Restoration strategies for wet meadows along an invasion front

Many natural communities include a significant component of difficult-to-manage invasive species. We explore invasive species removal strategies for mixed stands, taking advantage of the inherent resilience of native species. In a 16.8-acre wetland in Minnesota, a Phalaris arundinacea invaded zone forms an abrupt boundary with a Carex lacustris dominated zone. Using an adaptive management strategy and knowledge of seedbank behavior, we attempted to reverse the invasion front and encourage recolonization from the existing Carex population and the seedbank. Data from a seed longevity assay demonstrate that by year five Phalaris seeds lose viability when buried in ambient conditions along a hydrology gradient. Therefore, if Phalaris seed rain can be preempted by managing adjacent populations, it may be possible to re-establish the native community. Rodeo was broadcast in the Phalaris plots in September 2001 and spot treatments were applied each fall thereafter following an annual vegetation survey. An additional band of Phalaris outside the plots was also treated. In 2006, species richness was 40; an increase of 19 species from 2001. Dense flushes of Phalaris seedlings in 2002 and 2005 were managed with the annual herbicide application. Annuals (Bidens and Polygonum) are dominant in the early stages of the transition from Phalaris to Carex cover. By 2006, cover of C. lacustris in the plots was greater than cover of Phalaris. The adaptive management approach was an improvement over traditional invasive species management approaches. It allowed us to target successive management actions to outcomes of previous actions, taking advantage of community resilience.