A study of species richness and diversity in seed banks and its use for the environmental mitigation of a proposed holiday village development in a coniferized woodland in south east England

A survey was carried out to determine the density and species composition of germinable seed in the surface soil layers of 30 plots within a coniferized lowland woodland in East Kent in order to establish the resources available for habitat creation in the event of some areas being modified during a proposed holiday village development. The selected plots included conifer plantations (up to 69 years old), broad-leaved plantations and the semi-natural broad-leaved edges that remain on parts of the perimeter of the site which were used as the control. A total of 13 682 seedlings emerged from the soil samples during the four-month germination trials. Fifty-two species were identified of which eight were ancient woodland indicator species for south-east England. The most abundant species represented in the seed banks were: Juncus effusus, Rubus fruticosus, Carex sylvatica, Betula pendula and Agrostis tenuis. Between-site comparisons of coniferous plots of different ages revealed a marked reduction in the seed species and seed density in plantations over 65 years old. Results of soil nutrient and texture analyses ruled out the likelihood of edaphic factors being responsible for between-site differences in seed bank composition. Seed species richness and diversity (Shannon-Wiener diversity index) were greatest in the semi-natural broad-leaved edges, but the diversity index used also showed that two replanted conifer sites had high values despite few species being present. The usefulness and limitations of diversity indices in the context of seed bank studies is discussed. From the results of the study, management proposals for the site have been put forward in order to maintain floristic diversity and mitigate the impact of the proposed development.