Assessment of habitat, threats and population status for the federally-endangered wetland sedge, northeastern bulrush, Scirpus ancistrochaetus

Background/Question/Methods

Northeastern bulrush, Scirpus ancistrochaetus, is a federally-endangered emergent sedge that grows in small, temporary palustrine wetlands.  In 2007 and 2008, we performed surveys of 81 wetlands on public lands in Pennsylvania to characterize the habitat, to document population status, and to assess threats.  At each wetland, we measured areal extent, density of stems, and number of flowering culms of S. ancistrochaetus.  We also measured habitat variables including percent tree canopy cover, presence of invasive species, level of deer activity and size of wetland.  Additionally, we collected leaves for analysis of genetic diversity using RAPDs and microsatellite markers.  We performed pairwise correlations to examine relationships among habitat and S. ancistrochaetus variables.  For the 54 sites where previous data existed, we also made a comparative evaluation of the population trajectory.

Results/Conclusions

Wetlands containing S. ancistrochaetus were found at elevations between 240 and 640 m, with a median of 511 m and ranged from 90 m² to 6500 m² in area, with a median of 563 m².  Percent tree canopy cover was negatively correlated with stem density, areal extent of population, and proportion of flowering stems.  Wetland area was positively related to these variables, most likely due to fact that larger wetlands had lower percent cover and more open water.  The invasive species Phalaris arundinacea was present in 8% of wetlands, and is the probable cause of extirpation at one site.  Invasive Microstegium vimineum was a possible threat in 20% of wetlands.  Deer trampling or browsing was recorded in 40% of wetlands, with more significant impacts during the fall.  Bear activity, including wallows, was observed in 16% of wetlands.  For the 54 populations with previous data, 33% were stable, 11% increased, 28% decreased, and 26% suffered severe declines or were completely extirpated.  Clearly, more management and monitoring is needed to effectively conserve this species, as over 50% of populations experienced declines.  Existing managment recommendations at each wetland include no-cut buffer zones.  Our top recommendation for management is to cut in these buffer zones, reducing tree canopy cover to 50%.  At some sites, protection from animal activity and control of invasive plant species may be warranted.  Preliminary genetic diversity analyses indicate fairly low diversity in this clonal species; additional work will investigate diversity among and within wetlands in greater detail.  This information will be used to target sites for protection and management in a way that preserves the full complement of genetic diversity in this species.