Syntaxonomy and gradient analysis of common yew (Taxus baccataL.) communities in eastern Hyrcanian forests, northern Iran

Abstract

AbstractThe aim of this study is to outline syntaxonomical diversity of yew (Taxus baccataL.) in the eastern of Hyrcanian forests, Jahan Nama Protected Area (JNPA), and to identify their main environmental gradients. Vegetation units were classified using modified TWINSPAN (two‐way indicator species analysis) and were translated into syntaxonomic system. Syntaxa were determined by re‐arrangement of each relevé based on diagnostic species. Syntaxa were finally evaluated by diagnostic species and environmental parameters according to phi‐values and analysis of variance, respectively. Detrended correspondence analysis was used to visualize the dissimilarity of syntaxa and their relationships with the environmental factors. The classification of JNPA yew forests resulted in six vegetation units. These patterns were translated into four associations (Asso.), two sub‐associations (Subasso.) and two variants (Var.). (Asso.1)Fago orientalis‐Taxetum baccataeis found in northern aspects with lower slopes and higher soil depth; (Asso.2)Aceri velutini‐Taxetum baccataeis occurring in the moderate but rocky slopes. Asso.1 and Asso.2 are the same in altitude and involvingCarpinus betulusas a co‐dominant. (Asso.3)Carpino betuli‐Carpino orientalis‐Taxetum baccataedeveloped in the intermediate slopes. (Asso.4)Carpino orientalis‐Taxetum baccataeappeared in the highest slope of northeast and northwest aspects with shallow soil depth. The main factors determining the species composition of the JNPA syntaxa are slope, eastness, elevation, and clay content. Finally, we concluded that yew could be associated by different plant species with different ecological desirability in the eastern of Hyrcanian forests. This study also provided the specific pattern of forest community type betweenC. betulusandC. orientalisin the JNPA using species combination concept.