© 2006 The Authors DOI: 10.1111/j.1466-822x.2006.00262.x 34 Journal compilation © 2006 Blackwell Publishing Ltd www.blackwellpublishing.com/geb Global Ecology and Biogeography, (Global Ecol. Biogeogr.) (2007) 16, 34–42 RESEARCH PAPER Blackwell Publishing Ltd The role of land cover in bioclimatic models depends on spatial resolution Miska Luoto*, Raimo Virkkala and Risto K. Heikkinen ABSTRACT Aim We explored the importance of climate and land cover in bird species distribution models on multiple spatial scales. In particular, we tested whether the integration of land cover data improves the performance of pure bioclimatic models. Location Finland, northern Europe. Methods The data of the bird atlas survey carried out in 1986 –89 using a 10 × 10 km uniform grid system in Finland were employed in the analyses. Land cover and climatic variables were compiled using the same grid system. The dependent and explanatory variables were resampled to 20-km, 40-km and 80-km resolutions. Generalized additive models (GAM) were constructed for each of the 88 land bird species studied in order to estimate the probability of occurrence as a function of (1) climate and (2) climate and land cover variables. Model accuracy was measured by a cross-validation approach using the area under the curve (AUC) of a receiver operating characteristic (ROC) plot. Results In general, the accuracies of the 88 bird–climate models were good at all studied resolutions. However, the inclusion of land cover increased the performance of 79 and 78 of the 88 bioclimatic models at 10-km and 20-km resolutions, respec- tively. There was no significant improvement at the 40-km resolution. In contrast to the finer resolutions, the inclusion of land cover variables decreased the model- ling accuracy at 80km resolution. Main conclusions Our results suggest that the determinants of bird species distri- butions are hierarchically structured: climatic variables are large-scale determinants, followed by land cover at finer resolutions. The majority of the land bird species in Finland are rather clearly correlated with climate, and bioclimate envelope models can provide useful tools for identifying the relationships between these species and the environment at resolutions ranging from 10 km to 80 km. However, the notable contribution of land cover to the accuracy of bioclimatic models at 10–20-km reso- lutions indicates that the integration of climate and land cover information can improve our understanding and model predictions of biogeographical patterns under global change. Keywords Bioclimatic models, bird atlas, birds, climate, distribution, Finland, land cover, modelling. *Correspondence: Miska Luoto, Finnish Environment Institute, Research Department, Research Programme for Biodiversity, P.O. Box 140, FIN-00251 Helsinki, Finland. E-mail: miska.luoto@ymparisto.fi Finnish Environment Institute, Research Department, Research Programme for Biodiversity, P.O. Box 140, FIN-00251 Helsinki, Finland INTRODUCTION Assessments of the potential effects of climate change on biodiversity and the future range shifts of species have often been based on bioclimatic envelope models (Bakkenes et al., 2002; Beaumont & Hughes, 2002; Berry et al ., 2002; Pearson & Dawson, 2003; Thuiller, 2003; Huntley et al., 2004; Thuiller et al., 2005). These modelling strategies correlate current species distributions with climate variables, and then project spatial shifts in species climatic envelopes according to the climate change scenarios (Pearson & Dawson, 2003; Thuiller, 2003, 2004).