White-tailed deer herbivory impacts on plant community composition and recruitment in western New York deciduous forests

Abstract

In high densities, white-tailed deer (Odocolius virginiana) have a multitude of detrimental effects on plant communities, particularly in forest ecosystems. Through intensive herbivory and dispersal of native and invasive seeds, deer can be considered ecosystem engineers in the Northeastern and Midwestern United States. To measure how removal of deer herbivory changes plant community composition over time, I constructed four fenced deer exclosures and delineated four unfenced control plots in a Brockport, NY deciduous forest fragment with an estimated population of 17 deer/km2. After three summers of data collection, the average height of all tree seedlings and root suckers less than 2 m tall was significantly greater in each fenced plot than unfenced plot. Ground-level percent cover, abundance, and species richness were not yet affected by treatment, but percent cover of woody vine foliage was higher in the fenced plots. As expected, removing herbivory pressure has affected plant communities in Brockport Woods. To determine whether deer are concurrently transporting invasive species in this and other disturbed forests, I collected deer fecal pellet piles across 11 months. The average number of seeds found in each whole pellet pile was 11.4 (±11.6). Over 50% of the seeds and germinates found were from non-native species, seeds of which were particularly prevalent in pellet piles collected in the fall and winter. Of the 17 species that survived the gut and germinated in outdoor pots, only one species (Persicaria virginiana) successfully germinated under a forest canopy. As movers of an average of 388 seeds per day, many of which are 2 non-native, deer are important contributors to Northeast and Midwest seed dispersal and ecosystem dynamics.