Matskási István (szerk.): A Magyar Természettudományi Múzeum évkönyve 88. (Budapest 1996)

Csontos, P., Horánszky, A. , Kalapos, T. ; Lőkös, L.: Seed bank of Pinus nigra plantations in dolomite rock grassland habitats, and its implications for restoring grassland vegetation

Stand 1 - Above the cliff named "Ördög-torony". Average tree height is 10 m; stand age (Pinus) 55 years; diameter at chest height is 20.3 cm (S.d. 4.6); mean cover of the tree-layer is 65%. Share of tree species: Pinus nigra 40% and Fraxinus ornus 25%. The ash forms a spontaneous, uneven-aged, lower tree layer (with mean age of 25.2 years (S.d. 12.3). Stand 2 - The inner zone of the "Fehér-hegy". Average tree height is 16 m; stand age 55 years; diameter at chest height is 17.1 cm (S.d. 4.2); mean cover of the tree-layer is 80%. Pure stand of Pinus nigra. From both stands 17,500 enr soil were collected in 36 pieces of 6 cm deep soil prisms taken at random, on 24th October, 1991. The freshly fallen layer of needles was removed before cutting out the prisms. During winter the soil was kept outside and protected from light and additional seed rain. From 8th April, 1992, the samples were exposed to light and kept moist in a greenhouse of the University Botanical Garden. Emerging seedlings were identified then removed at weekly intervals. For seedling identification we used the Seedling Herbarium of the Botanical Department of the Hungarian Natural History Museum and the works by CSAPODY (1968) and MULLER (1978). In some cases seedlings were transplanted into flower-pots and raised till flowering stage. The standing vegetation of the two Pinus nigra plantations was sampled twice in 1993 (4th May and 25th June), by using five, 5 m x 5 m quadrats at each site. The percentage cover of each species was recorded, based on eye estimation, and the average cover values were calculated. Regarding data of different sampling times the higher cover values were considered for each species when the final tables were put together. Nomenclature follows TUTIN et at. (1964-1980). RESULTS AND DISCUSSION Altogether 52 individuals were identified in the germination tests, and these seedlings belonged to 28 species (Tables 1 and 2). The seed numbers per square metre were: 105.6 at the less closed tree-canopy (stand 1 ) and 66 under the pure pine forest (stand 2). If we consider values published for various grassland vegetations, like limestone grasslands (RYSER & GlGON 1985) or short-grass-, mixed grass- and Fescue prairie (RiCE 1989), where 400-8000 seeds/sqm are stored in the soil, then a considerable depletion of seed bank is obvious under the 55 year old pine plantations. Additionally, more than two thirds of the species were represented by single seeds only, again a sign of seed bank depletion (see Tables 1 and 2). A similar rate of seed bank impoverishment was detected (32 seeds/sqm) in a calcareous grassland when the original surface was covered by 1.6-1.8 m deep soil layer for 32 years (HENDRY et al. 1995), while depletion of woodland seed banks due to coniferization was discussed by WARR etal. (1994). The highest number of seeds were detected for Carex humilis (8 seeds; 26.4 seeds/sqm). However it was also present in the standing vegetation and occasionally may produce seeds under the shade of the pine forests. Beside Carex humilis, which occurred in both stands, in Stand 1 a further three species were present both in the seed bank and in the standing vegetation. However, the compositional similarity between seed bank and standing vegetation was extremely low (THOMPSON & GRIME 1979). Additionally an increasing dissimilarity was detected parallel with the share of Pinus nigra in the canopy.