Assessing the Plant Communities Changes by Effects of Vegetation Type, Physiography and Soil in Central Zagros Forest

A comprehensive study of vegetation changes requires consideration of all influential factors in the ecosystem. The Zagros forests, as one of Iran's most important forest ecosystems, contain diversified vegetation including trees, shrubs, and herbaceous species. Therefore, accurate identification of vegetation and knowledge of their ecological role can help in protecting natural resources and sustainable development. The aim of this study was to investigate the changes in herbaceous vegetation in the Hashtadpahloo forests of Lorestan province.

For this purpose, after physiognomic typing of the region, 21 multi-scales, modified Whittaker plots were randomly selected in pure oak type (Quercus brantii Lindl.), Mixed oak and Acer type (Quercus brantii Lindl., Acer monspessulanum L.), Shrubs and cushion plants type (Daphne mucronata Royle, Cotoneaster morulus Pojark), and rangeland type (grassland and rangeland species). Species richness, canopy cover of tree species, Physiographic factors such as slope, aspect and altitude were measured at 250 m2 (25×10) plots, and presence and cover percentage of each herbaceous plant was recorded at o.25 m2 plots. (0.25 × 1. Furthermore a combined soil samples were taken at 0–30 cm depths to determine soil properties. After measuring plant diversity indices such as Margalf, Mannick and Shannon Wiener indices and some physical and chemical characteristics of soil in laboratory, principle component analysis (PCA) was used to indicate the most important environmental factors affecting diversity indices in different types.

The results showed that there were significant differences among different vegetation types with respect to Menhinick and Margalef richness indices, aspect, slope, altitude, and canopy cover (p<0.05). While Simpson's and Pylo's indicators of diversity, dominance, and evenness had no significant differences among different types. The highest Menhinick and Margalef richness indices were observed in pure oak type, whereas rangeland type had the lowest richness indices and canopy cover and the highest slope and altitude. In addition, the soil variables absorbable potassium and magnesium had a significant correlation with the values of Manchinic, Margalf, Simpson, and Shannon-Weiner indices. Based on the PCA results, dominance, diversity, and species richness indices (constituent variables of the first component), edaphic factors (constituent variables of the second component), and eventually Physiographic factors such as slope, aspect, and altitude with canopy cover (constituent variables of the third component), describe the highest percentage of changes in the herbaceous community of the region respectively.

As a result, it can be acknowledged that due to the wide spread of Zagros forests, simultaneous attention to the three components of forest types, physiography and soil can favorably reflect the changes in the vegetation of the herbaceous vegetation of the Zagros, and they can be used in the management of these forests.