Brewing trouble: coffee invasion in relation to edges and forest structure in tropical rainforest fragments of the Western Ghats, India. A. A. Joshi, D. Mudappa, and T. R. Shankar Raman. 2009. Biological Invasions 11:2387-2400.
While invasive plant species receive a lot of attention, the focus is often on weed species that compete with crops — not the potential invasiveness of the crops themselves. Coffee is native to Africa, but of course is widely planted in tropical regions worldwide. Both varieties of coffee, Coffea arabica and C. canephora (commonly called robusta) are grown in India. In the Western Ghats of India, a biodiversity hotspot, coffee is often planted adjacent to fragmented forest reserves. This study looked at the spread of coffee into forest fragments at four sites that adjoined coffee farms, but varied in degree of disturbance.
Both coffee species were found in all the forest fragments, with whatever species that was cultivated in the adjacent farms being the most abundant. Stem density generally decreased as the distance from the the plantation edge increased for the coffee species planted in the adjacent farms. Stem density of arabica increased with disturbance level of the fragment. Robusta did not show such a pattern, and stem density was many times higher than arabica in fragments adjoining robusta farms, including the least disturbed, protected forest fragment. Further, there was a negative relationship between robusta invasion and native shrub density.
Robusta coffee growing in the forest, Anamalais, Tamil Nadu, India. Kalyan Varma, used with permission.
The main consumers and dispersers of coffee in India are the Asian Elephant, Lion-tailed Macaque (Macaca silenus), Sloth Bear (Melursus ursinus), and Brown Palm Civet (Paradoxurus jerdoni). Yet in this study the pattern of dispersal in one fragment, which was separated from the farm by a stream, and the sharp decline of coffee densities beyond 100 meters hints that small mammals might be important agents for dispersal in these systems. Larger mammals have bigger ranges, and the stream would not have acted as a barrier for them.
The authors concluded robusta may have a greater impact as an invasive species than arabica in this region. Whether this has to do with robusta being more adaptable, or just more fecund (robusta coffee plants can produce four times more fruits than arabica plants) needs further study.
I’ve not seen any similar research on the spread of coffee into forest fragments in Latin America. This may be because of a more limited number of potential animal dispersers, and, at least in many parts of Central America, less cultivation of robusta coffee.
You can find a summary of the paper at the Nature Conservation Foundation web site.
Thanks to Kalyan Varma for use of his photo of robusta
Joshi, A., Mudappa, D., and Raman, T. 2009. Brewing trouble: coffee invasion in relation to edges and forest structure in tropical rainforest fragments of the Western Ghats, India Biological Invasions DOI: 10.1007/s10530-009-9423-6
Revised on November 28, 2020