Long-term changes in understorey vegetation in the absence of wildfire in south-east dry sclerophyll forests

Abstract

Wildfire has shaped historic and contemporary vegetation assemblages in Australia. Ecological research has generally focussed on the effects of frequent fire on plant assemblages, with less attention given to the changes that occur in the absence of wildfire. Here we examine changes in understorey assemblages in dry sclerophyll forest catchments where wildfires have not occurred since 1973 and 1979 to determine if the initial floristics model applies. Understorey species (<2 m height) richness peaked approximately 5 years after fire with an average of 22.7 ± 0.4 (s.e.) species per 10 m2. These values declined throughout the study period resulting in an average of 13.4 ± 0.5 (s.e.) species per 10 m2 33 years after fire. Similarly, significant shifts in the understorey community composition were seen with increasing time since wildfire. These changes were attributed to a decrease in 40 species (24 resprouters, 16 obligate seeders) and an increase in 11 species (10 resprouters, 1 obligate seeder). Large shrub species richness (>2 m height) and stem density increased steadily until 10–15 years post-wildfire at which point they remained stable at ~3.2 species per 100 m2. In the absence of wildfire, these forests undergo significant changes in understorey/large shrub communities consistent with the initial floristics model.