CHOCOLATE4LIFE · Achieving sustainable agriculture in African cacao through DNA metabarcoding and food web models

Achieving sustainable agriculture in African cacao through DNA metabarcoding and food web models

Cocoa, which fuels the multi-billion dollar chocolate market, is grown in tropical rainforest—mostly in Sub-Saharan Africa on small, family owned farms. African farmers, which produce about 70% of cocoa worldwide, typically cannot afford pesticides, so they rely nature for pest insect removal, but neither farmers nor scientists know which birds and bats provide this service. Shade trees also provide habitat for the African birds and bats that undoubtedly save farmers millions of dollars through pest control. Surprising little is known from a scientific perspective about how to manage African cocoa plantations—either for improvement of agricultural production or for the benefit of biodiversity. However, cutting edge new genetics techniques now allow us to sequence the bits of insect and plant DNA left in birds and bat faeces. We can then map thousands of species in the food web, which ultimately can help us predict how agricultural systems will respond to management. Further, exclusion experiments (ie., covering cocoa trees with bird/bat-proof netting) can help us quantify the value of the ecosystem services. Ultimately, a high-resolution food web, along with exclusion experiments, will help us to understand the following: 1. Which birds and bats consume pest arthropods? 2. How much do birds and bats save farmers via ecosystem services? 3. What management scenarios benefit birds and bats? 4. And ultimately, what are win-win management scenarios that benefit BOTH African farmers and biodiversity? With this novel framework, we seek to build towards a system in which African farmers benefit through inexpensive, sustainable management of cocoa, and rainforest animals benefit through the planting of trees that mimic their natural habitat. Our exclusion experiment showed that relative to experimental trees with birds and bats excluded, control trees had 3.9 times more flowers and 3.2 times more large pods at high levels of shade cover (90%), whereas at low levels of shade cover (10%) trees had 5.2 times fewer Flowers and 3.7 times fewer large pods. This suggests not only that bats and birds consume large numbers of cocoa pests, but that the ecosystem services provided by birds and bats are even more important in full sun farms. More generally, we conclude that cocoa, though diverse in birds and bats, is not suitable as an alternative to primary forest as it lacks forest specialists, insectivores and ant-following birds. Well-managed cocoa farms are diverse (higher gamma diversity than forest), and may be suitable as buffers of primary forest or corridors between patches.

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