Exotic grass species from Eurasia were introduced to California by early settlers and have naturalized throughout the state, particularly in the Great Valley and adjacent foothills (the focus of this study). Though not fully documented, evidence suggests that pre-settlement grasslands were likely dominated by native annual forbs. There is no doubt that introduced plants have changed the species composition and productivity of current grassland habitats, but how do these changes alter ecosystem processes and how should these types be treated within the National Vegetation Classification? Relevés were sampled and analyzed across 5+ years in order to track vegetation dynamics across California grassland/prairie systems.
Results/Conclusions
Vegetation sampling and long term annual monitoring throughout the Great Valley ecoregion reveal that non-native species have partially replaced but have not eliminated native forb and grass species across much of the remaining habitat. The species composition and abundance within these grasslands fluctuates widely based on variation in annual precipitation and temperature, as well as other factors. We explore the cyclical dynamics within grassland types and conclude that patchy spatiotemporal processes enable the coexistence of natives and non-natives, recognizing that there are tipping points that can push communities from a natural state to one with total dominance by non-natives (e.g. soil tilling, removal of grazing). The invasion of non-native grasses in California has created a novel ecosystem that is still functioning with only subtle changes in ecosystem processes. The NVCS currently differentiates Californian native and ruderal grasslands at the Macrogroup level. This concept and hierarchical nomenclature must continue to evolve, especially since ruderal types are currently defined by non-diagnostic ubiquitous species in the genus Bromus, Avena, and Festuca. There are difficulties in differentiating California native types in drought years due to lack of germination and in recognizing and mapping the matrix of native and ruderal types.