Shade tree pruning effects on flowering and cacao yields in different cropping systems in a long-term trial in Bolivia

Abstract

Light access is the primary factor affecting yields in cacao-based agroforestry systems (CAFS). While CAFS ecosystem services provision is extensively documented, research on improving light access in CAFS remains scarce. Shade canopy pruning, a developing technique in Latin America, is part of the long-term SysCom Bolivia trial. It is undertaken twice a year, at the start of the rainy and dry seasons. This paper presents the results of a 5-year study on the relationship between CAFS canopy cover, flowering levels, cocoa yields, and pruning events from this trial. The seasonality and peak periods of flowering and pod production were independent from the cropping system, underlining both climatic- and genetically determined production patterns. Yet, flowering levels depended on canopy cover levels during the rainy season, which translated into different pod production levels in the following months. Average annual yields were 1300 kg ha-1 for full sun cacao, 780 kg ha-1 for agroforestry systems (AF), and 640 kg ha-1 for dynamic agroforestry systems (DAF), with rainy season canopy covers maintained at 25–35% for AF and 40–60% for DAF. The relationships between canopy cover, flowering, and cocoa yield were found to be exponential, indicating that the lower the canopy cover, the greater the yield increase could be expected from pruning. The lower levels of cover obtained in AF after the ‘flowering’ pruning triggered better flowering levels in comparison to DAF. However, these did not systematically translate into significantly higher yields, underlining the probable significance of the ‘ripening pruning’ for DAF’s cocoa yield. Overall, our results show (i) the great potential of timely shade canopy pruning and (ii) the need to adapt such a technique to systems’ diversity and density to make it cost/labour-effective and support its scalability.