Floristic diversity analysis along a fragmentation gradients: a case study of beech forests in the Molisean Appenines (southern Italy)

The process of fragmentation of natural habitats is increasing exponentially worldwide and represents one of the foremost threats to biological diversity. Forest fragmentation is considered to heavily affect the demographic and genetic structure of forest plant populations. Habitat fragmentation is a landscape process occurring when areas of continuous habitat are broken into smaller and discontinuous patches. In this paper we analyzed the effects of fragmentation on vascular plant diversity of Fagus sylvatica forest in central Italy (habitat of Community interest -92/43/ECC- “Appenine beech forests with Taxus and Ilex” - cod. 9210*). First, by integrating five parameters that describe beech forest patches structure (patch area, perimeter, shape index, corea area, euclidean nearest neighbor) we identified three levels of fragmentation: high, medium and absent. Then the vascular plants of each level of fragmentation were sampled following a random stratified design. The diversity of vascular plant species was analyzed considering two species groups: all sampled species and “diagnostic” species of the habitat 9210* (sensu Directive 92/43/ECC). We compared the biodiversity patterns of the different fragmentation levels by using rarefaction curves and Rényi’s profiles. We also tested the significance of the founded differences by a bootstrapping procedure. The diversity pattern of the two species groups (diagnostics and all species) showed two opposite trends. As the diversity of the entire pool of species increased on fragmented beech forests the diversity of the diagnostic group decreased. The differences between diversity values of high and low fragmentation levels resulted significant. Our results emphasize the existence of two diagnostic species: Cardamine kitaibelii and Paris quadrifolia that are indicators of not fragmented beech forests. Additionally the diversity pattern of the diagnostics species allow us to propose them as “focal species”, thus it represent a concrete indicator of the conservation status of the Fagus sylvatica with Taxus and Ilex forest.