Fire History and Soil Gradients Generate Floristic Patterns in Montane Sedgelands and Wet Heaths of Gibraltar Range National Park

Abstract

High rainfall escarpment areas along the Great Dividing Range provide habitats for sedgeland and wet heath vegetation in areas with impeded drainage. There are few studies of the processes that influence the floristic composition of montane sedgelands and heaths in relation to fires that sweep these landscapes. Gibraltar Range National Park contains extensive areas of sedge-heaths that remain mostly free from anthropogenic disturbance. These areas have a well-known fire history which provides an opportunity to test whether: 1) plant resources are related to time-since-fire; 2) floristic composition is more strongly related to physiographic factors than time-since-fire, and 3) floristic composition of vegetation is related to fire frequency. Physiographic position strongly influenced the vegetation's structure and floristic composition, with taller heaths confined to better-drained edges whereas sedgelands were more common in poorly drained slopes regardless of fire regime. In turn, these patterns were related to soil conductivity reflecting the fertility status of the soils. Upper slope heaths were more species rich than those lower in the landscape where soil conductivity was higher. Time-since-fire strongly influenced heath structure and species richness declined in the heaths with canopy closure at some sites. Floristic composition across the physiographic gradient was more divergent soon after fire and became more similar 15 years after fire. Fire frequency had no significant effect on shrub species richness, but frequent fires decreased the abundance of some woody species. Inter-fire intervals of less than seven years may reduce the abundance of some shrub species. Both the history of fire and ease of access make the sedgelands and wet heaths of Gibraltar Range an ideal location to assess the long-term effects of fire regimes in montane sedge-heaths.