Responses of native plant populations on an unprotected beach to disturbance by storm-induced overwash events

Abstract

Extreme climatic events disturb plant communities, altering species composition, and abundance. For herbaceous populations on coastal beaches, responses to disturbance are often spatially heterogeneous and depend on species’ life history. This study documents the effects of two overwash events, caused by Hurricane Irene in August 2011 and Superstorm Sandy in October 2012, on the abundance of native species on a low-lying, unprotected beach on Staten Island, New York, USA. Temporary plots (33 cm diameter) spaced at 3-m intervals along 30-m transects perpendicular to shoreline, were used in September 2007, 2011, 2012, and 2013 to survey lower (0–9 m), middle (12–21 m), and upper (24–30 m) regions of the same beach. The same procedure was used to quantify seedling recruitment in spring (May) after each overwash. Complex changes in density the year after each overwash were specific for distinct beach regions and depended on species’ life history. Rhizomatous perennial grasses (Ammophila breviligulata and Panicum amarum) maintained or increased ramet populations, possibly stimulated by sand deposition on the middle and upper beach. The first overwash was early enough in the growing season to permit subsequent seed production during autumn, and seedling recruitment occurred for three native annuals (Cenchrus tribuloides, Heterotheca subaxillaris, and Triplasis purpurea), and the tall perennial Solidago sempervirens the next spring. The second overwash was later in autumn and probably removed seeds from the site and/or deeply buried the seeds of two annuals (Cenchrus and Heterotheca) which did not recruit seedlings the next spring. Triplasis seedlings were abundant in a blowout on the lower beach. Given more frequent storms and sea-level rise in the future, it becomes imperative to maintain an assemblage of native plant species with diverse life histories when restoring coastal beaches.