Adopting cost-effective restoration portfolios for multi-objective ecosystem service optimization: A case study from Northern Shaanxi, China

The impact of vegetation restoration on ecosystem services (ESs) is a critical focus in the study of water-soil process for dryland areas. However, limited funding poses practical challenges in configuring restoration measures for achieving multi-objective optimization of water-soil resources. This study selected Northern Shaanxi, a pilot area of the Grain to Green Program (GTGP) in China, as a case study area and conducted field surveys on vegetation restoration and protection activities. On this basis, four scenarios with different weights or budgets were developed to optimize three water-soil ESs: baseflow regulation, phosphorus retention, and soil conservation. Using the Resource Investment Optimization System model (RIOS) model, which integrates watershed water-soil process and investment information, we simulated spatial portfolios of restoration activity and assessed their performance on the three ESs in future. The results indicated that forest tending and disaster prevention were critical for optimizing the three ESs, with the budgets of these two activities exceeding 70 % in all four scenarios. When the budget was increased, Ecological scenario 2 offered a more cost-effective approach to enhance ESs that simultaneously mitigate trade-offs among the three ESs. Under this scenario, the trade-offs between baseflow regulation and phosphorus retention, baseflow regulation and soil conservation, and phosphorus retention and soil conservation would decrease by 12.12 %, 31.43 %, and 15.38 %, respectively. However, current restoration measures alone are inadequate to meet future ecological or policy requirements for ES enhancements. By 2035, the area of phosphorus retention is expected to decline by a range of 14.84 % to 32.54 % under the four scenarios, with these areas of decline all located in the ‘blank zone’ of restoration activities. And none of the four scenarios could ensure the stability of soil conservation in aeolian-loess transitional areas. This study highlights the urgent need for implementing conservation agriculture practices and diversified restoration measures to ensure the long-term effectiveness of improving water-soil ESs.