جستجوی مقالات مرتبط با کلیدواژه « آنالیز چند متغیره » در نشریات گروه « آبخیزداری، بیابان، محیط زیست، مرتع »

Grazing effect on vegetation cover and soil factors in natural environments is inevitable. The present study was conducted to investigate the effect of grazing on soil factors and distribution of plant species in grazed and non-grazed areas in rangelands of western parts of Hoz-e-Soltan Lake, Qom. Systematic-randomized sampling method was used alongside of 4 transects. Adjacent to the transects 10 plots of 4 square meters were put within the exclosure and its outside. In each plot, soil samples from 0-30 cm depth were taken. The list of plants and their canopy cover were determined for each study site. Also, the properties of acidity, electrical conductivity, soil texture, lime, percentage of phosphorus, sodium, potassium, calcium, Magnesium, chlorine, carbonate, bicarbonate and nitrogen were measured. Using the CANOCO software, ordination of the plant communities was drawn according to the characteristics of the soil by conventional comparative analysis (DCA, CCA). The results showed that livestock grazing have impact on the relationship between vegetation and soil in this area. As the results showed, nitrogen in addition to salinity and sodium had a significant effect on vegetation changes in the grazed area. In fact, proper grazing management increases the amount of nitrogen in the grazed area. Which could be count on as a soil improvement tool in terms of nitrogen content increase. More nitrogen in its turn increases the presence of two important species namely Suaeda aegyptiaca and Artemisia sieberi. Results suggest that as livestock grazie from the shrubs, as the dominant plants of the area, the deterioration of other plants is prevented and the quality of forage production is increased. Therefore, by managing livestock grazing in the studied area and other similar steppe regions, improvement of vegetation composition gets possible and consequently soil properties improves in the long term.

The aim of this study was to investigate the effects of topographic, edaphic, climatic and landscape metrices on the distribution of plant communities in the altitude gradient of Moghan-Sabalan rangelands in Ardebil province. To determine and study the ecological species groups, 28 sites and 840 one square meter sampling plots were samples by the random systematic method. To determine soil factors, soil samples were collected from each site from 0–15 and 15-30 cm depth and physicochemical parameters were measured at the lab. Using TWINSPAN, vegetation of the study area was classified and then PCA and CCA were used to investigate the relationship between species and environmental factors. According to TWINSPAN results, four ecological groups were identified. The first ecological group is located in the opposite direction of elevation, slope, rainfall and patch area gradients, and the same direction with pH, clay and dispersible clay (the first depth), bulk density, edge density and patch area (coefficient of variation). The second and third ecological groups are located in the interfaces of the first and fourth ecological groups in terms of plant composition and environmental conditions. These two groups prefer the middle elevations. The fourth ecological group at the end of the elevation, rainfall, slope, patch area and inverse direction of clay and dispersible clay (the first depth) and typically prefer high altitudes and light texture soils.

Studying species diversity and analyzing of the relationships between plants, environmental factors and disturbance play an important role in studying the dynamics and management of ecosystems. We studied the species diversity patterns in relation to some physiographic factors and grazing along an altitudinal gradient of 1000 meters and at different altitudes with 100-m intervals. The Margalef, Sheldon, and Shannon-Wiener indexes were used to assess richness, evenness and diversity, respectively. Partial Canonical Correspondence analysis was used to investigate the relationship between vegetation, physiographic factors (with an emphasis on altitude) and grazing. The study of the relationship between altitude and grazing showed a significant correlation between these two factors (P <0.01, R2 = 0.55). Results showed that increased species diversity and richness was observed at lower altitudes up to 2200 meters above sea level; however, at the altitude above 2200 m, the species diversity and richness decreased. This result is consistent with the mid-domain effect (MDE) hypothesis. Overgrazing at low altitudes has led to a shift in vegetation toward annual and ruderals species. The areas with intermediate grazing had the highest richness and diversity and the areas with high and low grazing intensity had the lowest richness and diversity. This result is consistent with the intermediate disturbance hypothesis. Species evenness also increased with increasing grazing intensity, although these changes were not significant (P> 0.05). Therefore, the changes in species diversity along ecological gradients cannot be evaluated without considering the grazing intensity.

Knowledge of the physiological characteristic of tree and shrubs species and their adaptability to environmental factors is an important issue in species selecting for tree planting projects in water scarcity regions. Therefore, this investigation try to examine the chlorophyll content and stomatal conductivity in various species of trees and shrubs. The effects of environmental factors are also evaluated. The statistical population consisted of 12 trees and shrubs species that their chlorophyll content was measured by using “Chlorophyll Content Meter” and stomatal conductivity was measured in 10 days by using “Porometer” device. Air temperature and wind speeds were recorded at each measurement with a portable “Testo ”. Environmental data correlation with vegetation parameters were analyzed by multivariate data analysis. The results revealed that chlorophyll content and stomatal conductivity in different common species in urban green space have a widespread range. Nerium has the highest chlorophyll content and Ceasalpinia has the lowest chlorophyll content. Likewise, Fraxinus and Ceasalpinia have the highest and lowest stomatal conductivity. Stomatal conductivity rate in the morning is higher than any other time in a day. While, Ceasalpinia and Nerium show the highest negative correlation with temperature, Albizia and Cersis show the highest positive correlation. Wind increase stomatal conductivity in Pyrocantha and Robinia and decrease in Olea and Morus. It has less effect on other species.

