Social challenges to sustainability adoption among independent oil palm smallholders in Southeast Asia: a recent systematic review (2020–2025)

Independent smallholders play a crucial role in efforts to attain global sustainability in forests and agriculture. Nonetheless, these smallholders face serious socioeconomic issues that are often disregarded by policymakers. The desired sustainability benefits and the overall efficacy of landscape governance are ultimately undermined by this oversight, which results in slowing down adoption rates. This systematic review synthesized evidence regarding socio-cultural barriers, highlighting a gap frequently overlooked by economic and technical analyses. The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) protocol was employed to systematically analyze literature from the Web of Science and Scopus databases, identifying 30 primary studies published from 2020 to 2025 from which three interrelated thematic challenges emerged. Certification systems and barriers indicated structural exclusion, and unclear land legality restricted access to schemes. Former scheme smallholders represent 77 percent of certified Indonesian smallholders due to existing documentation. Existing group structures and institutional distrust limit participation. Livelihoods and economic viability exhibited significant vulnerability during transitions such as replanting, leading to income loss that was intensified by barriers to market access. In Indonesia, the smallholder sustainability index averages only 44.97 percent, primarily due to land conflicts and price volatility. Environmental governance and deforestation revealed a misalignment in policy, as zero-deforestation commitments enforced through supply chains frequently neglect the land-use realities of smallholders, consequently affecting forest frontiers and compliance behaviour. Cross-cutting issues encompass gender disparities, institutional fragmentation, and the underutilization of local knowledge, with less than 16 percent of smallholders employing local wisdom in waste management. The review concluded that equitable adoption required context-specific interventions that prioritized land ownership security, cooperative enterprise models, and flexible certification frameworks. Future research should examine digital inclusion, intergenerational knowledge transfer, and community-led governance to align global sustainability objectives with local socio-economic contexts.