Dune Slack Wetlands Vegetation Monitoring, Cape Cod National Seashore, 2009

Smith, Stephen; Wheeler, Jesse; Thime, Adam

During 2003–2004, a study was conducted to map and inventory interdunal vernal wetlands (dune slacks) across the Province Lands region of Cape Cod National Seashore. A total of 336 sites were found scattered throughout the entire expanse of the dune system, from southwest Provincetown to Truro (Smith et al. 2008). In 2009, using LIDAR (Light Detection and Ranging) elevations acquired in 2005, more potential dune slack wetlands were identified (based on elevations likely to seasonally intersec with the water table). These sites were then investigated to confirm whether wetland vegetation was present or not. If the former, the vegetation composition and structure were surveyed using visual estimates of cover (as in 2003). In addition to this general survey, an intensively monitored subset (IS) of fifteen wetlands (first established in 2003) were re-surveyed. An additional 11 wetlands were randomly selected, setup with permanent transects, and surveyed in order to expand the number of IS sites from 15 to 26. Significant findings • We mapped and inventoried 178 new wetlands. Their general structure ranged from 100% trees and shrubs to 100% graminoids/forbs. A total of 65 wetland plant species were found. Of these species, 62 were common to the 2003/2004 survey, while three (Rubus idaeus [American red raspberry], Salix sericea [silky willow], and Polygonum hidropiper [marshpepper knotweed]) had not been recorded previously. The most common species were Myrica pensylvanica (northern bayberry), Vaccinium macrocarpon (cranberry), Vaccinium corymbosum (highbush blueberry), Kalmia angustifolia (sheep laurel), and Juncus greenei (Greene’s rush). No federal- or state-listed rare species were found. • Analysis of vegetation change between 2004 and 2009 in the 15 original IS sites revealed clear evidence of succession, with woody species increasing in cover and herbaceous species diminishing. Unfortunately, the exotic Phragmites australis (common reed) also increased, particularly at one site that experiences occasional flooding by salt water. • Using water level loggers, we were able to acquire hydrologic data every 30 minutes within 10 wetlands from May 4 to August 15. This kind of high resolution water level data has never before been collected in any of these wetlands. This information revealed how complex hydrology is within these sites across the Province Lands dunes region. • Through this effort as a whole, we were able to expand the scope of long-term monitoring, add to our inventory of known wetlands, and collect data that allowed for change analysis and will provide critical information for the development of an official protocol, including statistical power analysis.