The patterns of the Populus euphratica forest and cropland changes upstream of the Tarim River under the policy-driven human activities during 1960–2023

The natural Populus euphratica forest surrounding the Tarim River has experienced significant deforestation since the 1960s. This forest loss is primarily attributed to cropland expansion and the excessive use of agricultural water resources, severely threatening the local riparian desert ecosystem. Using multi-temporal remote sensing imagery (1960-2023), this study quantifies the cropland-forest relationship by mapping cover changes between the Weigan and Tarim Rivers, analysing change patterns and policy drivers. Results show P. euphratica forests shrunk from 3891.72 to 2351.37 km(2), while cropland expanded from 1340.73 to 5879.65 km(2), with >90% deforested areas converted to cropland. The cropland landscape became more concentrated, with agricultural intensity +0.18/decade, while the P. euphratica forest became more fragmented, with intensity -0.5/decade. Despite multiple natural forest protection policies before 2015, agricultural development and farmland expansion dominated. The forest decline was remarkably rapid between 1960-1990 and 1990-2015; for every 1 km(2) increase in cropland, there was a corresponding forest decrease of 0.44 km2 and 0.35 km(2), respectively. After 2015, the P. euphratica forest rescue project was implemented, which prohibited the occupation of forest land. During this period, the ratio of forest decrease to cropland increase improved, with every 1 km(2) increase in cropland resulting in only a 0.22 km(2) decrease in forest area. Following the agricultural water price reform and the launch of water-saving policies in 2017, there was almost no conversion of P. euphratica forests into agricultural land after 2019. Therefore, the Grain for Green policy has helped prevent the rapid decline of P. euphratica forests. At the same time, market-based reforms in agricultural water pricing have accelerated the adoption of water-saving irrigation technologies, allowing more ecological water to reach the P. euphratica forests. This study provides valuable guidance for sustainable land management and ecosystem restoration in the oasis desert ecotone.