Dune slack wetland vegetation monitoring, Cape Cod National Seashore: Floristic changes between 2004 and 2019

Smith, Stephen

doi:10.36967/nrr-2287632

In 2019, the vegetation in 28 dune slack wetlands were surveyed along permanent transects, fifteen of which were originally surveyed in 2004 and subsequently in 2009 and 2014. An additional 38 sites were assessed in a more general way as was done in previous surveys as well. Significant findings are described below. • Significant floristic changes between 2004 and 2019 were detected at most sites • The process of succession from open, graminoid and forb-dominated systems to shrubby, more wooded communities continues • In general, the floristic changes were largely the result of declines in Juncus greenei (Greene’s rush), Cladium mariscoides (smooth sawgrass), and Vaccinium macrocarpon (cranberry) concurrent with increasing abundances of Pinus rigida (pitch pine) and Vaccinium corymbosum (highbush blueberry) • Continued succession will result in the disappearance of early successional, open habitat taxa (grasses, rushes, forbs) and the proliferation of woody shrubs and trees • Opportunities for new wetlands to form in this region of CACO are increasingly limited by dune stabilization through increasing vegetation cover. Over the long term, however, sea level rise is expected to push the fresh groundwater lens upwards – which could eventually flood topographic depressions that are currently dry • Phragmites australis (common reed), Salix cinerea (gray willow), Typha angustifolia (cattail), Rosa rugosa (salt spray rose) were four exotic species found in the surveys • The exotic, invasive Phragmites australis (common reed) increased at three sites where it was present in 2004, particularly at one site (RPA) where sea water from an adjacent salt marsh is now periodically flooding this wetland during large storms and extreme high tide events

Dune slack wetland vegetation monitoring, Cape Cod National Seashore: Floristic changes between 2004 and 2019

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