A comparison of environmental and vegetation variables between Carpinus betulus and C. × schuschaensis stands in Naghibdeh and Mazdeh forests (Sari, Mazandaran) and introducing a new hornbeam association

The genus Carpinus is considered as a common taxon in the temperate forests of the northern hemisphere, of which three species (Carpinus betulus, C. orientalis and C.× schuschaensis) were reported from the Hyrcanian forests of Iran. These are the main species of a number of Hyrcanian plant associations and usually appear with a high frequency. In this research, vegetation and the environmental conditions of C. betulus and C.× schuschaensis habitats were studied at the protected areas of Naghibdeh and Mazdeh forests. Data was collected using 46 relevés. Data collection and analysis were performed according to the Braun-Blanquet method. TWINSPAN was used to classify and analyze the vegetation data, and CCA ordination was used for the species-environment analysis. Based on the results, the vegetation was classified into four groups belonging to two associations: Querco castaneifolia-Carpinetum betuli Djazirei 1964 and Zelkovo carpinifoliae-Carpinetum schuschaensis ass. nov. in which the characteristic species of the new association were Carpinus× schuschaensis, Zelkova carpinifolia and Pyrus boissieriana. The topographic and soil texture variables were significantly different between the two communities. The first association was distributed on fairly low-gradient slopes (41% in average) with southwest aspect and in the soils with a higher percentage of silt, whereas the second one was established on steeper slopes (74% in average) with southeastern aspect and in the soils with more sand. The canopy percentage of the second association was significantly higher than that of the first one. These two associations are placed in the Parrotio-Carpinion Djazirei 1964.