The comparative ecology of Polystichum aculeatum, P. braunii, and P. lonchitis in Hordaland, western Norway

The comparative ecology of the three species of Polystichum in Hordaland, western Norway, has been studied. Species frequency data and environmental variables were recorded in 132 sample units from 10 different localities. The numerical methods used to analyse these data are two-way indicator species analysis, detrended correspondence analysis, canonical correspondence analysis, and Gaussian logit regression. The main floristic gradient in the data is closely related to altitude. The second floristic gradient follows patterns in precipitation and soil pH. The ordination and classification results show that P. braunii is primarily a plant of deciduous forests, P. aculeatum occurs in open or woodland habitats near the coast, and P. lonchitis favours open habitats with cool summers at either low or high altitudes. The Gaussian logit regression results suggest that low altitude, short distance from the coast, and high soil pH may be important in influencing the growth of P. aculeatum , whereas P. braunii appears to depend most strongly on high soil depth and humidity and an adequate but not too extensive snow-cover in winter. P. lonchitis is found to favour high soil and air humidity, high light intensity, and not too high summer temperatures. The results contribute to our understanding of the local, national, and European distributions of the three species. In western Norway, conditions appear to be generally favourable for P. braunii and P. lonchitis , but are clearly less favourable for P. aculeatum