Weed vegetation in the north-western Balkans: diversity and species composition

P>Surveys of weed vegetation of the western Balkan peninsula (1939-2006) were used to study changes in species composition. A large data set of arable weed vegetation was compiled and analysed with direct and indirect ordination, regression and beta (beta) diversity analysis. Five environmental variables (altitude, season, year, crop, phytogeographical region) were used to determine broad-scale changes in weed species composition. The most important parameter was phytogeography and the second was crop. Altitude and season were found to be less important, although significant, which contrasts with results from Central and Northern Europe. beta-diversity was higher in cereals and in summer, while decline along the altitudinal gradient previously demonstrated in Central Europe, was not observed. In southern parts of the studied area, thermophilous species have shifted to higher altitudes. The results and ranking of importance of environmental and spatial variables are discussed in relation to similar studies in Northern and Central Europe