<p>Land use change plays a pivotal role in determining the economic value of ecosystem services, especially carbon sequestration. This study investigates the long-term effects of different land use transitions on the valuation of carbon sequestration in the Kojur watershed, located in the central Alborz region of Iran, over five time periods: 2003–2013, 2003–2023, 2013–2023, 2023–2035, and 2023–2050. By integrating spatial datasets into the InVEST modeling framework, land use scenarios were evaluated comparatively to estimate the net present value (NPV). Also, to improve the accuracy of estimating the economic value of carbon sequestration, the future trend of carbon price was forecasted using ARIMA and GARCH time series models to realistically incorporate price changes in future periods into NPV calculations. The analysis included a carbon price of US$96 per tonne, a discount rate of 4%, and an annual carbon price growth rate of 0.44%. The Net Present Value (NPV) analysis revealed that the conversion of agricultural and rangeland areas to forests yields the highest long-term economic benefits, increasing from US$11,433 in the period 2003–2013 to US$63,344 by 2050. Conversely, the conversion of rangelands to rainfed croplands resulted in the most substantial economic losses, reaching US$31,158 in the long term (2050). The findings show that converting agricultural and rangeland areas to forests consistently yielded the highest long-term economic benefits, while converting from rangelands to rainfed croplands resulted in significant economic losses. These results emphasize the need for careful land-use planning and the protection of natural vegetation as essential tools in countering the negative impacts of land-use change.</p>