Forest disturbance events have become more prevalent and are predicted to increase in frequency and severity with a changing climate. Any forest disturbance event creates a shift in the carbon balance. Thus, there may be profound changes which impact future carbon storage capacities. While the impact of single disturbance events has been well documented, the combined effect of drought + fire, and how they may interact, remains a pressing yet largely unanswered question, particularly for non-coniferous forests.
A factorial design of plots in eucalyptus–dominated forest in southwestern Australia was established following a 2016 wildfire. There had been previous episodes of drought in this forest. Thirty-six plots were split across two levels of pre-fire drought (high, low) impact and two levels of fire severity (canopy scorched vs consumed). Data were collected on tree and shrub survival and regeneration, coarse and fine woody debris, stump survey and soil carbon
Preliminary results suggest that the largest tree mortality and subsequent carbon loss occurred in areas of high drought impact and high severity fire. These areas also experienced the least amount of seedling recruitment. Areas of forest experiencing lower fire severity and drought impacts resprouted more vigorously than the high severity and drought affected sites. These lower disturbance severity sites also had much higher seedling and resprout counts than the higher severity sites. In addition, stumps and roots from previous periods of logging were consumed by the wildfire further elevating carbon emissions.
Mediterranean-type eucalypt forests, long regarded as strongly fire resilient, may be undergoing significant changes in stand structure and carbon pool composition due to multiple, interacting stressors of varying severities such as drought and wildfire. The marked differences in resprouting and recruitment suggest that the future carbon storage of these forests may be markedly reduced. This work has repercussions for ongoing fire management, given the marked differences in sequestration and recruitment between the fire severities and pre-fire drought impacts. Given the prediction of more frequent and more intensive fires and droughts, global forests may not be a stable, predictable store of carbon into the future.