SOIL SEED BANK COMPOSITION ALONG A GRADIENT FROM DRY ALVAR GRASSLAND TO JUNIPERUS SHRUBLAND

Dry alvar grasslands on limestone on the Baltic island of Oland, SE Sw eden, are very species-rich as long as the traditional agricultural ex ploitation of grazing and fire wood collection continues. After abando nment, encroachment of Juniperus communis starts and a closed woodland can develop within 100 yr. A chronosequence, representing a successio nal series, was used for the comparison of sites still grazed, and sit es ungrazed for about 20, 55 and 80 yr, respectively. Out of the 58 ch aracteristic dry alvar grassland species 55 % disappeared from the est ablished vegetation after 80 yr of abandoning, and 80 % also vanished from the seed bank. Arenaria serpyllifolia, Trifolium repens, Agrostis vinealis, Linum catharticum, Polygala vulgaris, Cerastium fontanum, L uzula campestris, Achillea millefolium and Potentilla tabernaemontani were the only species left in the seed bank. More than 75 % of the dry alvar grassland species were classified as having a transient or shor t-term persistent seed bank. It is concluded that restoration manageme nt, by cutting junipers, of overgrown dry alvar grassland cannot rely on the longevity of seeds in the soil. Seeds have to be dispersed by w ind or grazing animals.