Conservation Reserve Program Vegetation Affects Occupancy of an Invasive Grass and Invasive Forb.

One of the largest contributors to grassland restoration projects in the United States is the Conservation Reserve Program (CRP), a program that converts marginal farmlands to perennial grassland, resulting in grassland restoration in an agricultural landscape matrix. Invasive weeds are a particular challenge of restoration in this context due to an abundance of propagule sources and pathways, high levels of soil disturbance, elevated nutrients, and legacies of past agricultural activities. Using edge-of-field surveys, we examined the prevalence of two invasive weedy species, Phalaris arundinacea (reed canary-grass) and Pastinaca sativa (wild parsnip), and related their prevalence to CRP contract parameters and vegetation factors to understand which factors improve biotic resistance to invasion during grassland restoration. We found the strongest correlates of weed presence were related to plant cover. High grass cover and forb cover were both strongly correlated with reduced P. arundinacea presence, and high forb cover was correlated to reduced P. sativa presence. High grass species richness was also correlated with lower P. arundinacea presence, but grass and forb richness were not significantly correlated with P. sativa presence. CRP contract parameters were not strong predictors of invasive presence; P. arundinacea was more frequent and P. sativa was less frequent in Wetland Conservation Practices, likely due to hydrology and soil moisture. Grassland restoration age was not a significant predictor for either species. We recommend practices that rapidly increase native plant cover during grassland restoration as a means to improve biotic resistance to weed invasion in an agricultural landscape. [ABSTRACT FROM AUTHOR]