The Effect of Afforestation with Diverse Species on Carbon Sequestration in Semi-Arid Areas of Kurdistan Province (Case Study: Sanandaj)

The occurrence of climate change, desertification, and destruction of natural resources necessitates the use of afforestation to protect soil, water and atmospheric carbon sequestration (3). Arid and semi-arid areas are suitable options for conducting carbon sequestration operations. In many parts of the world, forestry projects in semi-arid areas have been widely used to restore destroyed ecosystems and control soil erosion (39). Numerous studies in Iran and worldwide have shown that afforestation with various species has a positive impact on the process of carbon sequestration and improving soil quality (3, 14, 31, 9, 16). The purpose of this research is to examine the impact of an afforestation project on the reserve and carbon sequestration levels in the 40-year-old afforested regions of the Seranjiane region of Sanandaj. Due to the differing carbon sequestration potential of tree species, this research is aimed at evaluating the capacity of forestry with broad-leaved, coniferous, and mixed species to sequester carbon in the ecosystem.

Seranjiane Forestry - Dushan with an area of 96.7 hectares is located in the geographical longitude of 47° 0' 20" to 47° 1' 25" and latitude of 35° 13' 22" to 35° 14' 4" (Fig 1). Saranjayaneh Forest Park is a type of hand-planted forest park, which includes 40-year-old tree stands of pure Fraxin, pure Cupressus and mixed Fraxinus and Robinia. The control area is a natural rangeland that is next to the afforested area and has similar climate conditions and topography. The statistical method for determining sampling volume was used to calculate the appropriate number of sampling plots. The minimum area method was used to determine the appropriate plot size. Random-systematic sampling method was used to sample tree cover in each forest plot in the 6 plots measuring 20 x 10 square meters. In forestry stands and nearby rangeland, soil (0-30 cm depth), aboveground, underground, and litter biomass were sprayed using a random-systematic method. The amount of carbon sequestered in biomass (aerial and underground), litter, and soil was measured. The data was analyzed using one-way analysis of variance (ANOVA) and Duncan's test by SPSS version 24 software.

The findings revealed that afforestation has resulted in an increase in organic carbon storage compared to rangelands. The amount of organic carbon stored in rangelands, which is 49.05 tons per hectare, differs significantly from other treatments (Table 1). The cypress stand had the highest amount of organic carbon storage, which was 95.26 tons per hectare. The total amount of organic carbon stored per unit area in two mixed stands (81.61 tons per hectare) was not significantly different from that in sparrow's tongue (74.84 tons per hectare). Comparing the average carbon sequestration in underground biomass revealed that the mass of cypress with a carbon reserve of 0.25 tons per hectare exhibits a significant difference with a mixed mass of Fraxinus and rangeland at a level of 1% (Table 2). There was no discernible difference in the carbon reserves of the underground biomass between the other treatments and the rangeland. The comparison of the relative share of carbon sequestered in different forests revealed that there has been a significant increase in the average organic carbon storage compared to rangeland in all three forests. The highest amount of soil organic carbon (157.17 tons per hectare) was observed in the cypress forest. Calculating the Organic Carbon Reserves of the soil, it was calculated that there were 50.79 tons per hectare in the mixed mass and 27.76 tons per hectare in the Fraxinus mass. Rangeland was associated with the lowest amount of soil carbon deposition (48.50 tons per hectare). Fraxinus and two mixed stands had no significant differences in soil organic carbon reserves. The soil, plant biomass, and litter components in afforested stands and control rangeland revealed that the soil was the most important area for accumulating organic carbon storage in all the study treatments (Table 3).

This research revealed that afforestation in the studied area has resulted in a significant increase in carbon sequestration in aerial, underground, and litter biomass. Carbon sequestration rates for Sanandaj in cypress, mixed cypress, and Fraxinus stands are 1.15, 0.82, and 0.63 tons per hectare per year, respectively. The results of the present study showed that the amount of carbon stored in the aboveground and underground parts of the forest stands was significantly higher than the control rangeland, but there was also a significant difference between the forest stands in terms of the carbon sequestration capacity in the aboveground parts. The highest biomass carbon storage was observed in the C. sempervirens stand, and the mixed stands and F. rotundifolia had similar capacities in this respect. This is due to the C. sempervirens species' resiliency to cold and drought (24) and the low number of losses experienced by the C. sempervirens stand compared to the mixed stand and F. rotundifolia. This has resulted in an increase in plant biomass in the C. sempervirens stand and, consequently, an increase in the rate of carbon sequestration per unit area. Quantitative characteristics indicate that the C. sempervirens species is superior to the R. pseudoacacia species (20), as shown by research. In the soil sector, afforestation has also caused a significant increase in carbon sequestration compared to pasture, which was calculated to be 82.1% in the C. sempervirens stand, which was higher than in the mixed and F. rotundifolia stands. The amount of soil carbon sequestration in the mixed stand was 64% and in the F. rotundifolia stand was 51%. The amount of soil organic carbon reserves in ecosystems is affected by two factors: organic carbon input through plant biomass and organic carbon loss through decomposition (34). The greater the production capacity of aboveground and belowground biomass in different species, areas, and habitats, the greater the carbon storage in the tree trunk, litter, and soil. If the rate of factors leading to decomposition and loss of carbon from trees, litter, and soil is lower, the survival of carbon stored in ecosystems will increase and the amount of carbon sequestration will increase (21).Based on the findings, the accumulation of litter on the soil surface in the C sempervirens stand is deemed the primary factor responsible for elevating soil carbon sequestration. The C. Sempervirens species is the most suitable species for carbon sequestration in afforestation, as it can quickly grow, produce high litter volume, meet ecological needs appropriate for the region, and can withstand drought and cold condition. Planting trees in arid and semi-arid areas can lead to carbon sequestration in biomass (airborne and underground), litter, and soil, as evidenced by this outcome. In the study area, coniferous plants have a more significant impact on carbon sequestration than broad-leaved plants during afforestation. The research found that mixed cultivation has a more significant impact on carbon sequestration than pure Fraxinus cultivation because of the diversity of composition. Different tree species have different potentials for carbon sequestration. In the semi-arid regions of Kurdistan province and similar regions, coniferous species are the preferred option for carbon sequestration rates over broad-leaved species due to their lower water requirements.