Hedgerow Shading Reduces Heat Stress and Improves Cacao Physiology and Soil Fertility in Tropical Systems

This research article — posted as a non-peer-reviewed preprint on Research Square on 23 July 2025 — evaluates whether vegetation-based hedgerow shading can buffer heat stress in cacao (Theobroma cacao L.) on smallholder farms. Field experiments were carried out from July to December 2023 in Bulukumba Regency, South Sulawesi, Indonesia, at 70 m above sea level, during a period when average daily temperatures rose to 26–30 °C against a five-year baseline of 26–28 °C. Hedgerows combined native multipurpose species — coconut (Cocos nucifera), banana (Musa spp.) and Gliricidia (Gliricidia sepium) — in layered canopies. Drone imagery analysed in GIS classified 35 grid plots into three shade levels (0–25 %, 25–50 %, 50–75 %); nine plots and 54 cacao plants were monitored under a Randomized Complete Block Design, with ANOVA and Tukey HSD testing at α = 0.05. The 50–75 % shade treatment produced the strongest physiological and agronomic response: total chlorophyll rose to 310.2 against 196.5 under low shade, light transmission through the canopy reached 27.2 %, and stomatal density fell from 132.7 to 87.2 stomata per mm², indicating a water-conserving adaptation. Soil under dense shade showed higher total nitrogen (0.29 % versus 0.21 %) and a lower C/N ratio (7.67 versus 10.00), though pH, potassium and phosphorus declined. Vegetative growth was greatest under high shade — 247.5 cm in height, 7.8 cm stem diameter and 223.6 cm canopy width. The authors present hedgerow shading as an agroecological, locally resourced strategy for climate-resilient cacao in tropical regions facing rising temperatures. Note that the soil-fertility discussion identifies 25–50 % shade as the better trade-off, which sits in tension with the overall recommendation of 50–75 %.