Trends in evapotranspiration and streamflow following wildfire in resprouting eucalypt forests

The objective of this study was to estimate the recovery trajectory of evapotranspiration (E-t) and streamflow (Q) in resprouting forested catchments following wildfire. Recovery dynamics were assessed in mixed species eucalypt forests in south-eastern Australia which recover from disturbance largely via vegetative resprouting, and to a lesser degree, via seedling recruitment. Changes in E-t were evaluated in two ways. Firstly, we developed semi-empirical models of post-fire E-t following moderate and high severity wildfire. These models were based on datasets of plot-scale E-t, measured within five years post-fire, and published literature on post-fire changes in vegetation structure. Secondly, we analysed long-term Q records (25 years) from a mixed species catchment, including a 1-5 year period following a predominately moderate severity wildfire. We found that the overall length of recovery time for E-t and Q following wildfire was 8-12 years, which is much less than for eucalypt forests recovering via seedlings only. This emphasises the importance of functional responses to fire in forest ecosystems as a key driver of the hydrologic resilience of catchments, with resprouting forest types conferring relatively rapid recovery following disturbance. We also found that the recovery trajectory of post-fire E-t was dependent on fire severity. Increased E-t and consequent declines in Q occurred following moderate severity fire. In contrast, there was no evidence of increased E-t following high severity fire. Based on patterns of long-term Q and rainfall observed in a small mixed species catchment, declines in Q due to increased E-t following moderate severity wildfire were of similar magnitude to Q declines driven by a drought that coincided with the fire. We conclude that the coincidence of wildfire with drought exacerbates reductions in Q under moderate severity fire, resulting in greater Q declines. This is due to the enhanced rates of E-t, primarily driven by regenerating seedlings and higher rates of transpiration from surviving trees. (C) 2015 Elsevier B.V. All rights reserved.