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Past studies on changes in species distribution have mainly been based on analysis of range boundaries. In contrast, the method used here evaluates shifts in species' geographic centroids within a predefined area. We used presence/absence data on epiphytic lichens collected 1986 and 2003 from 64 sites in southern Sweden. A centroid was calculated each year, for each lichen species and substrate. The distance of centroid movement was evaluated in a permutation procedure. In total, 56 lichen species on 22 tree species were involved in the analyses, yielding 30 cases that had sufficient sample sizes both years to be evaluated. Out of these, three exhibited a significant movement of their centroid. The shift of lichen centroids of Hypogymnia physodes (L.) Nyl. and Vulpicida pinastri (Scop.) J.-E. Mattsson & M. J. Lai on the tree species Juniperus communis L. was 50 and 151 km with the direction 27° and 48°, respectively. For Hypogymnia physodes on Pinus sylvestris L., corresponding values were 41 km and 30°. The northnortheast shifts of these species in Sweden could be a response to a warming climate. [ABSTRACT FROM AUTHOR]