Ground-dwelling ants, beetles and spiders were surveyed at 239 forest sites in north-east New South Wales. The level of dissimilarity in species composition between these sites is analysed in relation to inter-site differences in a number of remotely mapped environmental and vegetational variables and inter-site geographical separation. Results of this analysis are compared with those obtained from analyses of spatial turnover in species composition of vertebrates and vascular plants. Biological dissimilarity between sites is correlated with inter-site environmental differences for all surveyed arthropod, vertebrate and plant groups. However, after controlling statistically for environmental differences, the correlation between biological dissimilarity and inter-site geographical separation is much stronger for ground-dwelling arthropods than for vertebrates and vascular plants. These results have important implications for the use of remote vegetation or environmental mapping as a surrogate for selecting reserves to conserve biodiversity. To reserve regional biodiversity in a biological group exhibiting high geographical turnover in species composition it is imperative that a reserve system not only include a portion of each mapped environment or vegetation class but that this sample is spread geographically to accommodate species turnover within each class.