Phytosociological study of the snowbed vegetation in the Northern Apennines (Northern Italy)
Petraglia, Alessandro; Tomaselli, Marcello
A phytosociological survey of the snowbed vegetation was made across the northern Apennines, combining the field method of the Braun-Blanquet approach with a numerical syntaxonomical analysis. 61 phytosociological relevés including vascular plants and cryptogams were classified by cluster analysis. The clustering procedure was the incremental sum of squares method based on the chord distance. Six plant associations could be reported belonging to the class Salicetea herbaceae: Salicetum herbaceae, Oligotricho hercynici-Gnaphalietum supini, Polytrichetum sexangularis, Luzuletum spadiceae, Poo-Cerastietum cerastoidis, Caricetum foetidae. Polytrichetum sexangularis and Luzuletum spadiceae were here firstly reported for the northern Apennines. An indirect gradient analysis was performed, based on a quantitative estimate of the ecological requirements of each vascular species for climatic (temperature) and soil parameters (moisture, pH, nutrient and organic matter content, gravel and fine texture). Estimates were based on Landolt's indicator values. The first canonical axis was firstly associated with nutrients and secondarily with humidity. The relevés characterized by higher soil moisture and nutrient content belong to the Poo-Cerastietum cerastoidis and Caricetum foetidae. The second canonical axis was firstly associated with dispersion and humus indicator values and secondarily with soil reaction and temperature. The relevés characterized by lower dispersion and humus content values belong to the Luzuletum spadiceae. A comparison with a study performed by one of the authors fifteen years ago in the same study area revealed that the increased number of relevés produced a relevant marked increase in the number of species, mostly of the bryophytes. The most relevant species increase was in the Oligotricho hercynici-Gnaphalietum supini. In the northern Apennines the snowbed associations are likely exposed to the risk of local extinction or of loss of "floristic typicity", as a consequence of the shortening in the duration of snow cover. The risk of disappearance could be particularly high for the Polytrichetum sexangularis, the only late snowbed association occurring in the study.