Seed bank composition and seedling survival in forest soil polluted with heavy metals

Seedling recruitment from forest soil polluted with heavy metals was studie d in order to determine the revegetation potential of the seed bank. The so il samples were collected from untreated and fertilised Scots pine stands a long a 8 km transect running SE from a copper-nickel smelter in SW Finland. The composition and size of the active seed bank and the survival of the g erminated seedlings were studied in greenhouse conditions. The average dens ities of germinated seeds of 15 species ranged from 250 to 4750 plants per m(2) at the six sites. Although vegetation was almost totally absent near t he smelter, germinable seeds of Betula pubescens, Calluna vulgaris, Pinus s ylvestris and Vaccinium uliginosum were found in the most contaminated soil . The number of Calluna vulgaris seedlings increased with increasing distan ce from the smelter, but no such trend was found for the other species. The mortality rate of the seedlings was highest in the soil samples collect ed near the smelter. Nutrient addition (stand-specific fertilisation with N , Ca, P and Mg) did not affect the number of germinated seeds, but liming s lightly reduced heavy metal induced death of the seedlings. The survival pr obability of Calluna vulgaris seedlings decreased with proximity to the sme lter. The results suggest that the recovery of Calluna vulgaris near the sm elter was prevented by a low availability of seeds in the soil, unfavourabl e germination conditions and unsuccessful seedling establishment. We conclu de that, despite the presence of viable seeds in polluted soil, revegetatio n from seed banks is not successful without soil mitigation to immobilise h eavy metals.