Effects of conservation on the diversity components and structure of plant communities in the Golestan National Park and surrounding areas

Heavy grazing including activities can threaten plant species diversity and selective grazing of livestock can lead to a steady rise in non-palatable vegetation and, as a consequence, the dominance of a few species in a region (Anderson and Hoffman, 2007). To assess the impact of environmental factors on different ecosystem species, diversity measurement methods can be used. In fact, the species diversity in an ecosystem reflects the impact of various environmental factors on ecosystems and their status (Hasenauer et al., 2000). Nowadays, overgrazing can be observed in meadows and pastures surrounding the Golestan National Park (Akhani, 2005) and this could become a serious threat to the ecosystem of the region.
Considering the importance of the above, In order to understand the different contributions of various components of diversity and the composition of plant communities in different habitats under a grazing gradient, an experiment was conducted in Golestan National Park (the Park) and surrounding areas during 2011-2012. To this purpose, four habitat types were selected consisting of: un-destroyed habitat in the Park, abandoned habitat (areas of the Park that have been uninhabited since 1963), habitat under seasonal grazing (Ghorkhod Protected Area and surrounding areas) and heavy grazing in villages surrounding the Park. Six replications were determined for each habitat. Species richness and percentage of canopy cover were measured using 1 m2 sampling plots at each replication. In this experiment, SHE analysis was used to separate the components of diversity. In addition, to gain more awareness about species composition of the different habitats correspondence analysis was used for ordination.
The results showed that diversity and species richness reduced with increased grazing intensity in the study habitats. In addition, the frequency distribution of species in the un-destroyed and abandoned habitats and in habitats under seasonal grazing was fitted to a log normal model, and for the habitat with heavy grazing it was fitted to a logarithmic series model. Based on the logarithmic series distribution model most species have been observed in lower abundance and a few species have a maximum frequency which underscores the dominance of a small number of plant species. This is the reason why plant species composition in habitats under heavy grazing tends towards the non-palatable species. In an experiment conducted by Todd and Hoffman (1999) heavy grazing led to reduction of palatable species. In addition, the composition of plant species from different habitats was various and the similarities between species and families were different in the diverse habitats: The species and families recorded in habitats under heavy grazing bore the greatest similarity to species and habitats belonging to seasonal grazing, abandoned and un-destroyed habitats, respectively.
The results show that excessive exploitation by grazing has led to the reduction of plant species diversity and a change in the composition of plant communities in the Golestan National Park and its surrounding area. Therefore, more attention to this destruction of the genetic reservoir would appear to be necessary.