamp white oak (Quercus bicolor) against insects and large mammals. We established six deer exclosures with trees located inside and outside each exclosure. Outside the exclosures, physical constraints only allow deer to feed up to a browseline on trees, whereas insects can potentially access all portions of the tree. Trees inside exclosures were only accessible to insect herbivores. Furthermore, insecticides were applied to half of the exclosures to create insect‐free (i.e., insecticide applied), deer‐free (i.e., inside exclosures), deer‐only (i.e., outside exclosures with insecticide), and herbivore‐free (i.e., inside exclosures with insecticide) environments. This design allowed us to analyze simultaneous defensive responses of individual trees to mammal and insect herbivores. We predicted that because insects represent a continuous threat, plants should invest in fixed concentrations of defenses (e.g., polyphenols, tannins, and condensed tannins), even when deer are absent. When deer are present, plants should increase investment in defenses in tissues that deer have access to. We found that plant defense strategies varied spatially on individual trees. When only insects were present, nutritional constituents (e.g., nitrogen and non‐structural carbohydrates) did not change but antinutritional constituents increased. Contrastingly, when deer were present, both nutritional and antinutritional constituents decreased. We found a decrease in insect functional group diversity when deer were present. Our findings suggest that plants may partition defense strategies depending on the most prominent herbivore pressure. However, changes in insect functional group diversity may result from either changes in plant defense strategy or intraspecific competition among multiple herbivores. Future studies should investigate patterns of chemical heterogeneity displayed by plants in response to diverse herbivore pressures.