Edaphic and topographic filtering of plant life forms in Mediterranean mountaintop communities

Environmental drivers filtering life forms at local scales are poorly investigated in general, and studies devoted to this topic in the Mediterranean mountains are still missing. We investigated the role of edaphic and topographic gradients in vegetation above 1900 m a.s.l. on Pizzo Carbonara (Madonie Mountains, Northern Sicily), a carbonate massif extensively affected by karst erosion that gave rise to a system of sinkholes and windy ridges alternating on the summit plateau. We sampled 42 vegetation plots, georeferenced with a sub-metric GPS. Different topographic variables were derived from the regional technical map of Sicily, with 2 m resolution, using QGIS. Additionally, several chemical and biochemical soil parameters were analysed for each plot. The species were split into three life-form groups: chamaephytes, hemicryptophytes, and therophytes. Data were analysed using different response variables: species richness, vegetation cover, and species composition. For the first two response variables, a Generalised Linear Model (GLM) was run. The compositional data were processed by distance-based redundancy analysis (db-RDA) through variation partitioning. Results show that life forms are subject to differential filtering by edaphic and topographic variables. These topographic conditions affect the relative performance of the co-occurring vascular plant species, and consequently, the structure and composition of local plant communities.