Relative drought tolerance of evergreen-rainforest and evergreen-savanna species in a long unburnt Eucalyptus savanna, north Queensland

Woody plant species that are typically restricted to rainforest were observed to have established in a Eucalyptus savanna. The savanna had never been grazed by exotic herbivores and had remained unburnt for a very long time. This unusual situation provided the opportunity to compare the frequency of damaged canopies (defined by >40% of the canopy with dead foliage) in evergreen rainforest and savanna species following a severe drought. It was found that there was no statistical difference in the number of damaged juvenile evergreen rainforest or savanna species. However, significantly (P<0.001) more savanna saplings had damaged canopies compared to evergreen rainforest species. These results are interpreted as demonstrating a tolerance of most dry evergreen-rainforest species to severe moisture stress. Only 7 out of the 26 species were deciduous and all of these were considered to be rainforest specialists. The predominance of evergreen species may reflect their greater capacity to opportunistically respond to favorable moisture conditions given the high variability of rainfall in the study region.