Small-scale pattern and mobility of plant species in Alvar grassland

Abstract: Studies of the small-scale pattern, mobility of plant species and the effects of cattle dung deposition and decomposition on the soil seed banks and the above-ground vegetation were carried out in an alvar limestone grassland in Gettlinge, on the Baltic island of Öland, Sweden.A new method for pattern detection using transect data Patch Size Frequency Analysis (PASFRAN), was developed. Three transects, each 50 m long and consisting of 500 quadrats of 10 x 10 cm, were analysed to describe the pattern of vascular plant species (phanerogams), mosses and lichens (cryptogams), and the correlation between them. PASFRAN revealed that 42% of all significant species patches had mean patch sizes in the range of 26 - 50 cm in diameter, which match the size of dung patches. Use of PASFRAN in combination with species association analysis. is considered effective in detecting relations between species and between species and environmental factors.Multi-species patterns, analysed by PASFRAN and Detrended Correspondence Analysis (DCA), were found at sizes from 20 to 240 cm, and included both cryptogam and phanerogam species. The cryptogam and phanerogam layers were correlated and the correlation increased with increase in grain size. Results suggest interactions between cryptogams and phanerogams.Separate transect and seed bank analyses were conducted to investigate the effects of dung patches on the soil seed bank and the vegetation. A six-scale decompositon degree was developed to classify the decomposition status of dung. Depositian and subsequent decomposition of dung patches add small-scale heterogeneity to the habitat, cause changes in the soil seed bank and the above-ground distribution pattern, and contribute to seed dispersal of certain species. These factors enhance both species mobility and resource availability, and in this way contribute to the maintenance of high species richness of the grassland.The turn-around time, defined as the time a species need to reach all microsites, was proposed to quantify species mobility. It is calculated by a simulation procedure based on the year-to-year variation of the species frequency. Application of this approach to six alvar species demonstrates that the turn-around time could be a useful measure of species mobility.