Application of a Kohonen's self-organizing map for evaluation of long-term changes in forest vegetation

Question Can a Kohonen's self-organizing map, which is robust to non-linear relationships between variables and their non-normal distributions, be effective in patterning the data on plant communities investigated with the classical Braun-Blanquet phytosociological method based on the ordinal scale? Does the application of the self-organizing map make it possible to obtain new information from the analysed plant communities when compared to the BraunBlanquet method alone? Location The Babsk nature reserve, Central Poland. Methods The analysed data were derived from two separate series of phytosociological studies on plant communities dating from periods 31 yr apart (1960 and 1991). The data consisted of 24 quantitative sampling lists of plant species (=phytosociological releves). The releves were analysed by the application of a Kohonen's self-organizing map and the indicator value (IndVal). Results The transformations from Querco roborisPinetum to Tilio cordataeCarpinetum betuli in the vegetation in the Babsk nature reserve over 31 yr were determined precisely. Valuable new data were also obtained on: (1) significant associations of individual plant species with the previous and recent phytocoenoses, i.e. diagnostic groups of plant species for each phytocoenosis; (2) abiotic conditions (determined retrospectively in the two study periods on the basis of ecological indicators for vascular plants); and (3) the concordance of phytocoenoses with the biotope. Conclusions The Kohonen's self-organizing map method and the IndVal made it possible to efficiently identify abiotic and biotic patterns for plant communities on the basis of the data expressed in the conventional Braun-Blanquet scale.