Changes in the occurrence and abundance of plant species in a Norwegian boreal coniferous forest, 1988–1993

Abstract

Økland, R. H. 1995. Changes in the occurrence and abundance of Dlants sDecies in a Norwegian boreal coniferois forest, 1988–1993. — Nord. J. Bot. 15: 415–438. Copenhagen. ISSN 0107–055X.Changes in the occurrence and abundance of vascular plants, bryophytes and lichens in a S Norwegian old‐growth coniferous forest were studied, using 1 m2 plots divided into 16 subplots. Fifty plots were analyzed for six consecutive years, 199 plots were analyzed at the beginning and the end of the study (in 1988 and 1993). Nonparametric tests were performed for combinations of species, data type (occurrence or abundance), forest type (spruce or pine), and time period (one‐year or five‐year). Results are interpreted by use of species persistence data, and by detailed comparisons with European long‐term and experimental studies. Abundance changes in the pine forest are probably due to short‐term (between‐year) climatic fluctuations, notably drought. Some effects of the observers are also seen. True five‐year trends were found in the spruce forest: (1) Deschampsia flexuosa (increase), (2) several vascular plant species with preference for richer sites, notably Oxalis acetosella (decrease), and (3) most bryophyte species (increase). True trends for vascular plants are discussed in relation to deposition of airborne nitrogen and soil acidification, while the increase of bryophytes probably is due to particularly favourable growth conditions in the five‐year period.