Herbage production and species richness in sub-alpine grasslands of different soil parent material in Northern Greece

Several abiotic and biotic factors were investigated as possible predictors of local species richness in two sub-alpine grasslands of Jenna and Belles Mountains in Northern Greece. For species richness modelling a hierarchical modelling framework based on generalized additive models was adopted. The two sub-alpine grasslands differed in aspect, altitude and soil parent material (volcanic origin, mostly trachyte, and andesite (TA) for Jenna and metamorphic rocks, mostly gneiss (G) for Belles). 12 fenced squared plots, 16 m2 each, were used per grassland, where soil properties, herbage production, species presence and cover of grasses, legumes and forbs were estimated. Mean herbage production was significantly affected by slope and altitude, soil K content and floristic composition as expressed by an ordination axis. Soil pH, floristic composition and average herbage production were significant predictors of forbs and total species richness. For the former, soil N content and for the latter the occurrence of Agrostis capillaris , were also included as significant terms in the predictive model. The predictors for grasses species richness were N content, having a positive effect, and average herbage production. In all cases higher species richness was predicted for intermediate values of average herbage production. Differential responses were found between forbs and grasses. The predictors of their species richness were different while for the case of the common predictor (N) the responses of the two groups were also different (grasses species numbers increase and forbs species numbers decreased with increasing N). Maximum species richness of grasses was observed at relatively low production levels while forbs species richness maximized at relatively high production levels.