Defining the habitat niche of Sorbus torminalis from phytosociological releves along a latitudinal gradient
Rasmussen, Kristine Kjørup; Kollmann, Johannes
Vegetation science has successfully focused on classification and mapping of plant communities. However, the existing large collection of relevés and related methods can also be applied for inferring the habitat niche of individual plant species based on their community context. This might be especially useful as a preliminary investigation of ecological factors important for survival and distribution of individual species on a large scale, and for species which are hard to study experimentally as for example longlived tall woody plants. In this study we analyse the community context of the rare European tree Sorbus torminalis and use the results to find the most important ecological factors describing its habitat niche. Relevés containing the study species were collected from Switzerland, Germany and Denmark, representing a gradient from a more central part of its submediterranean range to the northern border of distribution. The data set was analysed by TWINSPAN clustering and detrended correspondence analysis, and the results were correlated with plot and site descriptors as well as mean Ellenberg indicator values. The community context of sites containing S. torminalis showed a range from calcareous beech forest (Cephalanthero-Fagenion), hornbeam forests (Carpinion) and oak forests (Quercetalia robori-petraeae and Quercetalia pubescenti-petraeae), to tall-shrub (Rhamno-Prunetea) and dry grassland communities (FestucoBrometea). The main coenocline of the data set was correlated with the Ellenberg indicator values for light, moisture and nutrients which separate grasslands and shrublands from the forest communities. There was no shift in habitat niche along the latitudinal gradient, but the amplitude of the niche was found to be widest around 50° . We also discuss the methodological advantages and pit-falls of this promising approach in vegetation science.