Landscape partitioning among Triodia spp. (Poaceae) in the fire prone Kimberley, north-west Australia

The processes which determine the structure of plant communities vary across spatial and temporal scales. Climatic factors are more likely to influence community structure at a regional scale with more transient environmental effects such as disturbance or demographic interactions having a greater influence at local scales. Understanding these differences is important for managing communities at a landscape scale. Triodia spp. grasslands are the most extensive plant community in Australia, covering 1.4 million km 2, and yet little is known about the processes which structure these communities. We collected data on six sympatric Triodia spp. at the regional, landscape and local scale across the 325000ha property, Mornington Wildlife Sanctuary, in the Kimberley region of northern Western Australia to investigate the processes which structure this community. Regionally we looked for correlations between species distributions and substrate or rainfall. At the landscape scale we collected data on substrate, drainage and vegetation type and at the local scale we determined the extent to which individuals form mono-specific stands both along and across the contour gradient. Only one species, T.aeria, was found to be substrate specific and only T.epactia was restricted to the drier southern end of the property. The other species were not restricted by substrate or rainfall at the regional scale and were found to be habitat generalists at the landscape scale. All species grew in mono-specific stands with little to no mixing at shared boundaries. However, this pattern broke down when crossing the contour gradient on hillsides. The results suggest rainfall may influence the distribution of some Triodia spp. at a regional scale with interspecific competition, due to differences in post-fire regeneration niches, structuring the community at the local scale. At the landscape scale community structure appears to be influenced by feedback mechanisms involving differences in the post-fire regeneration strategies of sympatric species and subsequent competition for establishment microsites.