Cutting corners is a bad idea if you want to help rainforests grow. That's because square tropical forest fragments aren't hospitable to shade-loving seedlings, according to a report in the May issue of Conservation Biology. The finding could help scientists design more effective--and perhaps rounder--rainforest reserves.
Over the last century, logging and farming has turned huge swathes of the Amazon rainforest into a ragged patchwork of disconnected stands. The potential of these leftover patches to shelter rainforest plants and animals is largely unknown. To find out, the Smithsonian Institution and Brazil's National Institute for Research in the Amazon have for two decades led an effort to monitor 11 rainforest patches--from 2.5 to 250 hectares in size--scattered throughout cattle pastures 70 kilometers north of Manaus, Brazil.
As one part of the project, Julieta Benitez-Malvido of the National Autonomous University in Mexico City examined how the square shape of the rainforest fragments influenced the reproduction of shade-loving trees. Like researchers studying other logged forests, she found evidence of an "edge effect": the density of shade-tolerant seedlings decreased within several hundred meters of the fragment edge, where young trees are more exposed to sun, wind, and competition from invading species.
But she found that the edge effect is amplified in corners. In 250-hectare fragments, for instance, Benitez-Malvido found about 25% fewer seedlings growing in the corners than along other edges, and 40% fewer than in the centers. The study indicates that square fragments may shrink over time, she says, with smaller patches shrinking faster.
The "very interesting findings suggest that edge effects are additive--in corners, two create more problems than one," says William Laurance of the Biological Dynamics of Tropical Rainforest Fragments Project in Manaus. To avoid the problem, he says, reserve designers might want to consider planting trees to "round out those edges."