حسان علی

Today, reforested stands are one of the most important sources of forest carbon storage and one of the factors that reduce the process of destruction of natural areas. Above-ground biomass (AGB) plays an essential role in sustainable forest management and reducing global warming and is an important source of information. Allometric equations are an important tool for quantifying above-ground biomass in forests. In recent years, remote sensing techniques using non-parametric methods such as the Random Forest algorithm have been widely used to estimate forest tree biomass. In this research, the ability of Sentinel 2 data using the random forest algorithm to estimate the above-ground biomass of Arabdagh reforested stands in Golestan province was evaluated. In this study, 180 circular sample plots with an area of 400 square meters were measured using the cluster sampling method and the diameter at breast height (DBH) and tree height (H) were measured. Also, the exact coordinates of the centers of the sample plots were recorded using DGPS. Then, using the prepared allometric equations, the above-ground biomass of trees was calculated. In this study, Sentinel 2 pre-processed radiometric and geometrical data were used, and based on that, different vegetation indices were prepared. In the implementation of the random forest algorithm, the relationship between the characteristics of biomass as a dependent variable and the spectral values of vegetation indices as independent variables were investigated. Modeling was done using 75% of sample plots (135 sample plots) with random forest algorithm and validation of estimates was done using 25% of sample plots (45 sample plots). The results showed that NDVI and GNDVI indices had the highest correlation in the estimation of above-ground biomass and the random forest algorithm with 310 trees and 5 predictors and the percentage root mean square error of 35.83% and the coefficient of determination 0.51 was able to estimate the above-ground biomass of Arabdagh reforested stands. Also, the results showed that using the data of Sentinel 2, the random forest algorithm has estimated the above-ground biomass of trees more than the actual values. There is no significant difference at the 95% probability level between the estimated and real above-ground biomass values (p-value > 0.05). Also, among the independent variables used. The results of this research showed that Sentinel 2 data has been able to estimate the above-ground biomass of Arabdagh reforested stands with acceptable accuracy. According to the results of this article, it can be said that the information of the main bands and spectral indices played an important role in the estimation of above-ground biomass.

Accurate measurements of above-ground biomass and selection of the most appropriate allometric equations are major challenges in evaluating tree biomass. Therefore, the development of allometric equations for each species is essential for accurate above-ground-biomass estimation. This study aimed to estimate the stem biomass of three conifers Pinus brutia, Pinus pinea, and Cupressus sempervirens in Arabdagh reforest using the allometric equations. In order to model the stem biomass, three main characteristics of diameter at breast height (DBH), height (H) and wood density (𝜌), were used separately and in combination to fit the equations. The results of this study showed that if the DBH alone was available for the Pinus brutia, the obtained equation had the highest coefficient of determination (R2) (0.90). By adding H and 𝜌 into DBH in stem allometric equation, the R2 increased by 9% and RMSE % decreased by 12.63%. For Pinus pinea, the results showed that if the DBH was available the obtained equation had the highest R2 (0.99). By adding H and 𝜌 into DBH in stem allometric equation, the R2 and RMSE % values did not improve. The results of Cupressus sempervirens, showed that if the DBH was available the obtained equation had the highest R2 (0.98) and the lowest RMSE% (9.81%). By adding H and 𝜌 into DBH in stem alometric equations, the R2 increased by 1% and RMSE% decreased by 3.59%. The results can be used to estimate the above-ground biomass with these species in similar climate and soil conditions at a local scale.

Knowledge of forest inventory and estimation the exact volume of trees is one of the important features in planning for forest resources. The form factor is one of the most important factors in determining the exact volume of trees. To estimate the actual volume of trees, the form factor must be calculated. The aim of this study, determination of form factor for three species (Pinus brutia, Pinus pinea and Cupressus sempervirens) in the Arabdagh reforests, and comparison of the real form factor with the natural, artificial, and Hohnadl factors.

In this research four types of form factors including real, natural, artificial, and Hohnadl factors for three species (Pinus brutia, Pinus pinea and Cupressus sempervirens) were evaluated in the Arabdagh reforests, Golestan province. For this purpose, 39 trees )13 trees for each species) randomly selected in different diameter at breast height classes from 7.5 to 42.5 cm (2 trees of each diameter class). In each tree, height, diameter at breast height (D.B.H) and diameter at 0.1, 0.3, 0.5, 0.7 and 0.9 of tree height were measured, then 2-meter length logs from every tree were cut and separated and their diameter at two tops of 2 m length logs were measured. In addition, the height and diameter of the clog and the length of the tree was also measured. To calculate the exact volume of the trunk from the sum of 2 m long logs volumes and log using the Smalian formula. Then the form factors (real, natural, artificial, and Hohnadl) were calculated for every 3 species.

The results showed that true, natural, artificial, and Hohnadl form factor value were 0.49, 0.49, 0.41 and 0.45 (Pinus brutia) respectively. In addition, there was a significant statistical difference between artificial with true form factor (α = 0.05), but There was no significant difference between natural and Hohnadl form factor with the true form factor. The form factors (Pinus pinea) using real, natural, artificial and Hohnadl formulas was obtained 0.51, 0.47, 0.41 and 0.45 respectively. There was a significant difference between the real form factor with artificial and Hohnadl form factors. However, there was no significant difference between natural form factor with the real form factor. The form factors (Cupressus sempervirens) using real, natural, artificial and Hohnadl formulas were 0.55, 0.53, 0.48, and 0.48 respectively. There was a significant difference between the Hohnadl and real form factor. However, there was no significant difference between the real, natural and artificial form factors

According to the results of this research, we can conclude that the natural form factor can be used as an appropriate form factor for Pinus brutia, Pinus pinea, and Cupressus sempervirens, and Hohnadl form factor for Pinus brutia and artificial form factor for Cupressus sempervirens can ability replace the real form factor.