Scree vegetation in the northern Apennines (N-Italy)

Aims: This paper presents the results of phytosociological research on scree vegetation in the northern Apennines with the aim of comparing vegetation types classified in different syntaxa. The specific objectives were: 1) to identify, classify and describe the vegetation units of scree communities; 2) to pinpoint the main ecological gradients underlying different vegetation units; and 3) to identify a possible hierarchy of predictor variables explaining floristic differences between vegetation types. Study area: The study area lies on the northern border of the Italian Peninsula, between 44 degrees and 44 degrees 45' N and 9 degrees 20' and 10 degrees 45' E, characterized by a large variety of scree habitats and representing both a centre of endemism and a phytogeographic transition zone between the Alps and Apennines. Methods: The study was based on a dataset including 364 releves taken according to the Braun-Blanquet method, which were then classified following an unsupervised numerical procedure. Species fidelity was used to define the diagnostic species of the associations. PCA and RDA ordinations were employed to perform ecological analyses using both Ellenberg Indicator Values as indirect variables and directly measured or calculated variables. Results: A total of 15 plant associations were identified, belonging to 6 alliances and 4 different orders (Thlaspietalia rotundifolii, Arabido alpinae-Petasitetalia paradoxi, Achnatheretalia calamagrostis and Androsacetalia alpinae) within the class Thlaspietea rotundifolii. All associations were described according to their floristic composition, structure, syntaxonomy, habitat and distribution. Conclusions: Nine scree associations and two alliances - endemic to the study area - are described here for the first time. The syntaxonomic scheme followed is in accordance with that proposed in the EuroVegChecklist, with a few important exceptions. The largest variation in vegetation types was found along complex environmental gradients and the most important factors driving the difference between the four orders were gravel size, elevation and the geological substrate.