Deer overabundance in the Piedmont of New Jersey: implications for old field succession
Creators: name: Pisano, Benjamin
Publisher: name: No Publisher Supplied
Year: 2020

description: Densities of white-tailed deer, Odocoileus virginianus, in New Jersey have increased dramatically since the 1970s. Selective browse of hardwood tree species by overabundant deer has become problematic and can result in degraded secondary forests with diminished biodiversity. This thesis investigates the impact of overabundant deer browse on post agricultural succession communities related to three distinct plant assemblages responsible for driving succession: aboveground vegetation, the seed bank, and seed rain. The Hutcheson Memorial Forest Center (HMFC) in Somerset County of the New Jersey Piedmont served as the study location. Within HMFC are two old fields released from agriculture: the first field released in 1967 and the second field in 1984, each with permanent plots open and exclosed to deer that were installed in 1984. The goal of the first chapter of this thesis was to determine changes in aboveground vegetation of released agricultural fields over time and how the successional trajectories of the released fields change in presence of increased deer density. To do this, historic vegetation data collected in the 1990s was compared to 2017 data. Permutational multivariate analysis of variance (PERMANOVA) and nonmetric multidimensional scaling (NMDS) were used to investigate change over time. Linear mixed-effects models and ANOVA determined differences in cover between hardwood tree species and Juniperus virginiana (JUVI) between fields and plot treatments over time. Accelerated Piedmont succession was only observed in exclosed plots that received fencing immediately upon release from agriculture. Delayed Piedmont succession was observed in plots open to deer. The objective of the second chapter was understanding potential impacts of deer browse cascading from aboveground vegetation to the other two assemblages, the seed bank and seed rain. The focus of this chapter was to examine changes in tree species frequency between plot treatments and fields across all three assemblages. Analysis using NMDS and PERMANOVA determined a difference in average community composition of tree species relative abundance caused by field age across all three assemblages, while differences caused by plot treatment was only found in the aboveground vegetation. Spearman correlations determined that deer browse, similar to predation and disturbance, acts as a local, plot-scale process that shape tree species frequency in aboveground vegetation. Seed rain did not respond to deer browse and instead persisted in the presence of deer. Communities within each field were largely driven by successional stage/field age, a coarser, patch-scale process. Field age played a strong role in shaping communities largely due to the difference in timing of exclosure installation after each field’s release from agriculture. The focus of future research should include larger, more persistent samplings of each assemblage type that provides a better comprehension of interactions among the different assemblages.