Influence of small climatic variations on the species composition of roadside grasslands

Relations between the distribution of Arrhenatheretalia species from roadsi de grasslands of southern Belgium and variations in climatic parameters are described on the basis of a statistical sampling procedure integrating mul tivariate techniques (cluster analysis and DCA-ordination). The authors exa mine the influence of small macroclimate features, such as mean annual rain fall (1100-1400 mm), mean annual temperature (7.0-8.2 degreesC), mean annua l number of frost days (90-120) and mean annual number of snow days (28-35) , on the floristic composition of roadside grasslands from High Ardennes (5 25-570 m a.s.l.) (19 samplings) and Middle Ardennes ecological sectors (330 -500 m a.s.l.) (26 samplings). Cluster analysis revealed two distinct clusters of vegetation samples which are likely to be arranged along a climatic gradient. Sample scores on the first DCA-axis were significantly correlated with climatic parameters. Mean annual number of frost days was the factor which best explained the differ ences between plots, when analysed with a linear regression. These results indicate that very small macroclimate variations in general a nd in the number of frost days in particular, are determinant of compositio nal variation in roadside plant communities.