UC Irvine

Howdroughtandfiredisturbance influence different levelsofbiological organization is poorly understood but essential for robust predictionsoftheeffectsofenvironmental change. Duringayearofseveredrought, we conductedaprescribedfireinaMediterranean-typecoastalgrasslandnear Irvine,California.Inthe weeks following thefirewe experimentally manipulated rainfallinburned and unburned portionsofthegrasslandto determine howfireanddroughtinteract to influence leaf physiological performance, community composition, aboveground net primary productivity (ANPP) and component fluxesofecosystem CO2 exchange and evapotranspiration (ET).Fireincreased leaf photosynthesis (A(net)) and transpiration (T)ofthe native perennial bunchgrass, Nassella pulchra and the non-native annual grass, Bromus diandrus but did not influence ANPP or net ecosystem CO2 exchange (NEE). Surprisingly,droughtonly weakly influencedA(net) and Tofboth species but strongly influenced ANPP and NEE. We conclude that despite increasingexperimentaldroughtseverity,prescribedfireinfluenced leaf CO2 and H2O exchange but had little effect on the component fluxesofecosystem CO2 exchange. The differentialeffectsofprescribedfireon leaf and ecosystem processes with increasingly severedroughthighlight the challengeofpredicting the responsesofbiological systems to disturbance and resource limitation.