Long-time record of fire and open canopy in a high biodiversity forest in southeast Sweden

摘要

We studied a ca 200 ha large forest site that holds an exceptionally large number of red-listed saproxylic beetles. We conducted pollen, charcoal and dendroecological analyses to reveal the long-term stand-level history of the site. We also investigated which of the red-listed saproxylic beetles recorded at the site are probably dependent on forest fires or structures that are created by fires. Pollen from Pinus and Betula dominate the pollen diagram, and the pollen record shows that the canopy is more closed today than ever during the last 2500 years. Large amounts of charcoal fragments were found throughout the core except during three shorter periods, one of which is the latest ca 200 years. The dendroecological investigation revealed I I different fires, the earliest dated to AD 1586 and the last dated to AD 1868. Of the 105 red-listed saproxylic beetles recorded at the site, at least 12 are associated with open forests with Pinus sylvestris or Birch spp. trees. We conclude that the fires, as recorded both by the charcoal and dendroecological analysis, kept the site largely open in the past, and this is likely one important explanation for the high conservation value of the site today. Other important factors could be that the site is rich in boulders, the relatively warm summer climate in the region, that Picea abies has not been planted in the surroundings until recently, and finally the presence of many old trees. The study supports the theory that fire could have been an important factor for keeping some forest types open before the large human impact on the northwestern European forests started.