جستجوی مقالات مرتبط با کلیدواژه « تاج پوشش » در نشریات گروه « محیط زیست »

Updated information in quantitative and qualitative properties of forests are useful in describing ecosystem sustainability, and designing management and conservative plans. According to importance of canopy cover parameter in the Zagros region and cost and time consuming processes of field measurement methods, in this study performance of remote sensing and geostatistics techniques to estimate forest canopy cover of Baghan region, Marivan city, were investigated.

 First, the number of 89 plots (each 0.1 Hectare) were selected based on random sampling method. In each plot, information of tree crown and center geographic coordinates of that plot were recorded. Remote sensing method was carried out using Landsat satellite images (TM) and multiple linear regression model. After image processing, spectral values of the corresponding field plots were extracted from the original images and synthetic bands composed of vegetation indices and principle component analysis. In geostatistic method, the estimation was performed using ordinary kriging from a fitted exponential model to the semivariogram.

 The calculated variograms of canopy cover showed relatively strong spatial autocorrelation fitted by exponential models and cross-validation results showed an unbiased estimation of canopy estimation. Compared with the remote sensing method (with R2= 0/52 and RMSE= 16/47), the results indicated that Kriging model (RMSE= 9.21, R2= 0.69) showed a more accurate estimation of forest canopy cover.

The results showed that geostatistics techniques can be used as an efficient tool for mapping the forest canopy in the same regions (Zagros Forest).

 One of the most important active remotely sensed data for quantification of different attributes of forest stands is LiDAR data. A research hotspot in this subject is to estimate forest biomass using different LiDAR derived metrics.

Forest biomass was measured in 127 systematically designed 900-meter square rectangular plots in two different sites (dense and sparse sites). LiDAR data was inspected for any possible error. DTM, DSM, and CHM were extracted from LiDAR data and different metrics at plot level were calculated. For modeling, stepwise regression was applied. 

 Result showed a moderate precision for biomass estimation using LiDAR data in a way that the coefficient of determination and root mean square error (Ton/ha) for biomass estimation of leaves, twigs, branches, bole, and whole tree were 0.58-28, 0.54-23, 0.68-1.35, 0.68-1.53, .65-3.69, respectively. 

 Due to high error of determination of tree tips in broadleaves forests especially in coppice stands which have low tree height with irregular shapes; the error of the estimation of tree height using LiDar data is high. Better results demand further researches.

Urban is a unique and inconsistently defined land cover including green and grey infrastructures. Tree covers that can store large stocks of carbon. There are several ways to estimate a tree's CO2 sequestration. In this study, Google Earth images were used for mapping tree covers in the Hamadan urban scale with an area of 7422 hectares. First, a 50-meter buffer was applied on two sides of the main streets. Then, it was classified into three groups called high, medium, and low density based on the percentage of greenery. In each group, the information of 265 trees (the total of 800 trees) were recorded randomly such as allometric data and canopy diameter of trees. An Object-Oriented approach was applied to extract the area and canopies of individual urban trees. The total number of trees and their location were estimated by dividing the total of trees canopy by the average of the individual urban trees canopy. Allometric equations were used to estimate the dry biomass of tree species. Based on the results, the main species in the study area include maple, black locust, sycamore, manna ash, cypress, fir tree, and elm. The average amount of organic carbon stored in individual and street trees with asphalt and cobblestone pavement is estimated to be about 88.29 kg, which differs significantly from those with the surface covered by soil and grass (an average value of 148.79 kg). In total, the amount of organic carbon stored by Hamadan urban trees is estimated to be 1.6 tons per hectare.

Fire is one of the dynamic and effective factors on forest and rangeland ecosystems so that the evaluation and monitoring of its effects has an important role in planning and management of natural ecosystems. To determine the short-term effect of fire on vegetation changes, a burned area and a homogeneous area without fire (control) in Vanon Khalkhal region were selected. Four transects with length of 200 m were established using systematically random method and 10 plots of the 1 m2 were installed on each transect at a distance of 20 m. Vegetation sampling was done for 3 years in 2018, 2019, and 2020. The results showed that there was a significant difference in density, forage production and canopy cover percentage during the studied years. The average plant density in burned area in 2018, 2019 and 2020 years were 25.05, 31.65 and 33.91 N/m2, respectively and in the control area at the same time were 17.74, 18.17 and 22.84 N/m2, respectively. Forbs decreased from 40.1% of canopy in the control area to 23.4% in the burned area, while grasses increased from 28.2% in the control area to 59.4% in the burned area. Therefore, the fire has been effective in increasing grasses and reducing forbs. In general, Bromus tomentellus, Festuca ovina, Agropyron repensis and Agropyrun trichophorum due to their fire resistant and presence in the burned area are recommended for the rehabilitation of burned areas.

Old trees, as one of the most important genetic reservoirs, have high value for all countries. During their long life (sometimes up to several thousand years), these trees have witnessed numerous natural changes and environmental stresses and can be studied as a living history. In this research, in the framework of the national project for identifying and introducing Iranian old trees, a database of old trees of Qom province was prepared. After gathering the necessary information about the old trees from provincial colleagues and local sources during several field visits, a total of 21 tree species over 200 years old were identified that met the criteria for entry into the country's old trees database. In terms of geographical distribution, these trees were in the range of Kahak (9), Qom (3) and Dastgerd (9). Plane-tree with 10 trees was the most abundant species, followed by Berry with eight trees, and Caucasian hackberry, Willow and Cypress each with one tree. The trunk perimeter of trees recorded ranged between 3.1 to 12.5 m and their height ranged between 5.5 to 21.2 m.The oldest tree in the province was Aphine juniper with approximately 810 to 860 years old. According to the description made for each tree, the process of recording the selected trees was carried out by the supervisor of national project, and consultation with the Cultural Heritage and Tourism Organization was undertaken to register the selected trees in the form of national natural heritage.