Partitioning floristic variance in Norwegian upland grasslands into within-site and between-site components: are the patterns determined by environment or by land-use?

This study presents a quantitative partitioning of the variance in floristic data from grazed semi-natural vegetation of summer farms in Roldal, western Norway. The data consist of 189 taxa recorded in 107 4-m(2) sample plots within 10 summer farms with different land-use histories. Thirty-five environmental variables were recorded, including altitude, slope, radiation, geology, soil chemistry, and past and present land-use. A series of (partial) canonical correspondence analyses (CCAs) were used to partition the total variation into within-farm and between-farm components, and to investigate the explanatory power of different groups of environmental and land-use variables at the two scales. The results show that: (1) although local gradients are of overriding importance for floristic composition, landscape-scale processes also contribute significantly to the observed patterns; (2) the measured land-use and environmental factors account for comparable amounts of compositional variance at the two scales; and (3) even if the relative contributions of the two classes of explanatory variables are comparable, details differ, showing that broad-scale environmental and land-use patterns are not just scaled-up versions of the fine-scale patterns or vice versa. These results support a multi-process view of vegetation patterns.