Quantifying the effects of deer browsing on vegetation establishment, growth and development in overwash fans: 2015-2016 post-Hurricane Sandy assessment

Kilheffer, Chellby; Ries, Lindsay; Raphael, Jordan; Underwood, H.

This Natural Resource Report is the first of a five-part series in response to Agreement Number P14AC00469, which was awarded to the co-authors in response to Hurricane Sandy. Hurricane Sandy dramatically impacted coastal New England in 2012. Many areas of Fire Island National Seashore (40.669, -73.051) were inundated or eroded, and several primary dunes were overwashed by storm surge. The cooperative agreement addressed the following tasks: (1) assess effects of white-tailed deer browsing on vegetation establishment, growth, and development in key overwash zones on Fire Island National Seashore, (2) expand vegetation monitoring developed for the Sunken Forest into additional maritime forest zones on Fire Island, (3) document daily, seasonal, and annual movements of white-tailed deer on Fire Island, and (4) explore how access to food, thermal cover, and fresh water affect activity and space use of white-tailed deer between heavily urbanized western communities of Fire Island and the Wilderness Area. This report solely addresses objective (1) listed above. The remaining four reports in this series include three reports addressing each of the remaining objectives and a comprehensive report addressing Fire Island’s resilience to future disturbance. Hurricane Sandy provided a unique opportunity to better understand the potential effects of white-tailed deer (Odocoileus virginianus borealis) on recovering vegetation in areas overwashed by Hurricane Sandy in the Otis Pike Fire Island High Dune Wilderness Area. White-tailed deer are the dominant herbivore on Fire Island and they are known to decrease plant diversity, limit reproduction and growth of some plant species, and facilitate growth and expansion of non-native species through selective browsing. Deer also negatively affect the federally-threatened seabeach amaranth plants along the island’s beaches. Deer impacts to forest understory and regeneration have been documented in Fire Island’s Sunken Forest for decades, though their impacts to recovering dune vegetation are less understood and could restrict the resilience and recovery of primary dunes. Through use of several vegetation assessment methods, including point intercept and paired permanent exclosures, and deer monitoring with trail cameras, we documented high variability in among-overwash species richness, vegetation cover, and local deer abundance. We observed 29 vegetation species among overwash fans between 2015 and 2016. Greater vegetation cover was observed in northern (i.e., inland) areas of all overwash fans, and greater cover and species richness were documented in fenced permanent plots than in control plots. The greatest effect of deer browsing to recovering dune vegetation was in total vegetation cover, which was significantly greater in fenced permanent plots. Any amaranth plants left open (i.e., un-exclosed) were often heavily browsed and experienced early onset mortality without reproducing. Since Hurricane Sandy, total vegetation cover in overwash fans has significantly increased each year, despite deer activity and a regional drought in 2016. While deer graze and browse vegetation in overwash fans, deer and humans trample vegetation in some overwash fans and separating effects of each is not possible from exclusion studies alone. Two overwash fans have been consistently impacted by coastal disturbances since Hurricane Sandy, further complicating their recoveries. Monitoring of dune vegetation could continue as communities transition from predominantly grasses to shrubs and forbs to assess effects of deer as palatability of vegetation improves.

Quantifying the effects of deer browsing on vegetation establishment, growth and development in overwash fans: 2015-2016 post-Hurricane Sandy assessment

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