Changing dominance of key plant species across a Mediterranean climate region: implications for fuel types and future fire regimes

Herbaceous and woody plants represent different fuel types in flammable ecosystems, due to contrasting patterns of growth and flammability in response to productivity (moisture availability). However, other factors, such as soil type, fire regimes and competitive interactions may also influence the relative composition of herbaceous and woody plants within a community. The Mediterranean climate region of south eastern Australia is transitional between two contrasting fuel systems; herbaceous dominated in the dry north, versus woody plant dominated shrublands in the relatively moist south. Across the rainfall gradient of the region, there are confounded changes in dominant soil types and fire frequency. We used model-subset selection using Akaike's Information Criterion to examine potential driving mechanisms of community compositional change from herbaceous (e.g. Triodia scariosa, Austrostipa sp.) to woody plants (e.g. Beyeria opaca, Leptospermum coriaceum, Acacia ligulata) by measuring relative cover across combinations of rainfall, time since the last fire (TSF) and soil type. We examined the relative influence of environmental versus competitive interactions on determining the cover of perennial hummock grass, T. scariosa, and co-occurring woody shrubs. Rainfall and soil types, rather than competition, were the over-arching determinants of the relative cover of grasses and shrubs. Given the sensitivity to rainfall, our results indicate there is strong potential for the nature of fuel, flammability and fire regimes to be altered in the future via climate change in this region.