Patterns of plant diversity in ironstone ranges in arid south western Australia

Patterns of plant diversity were examined across 24 ironstone ranges in arid south western Australia. The high levels of beta diversity displayed between ranges primarily resulted from high turnover of perennial species and was not influenced by the lower species richness on the more arid ranges. The variance in composition of the vegetation across the ranges was evenly distributed between the broad spatial pattern and environmental factors measuring climate gradients, local site variables and soil chemistry. In contrast broad scale spatial and climatic gradients were most important in explaining the variance in perennial species richness. Ranges along the boundary of the Arid Zone appear to have acted as refugia during the climatic cycles of the Tertiary with several hotspots of species endemism and taxa with distributions centered on these ranges. On the more arid ranges these specialist ironstone taxa are largely absent. The variation in richness of these specialists taxa was strongly influenced by patterns in soil chemistry in addition to the broad scale spatial and climate gradients. The concentration of the ironstone specialist taxa is largely coincidental with the most prospective areas for iron ore mining and this will provide considerable challenges in conserving these unique ecosystems. ► The isolated ironstone ranges of arid south western Australia showed high beta diversity both within and between ranges. ► The high beta diversity between ranges was largely due to high species turnover between ranges. ► Species richness patterns were most strongly correlated with broad scale spatial and climate gradients. ► Compositional patterns were correlated with environmental and spatial pattern across a number of different scales. ► Areas of highest conservation concern occur along the arid zone boundary with two hotspots of specialist ironstone taxa.