The increasing importance of nitrogen deposition and exotic grass invasions as a driver of responses to precipitation pulses in arid shrublands

Arid shrublands in the Southern California are increasingly inundated with drivers of global change, particularly dry nitrogen (N) deposition and exotic grass invasions. The dependence of both grass phenology and soil N processing on water availability suggest that plant and biogeochemical activity will become even more strongly connected to seasonal precipitation cycles as perennial, N-poor shrublands convert to annual, N-rich grasslands. In the context of pulse dynamics, Southern California aridlands may converge on increasingly pulsed ecosystem processes strongly driven by infrequent precipitation.