Effects of experimental acidification, nitrogen addition and liming on ground vegetation in a mature stand of Norway spruce (Picea abies(L.) Karst.) in SE Sweden

During the period 1976-1991, a combined experiment of acidification, liming and nitrogen addition in a mature spruce stand was conducted at Farabol in south-east Sweden. The aim of this study was to investigate the effects of these treatments on the ground vegetation 0, 1, 5 and 15 years after experimental establishment. The treatment regimes were nitrogen (200 kg N ha -1 , repeated three times at 4-5-year intervals, totally 600 kg N ha -1 ), sulphur powder (50 and 100 kg S ha -1 a -1 , totally 600 and 1200 kg ha -1 ), sulphur plus nitrogen (600+600 kg ha -1 ) and limestone (500 kg ha -1 a -1 , i.e. totally 6000 kg ha -1 ). The results showed that nitrogen addition and liming promoted the abundance of the grass Deschampsia flexuosa , while acidification had a negative effect on D. flexuosa and herbs in the field layer. There was a negative reaction giving immediate damage to the bryophytes in connection with additions of nitrogen, sulphur powder and lime. The magnitude of damage and the capacity to recover varied among species as well as among treatments. The recovery from immediate damage after liming was much faster than after the treatments with sulphur powder and/or nitrogen. A negative interaction between sulphur powder and nitrogen was found for herbs and mosses where the combined effects were stronger than the effects of a single treatment alone. Acidification also had a negative effect on the total number of species. The results of this study showed that acidification and nitrogen deposition could negatively influence forest vegetation by changing the nutrient availability in the soils. Liming led to an improved growth of the forest ground vegetation and the flora changed towards a more nitrophilic species composition.