Vegetation trends in relation to decreasing atmospheric deposition in southern Sweden 1983-1996

In the northeastern part of southern Sweden, anthropogenic sulphur and nitrogen deposition have decreased strongly since the mid-1980s. In the Southwest, S deposition has decreased less, while N deposition has remained constant. I have compared the trends of species richness, Shannon- Wiener diversity, and cover of vascular plants between the NE and SW using analysis of covariance. In each region, the variables were measured 1983 through 1996 at four sites representing bogs, pine forests and two types of spruce forests. Species richness, diversity, and cover decreased faster in the NE (-2.5%/yr, -0.036/yr, -4.3%/yr) than in the SW (-0.8%/yr, -0.026/yr, -3.0%/ yr). The differences were significant for species richness in all vegetation types, for diversity in all vegetation types but pine forests, and for total cover in bogs. Cover of species known to occur primarily on nitrogen-rich, neutral to alkaline soils decreased faster in the NE (-6.8%/yr) than in the SW (-1.7%/yr). Cover of species known to occur primarily on nitrogen-poor, acidic soils decreased equally in both areas (-3.7%/yr). I suggest that the stronger effects in the NE are due to the simultaneous reduction of N supply and acidification. Species with a stronger demand for N presumably decreased because of reduced N supply, whereas species tolerant of high soil acidity decreased because they were outcompeted by less tolerant species.

86. Annual Meeting of the Ecological Society of America. Madison, Wisconsin (U.S.A.)