Localities and sites of the Southeastern-Alpine endemic species Spiraea decumbens Koch in Breginjski kot (Northwestern Slovenia)

Abstract

The eastern distribution limit of Spiraea decumbens s. str. is in Breginjski Kot (northwestern Slovenia), where we recorded 49 localities of this eastern-Alpine endemic plant species. We determined two new localities in a new quadrant (9746/4) on riparian rocks of the Nadiža River under Mt. Mija at Kozja Peč, which is currently the southeasternmost point of its entire distribution area. We conducted a phytosociological survey of 26 localities. This endemic occurs in dolomite rock crevices in stands classified within the association Spiraeo-Potentilletum caulescentis. On dolomite screes and torrential fens it is found to dominate on small areas in the successional stages, classified into the provisional association Aquilegio einseleanea-Spiraeetum decumbentis (alliance Petasition paradoxi) and into the new association Spiraeo decumbentis-Seslerietum calcariae (alliance Caricion austroalpinae). These stages are gradually becoming overgrown with thermophilous deciduous trees, and in one of the relevés we found the studied species in an open hop hornbeam stand classified into the association Fraxino orni-Ostryetum. Its populations are vital and unthreatened, except in the two new localities under Mt. Mija, which call for special protection due to their small size and a possibility of being backfilled with gravel.