Resilience of a thinned Eucalyptus regnans forest to long-term drought

Abstract:

The duration and severity of drought has been predicted to increase with climate change. Understanding vegetation response to protracted drought is important to predict their future response and develop adaptive management strategies. We examined the transpiration of Eucalyptus regnans forest at the end of the Millennium Drought, which affected southeast Australia from the mid-1990s to 2009. The forested catchment, Crotty Creek, has been subjected to a strip-thinning treatment in the early 1980s. Measurements of sap flow were conducted using the compensation heat pulse technique over 13 months from December 2009. Transpiration appeared to be energy-limited rather than water-limited, with daily maximum VPD and solar radiation being good predictors of sap flux density. The perennial streamflow and unlimited transpiration at the end of the drought indicate a large soil-water buffer in the system. The post-thinning evapotranspiration (ET) of the catchment was likely to be lower than ET of an undisturbed catchment with similar stand age (70-year old) due to the lower post-thinning basal area. In contrast to this, the streamflow of a dryer, 34-year old mixed eucalypt forest ceased for several months during the same drought. Thus, the resilience of E. regnans forests during a severe drought may depend on the soil-water buffer and stomatal control, while silvicultural treatment may help reduce water stress in dryer and younger forests.