Supplementary file 1_Carbon labels and carbon trading as market-based incentives for conserving traditional upland rice: a case study from Hainan, China.docx

A comparative analysis framework is constructed to compare the incentive strength, operation cost and institutional positioning of market-based carbon instruments and existing differentiated public ecological compensation schemes.</p>Results<p>The Shanlan rice conservation system has established a verified carbon sequestration rate of 2.1 t CO₂/ha/yr, completed the first provincial carbon market transaction of RMB 530,000 in 2024, and officially released the dedicated Shanlan rice carbon label at the 2024 Hainan Winter Trade Fair.

At the current carbon price of RMB 50/t, the annual carbon revenue per mu is only about RMB 7, accounting for roughly 3% of the existing public ecological compensation standard of RMB 200–220/mu. The carbon accounting parameter has already been embedded into the local ecological compensation calculation algorithm as an ecological service value component.</p>Discussion<p>The empirical results confirm that current carbon market instruments can only play a complementary rather than substitution role for public ecological compensation in traditional crop conservation scenarios, and their near-term value is more institutional than purely financial.

The ambiguity between modeled sequestration parameters and actual measured conservation outcomes still limits the credibility of such market mechanisms. Three core propositions including incentive complementarity, measurement validation and long-term institutional stewardship are proposed to support future comparative research on similar agrobiodiversity conservation practices.</p>