Multiple fires have not previously been considered a threat to the carbon stability of the fire-tolerant eucalypt forests of south-eastern Australia due to the reliable post-fire resprouting of the dominant eucalypt trees. However, the robustness of this assumption to multiple fires of different severity and frequency has not been tested. We bring together empirical evidence from three large-scale, multi-site studies to examine the influence of factorial combinations of low and high fire severity, and low and high fire frequency (≥ or <10 years) on the stand-level carbon stability of fire-tolerant eucalypt forests. Our evaluation examines fire effects on carbon stocks in the two principal carbon pools – live trees and soil – within five years of the last fire. In particular, we were interested in potential changes in percent live-tree carbon (stocks in live trees as a percentage of stocks in live plus dead trees) as an indication of changes in the ongoing capacity of the forests to sequester carbon.
Results/Conclusions
Effects of multiple fires on both soil and tree carbon varied with fire severity and frequency. Infrequent low-severity fires maintained or enhanced carbon stability through negligible change in percent live-tree carbon and some increases in soil carbon. Effects of frequent low-severity fires and infrequent high-severity fires varied but our data indicated potential for changes in carbon stability through decreases in either percent live-tree carbon or in soil carbon. The greatest threat to the stand-level carbon stability of these forests was associated with frequent high-severity fires, which decreased both percent live-tree carbon and soil carbon. More frequent, more severe fires are predicted for south-eastern Australia in the coming decades. Our evaluation suggests that active management will be required to maintain the carbon stability of fire-tolerant eucalypt forests in the future, particularly given the increased likelihood of other perturbations (drought, insect attack) associated with a drier and hotter climate.