| چکیده انگلیسی مقاله |
Abstract Background and objectives: Prediction of species richness and diversity patterns are used to develop conservation strategies for biodiversity under regional and global environmental changes. Since modeling the distribution of plant species can provide useful and important information about identifying and introducing potential habitats of plant species, and also few studies have been done in the field of modeling species richness using environmental variables in Iran, so the study of modeling Species richness is important and necessary in the management of vegetation, which is the aim of this research. Methodology: Therefore, study of them will help to rangeland management. Such investigation was conducted in the Sorkh Grieve rangeland with an area of 2620 ha. For sampling of vegetation and soil was used random-systematic stratification method. In each slope of area was established one transect with a length of 100 meters in the direction of the height gradient and 10 plots were established along it. A total of 260 plots of 1 m2 were used. In each plot, the list of species, percentage of species cover, and percentage of litter, rocks and number of species were recorded. Three soil samples were taken from a depth of 0-30 cm along each transect and some physical and chemical properties were measured in the laboratory. Physiographic variables were determined in Arc GIS software. Climatic factors were collected for a statistical period of 15 years. Predictive climate variables in this research included annual relative humidity, average annual temperature, and average annual rainfall. The physical and chemical characteristics of the soil that were used included the percentage of moisture, sand, clay, silt, pH, EC, organic carbon, nitrogen, phosphorus, and potassium. Prediction of species diversity indices of plants was done with two methods: generalized linear model (GLM) and, enhanced regression tree model (BRT). Analysis of the importance of environmental variables for GLM and BRT models was done in the biomode2 package. R2 and RMSE coefficient of explanation was used to evaluate the models. The area under the curve (AUC) criterion was used to compare the performance of these models. Results: The results of the GLM model showed that altitude, silt, average annual rainfall, nitrogen, and average annual humidity were the most effective environmental factors affecting species richness, respectively. Also, in the BRT model, the results show that the variables of height, soil acidity, average annual humidity, and clay are the most important in species richness, respectively. The results of the GLM model showed that among the richness and species diversity indices, the highest R2 related to the richness index was 0.33. Also, the most important variables affecting this index were nitrogen, acidity, electrical conductivity, rainfall, and humidity. The results of the BRT model showed that among the examined indices, the highest R2 was related to the Shannon diversity index of 0.37. Also, the most important variables affecting this nitrogen index were altitude and clay percentage. and humidity. In general, according to the results obtained from the present research, it appears that the environmental parameters affecting richness by the GLM model include altitude, average annual rainfall, average annual humidity, nitrogen, and silt. By the BRT model was the altitude, annual humidity, acidity, and clay. The evaluation results of the two models showed that the area under the curve (AUC) of the GLM model was 0.61 and the BRT model was 0.72, which shows that the BRT model performed better in modeling species richness in the region. Conclusion: The result of this research provides good information about the distribution of plant species and affecting environmental factors on their diversity and richness for rangeland managers in the region. It is suggested that rangeland managers use the results of this research and similar research and give spatial importance to the environmental factors affecting the distribution and richness of species. |