Relict seed bank of dolomite grasslands in the soil of Pinus nigra plantations

Abstract

Following the decline of pasturing, large Pinus nigra plantations were established on the dolomite slopes of the Hungarian Central Range. In the latest decades of the 20th century the nature conservation approach became stronger, thus resulting an increased effort to remove the alien Pinus nigra from the landscape and to support grassland restoration on steep slopes of dolomite hills. Soil seed bank could be a useful source in vegetation restoration, therefore in this study relict seed bank of grassland vegetation in the soil of pine plantations was investigated.
Soil samples were collected from 45–50 years old pine plantations at two study sites (Ördög-torony and Fehér-hegy) in the Budai Mountains. From each site 17 500 cm3 soil was taken from the upper 6 cm soil layer, then the samples were exposed to germination in an unheated green-house for seven months.
Number of species recorded from the seed bank was 18 at Ördög-torony and 13 at Fehér-hegy, whereas seed density was 105.6 seed/m2 and 66 seed/m2, respectively. Three major groups were distinguished in the species pool of the seed bank: 1) species of dolomite grasslands (43%), 2) species of other natural or semi- natural vegetation types (18%) and 3) weeds or alien species (39%). Regarding the group of dolomite grassland species, long-term persistent seed bank type was proved for Campanula sibirica, Colutea arborescens, Filipendula vulgaris, Polygala amara, Teucrium chamaedrys and Viola rupestris.
From the results the following major conclusions can be drawn. i) In the vegetation of dolomite grasslands relatively few species maintain persistent seed bank, thus the survival for several decades in the soil of pine plantations is exceptional, rather than rule. Among the dominant species long term persistence was not detected. ii) Therefore, in the restoration plan of these grasslands additional sowing of dominant species (especially the matrix grasses) is suggested to promote and accelerate natural succession. iii) Beside species group 1, weeds (group 3) can also play an important role in the restoration of dolomite grasslands. That is, they produce a considerable vegetation cover within short time (in the very beginning stage of succession), thus reducing soil erosion on the steep slopes, and later – as being week competitors and less tolerating abiotic stresses than the obligate dolomite grassland species – they decline naturally, after few years.