Associate Professor The George Washington University Washington, DC, United States
Abstract: Ungulate herbivory often alters the abundance, diversity, and community composition of vegetation communities through preferential herbivory. Native ungulates are typically associated with facilitating invasive plant species indirectly through apparent competition; over-browsing the native plant community thereby reducing the biotic resistance of that community. However, the dynamics between non-native ungulates and invasive plant species are not well established. These dynamics are of particular concern on the Eastern Shore of Maryland where the invasive common reed (Phragmites australis) and the non-native sika deer (Cervus nippon) are prevalent. We investigated the effects of a non-native ungulate herbivory on the understory plant community and their influence in facilitating the spread of P. australis from the marsh-forest ecotone into the coastal forest. Three paired cage exclosure and control plots were established across 4 sites on the Eastern Shore of Maryland. We monitored percent cover, species abundance, species diversity and community composition for four years in each exclosure and control plot. In order to test the ability of the understory plant community to resist invasion of P. australis once released from browse pressure and the direct influence of sika deer herbivory on P. australis, we transplanted seedlings into each cage exclosure and control plots. We found that sika deer have a similar impact on the native plant community as native ungulates, however, Phragmites survival was more influenced by herbivory from sika deer than the biotic resistance of the recovered plant community. These findings highlight that a non-native ungulate's direct impact on an invasive species can outweigh its indirect facilitation of that species.
