Mansoureh Kargar; Zeynab Jafarian; Reza Tamartash; Seyed Jalil Alavi
Volume 25, Issue 3 , November 2018, , Pages 512-523
Abstract
Ecologists and environmental managers emphasize the use of predictive models to examine the species distribution patterns. The purpose of the present study was to investigate the efficiency of the generalized linear model (GLM) and generalized additive model (GAM) in determining the ...
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Ecologists and environmental managers emphasize the use of predictive models to examine the species distribution patterns. The purpose of the present study was to investigate the efficiency of the generalized linear model (GLM) and generalized additive model (GAM) in determining the relationship between vegetation and environmental factors in Khetteh Riz Rangelands. Environmental factors studied included soil characteristics, topographic factors and climatic factors. A classified-random sampling was performed and three dominant species, Bromus tomentollus, Ferula ovina, and Agropyron repens, were identified. The results showed that in the GLM model for Ferula ovina species, the variables of phosphorus content and slope were effective. For species Bromus tomentollus and Agropyron repens, the variables of annual moisture, rainfall, silt, and slope were effective. In the GAM model, the available moisture, silt and organic matter were the factors affecting the distribution of Ferula ovina. The silt, potassium, pH, and annual moisture content were the factors affecting the distribution of Agropyron repens. In addition, slope and silt were the variables affecting the distribution of Bromus tomentollus in the GAM model. The values of AUC, calculated for the GLM (0.63) and GAM (0.70), indicate the accuracy of the model to be acceptable.
Zeynab Jafarian; Farzad Ahmadi; mansoureh Kargar
Volume 24, Issue 4 , January 2018, , Pages 768-777
Abstract
This study was carried out in Bolban Abad, Kurdistan province, Iran, in order to investigate the changes in species diversity and functional diversity of vegetation under different grazing intensities. In this study, the data of three sites with different grazing intensity (low, moderate and heavy) were ...
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This study was carried out in Bolban Abad, Kurdistan province, Iran, in order to investigate the changes in species diversity and functional diversity of vegetation under different grazing intensities. In this study, the data of three sites with different grazing intensity (low, moderate and heavy) were collected. Indices of species diversity including: richness (S), Shannon (H), evenness (E) and Simpson (D) and the functional diversity index (convex hull hyper-volume (CHull), Functional Richness (FRic), Functional Evenness (FEve), Functional divergence (FDive) and index Rao (Rao) were calculated for all sites. FD package and generalized canonical discriminant analysis (gCCA) were used in R 3.1.1to calculate these indices and determine the effect of grazing intensity on diversity indices. In addition, Duncan's test was used to compare the means of grazing intensities. Results showed that the species diversity indices, species richness index (S) and Shannon (H) were reduced by increasing grazing intensity. According to the results of generalized canonical discriminant analysis, species richness showed little change in response to grazing and CHull index showed an increase under grazing. Also, species functional traits were decreased with increasing of grazing intensity.
Amirhosein Kavianpour; zeynab Jafarian; Abazar Esmaeli Ouri; Ataollah Kavian
Volume 23, Issue 3 , January 2017, , Pages 593-605
Abstract
Soil is a suitable bed for plant growth and development of vegetation, so that if it is not conserved, it will result in the nutrient deficiency, soil erosion and degradation of natural resources. In this research, the spatial variability of some chemical and physical properties of soil was investigated ...
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Soil is a suitable bed for plant growth and development of vegetation, so that if it is not conserved, it will result in the nutrient deficiency, soil erosion and degradation of natural resources. In this research, the spatial variability of some chemical and physical properties of soil was investigated in different vegetation covers (minimum, moderate and maximum) and different grazing intensities including reference area (light grazing), key area (moderate grazing) and critical area (heavy grazing) in the winter rangelands of Nasho, Mazandaran province. Soil samples were collected from 0-30 cm depth according to a systematic grid (30×30 m) and then transferred to the laboratory. Soil chemical and physical properties including acidity (pH), Electrical Conductivity (EC), caco3, bulk density, particle density, total phosphorus, total nitrogen, available potassium, organic matter, initial moisture content, percentage of clay, silt and sand, sodium, calcium, and magnesium were measured in laboratory. In addition, soil surface resistance was measured in the field with a portable penetrometer. The results of statistical analysis showed that different grazing intensities had significant effects on organic matter, available potassium, pH, EC, caco3, calcium, bulk density, initial moisture content, and surface resistance of soil. Different vegetation covers had significant effects on silt percentage, organic matter, pH, EC, calcium and initial moisture content of soil.
Zeinab Jafarian; Hossein Arzani; Mohammad Jafari; Ghavamedin Zahedi; Hossein Azarnivand
Volume 19, Issue 3 , December 2012, , Pages 371-381
Abstract
This research was aimed to investigate the relationships between dominant rangeland species and environmental factors in the Rineh rangelands located on the southern slope of Damavand Mountain. Stratified random sampling method was applied and the study area was classified to 37 sample units based upon ...
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This research was aimed to investigate the relationships between dominant rangeland species and environmental factors in the Rineh rangelands located on the southern slope of Damavand Mountain. Stratified random sampling method was applied and the study area was classified to 37 sample units based upon elevation, slop and aspect.
In the study area, 750 plots 1m2 and 75 plots 25m2 were established. One hundred and fifty soil samples were dug at the depth of 0-30 cm and 16 soil properties including pH, CaCo3, bulk density, particle density, total phosphorus, total nitrogen, absorbed potassium, organic matter, saturation moisture, soil texture, field capacity, permanent wilting point, available water capacity and water holding capacity were measured in laboratory. After collecting the climate data, 16 climate factors including average relative humidity, average rainfall, average temperature, average minimum temperature, average maximum temperature in spring, summer and annual as well as annual frost days were selected to reconstruct the missing data. IRS images including red and near-infrared bands and PAN band as well as combined bands derived from RVI, NDVI, and PCA were selected. Regression equation was developed for each species using logistic regression. Results indicated that most of the factors including slop, aspect, average minimum temperature in spring, number of frost days, average daily temperature in summer, and most of the soil factors were entered in regression models. Also, satellite data were used as effective tools in showing the presence of plant species.