Conservation of the Matrix I: Ants in Coffee Plantations

While most conservation planners focus on preserving specific areas, new research shows that an area’s surroundings may be just as important. The need to include the “outside” in conservation planning is highlighted in a pair of papers in the February issue of Conservation Biology. Specifically, ant diversity near forest fragments is higher in shade than in sun coffee farms, and salamander abundance is higher in disturbed streams that are confluent with undisturbed streams.

“We propose that the matrix within which habitat fragments occur is of equal importance,” say Ivette Perfecto and John Vandemeer of the University of Michigan in Ann Arbor in the first paper.

The researchers determined the diversity of ground-foraging ants in and around La Montanita, a 37-acre tropical mountain forest reserve in southern Chiapas, Mexico. They used ants as an indicator of biodiversity because insects are the most diverse group of species, and ants comprise most of the insect mass in the tropics. The reserve is a forest fragment that lies between two types of coffee farm: a shady, organic farm overplanted primarily with native trees, and a sunnier, conventional farm that uses pesticides and herbicides.

After petroleum, coffee is the most-traded commodity in the world, and coffee plantations have replaced much of the tropical mountain forest, fragmenting what remains into small patches.

One of the keys to conserving broken-up habitats is making sure that species can still travel from fragment to fragment. The ants, for instance, need to fly among forest fragments to establish new colonies.

Perfecto and Vandemeer found that the number of ant species was similar in the forest fragment and the shady, organic farm (23 vs. 16), but was much lower in the conventional farm (7). They also found that while ant diversity on the farms decreased with distance from the forest fragment, this drop-off was much slower on the shady, organic farm. On the latter farm, ant diversity was still high about half a mile from the forest fragment. In contrast, on the conventional farm, ant diversity had already dropped to its lowest level just 65 feet from the fragment.

The researchers conclude that rather than connecting fragments with habitat corridors, in some cases it would be more effective to focus on making the area surrounding the fragments more conservation-friendly. “Attention to the agroecosystem that makes up the majority of the matrix may be key to conservation at the landscape level,” they say.

For tropical mountain forests, this means promoting shade-grown coffee. Coffee prices are at a 30-year low and many small producers are converting coffee farms to cattle pasture, subsistence crops, or even coca, says Perfecto. One way to reverse this trend would be to link shade-grown coffee to the Fair Trade system, which guarantees certified coffee producers three times the current price of coffee.

Further Information:

Perfecto, I. and J. Vandermeer. 2002. Quality of agroecological matrix in a tropical montane landscape: ants in coffee plantations in southern Mexico. Conservation Biology 16:174-182.