Knowledge on the effects of environmental factors affecting the distribution of plant communities provides information about ecological characteristics of species as well as the conditions of vegetation habitat. The current study was performed in Halejerd, west of Tehran to investigate the effects of environmental factors on the distribution of plant sites. This research was aimed to identify the most effective factors on the establishment of plant sites. After identifying the region, vegetation types were selected and sampling was done by random-systematic method. Minimal area method was used to determine the plot size. Five vegetation types were identified. Three soil profiles were dug in each vegetation type and two soil samples were taken from two soil depths. Soil characteristics including soil texture, pH, electrical conductivity, potassium, nitrogen, phosphorus, organic matter, organic carbon and TNV were measured. Result showed that the studied plant sites differed in terms of soil characteristics and the factors of each component were characterized. According to the obtained graph and considering variable coefficients, the content of silt and potassium increased in the first component while in the second component the content of sand and nitrogen increased. Also, soil chemical and physical characteristics are involved in the separation of vegetation types. Important and effective physical and chemical characteristics were sand, silt, potassium and nitrogen, respectively. In order to analyze the environmental factors (soil characteristics) associated with the distribution of plant sites principal component analysis (PCA) was used. Results showed that there was a special relationship between the distribution of different vegetation types and soil characteristics. Also it was found that edaphic factors including soil texture, potassium and nitrogen were more effective in species distribution.

Knowing of vegetation spatial models related to nutrition elements variations and their sources can help us in suitable management of Basin. So، this research was investigated the relationship between macro and micro elements with indicator species in Lar basin. First، the land units were obtained in study area and sampling was done by randomly-systematic method in each land unit after field surveying. Size and number of plots was obtained based on minimal area and statistical method respectively. Kind of species for sampling was determined by TWINSPAN analysis. Then vegetation percentage and frequency was recorded in each plot. Soil and plant sampling was done in each plot and soil physico-chemical characteristics and nutrition elements was calculated by ICP in lab. Data analysis was done by analysis of variance، regression and correlation coefficient in SAS 9. 1 Software. The relation between soil elements and species was determined by DCA and CCA analysis in Canoco for Win4. 0 Software. The results showed that the plants nutrition elements were more than the soil. The relationship between the nutrition of different species and soil absorbable elements wasn’t constant and depended on site condition such as moisture، pH، chalk، organic matter and texture. Also، the other elements in soil were affected on plant-soil relations.

Knowledge of environmental factors and their effects on vegetation is necessary for sound rangeland management. In this study we applied multivariate analyses to determine the effects of soil and topography on upland rangeland vegetation and also the amount of variance explained by them. 30 homogenous units according to slope, aspect and elevation were determined and then vegetation was sampled in 320 plots (1x1 m). This was done along transects and cover percentage of each species present in each plot was recorded. Also, up to 3 soil samples were taken in each homogenous unit. Result of cluster analysis showed a total of 12 sub-association of vegetation and then we described them according their species composition. Thereafter, results of ordination methods showed that two measured environmental factors significantly influenced vegetation. Here we first found five groups of species in DCA analysis. Then using CCA we found how these groups were related to specific environmental factor. Also 12 sub-association of vegetation showed some correlation with environmental factors. Variance partitioning showed that 57.4% of vegetation changes in this mountain rangeland was explained by soil properties and this was only 39.4% for topographic factors. The combined effect of two factors was responsible only for 3.2% of vegetation changes.

The original aim of this research was investigation on relationship between climatic and physiographical factors and plant species to determine the most effective factors of separating vegetation types in Rineh Rangeland. Random Equal-stratified sampling procedure was used for vegetation sampling. 10-20 quadrates were located in each homogenous unit randomly. Floristic list, density and canopy cover percentage were determined in each quadrate. Elevation, slop and aspect were physiographical factors. Mean minimum temperature, mean maximum temperature, mean daily temperature, mean relative humidity, month and annual precipitation and freezing days were selected for analysis. Incorrect data was reconstructed by correlation and normal ratio methods (Mahdavi 1374). In order to find effective analysis were used, both classification included CA and TWINSPANM classification and ordination techniques included PCA, DCA, and CCA. The TWINSPAN classification of the 75 samples sites have resulted ten groups. Using PCA 99.348 % of variance was accounted using the first three principal components. DCA axis 1 showed significant correlations with climatic factors and elevation, this suggest that DCA axis 1 represented climatic and elevation factors gradients. CCA analysis explained 16% of the cumulative variances. This result suggest that other factors affect vegetation such as soil and biological factors then should be studied in future researches.