Species composition and structure of vascular plants and bryophytes on the water level gradient within a calcareous fen in North Estonia

Abstract

We examined the relationship between the composition and structure of vegetation and hydrology and microtopography within the Paraspollu calcareous-rich fen (North Estonia). Species composition, depth to groundwater level (+ 6 to - 40 cm), pH (6.1-7.1), and electrical conductivity (220-840 µS cm -1 ) were recorded in 23 releves of 1 m 2 along transects over the site. The species composition and coverage of vascular plants depended on the extent of water level fluctuations and water conductivity, those of moss species additionally also on microtopography. A total of 44 bryophyte and 57 vascular plant species were identified, including 14 protected and rare species. Nonmetric multidimensional scaling and the Monte Carlo test were used to describe compositional variation and identify significant habitat variables separately for vascular plant and bryophyte species. The relationship between the species composition of field and surface layers was nonsignificant. Three of the five assemblages distinguished by two-way cluster analysis, Carex panicea-Schoenus ferrugineus-Drepanocladus cossonii, Phragmites australis-Calliergonella cuspidata, and Molinia caerulea-Carex davalliana, represent the calcareous tufa-forming fen type. The other two are distributed on the moderately drained part of the fen. The number and coverage of rich fen species decreased sharply as the coverage of M. caerulea exceeded the 30% level and seasonal fluctuation of water level was over 25 cm.