© 2011 E. Schweizerbart’sche Verlagsbuchhandlung, Stuttgart, Germany DOI: 10.1127/1868-5749/2011/019-0050 www.schweizerbart.de 1868-5749/019-0050 $ 5.40 Patterns of vegetation community distribution in a large, semi-arid floodplain landscape Martin Thoms & Melissa Parsons with 2 figures and 3 tables Abstract: Despite the increasing acceptance of the shifting mosaic model of floodplain vegetation community organization, there is little quantitative analysis of patterns of floodplain vegetation organization in unconfined valley settings. This study examines the organization of vegetation community and land cover types in a large (10 519 km 2 ) unconfined floodplain landscape (the Lower Balonne floodplain, NSW, Australia). We analysed a published 1:50 000 vegetation map using landscape metrics of the area, shape and interspersion & juxtaposition of eight types of vegetation community and land cover patches. Rather than forming a predictable linear gradient across the floodplain, vegetation communities of the Lower Balonne floodplain landscape depict a heterogeneous patch mosaic. Grassland forms the matrix element of the landscape because it dominates the floodplain (40 % of the total landscape area), occurs in large patches, and is highly interspersed among the other vegetation community and land cover types. Coolibah and river red gum trees occur along the major river courses and form the corridor element of the floodplain landscape. The other land cover types form the patch element of the floodplain landscape, where each land cover type has a characteristic patch area, shape and interspersion or juxtaposition. Conventional riverine vegetation monitoring generally focuses on the narrow riparian strip immediately adjacent to the main channel. The application of such approaches in the Lower Balonne floodplain would fail to capture the dominant matrix and patch elements of the floodplain vegetation landscape. We suggest that new techniques of vegetation assessment need to be developed for large, unconfined floodplains to monitor changes in the composition and configuration of the ma- trix, corridor and patch elements of the vegetation mosaic. Keywords: floodplain landscapes, landscape ecology, patches, riparian vegetation River Syst. Vol. 19/3, p. 271–282 Published online August 2011 Authors address: Riverine Landscapes Research Laboratory, Geography and Planning, University of New England, Armidale, NSW 2351, Australia; martin.thoms@une.edu.au Article Introduction Established models of river system organization have viewed floodplains as ecotones, where riparian corridors form boundaries between terrestrial and riverine areas (Naiman & Decamps 1990), or as aquatic terrestrial tran- sition zones, where floodplains form a moving littoral zone related to the flood pulse (Junk et al. 1989). When landscape ecology was taken ‘into the water’, rivers and floodplains began to be viewed as internally heterogene- ous landscapes (Wiens 2002), which Stanford et al. (2005) termed the shifting habitat mosaic. Viewed as a shifting mosaic, flow, sediment movement, large wood deposition and riparian vegetation regeneration generate irregular and dynamic patches in floodplain landscapes (Stanford et al. 2005). The spatial organization of patches can sub- sequently influence the overall productivity of floodplain landscapes and the flux of materials within and between floodplains and the river channel (e.g. Tabacchi et al. 1998, Malard et al. 2000, Latterell et al. 2006, Whited et al. 2007, Thorp et al. 2008, Southwell & Thoms 2011). Regardless of the model used to describe floodplains, the valley setting (Hynes 1975) and physical dimensions of the floodplain (Gupta 2007) ultimately set the bound-