Biased vegetation patterns and detection of vegetation changes using phytosociological databases. A case study in the forests of the Babia Gora National Park (the West Carpathians, Poland)

Abstract

Abstract. A huge number of phytosociological releve ´s, which have been collected inEurope during the last century, seems to be a useful point of reference for analyses oftemporal changes in vegetation. The high degree of subjectivity during data collection,however, makes difficult the comparison between data sets collected at different time bydifferent authors. Being aware of this we attempted to reveal 30-year changes in strictlyprotected old-growth mountain forests. We compared two sets of releve ´s: a subjectivephytosociological sample collected in the 60s and a systematic random one from the 90sof the XX century.Standard phytosociological data gave distinct vegetation units with transitional patchespoorly represented. This was observed both in the gradient between beech and coniferousforests in the montane belt and in the altitudinal gradient including two forests belts. Onthe contrary, the random sample did not indicate discontinuity in any of these gradients.We suggest that in spite of better representation of rare plant communities, in the sub-jective sample a considerable part of vegetation variability was omitted to emphasizedifferences between associations.Most species positively distinguishing syntaxa were more frequent in the subjective sam-ple because of preferential sampling in patches with a high number of such species. Therewere few diagnostic species with higher frequency in the random sample or with similarfrequencies in both samples. Such results were interpreted as an evidence of spreading ofthese species. Comparisons between samples revealed the expansion of heliophilous spe-cies typical for communities of Betulo-Adenostyletea and dramatic regeneration de-cline of Abies alba, Acer pseudoplatanus and Picea abies .Keywords: phytosociology, sampling method, vegetation change, West Carpathians.