Ecology and management of an invasive veldt grass, Ehrharta erecta
Ehrharta erecta is a highly invasive perennial grass actively spreading in forest understory habitats across coastal California. Despite the attention placed on this species as a wildland weed, there is little published information on its impacts or control. We quantified the impacts of E. erecta on native plant physiology and ecology in mixed evergreen forest and we also compared the efficacy of herbicide and manual removal as management strategies. All surveys and experiments were conducted on the campus of the University of California, Santa Cruz. We compared native cover, richness, and diversity in E. erecta-invaded, non-invaded, and removal plots (2m x 2m) at 12 sites. To investigate if E. erecta alters plant-fungal mutualisms, we compared percent colonization of arbuscular mycorrhizal fungi in Stachys bullata and Clinopodium douglasii roots in invaded and non-invaded sites. In a separate experiment, we manually removed E. erecta from around focal individuals of these native plants and compared transpiration rates and chlorophyll content after removal to unmanipulated controls.
One year after implementation of management methods, Ehrharta erecta was strongly reduced in herbicide and manual removal plots relative to the control. Reestablishment of E. erecta after removal was greater in sites where E. erecta was manually removed compared to herbicide plots. However, one year following treatment, manual removal plots had higher percent cover and diversity of native plants than herbicide plots, suggesting that native plant restoration would be an important component of any large scale removal of E. erecta with herbicide. Both S. bullata and C. douglasii had significantly less mycorrhizal colonization at invaded than non-invaded sites. When E. erecta was manually removed, both transpiration rate and chlorophyll content in S. bullata were significantly increased relative to control S. bullata. In C. douglasii, however, we observed lower transpiration rates and higher chlorophyll fluorescence in treatment individuals than control individuals, and there was no difference in chlorophyll content between control and treatment individuals. The results of our research show that E. erecta negatively affects the competitive ability of native plants and that E. erecta populations can be successfully managed through manual removal and herbicide application.