جستجوی مقالات مرتبط با کلیدواژه « جنگل تراشی » در نشریات گروه « آب و خاک »

Forests have important role for ecosystem maintenance, and deforestation is one of the factors in degradation of soil quality.  In this study, using multivariate analysis, soil quality index was evaluated in three land uses including forest, grassland, and cropland at two depths of 0-10 and 10-20 cm in Sidasht of Guilan Province, Iran. The weighted additive soil quality was calculated using two methods (1) Minimum data set (MDS1) and (2) Revised minimum data set (MDS2). Also, each feature’s variance and communality and two scoring methods, namely, linear and non-linear, were compared and evaluated. In MDS2, the effects of land use on soil quality index (SQI) indicated that the mean values calculated by the non-linear scoring method was significantly more precise than the linear one. Soil quality indices in forest and grassland had the maximum values when compared to cropland. SQIW2-MDS2-NLS had the highest sensitivity index (SI= 3.14). In MDS2, the soil properties including silt, Mean Weight Diameter, pH, CaCO3 and available phosphorus were selected. Efficiency ratio of MDS2 was 80% and in soil quality assessment, MDS2 had higher efficiency than MDS1. Soil condition and change of soil management practices were reflected in MDS2 more clearly than in MDS1. Accordingly, SQIW2-MDS2-NLS method was the best means for evaluating the effects of deforestation on soil quality in the studied area.

Assessing the variation of different soil properties through the land use changes may provide useful information for land managers. The present study aimed to assess the soil quality variation due to the land use changes from dense (non-degraded) to semi-dense (degraded) oak forest and then to dry-farming in Mokhtar plain located in Yasouj region. A total number of 100 surface soil samples were collected in order to analyses of the selected physicochemical soil properties. After statistical analyses, the continuous distribution maps were prepared for all soil variables using ordinary kriging and inverse distance weighting methods in ArcGIS software (ver. 10.2; ESRI). Analyses of the average values of selected soil properties showed that after changing the land use from dense to the degraded oak forest and then to dry-farming, organic matter and CEC changed in a decreasing trend and bulk density changed in an increasing trend. Moreover, electrical conductivity, carbonate calcium equivalent and clay percentage decreased in lower contents; whereas soil pH and sand percentage inconsiderably increased. Among the soil properties, organic matter content as one of the most important soil quality indices showed a significant change with an average of 6.74%, 3.42% and 1.58% in dense forest, degraded forest, and dry-farming lands, respectively. Supporting these findings, spatial distribution maps of the selected properties revealed that the most optimum soil properties were found in the southwest of the studied area, i.e. in the soils covered with dense oak forest; whereas increasing distance to the dry-farming lands in the northeast of the area, the selected soil properties were adversely changed. According to these findings, it can be stated that wide deforesting and land use change have been led to the considerable soil quality decline and therefore if deforesting will not be stopped a huge portion of the studied soils may lose their vital capabilities.

In recent decades, site-specific management (SSM) has been specifically considered to achieve to increased input efficiency, improved economic margins of crop production and reduced environmental risks. Short-scale spatial variability of soil properties caused more necessity of SSM techniques. Natural variability of soil results from complex interactions between geology, topography and climatic factors, as well as land use change and land management strategies. Deforesting and vast land use changes are considered as the important land management strategies that have been extensively used in recent decades. Therefore, determining the effects of land use change on soil properties in conjunction with local environmental conditions and on the spatial variability of soil properties may drastically help the land use planners. Therefore, the present study was done aimed to explore the effects of oak trees deforesting in Shah-Mokhtar region in Yasouj and land use changes to dry farming on the spatial variability of nutritional elements using geostatistical techniques. The present study was conducted in a Shah-Mokhtar, north, and northwest of Yasouj, in Kohgiluyeh Province, southern Iran. Spatial variability of seven soil fertility properties, including N, P, K, Fe, Cu, Zn, and Mn concentration in soil, were examined in three land uses, including dense forest, degraded (semi-dense) forest and rain-fed lands. A total of 100 surface (0-30 cm) soil samples were collected and analyzed for the nutritional elements after preparing in the laboratory. Data were analyzed statistically and their normal distribution pattern was examined using the Kolmogrov-Smirnov test. In the geostatistical analyses step, the spatial structure of studied variables was analyzed by fitting the suitable authorized models on calculated experimental semi-variograms. The concentration of studied elements was interpolated using ordinary kriging (OK) and inverse distance weighting (IDW) estimators and finally, the spatial distribution map of each soil nutrient was prepared using ArcGIS 10.3. The results showed that the highest mean soil concentration of almost all of selected nutrients belonged to the dense forest lands and due to the land use changes to the degraded forest and then dry farming, average values of selected elements significantly decreased. Among the studied properties, soil N concentration with an average of 0.34%, 0.17% and 0.08% in dense forest, degraded forest, and rain-fed soil samples, had the most decrease caused by deforesting. Semi-variogram analyses showed that spherical model had the best performance. For interpolating the soil K and Mn concentration, IDW method and for other studied elements, OK method was efficiently used. The spatial correlation class was strong for N, Cu, and Fe; whereas a moderate class was calculated for soil P and Zn concentration. The spatial distribution maps of selected nutrients revealed that the dense forest and dry farming soils had the highest and lowest contents of soil nutritional elements. According to the findings of the present study, it can be stated that degradation of oak forest may lead to the significant decrease of soil nutritional elements, specifically soil N concentration as one of the main soil fertility quality. Therefore, it seems that not only the significant soil quality decline but also the extensive degradation of whole ecosystem and unfavorable climatic consequences will be the unavoidable results of deforesting in Shah-Mokhtar region.

