Fine‐scale five‐year vegetation change in boreal bog vegetation

Abstract

Abstract. Within an ombrogenous part of N. Kisselbergmosen, Rødenes, SE Norway, fine‐scale changes in species abundance, successional trends relative to the main gradients (as represented by DCA axes), and co‐ordinated change within pairs of the bottom layer species are studied. Data sets were sampled twice with a five‐year interval, and included species abundance and cover of mud bottom, naked peat and litter in 436 sample plots (16 cm× 16 cm), and species abundance in 6976 subplots (4 cm× 4 cm). Depth from the surface of subplots to the water table was estimated in 1991. Most summers and growing seasons were somewhat drier than normal in the 5‐yr period. The area covered by mud‐bottom, naked peat and litter increased significantly, as did the frequencies of the dwarf shrubs Calluna vulgaris and Andromeda polifolia in hummocks and upper lawn. Sample plots were significantly displaced downward the peat productivity gradient (DCA 2), reflecting the reduced cover of many bottom layer species, including all Sphagnum spp. Significant coordinated changes in cover of bottom layer species are described. The changes observed in hummocks support the existence of a local regeneration cycle, as suggested by other researchers. Some of the vegetation changes seem parallel to those reported from areas with a higher nitrogen deposition, but it is not likely that nitrogen deposition alone is the major cause of the observed changes. Between‐year variation in population size and climatic fluctuations may as well explain the observed changes.