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Changes in Distributions of Selected Vascular Plants in a Baltic Archipelago

Numers, Mikael von
Annales botanici Fennici 2015 v.52 no.1–2 pp. 101-119
geographic information systems, global warming, islands, microclimate, probability, regression analysis, topography, vascular plants, Baltic Sea, Finland
The aim of the study was to find indications of climate change by studying changes in frequency and distribution patterns of 18 plant species occurring predominantly on islands. I compared climate-related predictors of islands with species extinctions to islands with colonizations. The study was conducted on 436 islands in the archipelago of SW Finland in the northern Baltic Sea. The data were collected between 1996 and 2012 and, the historical data mainly in the 1930s. I measured predictors, including area, exposure and topographical diversity, in a GIS and used binominal logistic regression to determine which predictors exert an influence on the probability of species occurrence. The number of observations of the selected plants increased by 8.4%, but not by as much as all plant species occurring on the studied islands (10.6%). Species with a generally northern distribution in Finland increased more than thermophilic species. An unambiguous effect of climate warming on the selected plants is not evident. One of the proposed reasons for this is the small-scale topography and the mosaic of different microclimates on the islands that buffer the effect of a large-scale climate warming.