Soil acidification and vegetation changes in deciduous forest in southern Sweden

Thirtyfour deciduous forest sites in southern Sweden, originally studied in 1949-1970, were resampled in 1984/85. The average pH change in the humus layer was-0.78 and-0.23 in soils originally studied 30-35 and 15-20 years ago, respectively. Cover changes in the field layer were measured and related to pH changes. The number of species had increased in spite of pH decreases, reaching a maximum at pH 4.0-5.0, while the total cover of the field layer was unchanged.Two groups of species showed no correlation with pH decreases in the humus layer. A large number of species had increased in cover on a majority of sites over the entire species specific pH interval, including nitrophilic species (Rubus idaeus, Chamaenerium angustifolium, Aegopodium podagraria, Stellaria nemorum). A few species had decreased in cover on a majority of sites (Polygonatum multiflorum, Pulmonaria officinalis, Dentaria bulbifera). Some species showed a covariation with pH changes, decreasing in cover in sites in the acidic part of the pH interval (Mercurialis perennis, Lamium galeobdolon, Galium odoratum, Oxalis acetosella, Luzula pilosa). Without excluding other factors, this paper suggests that the increased nitrogen deposition and the increased acidity in the humus layer might cause some of the cover changes in the presented species.