While most conservation planners focus on preserving certain areas, new research shows that an area's surroundings may be just as important. 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.
The need to include the "outside" in conservation planning is highlighted in a pair of papers in the February issue of Conservation Biology.
"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 farms: 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 while the number of ant species was similar in the forest fragment and the shady, organic farm (23 vs. 16), it 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 dropoff 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 already established Fair-Trade system, which guarantees certified coffee producers three times the current price of coffee.
The second paper showing that what's around an area can be critical to conserving what's in it is by Winsor Lowe and Douglas Bolger of Dartmouth College in Hanover, New Hampshire.
Lowe and Bolger studied how logging near 25 headwater streams in New Hampshire affects spring salamanders, which are pink, up to 8 inches long, and rarely seen. Because amphibians are extremely sensitive to conditions in water as well as on land, they are good indicators of the overall ecological effects of logging. The researchers accounted for factors including the time since the last timber harvest, stream sedimentation, the presence of predatory brook trout, and the proximity of other salamander populations.
In the northeastern U.S., the diversity of stream amphibians is highest in headwater drainages. However, headwater streams are barely protected. For instance, they are often developed without mitigation under the Army Corps of Engineers' current nationwide permits. Disturbance of headwater steams can increase flooding, erosion and sedimentation downstream. Logging is the primary disturbance to headwater streams in the northeastern U.S.
Lowe and Bolger found that streams had more salamanders when they were confluent with another stream (that is, when two streams ran into each other) than when they were isolated. Notably, confluent logged streams had 40% more salamanders than isolated ones. This suggests that population connectivity may help protect salamanders in disturbed streams. The researchers speculate that confluent streams might benefit salamanders by letting individuals from an unlogged stream disperse to a logged one. "Dispersal might help prevent local population extinction in the disturbed streams," they say.
The next step is finding out how the salamanders move from stream to stream. If they disperse via the riparian edge along streams, managers should extend protection of riparian areas along headwater streams (those further downstream are currently protected). On the other hand, if the salamanders disperse overland, then this needs to be accounted for when managers decide when and where to harvest timber.
*Ivette Perfecto (011-52-962-626-0717, firstname.lastname@example.org) [NOTE: she will is currently in Mexico]
*John Vandemeer (734-764-1446, email@example.com)
*Guillermo Ibarra (011-52-962-628-1077 X 5300, firstname.lastname@example.org)
*Russell Greenberg (email@example.com)
For copies of papers, contact Robin Meadows: firstname.lastname@example.org