Fire and regeneration: the role of seed banks in the dynamics of northern heathlands.

摘要

Questions: How do species composition and abundance of soil seed bank and standing vegetation vary over the course of a post-fire succession in northern heathlands? What is the role of seed banks - do they act as a refuge for early successional species or can they simply be seen as a spillover from the extant local vegetation? Location: Coastal Calluna heathlands, Western Norway. Methods: We analysed vegetation and seed bank along a 24-year post-fire chronosequence. Patterns in community composition, similarity and abundances were tested using multivariate analyses, Sorensen's index of similarity, vegetation cover (%) and seedling counts. Results: The total diversity of vegetation and seed bank were 60 and 54 vascular plant taxa, respectively, with 39 shared species, resulting in 68% similarity overall. Over 24 years, the heathland community progressed from open newly burned ground via species rich graminoid- and herb-dominated vegetation to mature Calluna heath. Post-fire succession was not reflected in the seed bank. The 10 most abundant species constituted 98% of the germinated seeds. The most abundant were Calluna vulgaris (49%; 12 018 seeds m-2) and Erica tetralix (34%; 8 414 seeds m-2). Calluna showed significantly higher germination the first 2 years following fire. Conclusions: Vegetation species richness, ranging from 23 to 46 species yr-1, showed a unimodal pattern over the post-fire succession. In contrast, the seed bank species richness, ranging from 21 to 31 species yr-1, showed no trend. This suggests that the seed bank act as a refuge; providing a constant source of recruits for species that colonise newly burned areas. The traditional management regime has not depleted or destroyed the seed banks and continued management is needed to ensure sustainability of northern heathlands.