Functional traits variation along elevation gradient are climate-context: the case of sub-Mediterranean mountain grasslands

According to niche theory environmental factors operate like a filter promoting the coexistence of species with similar ecological niches. Contrary, competitive interactions promote niche differentiation increasing functional traits dissimilarity of co-occurring species. These two processes act simultaneously but given a small study scale, the predominance of one over the other should depend on the intensity of environmental restrictions. Elevation gradients have been extensively used to test these assumptions, as environmental constrained increase along elevation, mainly due to temperature decrease. However, in the Mediterranean region precipitation increases along elevation determining an overall humped-back gradient of environmental restriction, with higher restriction at the lower and higher elevation. We analysed changes in functional trait patterns relative to Leaf-Height-Seed scheme along a sub-Mediterranean elevation gradient to test whether community functional patterns responded to this particular environmental gradient. We hypothesized that trait dispersion is higher at middle elevations and that trait means reflected the communities’ response to environmental restrictions. The study area was carried out on dry grassland of the Velino massif (Central Apennines). We collected species cover for 45 environmentally homogeneous plots (4 m2) along and elevation gradient from 1325 to 2375 m a.s.l. To explain changes in functional patterns at community level, we performed generalized least square models with elevation as explanatory variable, choosing the most appropriate variance structure by the minimum AIC criteria. We found that all functional indices responded to elevation changes, except for mean values of specific leaf area. We found at lower and higher elevations, communities displayed adaptation to more environmentally restricted conditions, i.e. low plant height and low seed mass. Moreover, lower trait diversity values at low and high elevations indicate that climatic conditions restricted the number of strategies in the community. On the contrary, more favorable environmental conditions in the intermediate part of the elevation gradient seems to lead to higher trait diversity. Our results are in accordance with both niche theory and the stress gradient hypothesis. Nevertheless, the also pin-point the necessity of considering the specific climatic context when trying to generalize the elevation-functional patterns relationships.