Reestablishing the competitive hierarchy in an invaded California grassland through the process of habitat restoration following a prescribed burn

Land use practices over the past several hundred years have had a dramatic effect on many of California's ecosystems. As a result, native grasslands have become one of the state’s most threatened ecosystems. Close to 90% of the plants listed on California's Inventory of Rare and Endangered Species occur within grasslands. Native species can account for less than 1% of the composition of most California's grasslands today. Invasive species such as annual grasses (Poaceae) and Centaurea solstitialis ‘yellow star thistle’ (Asteraceae) from Europe were introduced to California and have rapidly overtaken exposed grasslands. Prescribed burns have demonstrated to be an effective management tool for reducing the density and seed bank of exotic grasses and forbs. Repeated burns have decreased C. solstitialis populations by as much as 99%; however, further research has shown that without continued management, C. solstitialis will reestablish in treated areas. I hypothesize that planting native grassland species will suppress the reestablishment of invasive species following a prescribed burn. Seeds of the perennial bunch grasses, Stipa pulchra, Bromus carinatus, and Elymus glaucus, along with Grindelia camporum, and Madia elegans were collected from the restoration area within the watershed of Big Chico Creek in the summer of 2012 and propagated in a greenhouse. Two separate fields, which were invaded with non-native annual grasses and C. solstitialis along Big Chico Creek, were burned in the fall of 2012. Three separate 4m x 7m blocks were established in each of the fields following the burn. Each native species treatment was planted into separated 1m² plots and replicated four times within each of the blocks using systematic randomization. Planting of 1,152 native grass plugs, 216 Grindelia plugs, and 48 1m2 direct seed treatments of mixed bunch grasses and Madia elegans was completed in the winter of 2012-13. The native species treatments were then monitored once a month over the course of fifteen months to determine their survival and composition. The establishment of native species through the process of restoration was found to be successful within each of the invaded grasslands. Out-planted perennial plug survival rates ranged from 38-97%, with percent cover values accounting for between 19- 52% upon the completion of the experiment in May of 2014. In addition, the out-planted treatment plots were found to reduce the percent cover of C. solstitialis by as much as 28% as well as non-native annual grasses by 40%. Using the most effective perennial species in grassland restoration efforts may aid in shifting the competitive advantage back to favor native taxa over the long term through mitigating the cycle of future invasion.