Estimation of Economic Value of Gas Regulation Function in Rangeland Plant Species of Different Ages (Case study: Shahriar Township)

Background and Objectives: Climate change, driven predominantly by anthropogenic emissions of greenhouse gases, presents one of the most formidable challenges of the 21st century, with far-reaching implications for ecosystems, economies, and human welfare. Carbon dioxide (CO2) is the primary contributor to this phenomenon. In this context, terrestrial ecosystems, particularly rangelands, have gained significant attention for their critical role in climate regulation through the natural process of carbon sequestration. Rangelands, covering approximately half of the world's land surface, are substantial reservoirs of carbon, storing significant amounts in both biomass and soil organic matter. Beyond carbon storage, these ecosystems provide the vital service of oxygen production through photosynthesis. However, the economic value of these regulating services -carbon sequestration and oxygen supply- often remains intangible and overlooked in traditional land-use planning and policy frameworks, leading to their undervaluation and potential degradation. Economic valuation is a powerful tool to internalize these external benefits, making the case for conservation, sustainable management, and investment in ecosystem restoration. This study, therefore, aims to quantify and estimate the economic value of the gas regulation function -specifically CO2 absorption and O2 production- provided by vegetation cover in afforested rangelands of different ages in the Shahriar region, Iran. The research focuses on key native shrub species to inform cost-effective strategies for rangeland rehabilitation and climate change mitigation.
Materials and Methods: The study was conducted in the Shahriar region, located southwest of Tehran. The area features an arid to semi-arid climate. The research employed a systematic-random sampling design to ensure representative data collection across different vegetation treatments. The studied treatments included stands of Atriplex canescens at three different age classes (11, 16, and 26 years old) and an 18-year-old plantation of Haloxylon aphyllum (commonly known as Saxaul). Within each treatment, sample plots were established (5×7 m for Atriplex and 7×8 m for Haloxylon), and above-ground and below-ground biomass were harvested. The organic carbon content of the plant samples was determined using the dry combustion method in an electric furnace at 375°C. The amount of sequestered carbon was calculated based on the organic matter content, assuming that organic carbon constitutes 50% of the organic matter (OC = OM * 0.5). The annual carbon sequestration rate per hectare was then derived for each species and age class.
The amount of CO2 absorbed from the atmosphere was calculated using the established stoichiometric ratio of 3.67 (the molecular weight ratio of CO2 to C). Concurrently, the annual oxygen (O2) production was estimated based on the photosynthesis formula and the net primary production (dry biomass) of the vegetation. For the economic valuation, a two-pronged approach was used. The economic value of carbon sequestration was estimated using the shadow price method, which reflects the social cost of carbon emissions or the potential cost of mitigation. A shadow price of $24.48 per ton of carbon (based on values for the year 2020) was applied. The economic value of oxygen production was estimated using the replacement cost method, which calculates the cost of producing an equivalent amount of oxygen industrially. All monetary values were calculated in both US dollars and Iranian Rials based on the annual average exchange rate.
Results: The results revealed that the total annual biomass production across the 480-hectare study area was 197.10 tons. On a per-hectare basis, the rangeland ecosystem annually absorbed an average of 0.65 tons of CO₂ (equivalent to 0.17 tons of carbon) and produced 0.48 tons of O₂. A comparative analysis between the different vegetation types and ages showed significant variation. The 18-year-old Haloxylon aphyllum plantation exhibited the highest carbon sequestration capacity at 0.26 tons of carbon per hectare per year, followed by the 26-year-old Atriplex canescens (0.21 t C/ha/yr), the 16-year-old Atriplex (0.19 t C/ha/yr), and finally the 11-year-old Atriplex (0.12 t C/ha/yr). A similar trend was observed for oxygen production.
The aggregate economic valuation underscored the substantial value of these ecosystem services. The total shadow value of carbon sequestered across the entire area was estimated at $2,126.44 per year. The economic value of the annual oxygen production was far more significant, estimated at $52,820.97 per year. In synthesis, each hectare of rangeland in the study area provides an annual economic benefit of approximately $114.4 solely from its gas regulation functions. When aggregated, the total annual economic value of CO2 absorption and O2 production for the 480-hectare site reached $54,947.42.
Conclusion: This study conclusively demonstrates that rangeland ecosystems, even in arid regions, provide considerable and economically valuable services in regulating atmospheric gases. The findings highlight that the capacity for carbon sequestration and oxygen production is influenced by both plant species and stand age, with older woody shrubs like Haloxylon and mature Atriplex stands showing superior performance. The substantial economic values estimated -particularly for oxygen production- challenge the conventional perception of rangelands solely as fodder sources and reposition them as vital natural capital assets. Integrating these economic values into national environmental accounting, development planning, and payment for ecosystem service (PES) schemes is crucial. Such integration can justify and incentivize investments in sustainable rangeland management, rehabilitation of degraded lands, and policies that prevent conversion and overexploitation. Ultimately, recognizing and quantifying the economic worth of these hidden services is a fundamental step toward making informed decisions that ensure ecological sustainability, climate resilience, and long-term human well-being. Future studies should incorporate soil carbon pools and the effects of different management practices to provide a more comprehensive valuation.