Reversal of Rainforest Invasion and Recovery After Drought in Australian Savanna

ABSTRACT Fire and drought are important influences on the structure and floristics of tropical savanna, but determining the sensitivity of rainforest invasion in savanna to fire and recovery after drought requires long‐term monitoring. A savanna in north Queensland invaded by rainforest after a long fire‐free period was monitored within a 1.56 ha plot after drought and subject to nine fires over 16 years. Savanna tree densities increased, mostly resulting from suckering, but rainforest trees declined to 19% of the pre‐burn density. Savanna basal area declined halfway through the monitoring period to 9.6% of the original measurement after drought. By contrast, rainforest basal area was reduced to 0.0 m 2 ha −1 in the same period after being subject to four fires and remained at zero for the course of monitoring. Savanna basal area recovered to 16.9% of its original value by the end of monitoring. The study confirms the fire resilience of Australian savanna trees, Eucalyptus and Corymbia, relative to rainforest trees and indicates that regular burning maintains savanna in a pure state without rainforest invasion. Nevertheless, drought caused the collapse of the savanna tree layer despite an absence of livestock grazing. Such declines and gradual recovery are a natural dynamic in savanna with multi‐year rainfall deficit.