Valuation of ecosystem services in the Fandoghlo forests with emphasis on provisioning and regulating services (water yield, soil conservation, carbon storage, and timber and non-timber forest products)

Introduction
Forests are among the most valuable natural ecosystems on Earth, providing a wide range of provisioning, regulating, supporting, and cultural ecosystem services. Despite their ecological and socio-economic importance, many ecosystem services are not traded in conventional markets and are therefore overlooked in land-use planning and policy decisions. Economic valuation of ecosystem services provides an effective framework for incorporating environmental benefits into natural resource management and sustainable development strategies. The Fandoghloo Forest, located in Ardabil Province in northwestern Iran, is one of the country's most important hazelnut forest ecosystems and forms part of the Hyrcanian Forest landscape. Besides supplying timber and non-timber forest products, the forest plays a vital role in water regulation, soil conservation, and carbon sequestration. However, increasing anthropogenic pressures and land-use changes threaten these ecosystem functions. Therefore, quantifying and economically valuing these services is essential for supporting sustainable forest management.
Accordingly, this study aimed to evaluate the economic value of major provisioning and regulating ecosystem services of the Fandoghloo Forest, including timber production, non-timber forest products, water yield, soil conservation, and carbon storage.
 
Materials and Methods
The study was conducted in the Fandoghloo Forest within the Samian watershed, Ardabil Province, Iran. Three forested sub-watersheds (Aladizgeh, Soha, and Kalesar) were selected for analysis. Forest inventory data were collected using systematic random sampling. Fifteen 10 × 10 m plots were established in each sub-watershed, where all trees with DBH > 2.5 cm and height >1.3 m were measured. Aboveground biomass was estimated using species-specific allometric equations and converted to economic values using the market price method. Non-timber forest products were assessed based on hazelnut production and local market prices. Regulating ecosystem services were quantified using the Integrated Valuation of Ecosystem Services and Tradeoffs (InVEST) model. Water yield was estimated using the Budyko water balance approach, soil conservation was evaluated using the Sediment Delivery Ratio (SDR) model based on the Revised Universal Soil Loss Equation (RUSLE), and carbon storage was calculated from four carbon pools including aboveground biomass, belowground biomass, soil organic carbon, and dead organic matter. Economic valuation was performed using different approaches depending on the ecosystem service. Timber and non-timber forest products were valued using the market price method, whereas water yield, soil conservation, and carbon storage were valued using the replacement cost approach. Carbon storage was converted to CO₂ equivalent using a carbon price of USD 53 per ton of CO₂.
 
Results and Discussion
Among the provisioning services, the Soha sub-watershed exhibited the highest economic value of timber production, estimated at approximately 3.09 billion IRR ha⁻¹, followed by Aladizgeh with 2.86 billion IRR ha⁻¹ and Kalesar with 1.83 billion IRR ha⁻¹. The superior timber value in Soha is mainly attributable to its greater forest density, larger standing biomass, and a higher proportion of mature forest stands. These characteristics enhance wood volume per unit area and consequently increase the market value of timber resources. In contrast, the lower timber value observed in Kalesar reflects its relatively lower forest biomass and a greater proportion of other land-use types. The valuation of non-timber forest products demonstrated that Kalesar generated the highest economic return, with hazelnut production valued at approximately 896 million IRR ha⁻¹ yr⁻¹, whereas Aladizgeh produced an estimated 176 million IRR ha⁻¹ yr⁻¹. No commercial hazelnut production was recorded in the Soha sub-watershed. These findings highlight the considerable contribution of non-timber forest products to local livelihoods and rural economies. The assessment of regulating ecosystem services further demonstrated the critical environmental functions of the forest ecosystem. Water yield analysis using the InVEST model indicated annual economic values of approximately 169.6 million IRR ha⁻¹ for Aladizgeh, 169.2 million IRR ha⁻¹ for Soha, and 154.4 million IRR ha⁻¹ for Kalesar. The relatively similar values among the sub-watersheds indicate comparable climatic conditions, while differences are primarily associated with variations in land cover, vegetation density, and evapotranspiration characteristics. Soil conservation analysis revealed substantial differences among the sub-watersheds. The highest economic value of soil conservation was estimated for Soha (174.5 million IRR ha⁻¹ yr⁻¹), followed by Kalesar (160.5 million IRR ha⁻¹ yr⁻¹) and Aladizgeh (76.3 million IRR ha⁻¹ yr⁻¹). These results emphasize the effectiveness of well-preserved forest cover in minimizing soil erosion and sediment transport. Carbon storage assessment showed that forest land contained the highest carbon stock among all land-use classes, whereas residential areas stored the least carbon. Forest ecosystems stored substantially larger amounts of carbon in aboveground biomass, belowground biomass, soil organic carbon, and dead organic matter than agricultural or rangeland ecosystems. The estimated economic value of carbon storage was approximately 4.2 billion IRR ha⁻¹ in all three sub-watersheds because identical carbon density coefficients were assigned to each land-use category in the InVEST model.
Conclusion
The findings demonstrate that the Fandoghloo Forest provides substantial provisioning and regulating ecosystem services with significant economic value. Among the studied sub-watersheds, Soha exhibited the highest overall ecosystem service value, emphasizing its priority for conservation and sustainable management. Integrating ecosystem service valuation into forest management and land-use planning can improve decision-making and strengthen conservation policies. Although the InVEST model proved effective for quantifying ecosystem services, the results are subject to uncertainties associated with model parameterization, the use of standard coefficients, and limitations in field validation. Future studies should incorporate locally calibrated parameters, consistent economic valuation baselines, and additional ecosystem services to improve the accuracy and comprehensiveness of ecosystem service assessments.