Data from: Large herbivores trigger spatiotemporal changes in forest plant diversity

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 (Odocoileus virginianus) 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 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 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 ungulate-driven homogenization hypothesis,
compositional shifts and changes of alpha diversity were poor predictors
of beta diversity loss. 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.