Data from: High species diversity and turnover in granite inselberg floras highlight the need for a conservation strategy protecting many outcrops

Determining patterns of plant diversity on granite inselbergs is an
important task for conservation biogeography due to mounting threats.
However, beyond the tropics there are relatively few quantitative studies
of floristic diversity, or consideration of these patterns and their
environmental, biogeographic and historical correlates for conservation.
We sought to contribute broader understanding of global patterns of
species diversity on granite inselbergs and inform biodiversity
conservation in the globally significant Southwest Australian Floristic
Region (SWAFR). We surveyed floristics from 16 inselbergs (478 plots)
across the climate gradient of the SWAFR stratified into three major
habitats on each outcrop. We recorded 1060 species from 92 families. At
the plot level, local soil and topographic variables affecting aridity
were correlated with species richness in herbaceous (HO) and woody
vegetation (WO) of soil-filled depressions, but not in woody vegetation on
deeper soils at the base of outcrops (WOB). At the outcrop level,
bioclimatic variables affecting aridity were correlated with species
richness in two habitats (WO and WOB) but, contrary to predictions from
island biogeography, were not correlated with inselberg area and isolation
in any of the three habitats. Species turnover in each of the three
habitats was also influenced by aridity, being correlated with bioclimatic
variables and with inter-plot geographic distance, and for HO and WO
habitats with local site variables. At the outcrop level, species
replacement was the dominant component of species turnover in each of the
three habitats, consistent with expectations for long-term stable
landscapes. Our results therefore highlight high species diversity and
turnover associated with granite outcrop flora. Hence, effective
conservation strategies will need to focus on protecting multiple
inselbergs across the entire climate gradient of the region.