عنوان مقاله [English]
Background and aims: One of the most important issues in the plant ecology is vegetation classification. Statistic and unbiased sample are the bases of quantitative plant ecology. This study profited stratified random sampling. Each strata comprise a physiognomic vegetation type in study area. This study aimed to classify vegetation types, to investigate plant diversity and to assess the most important factors that affect distribution of vegetation communities.
Material and methods: The study area, Perk forest, was located in the south west of Khorramabad with 2920 ha area. Stratified random sampling method was used to collect data. Based on the field observation (differences in physiognomy and vegetation structure), four distinct vegetation types including, Quercus-Graminae, Quercus-Acer-Pyrus, Quercus-Astragalus-Daphne, and Quercus-Achantolimon-Lonicera were recognized in this region. Sampling was performed in the spring and summer 2011, and a total 29, 400 m2 plots and 40, 4 m2 were established.
Two-way indicator species analysis (TWINSPAN) and Detrended Correspondence Analysis (DCA) methods was used. Four distinct ecological groups were identified in this region using these two methods. Indicator values for each species in different ecological groups were determined. Then in each ecological group species richness, Simpson and Shannon-Wiener's indices of diversity and Smith and Wilson's index of evenness were computed. Among numerous measured variables the most important physiographic variables were determined by principal component analysis (PCA) method.
Results: Based on the results indicator species of the first, second, third, and fourth groups include (Acer monspesulanum L.، Bromus tomentellus L ، Colchicum persicum Baker ، Euphorbia orientalis L and Pyrus syriaca Boiss) (Euphorbia sororia Schrenk ، Minuartia hamate (Hausskn.) Mattf ، Quercus brantii Lindl and Valerianella vesicaria (L.) Moench) (Agropyrun repens (L.) P.Beauv ، Daphne mucronata Royal ، Echinops orientalis Trutv ، Polygonum aviculare L ، Stachys ballotiformis Vatke and Thalictrum sultanabadense Stapf) (Acantholimon brachystachyum Boiss. in Bunge ، Acanthophyllum kurdicum Boiss. & Hausskn. in Boiss ، Ferulago angulata (Schlecht.) Boiss and Lonicera nummularifolia Jaub. & Spach) respectively. Based on the results the highest values of species richness and diversity and evenness were assigned to the first group and the highest evenness value was assigned to the second group. There were significant differences in species richness, Simpson and Shannon-Wiener's index of diversity, and Smith and Wilson's index of evenness based on Analysis of variance (ANOVA) results, among different ecological groups.
Conclusion: it is concluded that the results of Two-way indicator species analysis and Detrended Correspondence Analysis by using unbiased sample correspond to vegetation composition and physiography of terrain and the changes in environmental conditions lead to changes in vegetation composition in distinct ecological groups.The elevation was the most important factors in constructing distinct ecological groups, based on the results of principal component analysis (PCA) method.