Vegetation – environment relationships of the Hamersley Ranges, a mountainous desert of north-west Australia

Abstract

Understanding environment-vegetation relationships provides important ecological insights, and here we examined such relationships for the Hamersley Ranges of North West Australia. We were particularly interested to see if such relationships were similar to those of other mountainous deserts. We used direct gradient analyses of floristic and environmental variables (constrained ordination), supplemented by identification of environmental differences between plant communities, assessment of environment-vegetation associations and partitioning of the floristic variance between environmental, climatic and spatial variables. Most communities could be differentiated from others according to environmental variables, with slope, surface stone cover, topsoil phosphorus and pH particularly good at differentiating between plant communities. There was strong association between communities and classes of landform and/or geological substrate. Gradient analysis demonstrated the primary floristic gradient was linked to a complex of several topographic, edaphic and geomorphic variables. This was interpreted as floristic change along broad topo-sequences from mountain/ridge tops to valley floors over which gradients in key environmental variables occur. Gradient analyses of other mountainous deserts have reported similar findings. A key distinction in the complex gradient identified for the Hamersley Ranges is the inclusion of topsoil phosphorus (rather than nitrogen) and time since last fire. The second most important floristic gradient was linked to soil pH and conductivity, which reflects floristic variation due to differences in geological substrate throughout the study area.