Effectively controlling Phalaris arundinacea L. in wet meadow restorations and subsequent native species establishment.

摘要

Invasive species present barriers to native species establishment in restorations; therefore control of invasive species is often crucial to ecosystem recovery. Effective control practices are needed for Phalaris arundinacea, a rhizomatous perennial grass that preempts native vegetation in northern US wet meadow restorations. Current control methods involve spring burning followed by a glyphosate herbicide application, but do not consistently result in removal of P. arundinacea and native species establishment. This dissertation investigated P. arundinacea biology and ecology to suggest effective strategies for control and subsequent establishment of wet meadow vegetation. A large-scale field experiment determined that glyphosate herbicide was most effective when applied late season (mid-August) after the onset of carbohydrate flux to rhizomes. Also, burning contributed to reduction of P. arundinacea populations, not by reducing P. arundinacea biomass or increasing effectiveness of herbicide applications as previously thought, but by reducing the P. arundinacea seed bank. P. arundinacea post-control recolonization prevented establishment of native species in the field experiment, despite effective use of burning and herbicide followed by a native species seeding. A mesocosm experiment demonstrated that post-control wet meadow species establishment was limited by a low threshold level of P. arundinacea seed density, and that P. arundinacea established from minimal seed densities, even when native species seed density was high. In a uniform planting study, the growth of an individual P. arundinacea plant when unconstrained was rapid, particularly aboveground growth during the initial establishment period. P. arundinacea grew faster than has been reported for other species, which may contribute to P. arundinacea's aggressive nature. Reported failures of wet meadow species to establish may be due in part to ineffective control practices for P. arundinacea. However even with effective use of burning and herbicide and seeding with native species, additional management (multiple seasons of site preparation control and post-restoration aftercare control) will be necessary to limit P. arundinacea reinvasion sufficiently to establish wet meadow species. Reducing P. arundinacea propagule pressure in the landscape (by limiting the use of this species for forage and conservation purposes) will decrease resources required to promote ecosystem recovery of wet meadows in the northern US.