Classification of forest communities (co-)dominated by Taxus baccata in the Hyrcanian forests (northern Iran) and their comparison with southern Europe

Abstract

English yew (Taxus baccata) is one of the few gymnospermous species present in the Hyrcanian forests, and it is listed as a rare and endangered species prone to extinction in Iran. This study aims to determine the ecological capability of Taxus baccata in the Hyrcanian region by identifying the diversity of plant communities dominated by this species, and to compare their floristic composition with the Taxus communities of southern Europe (Sicily, Corsica, Sardinia). We collected 408 releves in the central and eastern part of the Hyrcanian forests. The classification of plant communities was performed using TWINSPAN. Phi-coefficient index, constancy ratio, and the ratio of average cover were used to determine diagnostic species in each vegetation unit. The expert system language of the JUICE program was applied to create formal definitions for syntaxa. The relationship between species and environmental factors were investigated with DCA. The environmental differences among the syntaxa were also tested with one-way ANOVA. Sums of constancy and average species cover of the diagnostic species of classes according to the EuroVegChecklist were computed. We distinguished five associations within three alliances. Of these, two associations and one alliance are new for science. Annual precipitation, elevation and annual temperature which are affected by elevational as well as longitudinal gradients were found to be important factors affecting the diversity of Hyrcanian Taxus communities. The constancy sum of diagnostic species was the highest for the class Carpino-Fagetea sylvaticae in all Hyrcanian and European units except for one Taxus community in Sardinia. We conclude that the Hyrcanian and southern European Taxus communities are similar in their floristically and ecological properties. Yew communities in the central Hyrcanian forests are associated with humid temperate diagnostic species, while semi-humid temperate plants are frequent in the eastern Hyrcanian forests, similar to the yew communities in southern Europe.