Investigating the biomass and carbon stock of the tree layer in the Marivan forests (Case study: Garan and Dolah Naw forest stands)

Background and objectives: The Zagros forests vegetation area, with an area of more than 5 million hectares and providing more than 40% of the country's water, is ecologically very important. The forest covers 256,000 hectares of Kurdistan province (8.8% of the province) and makes a significant contribution to carbon sequestration. Atmospheric carbon dioxide has increased significantly in recent decades. In reducing atmospheric carbon dioxide, vegetation and the soil beneath it play a very important role. The aerial parts of trees (the ground layer) contribute greatly to biomass production and carbon sequestration. The purpose of this research was to investigate the carbon sequestration of the tree layer in two sample plots: Garan (Gargh and protected stands) and Dolah Naw (typical forests of the province).
Methodology: In order to carry out this research, two samples from Garan and Dolah Naw in Marivan County were selected. In each region, a square sample plot of one hectare was established, and with 100% statistical inventory, quantitative characteristics, including tree species, breast diameter, tree height, crown height, and crown area, were recorded. In both sample plots, the trunks and top branches of the trees were sampled, and for this purpose, three trees were selected for each species in each plot. Samples were taken from the trunk, main branches, and secondary branches of the trees. In the laboratory, the wet weight, dry weight, and carbon percentage of wood samples were calculated by burning the dried samples in an electric furnace. Then, the above-ground biomass of trees was calculated using allometric equations, and finally, the carbon stock of all trees was estimated. The quantitative parameters and the average of the above-ground biomass and carbon stock were compared. An independent t-test was used to compare quantitative parameters and carbon storage in the two sample plots of Garan and Dolah Naw.
Results: The findings of the research showed that the amount of biomass on the ground in Dolah Naw and Garan sample plots was 45.3 and 41.4 tons per hectare, respectively. In the Dolah Naw sample plot, two species, Quercus brantii and Q. infectoria, with a total of 24.68 tons per hectare, accounted for 54.5% of the biomass of the tree layer. The carbon stock of the tree layer in Dolah Naw and Garan samples was calculated as 22.4 and 20.3 tons per hectare, respectively, and the results of the independent t-test showed a significant difference between the quantitative characteristics of diameter at breast height, total height, tree crown area, biomass, and carbon storage in the two sample plots. The contribution of the Q. infectoria species to carbon sequestration in Dolah Naw and Garan samples was 6.48 and 9.13 tons per hectare, respectively. On the other hand, the averages of quantitative characteristics, including tree height (3.7 meters), diameter at breast height (15.79 cm), and crown area (6.77 square meters), in the Dolah Naw sample plot were greater than those in the Garan sample plot.
Conclusion: The general results showed that the carbon storage of Dolah Naw stands (wood biomass with slightly higher forest characteristics) was greater than that of Garan forest. To optimally manage these forests and increase carbon dioxide storage, it is essential to manage and control the factors of forest destruction (such as the development of agriculture under the forest canopy, intensive grazing, excess livestock capacity, fire management and control, coal mining, and other factors) and take action in degraded areas to promote reforestation and afforestation using native species (Quercus brantii, Quercus infectoria, Quercus libani, and Pistacia atlantica) in the destroyed stands.