Season and timing of moisture availability predict composition of montane shrub-dominated wetlands at distributional limits in eastern Australia

Abstract

We explore the environmental effects on variation in floristic compositional among montane shrub-dominated wetlands at the edge of their geographic distribution within the New England Batholith of eastern Australia. Canonical Correspondence and Redundancy Analyses revealed patterns and gradients in vascular plant species and families of bog communities. Variance partitioning quantified the relative contributions to variation in: (1) species composition; and (2) family composition due to climate, space, and landscape variables. Eleven of the 55 explanatory variables explained 29.2% of the total variance in the species dataset. Climatic factors were overall the best explanatory variables followed by spatial and then landscape characteristics. We found that climate variables were of most importance in determining whether shrub-dominated wetlands will occur at all and also their composition, which is in contrast to results from other studies not conducted at the edge of community distribution. Climate variables associated with seasonality were found to be highly significant correlates of composition as has been found for montane shrub-dominated wetlands in other parts of Australia. The season in which moisture availability becomes critical varies across different rainfall climatic zones. Under current predicated changes in regional climate, it is likely that an increase in variability and seasonality of climate will cause a retraction in the distribution of Australian montane bogs.