Patterns of vegetation community distribution in a large, semi-arid floodplain landscape

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 km²) 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 matrix, corridor and patch elements of the vegetation mosaic.