A redefinition of geographic boundaries between Festuca paniculata (L.) Schinz & Thell. associations in the western Alps

Festuca paniculata communities in Valle d’Aosta (NW Italy) can contribute to the definition of the geographic boundaries between the western Alps phytosociological associations, due to their intermediate position between Insubrian and inner-alpine communities. In order to describe the phytosociology and syntaxonomy of F. paniculata communities in the study area, 17 original relevés data were analyzed. The communities were referred to Junipero-Festucetum spadiceae juniperetosum nanae, previously described in the Meje-Ecrins-Pelvoux Massif (France). Our results exclude the presence in Valle d’Aosta of Centaureo uniflorae-Festucetum spadiceae, supposed by previous works, and define in Colma di Mombarone (Biella and Torino districts) the western boundary of the Insubrian association Polygalo chamaebuxi-Festucetum paniculatae. The border between Junipero-Festucetum spadiceae and Polygalo chamaebuxi-Festucetum paniculatae is in accordance to difference in continentality conditions, that divides the outer areas of the Insubrian region with the subcontinental and continental zones of Valle d’Aosta.