Habitat destruction has greatly reduced the extent of prairies in the United States. Many remaining prairie fragments are poor quality and face threats including invasion by nonnative species and biodiversity loss, which soil nutrient enrichment can promote. Soil carbon addition offers a possible restoration tool to counter these threats by stimulating microbial activity and immobilizing nutrients. This process can potentially improve conditions for native species that are often outcompeted under high nutrient conditions. We tested the efficacy of carbon addition for controlling nonnative species in two Oregon prairies by creating treatments of varying nutrient availability and monitoring plant community responses for two growing seasons. Experimental treatments included carbon (sucrose) addition, ambient soil nutrients (controls), and nutrient addition (NPK fertilizer). Community composition differed significantly among nutrient treatments at both sites in both growing seasons. Carbon addition significantly reduced vascular plant cover while nutrient addition increased cover compared to ambient nutrient availability. Nutrient manipulation did not affect native grasses, but it reduced nonnative grasses under carbon addition and increased them under nutrient addition. By the second year of the experiment, both carbon and nutrient addition reduced nonnative forbs. Nutrient manipulation affected the richness of nonnative species more than that of native species; it increased or did not affect nonnative richness under nutrient enrichment and decreased it under carbon addition. Our results suggest that nutrient enrichment promotes the success of nonnative species and that carbon addition can counter these effects on a species- and site-specific basis.
Cascadia Prairie-Oak Partnership
Providing coordination for the technical prairie community in the Willamette Valley, Puget Trough, Georgia Basin (WPG) ecoregion and beyond.