Natural Disturbances Affect Invasion Resistance in a California Grassland

California grasslands have experienced a widespread invasion of non-native grasses; however, in spite of this invasion remnant patches of native grassland communities still persist. However, natural disturbances such as fire may alter the ability of native communities to resist invasion. In this study, we used naturally occurring patches of native and non-native dominated grassland communities to evaluate how a large disturbance such as fire may affect the invasion resistance of both native and non-native dominant communities. We followed paired communities of native and non-native dominated grasslands at 8 sites in Orange County, California, from 2007-2010. The communities experienced a natural wildfire in 2008. We compared how the different communities were able to recover and resist invasion by measuring species abundance and productivity. We found that non-native communities did not differ in species composition after the fire. However after the fire, native community composition depended on the abundance of one native species, Nassella pulchra, where communities high in its abundance had lower non-native grass abundance. While high diversity communities maintained their diversity, diversity did not play a role in the native community’s resistance to invasion, contrary to our hypotheses. These results illustrate the high resistance of non-native dominated California grasslands and the variable invasion resistance of remnant native dominated grasslands. It is important to understand how communities respond to disturbances as complex dynamics can make land management challenging; however long-term monitoring of areas may elucidate factors that can help predict community responses and maintain native dominant communities.