Fen grassland vegetation under different land uses (Biebrza National Park, Poland)

Abstract

The majority of European fen grasslands are seminatural and require appropriate management to maintain their high natural value. The research area was located in the middle basin of the Biebrza River Valley, where fen grasslands vegetation was i) grazed by Konik horses, ii) mowed once every 2–4 years, or iii) abandoned for 16 years. The question was as follows: How do different land use types affect the floristic composition and restoration of abandoned fen grasslands? In the examined sites we measured floristic composition and soil physicochemical parameters. The observed changes in the floristic composition resulting from the introduction of the new type of land use were significant and they occurred in a relatively short period of time. With the cessation of mowing for 16 years, the intermittently wet Molinia meadows were replaced by trees and shrubs of alder woodlands (Alnetea glutinosae class), and the plant species diversity significantly decreased. The mowing of the Molinion meadows once every 2–4 years proved to be sufficient to prevent the encroachment of trees, but it was not enough to stop the expansion of Molinia caerulea. In the site grazed with Konik horses for 13 years, the primary fen grassland vegetation (Scheuchzerio-Caricetea nigrae) was replaced by species of low, trampled swards and intermittently wet meadows (Molinio-Arrhenatheretea class). The soils under all of the sites differing in the land use type were classified as Eutric Rheic Hemic Histosols. They were typical peatland soils, slightly acidic to neutral. The results of the soil analyses indicate the high natural states of the studied areas and that their extensive use only slightly affected their physicochemical properties. Greater soil bulk density was noticed under the pasture than under the abandoned and mowed sites, but the extensive grazing of Konik horses caused only a slight increase in volumetric density to 0.19 g cm−3. Our results show that on both the mowed and the grazed sites, the content of soil organic matter and soil organic carbon was higher than that on the abandoned site. In the mowed part as well as in the grazed part, long-lasting monitoring of the effects of the management strategies used on vegetation and soil properties is still needed.