The soil quality is defined as the ability of soil to function as an essential part of the human habitat. In this study, the effects of land use change (conversion of forest lands into agricultural lands) on the soil physical quality were studied in the Gilan-e-Gharb region. For this study, soil samples were collected from surface and subsurface layers of both land uses, and the peak and shoulder slope positions, in Miandar and Vidjanan catchments. Soil physical properties such as soil texture and particle size distribution, soil hydraulic conductivity, bulk density, mean weight diameter of aggregates, water holding capacity, and the soil organic carbon content were measured. The results showed that land use change of the forest to agricultural lands resulted in a sharp decline in the soil organic matter (52%) and an increase in silt and sand percentage and soil bulk density. Also, deforestation decreased the mean weight diameter of aggregates (from 0.39 to 0.14 mm in Miandar) and clay percent. It caused a reduction in the total porosity followed by a decrease of soil water holding capacity, and a decrease in the saturated hydraulic conductivity (from 10.34 to 1.86 cm/h), as well. In general, the results proved that the land use change from forest to agriculture severely decreased soil physical quality and its productivity.

Land use changes such as conversion of forest to cultivated land significantly influence soil properties and modify soil forming processes. In order to study the effects of different land use on soil physical، chemical and biological properties، five sites of mountain landforms consisting of Bijarbagh (granite parent rock)، Zemeidan (basaltic andesite parent rock)، Alisorod (phyllite parent rock)، Khorma (basaltic andesite parent rock)، and Leil (andesitic basalt parent rock)، located in part of Lahijan and Langaroud regions were selected. Each site had forest cover and tea garden next to it. A representative profile in each land use was dug and three locations around the profile were selected for soil sampling (0-30 cm). This study was conducted in a factorial arrangement and completely randomized block design (CRBD). Results indicated that land use changes and parent material had significant effect on soil physical، chemical، and biological properties. Land use changes (forest to tea garden) significantly increased clay، silt، bulk density، and free iron oxides (Fed) with mean values of 12%،10. 5%،17%، and 5. 5 percent، respectively، but significantly decreased sand، pH، organic carbon (OC)، exchangeable Ca+Mg، exchangeable K، CEC، amorphous iron oxides (Feo)، biomass respiration contents and bacterial population with mean values of 3. 7%، 11%، 17. 7%، 29. 9%، 32. 6%، 18. 3%، 24%، 34%، and 22 percent، respectively.

In order to study land degradation from the soil genesis and micromorphological perspective، ten soil profiles were dug and described on five slope positions in both forest and deforested cultivated land. The soil samples were taken from all horizons for physico-chemical analysis and micromorphological studies. Forest soils had a well developed argillic and calcic horizons and also mollic epipedon. These soils were classified as Alfisols and Mollisols. Carbonate leaching into the depth of soil profile and translocation of clays to lower layers and formation of developed soils are by no means related closely with the dense forest cover and its subsequent landscape stability and favorable leaching conditions. Dominant soil orders in this area were Inceptisols and Mollisols. In cultivated landuse، no argillic horizon was observed except in toeslope position. Absence of argillic horizon or its elimination following deforestation is one of the most important and obvious pedogenetic evidences of land degradation after land use change. Outcropping of high carbonatic layers (calcic horizon)، disappearance of mollic and formation of ochric epipedon، presence of redoximorphic features attributed to runoff in lowland، decrease of solum thickness، and change of soil color were the other pedogenic indicators for land degradation in the study area. Microscopic observations showed that granular and crumb microstructures with high porosity were converted to massive and compact ones with low porosity in the deforested area. Disappearance of clay coatings besides absence of excremental pedofeatures were the other important micromorphological evidences of erosion and land degradation.

To investigate the degree of forest degradation and the effect of land use change on selected soil quality attributes in loess-derived landforms, samples were taken from different land uses including forest, rangeland, degradated rangeland and farmland in Pasang watershed located in the Galikesh area of Golestan province (37°16'N, 55°30'E). The annual average temperature and mean precipitation of study area were 15°C and 730 mm respectively. Organic matter, pH, EC, CaCO3 and nutrients (N, P, K) as chemical indicators, hydraulic conductivity, bulk density and porosity as physical indicators and soil respiration as biological indicator were measured. The results showed that the amount of organic matter decreased three percent when it was turned from forest to farmland, and increased two percent from farmland to rangeland. The amount of CaCO3 in surface layer of deforested area was more than in the forest soils. The amount of soil N in forest and soil P and K in rangeland were higher than in other land uses. Bulk density and porosity in forest and MWD in rangeland were higher than in other land uses because of the decrease in organic matter due to farming activities. Soil respiration in forest was highest as compared to in other land uses. Difference of enzymes activities (L-asparaginase and Dehydrogenase) compared to microbial respiration indicates that enzymes activity is related to specific biological processes while soil microbial respiration basically depends on the general activity of soil microbial population. It could be concluded that amount of organic matter, soil N, bulk density, porosity, MWD, soil respiration and enzymes activities are suitable indicators for soil quality evaluation in this area.