Drivers of grassland resistance and recovery to long term drought

Climate change is expected to increase the intensity of drought in many parts of the world with potentially significant consequences for grasslands. Grassland resilience will depend on its resistance to degradation during drought and ability to recover. We examined the response of grassland biomass to the millennium drought (2002-2010), with rainfall deficits comparable to the hottest and driest climate change scenarios projected for 2030. Following the drought, extreme rainfall occurred in 2010-2011. This juxtaposition between intense and protracted drought and subsequent intense rainfall phase allowed investigation of grassland resistance to drought and recovery in more favourable conditions. We analysed 2,549 grassland sites in the Darling Downs, Queensland using remotely sensed Enhanced Vegetation Index (EVI) data. We modelled trends in a prolonged drought (resistance) and subsequent wet phase (recovery) as a function of hydro-climatic and land use drivers, using boosted regression trees (BRTs), to determine drivers of grassland resistance and recovery. Multiple factors explained trends in EVI for both resistance (CVpred/obs. = 0.69) and recovery (CVpred/obs. = 0.61). During drought, resistance decreased as the proportion of agriculture increased and woody vegetation decreased. In contrast, there was little relationship with agriculture during recovery and increased woody vegetation had a negative relationship with recovery. High levels of soil moisture corresponded to both increased resistance and recovery. The drivers we examined had differential effects for grassland resistance and recovery, which may have implications for the ongoing resilience of these systems under future climate change.