Invasive Species Compendium

Detailed coverage of invasive species threatening livelihoods and the environment worldwide

Abstract

Shrub establishment under experimental global changes in a California grassland.

Abstract

Accelerating invasion of grasslands by woody species is a widespread global phenomenon. The native shrub Baccharis pilularis has recently increased in abundance in some California grasslands, with large local community and ecosystem effects. I investigated potential contributions of (1) future global climate and atmospheric changes and (2) variation in moisture and nutrient availability to increased Baccharis germination and early establishment rates. I examined responses of Baccharis seeds and seedlings to simulated warming (+1-2°C) and elevated CO2 (+300 ppm) in a 2-year field experiment. Warming and CO2 treatments were applied at ambient and increased water and nitrogen levels chosen to simulate future increases in precipitation (+50%) and N deposition (+7 gN m-2 y-1). Elevated CO2 and water addition each increased or accelerated germination. Herbivory strongly reduced seedling populations during the winter wet season; drought further reduced seedling survival in the spring. Overall Baccharis survivorship was extremely low (<0.1%) across all treatments, complicating the interpretation of global change effects.