Vegetation composition dynamics in peatlands used as buffer areas in forested catchments in southern and central Finland

Abstract

Peatland buffer areas are important means in reducing sediment and nutrient loading from discharge waters in a variety of landscapes; however, use of natural mires as buffer areas may induce unwanted changes in the plant species composition. Vegetation composition dynamics were studied at one rewetted peatland and two natural peatlands used as buffer areas in forested catchments in southern and central Finland. In addition to the sediment and nutrient loads from the upstream catchments, the buffer areas received nitrogen and phosphorus from two artificial additions made in 2003–2005 and 2008 in order to simulate loads caused by forestry operations. The first vegetation inventory was done in the year of buffer construction (1996 or 2000), the second inventory 4–5 years after the first one, and the third inventory after 9–13 years. The vegetation composition changed significantly at all three buffer areas. Grasses and sedges, as well as herbs were generally favored by the use of peatlands as buffer areas, and at the species level, the coverages of Menyanthes trifoliata and Calamagrostis purpurea increased the most. At the two natural sites, the change in vegetation composition was more apparent in the upstream parts of the buffer areas, probably because they received more sediments and nutrients than the lower parts. Also, the vegetation changed significantly more in the lawn-level surfaces than in the hummocks. As the vegetation composition in natural peatlands used as buffer areas is likely to undergo significant changes, the use of endangered mire site types should be avoided.