Season and timing of moisture availability predict composition of montane shrub-dominated wetlands at distributional limits in eastern Australia John T. Hunter A,C and Dorothy M. Bell B A School of Behavioural Cognitive and Social Sciences, University of New England, Armidale, NSW 2351, Australia. B Botany, School of Environmental Sciences and Natural Resources Management, University of New England, Armidale, NSW 2351, Australia. C Corresponding author. Email: jhunter8@bigpond.com 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. Additional keywords: climate change, fire, ordination, seasonality, spatial context, summer-dominant rainfall, variance partitioning. Received 22 January 2013, accepted 4 March 2013, published online 18 April 2013 Introduction In Australia, only a very small amount of the land area is montane, much of which is along the Great Dividing Range. The New England Tableland Bioregion forms a major part of this upland area, generally encompassing altitudes of ~800–1600 m incorporating an area of 3 004 202 ha (3.6% of the state of New South Wales). Within this region, most non-riverine wetlands fall within three broad categories locally known as lagoons, fens and bogs. Lagoons are shallow temporary lentic wetlands occurring at altitudes above 900 m predominantly on basaltic soils and are dominated by emergent macrophytes (Bell et al. 2008). Fens occur in flat or concave valley floors from altitudes generally above 400 m; are comparatively mineral rich, alkaline or moderately acidic (Beadle 1981; Keith 2004; Hunter and Bell 2009) and are dominated by soft-leaved tussock sedges (usually Carex; Hunter and Bell 2009). Both lagoons and fens lack a sclerophyllous shrub component. Bogs occur on a broader range of physiographic positions generally above 800 m altitude, with waters that are acidic and nutrient poor (Keith 2004; Whinam and Hope 2005; Hunter and Bell 2007). These communities are structurally dominated by sclerophyllous shrubs but with a herbaceous understorey and Sphagnum is often present (Hunter and Bell 2007). Peat development is very poor and may only be a few centimetres deep and rarely extends to any great depth. However, from an Australian perspective these communities are included within mires (Benson and Ashby 2000; Whinam et al. 2001; Whinam and Chilcott 2002; Whinam et al. 2003; Keith 2004; Hope and Kershaw 2005; Whinam and Hope 2005; Hunter and Bell 2007, 2009). Montane wetland environments are extremely limited and are significant if only due to their rarity within the landscape. However, they are also under threat by anthropogenic land-use practices such as draining, grazing, burning, peat mining and climate change (Benson and Ashby 2000; Whinam et al. 2001, 2003; Whinam and Chilcott 2002; Hope and Kershaw 2005; Hunter and Bell 2007, 2009; Benson and Baird 2012). Although there are some outliers (in western Victoria and eastern South Australia), montane bogs are mainly restricted to CSIRO PUBLISHING Australian Journal of Botany http://dx.doi.org/10.1071/BT13017 Journal compilation Ó CSIRO 2013 www.publish.csiro.au/journals/ajb