Seasonal variation in the seed banks of native woodland and coniferous plantations in Northern Spain

The effect of forest type (native woodland and two types of plantation: evergreen coniferous Pinus radiata D. Don and deciduous coniferous Larix kaempferi Lamb.) and season on the composition and density of the soil seed bank were studied in a replicated experiment in the Basque Country, northern Spain. Spring was the season with the largest germinable seed bank and the highest species diversity. The seasonal variation of the seed bank was mainly due to the phenology of the species rather than to the environment (i.e. tree species). The highest number of seeds and species in the seed bank was found in the larch plantation. The greatest similarity among the seed bank of the different forests was due to the presence of broad ranged species. Species belonging to this group were mainly present in the seed bank. The presence of seeds of some native held layer species such as Arum maculatum, Oxalis acetosella, Blechnum spicant (spores) or Danthonia decumbens in the seed bank was favoured by the coniferous plantations. However, most of the field layer species were not found in the seed bank. As the typical woodland species, which do not have a persistent seed bank, are the first ones to disappear from vegetation in coniferous plantations, future management plans should aim to maintain a balance between plantations and natural woodlands and the frequency of cutting, in order to maintain local species diversity. (C) 2000 Elsevier Science B.V. All rights reserved.