Abstract: Targeted removal is a common practice used to control undesirable plant species during restoration and land conservation. Removal of invasive plants are often followed by ‘secondary invaders’, species that opportunistically take advantage of the disturbance and open space freed up by invasive control. Functional traits related to plant function can help explain which native species will best perform as a secondary invader. We explore the role different native plant traits and alternative growth strategies have for determining which natives are most successful with and without reduced invasive competition in a factorial design with episodic drought. In a glasshouse in Davis, CA we grew full (10 individuals) and reduced competition (2 individuals) potted communities for eight invasive species (Anthoxantum odoratum, Briza maxima, Centaurea solstitialis, Elymus caput-medusae, Holcus lanatus, Rumex acetosella, Phalaris aquatica, Plantago lanceolata). We sowed each potted community with two individuals of five California native grassland species (Achyrachaena mollis, Bromus carinatus, Clarkia unguiculata, Elymus condensatus, Festuca microstachys, Nemophilla maculata). We implemented an episodic drought, where water was withheld until evidence of drought stress, to determine how drought influences trait divergence and species success. We measured plant height, leaf length, survival, productivity, specific leaf area, specific root length, root diameter and leaf and root dry matter content. We found that certain species were more sensitive to drought, which was compounded by competition for some, but not all species. In particular, annual invasive grasses were resistant to drought, and native grasses typically had higher survival in drought compared to native forbs. Native plant survival was dependent on the cohabiting invasive species and was lower when in competition with forbs compared to grasses and was higher when there was reduced competition. We found that native species that were functionally distinct from invaders and fast growing were more successful during reduced competition. During drought we found that key trait combinations related to alternative plant strategies for stress helped explain differences in productivity and survival.
