PS 32-23
Meta-analytical synthesis of the impacts of white-tailed deer on the diversity and productivity of understory flora in North American forests
The abundance of white-tailed deer (Odocoileus virginianus) in much of North America far exceeds that of historic levels. Considerable effort has been extended to describe the consequences of deer overabundance on, among other ecological parameters, plant diversity and productivity. However, a quantitative synthesis of this work has not been done. We conducted a meta-analysis of published studies describing the impacts of deer exclusion on species richness, species diversity, and productivity of understory plant communities in the deciduous forest biome of North America. We included all studies in the meta-analysis that 1) provided site-specific information on the location and duration of the study, the size of plots, and deer density, and 2) reported statistics (mean, variance, and replication) necessary to compute standardized mean differences between control and exclusion plots.
Results/Conclusions
We found 19 studies that reported one or all of the ecological parameters described above, plus all of the site-specific information. However, because most studies reported results for only subsets of the understory communities (e.g., woody species), meaningful analysis was possible for only total species richness and total species cover. Average effect sizes computed from this synthesis indicate negative impacts of white-tailed deer on the species richness (Hedges' g = -0.59; 95% CI = -1.06, -0.13) and cover (Hedges' g = -0.86; 95% CI = -1.40, -0.33) of plant communities in North American deciduous forests. Meta-regressions using site-specific moderators are forthcoming. This synthesis confirms the often observed negative impacts of white-tailed deer on plant community composition and productivity. We conclude that, in general, white-tailed deer occur at densities that overshoot the biological carrying capacity of the forests they inhabit. However, more thorough reporting of impacts on specific plant groups (e.g., place of origin, taxonomy) is needed to build a more robust understanding of the influence of contemporary deer overabundance on understory plant communities in deciduous forests.