Cocoa pods harvested.
The researchers found that under a shade-tree cover of approximately 30 percent, shade trees had a predominantly positive effect on cocoa plants compared to areas without shade trees. This amount of shade is ideal for keeping pests and diseases in check while maintaining maximum soil moisture. The cooling effect on temperature, the number of animal and plant species in the field, and the carbon sequestration all increase with an increase in the amount of shade. Up to about 30 percent shade, cocoa yield is not compromised. More shade, however, reduces the yield, as additional trees compete more intensely with the cocoa plants for light, water and/or nutrients. “The optimal amount of shade is therefore a cost-benefit consideration,” Blaser explains. There is one promise that the shade trees seem, however, unable to keep: the amount of nutrients in the soil does not automatically increase with a rise in the number of trees.
Eco-friendlier = more stable
All in all, the inclusion of shade trees in cocoa fields had a predominantly positive effect on ecosystem services, though the researchers emphasise that even the best agroecosystem cannot replace the ecosystem services provided by natural ecosystems when it comes to, say, carbon fixation or biodiversity. As Six says, “Agriculture is never natural; the idea behind agroecology is simply to infuse more ecology into agriculture”.
Blaser continues: “More ecology can make farming more sustainable and more stable.” For example, a higher diversity of plant species in an agricultural system can potentially keep diseases from spreading and the temperature buffering effects of shade trees could contribute to higher yield stability under extreme weather conditions. “Combined these effects can lead to improved and above all longer-term yield“.
Further potential to optimise agroforestry systems
Wilma Blaser is delighted: “Thanks to our research on shade trees, we were able to put forward specific recommendations for the optimum degree of shade in cocoa farming.” The research even showed that cocoa crops could tolerate more shade than previously thought, without having a serious negative impact on the harvest. Still, efforts to increase cocoa yields in agroforestry systems require additional measures in cultivation. Blaser clarifies by saying, “Targeted application of fertiliser, timely pest control, regularly pruning, or weeding could potentially increase cocoa yields even under a higher shade canopy.”
There is still potential to optimise the choice of the right shade tree in agricultural systems, and Blaser wants to concentrate on shade-tree characteristics in her next project. She found 38 species in the farms she worked in, including orange, mango and avocado trees, all of which have different types of canopy and root systems. For example, some of them could be better soil improvers than others. Blaser aims to investigate which ones make the best shade trees for cocoa plantations.
