Coffee Growers Get Help From Bees, Birds and Bats

Intensified farming means coffee grown on the slopes of Mount Kilimanjaro, in East Africa, is increasingly not being grown in the shade. This could lead to a stagnation in coffee bean yields as animal species that pollinate coffee and feed on pests could go in decline as more and more shade-providing trees are cut down to make room for plantations.

Shade from banana trees and other tall trees is being reduced as farmers increasingly replace "conventional coffee varieties, which rely on shade, [with] varieties that tolerate lots of sun and are more resistant to fungi," explained Ingolf Steffan-Dewenter, a tropical ecologist at the University of Würzburg's Biocente. The bushes and small trees producing coffee generally grow 10 to 12 feet high when cultivated.

This research, led by Steffan-Dewenter and his doctoral student Alice Classen, explores the effect of bees, birds, bats and other animals on the coffee's yield.

"The tropical experts conducted experiments in 12 areas on the slopes of Mount Kilimanjaro in Tanzania, located in all three cultivation systems (Chagga gardens, shade plantations and sun plantations). They used finely woven nets to prevent animals' access to the coffee flowers or even to entire coffee trees. Then they examined how the presence or absence of the 'animal service provider' affects the quantity and quality of the harvest," said a press release announcing the findings.

The results revealed that when bats and birds had access to the plants, the yield was 10 percent higher. "We believe that this is due to the fact that the animals eliminate pests that would otherwise feed on the coffee plants" said Julia Schmack. The reason could lie in the fact that reduced leaf damage from pests decreases the number of coffee cherries that fall from branches.

Even though the coffee variety, Coffea arabica, is self pollinating, access by bees and other pollinating insects contributed to a 7 percent heavier cherry.

"So, the effects of pollination and pest control complement each other perfectly; both are important for higher yields," said Steffan-Dewenter: "Birds and bats provide more cherries; bees and other pollinators ensure better quality."

Despite these findings, the study concluded that intensified farming seems to have no negative effect. The impact of the animal provided services on the harvest was equal in all three cultivation systems, even in the unshaded plantations. "We put this down to the mosaic landscape structure on Mount Kilimanjaro with its gardens, forests and grasslands," said Classen. Great numbers of small divisions in the landscape could mean, pollinators, birds and bats still find a suitable nesting places, and from there spread into the plantations.

"However, it is likely that these seemingly stable ecosystem services rest on shaky foundations in the sun plantations," believe the Würzburg scientists. This is due to the fact that other unrecorded pollinators, such as wild bees, hoverflies and butterflies, could be a major contributor to coffee yields. Disruption to these populations could further impact coffee harvests.