A shady future for my favourite fruit, coffee

Planting shade trees in the middle of coffee plantations might just be the best way to save them from Coffee Berry Borer, a pest thriving as temperatures rise in East Africa.

Juliana Jaramillo from University of Hannover in Germany, along with colleagues from Nairobi, USA and our very own Aaron Davis from Kew, used climatic models for East Africa to predict a doubling of the number of generations of Hypothenemus hampei, the Coffee Berry Borer (from 5 to 10 a year). Their results have just been published in the open access journal PLoS ONE.

It's predicted temperatures in Africa will rise from 0.2 to over 0.5 degrees C per decade, and that rainfall will increase by up to 20% in summer and drop by up to 10% in winter by 2050. Droughts and floods are likely to be more common.

All this means the world's 'most valuable tropical export crop', coffee, valued at about US$90 billion a year, is under threat from 'the most important biotic constraint on coffee production', the Coffee Berry Borer.

Luckily, Coffee Berry Borers don't like shade. Or at least they prefer their berries warm. Strategically planted trees within the coffee plantation can reduce temperatures around the coffee berries by up to 4 degrees C. The shade trees will also help with soil and water conservation and provide a refuge for a bunch of friendly bugs, including some that enjoy eating our Coffee Berry Borer.

Jaramillo and co-authors suggest these shade trees could also be food plants (that is, a food other than coffee...) leading to a more diversified, and healthy, plantation.

So if Coffea arabica and Coffea canephora are to continue as a much needed East Africa export, supplying London coffee drinkers with our daily caffeine requirement, we should start propagating shade trees now.

And don't forget the Australian Coffea brassii (see my earlier blog on the first Australian native coffee species) which might contribute a gene or two to help us breed our way out of a future coffee crisis.

Image: coffee beans sunning themselves in the First Farm garden, in Royal Botanic Gardens Sydney.