A Review on Intercropping Strategies in Plantation Crops: Designing Multifunctional, Climate-Resilient and Profitable Perennial Systems

Plantation crops occupy vast areas of the humid and sub-humid tropics and generate livelihoods for millions of smallholders and estate workers, yet many plantation landscapes remain simplified, input-intensive and vulnerable to climate variability, pests, price shocks and soil degradation. Intercropping and broader forms of diversification within perennial plantations are increasingly positioned as practical routes towards sustainable intensification, capable of stabilising income while improving resource-use efficiency, soil health, biodiversity and climate outcomes. This review synthesises evidence on intercropping strategies in major plantation crops, with emphasis on oil palm, coconut, rubber, coffee and cocoa systems, and draws out cross-cutting design principles for spatial and temporal arrangement, species selection and management. Recent research highlights that well-designed intercrops can deliver complementary canopy and root resource capture, improve nutrient cycling via legumes and litter pathways, buffer microclimatic stress through shade, and strengthen biological control through understorey habitat management. Nonetheless, intercropping benefits are contingent on careful matching of companion species to plantation phenology and market context, as well as on operational compatibility with harvesting logistics and labour constraints. The review proposes an integrated framework that links plantation stage (immature versus mature), limiting resources (light, water, nutrients) and targeted services (income, soil protection, pest regulation, carbon) to recommended intercropping options and monitoring indicators. It concludes with implementation priorities and research needs, including long-term trials spanning full plantation cycles, multi-criteria performance assessment and decision-support tools that translate ecological interactions into actionable farm design.