Luke, S. H. | bioRxiv Science

bioRxiv2026

Planting set-up and local environmental conditions affect outcomes in tropical agricultural restoration

1. Fine-scale environmental metrics, including spatial configuration and identity of surrounding plants, can strongly influence plant survival and ecosystem functioning. However, tropical restoration projects rarely test their role. Within the Riparian Ecosystem Restoration in Tropical Agriculture (RERTA) Project, located within oil palm plantations in Indonesia, we investigated how the spatial configuration and position of enrichment-planted trees influenced restoration outcomes within actively restored riparian margins. 2. We compared the enrichment plantings' response to fine-scale spatial conditions, either planted with conspecific (same-species) or heterospecific (mixed-species) neighbours for six planted tree species (Peronema canescens, Shorea leprosula, Alstonia scholaris, Artocarpus integer, Calophyllum inophyllum, and Albizia chinensis), in restoration areas with mature oil palms either left in place (shaded) or removed (unshaded). We also tested whether restoration outcomes varied with position within the margin (river, middle, or edge). We measured plantings response as seedling survival and height (monitored over eight years) for all six species of trees. 3. We also carried out more detailed observation on multiple ecosystem functions associated with focal trees of three of the species (Peronema canescens, Alstonia scholaris, and Albizia chinensis), measuring differences by planting configuration and distance to river edge. Functions measured included: herbivore predation, leaf herbivory, litterfall, soil chemical properties (organic carbon, cation exchange capacity, total nitrogen, and phosphorus), and soil physical properties (bulk density, aggregate stability, friable soil content, and A-horizon depth). 4. Survival and height did not differ between conspecific and heterospecific neighbours, but did with position within the riparian margin, but only when analysed by treatment and time. Planting configuration and position influenced ecosystem functions; heterospecific plantings had greater soil aggregate stability and higher ant densities, while increasing distance from the river was associated with lower arthropod abundance and herbivory but greater predation. 5. Our findings demonstrate that planting outcomes are strongly context-dependent, with local seedling configurations, position within the riparian margin, and restoration treatment interacting to influence restoration success and local ecological conditions. Our findings provide experimental results to inform planting strategies and restoration protocols in agricultural landscapes.

ecology↗

bioRxiv2026

From margins to mainstream: restoration of riparian margins to support oil palm sustainability in modern and future climates

Palm oil is the worlds leading vegetable oil, with production continuing to expand, particularly across Southeast Asia. Within established plantations, conserving and restoring riparian margins can reduce erosion, improve connectivity, and support biodiversity. Simultaneously, climate change is increasing thermal stress within tropical agricultural landscapes, raising the potential importance of riparian buffers as microclimatic refugia, although this has not previously been evaluated. The Riparian Ecosystem Restoration in Tropical Agriculture (RERTA) Project is a long-term Before-After Control-Impact experiment established within oil palm plantations in Riau, Indonesia, to evaluate alternative riparian restoration strategies following plantation replanting. Treatments included passive restoration (retaining mature oil palms and allowing natural regeneration), active restoration (enrichment planting with six native tree species), and a control (replanting immature oil palms to the river edge). Six years after restoration, we assessed vegetation structure using terrestrial laser scanning and thermal stability using temperature loggers and thermal imaging. We also evaluated the long-term temperature buffering capacity of each treatment under current and projected climates using CHELSA climate data and downscaled outputs from multiple General Circulation Models under Shared Socioeconomic Pathway scenarios for 2045 and 2085. Active restoration produced greater structural complexity, a more closed canopy, and cooler, more thermally stable conditions than passive restoration and control treatments. Restored margins also contained significantly more cool surface microhabitats, reducing thermal extremes under both current and future climate scenarios. Our findings demonstrate that active restoration of riparian margins can enhance thermal buffering and create microclimatic refugia for biodiversity within tropical oil palm landscapes. As agricultural intensification and climate change continue to reshape tropical ecosystems, restoring structurally complex riparian vegetation will be critical for sustaining biodiversity and the ecosystem services upon which agricultural production depends.

ecology↗