Succession after prescribed burning in coastal Calluna heathlands along a 340-km latitudinal gradient

摘要

Questions The coastal heathlands of northwest Europe are classified as highly endangered and a habitat of high conservation importance throughout their geographic range. Previous research into heathland vegetation dynamics has typically been carried out within single sites or regions, and hence little is known about the variability of land-use effects and successional dynamics along biogeographic gradients. We test the hypothesis that the bioclimatic gradient is a key factor shaping post-fire regeneration dynamics in Calluna heathlands, with progressively slower regrowth and lower post-fire pioneer species richness towards colder climates. Location Wet and dry Calluna heath vegetation in five sites spanning a 340-km latitudinal gradient along the west coast of Norway (60.70 degrees-63.79 degrees N). Methods A repeated measures design was used, with floristic data recorded from permanent plots in a number of experimental post-fire successionsover a 3-yr period (n=344). The data were analysed using multivariate ordination techniques: detrended correspondence analysis, partial redundancy analysis and principal response curves, and mixed effects models. Results Regeneration rates decrease from south to north and the wet heath stands regenerate faster towards the pre-fire community composition than the dry stands. Calluna decreases immediately after fire in all sites, but increases from the second year onwards, with the southernmost site having the fastest return. Regeneration of grasses, herbs, mosses and lichens is also faster in the south. Across all sites, species richness decreased the first year after fire, followed by an increase that exceeds pre-fire levels by the second year. The number of pioneer species entering the heathlands after fire decreases northwards. Conclusions We found considerable geographic variation, not only in species composition, but also in post-fire successional trends and dynamics. This is probably linked to higher productivity and larger pools of pioneer species in southern sites, and higher growth rates of shrubs and mosses in the wet heath habitat. This calls for conservation of a geographically diverse set of heathland sites, as well as development of regional- and site-specific management plans.