Desirable site conditions for introduction sites for a locally rare and threatened fern species Asplenium septentrionale (L.) Hoffm

Forked spleenwort, Asplenium septentrionale (L.) Hoffm., is mainly a petrophilous fern species of European mountains and very rare in Estonia, a country with flat topography and few rocky habitats. The single extant population is very small, occupies a restricted area, and is threatened seasonally by adverse human activity. An introduction project of the species was prepared according to the A. septentrionale Management Plan. The goal of the project is to introduce new populations of the species in new protected sites from ex situ propagated young sporophytes. The aim of this study was to obtain detailed data on the species ecology and provide information for selecting suitable introduction sites. We carried out a factorial pot experiment on light availability, soil pH and soil biota gradient in order to ascertain optimal growth and development conditions for A. septentrionale. Soil and light conditions must be considered the most important factors affecting species growth and reproduction, particularly under conditions of largely fluctuating water regime. Experimental plants grown in abiotic conditions closely emulating the natural habitat were the most successful and may, therefore, represent the optimal establishment potential. The survival of plants was greater, and plants grew larger with a higher number of longer leaves in acidic soil (pH 4.9) than in neutral soil. Plants performed best under high, approximately 75% total available illumination. Deep shade (90%) and well as full daylight had strong negative effect on the plants. No positive effect of “home-soil” biota was detected.