Plant community composition and disturbance in Caspian Fagus orientalis forests: which are the main driving factors?
Shakeri, Zahed; Mohadjer, Mohammad Reza Marvie; Simberloff, Daniel; Etemad, Vahid; Assadi, Mostafa; Donath, Tobias W.; Otte, Annette; Eckstein, R. Lutz
The oriental beech forests along the southern Caspian Sea shores of Iran are characterized by high biodiversity and high ecological value. However, there is little information concerning factors governing community composition and the presence and abundance of invasive plants. In the present study we aimed to evaluate the main drivers of community composition, diversity, and establishment of invasive plants in disturbed and undisturbed Fagus orientalis communities. We sampled 104 vegetation relevés in undisturbed and disturbed sites of the “Kheiroud Investigation Forest in northern Iran and collected data on a large number of environmental variables concerning soil properties, light conditions, and topography. Data analysis consisted of a forward selection of significant explanatory variables followed by partial CCA analyses. Additionally, we carried out indicator species analysis of groups of relevés affected by different disturbance types and analyzed effects of disturbance on species richness, diversity, and evenness using general linear models. CCA results showed that disturbance, soil properties, light conditions and elevation explained 22.6% of the total variation in floristic composition. Gap and gap + grazing were the most important disturbance types affecting community composition. Disturbance had significant but rather weak effects on species richness, evenness, and the Shannon index. The most obvious effect of disturbance was on species composition, as revealed by significant groups of indicator species for different disturbance types. Most of the indicator species in grazed sites were unpalatable, poisonous, and creeping species, which are avoided by cattle. Grazing led to decreased abundance of indicator species and species characteristic of old-growth Fagus forests. The most intensive disturbance type “harvesting + gap + grazing was associated with invasion by native vascular plant species not typically found in beech forests (apophytes).