EFFORTS to re-establish the world's mahogany trees are misfiring. "Green" forestry practices, such as selective logging, are not helping saplings as much as clearing large patches of rainforest.
"Forest departments around the world have invested millions of dollars doing something that doesn't work," says Laura Snook of the Indonesia-based Center for International Forestry Research (CIFOR). Snook and her team in Central America have found that planting mahogany under the forest canopy-a practice known as enrichment-is futile.
Mahogany is the most valuable Amazonian hardwood on the international market, and the rapid loss of the tree over much of its range in Central America and Amazonia reflects not just the intensity of logging activities, but also mahogany's failure to regrow successfully in logged areas.
Part of the reason is that mahogany thrives on natural catastrophes. Snook's team has found that it needs events such as hurricanes and fires to survive. "If we are to encourage the regeneration of mahogany," she says, "we need to learn how to mimic nature."
To reproduce and prosper, mahogany needs plenty of sunlight. This is a rare commodity in both primary rainforest and selectively logged forests, but is readily available when forests are struck by hurricanes, which are often followed by fires. Because mahogany can withstand strong winds and fire, it is often the sole species to survive and set seed, and its saplings get a head start on other species. By the time they catch up, its crown is already at the top of the canopy.
Five years ago, Snook and Patricia Negreros-Castillo of Iowa State University set up a series of experimental plots in Mexico to work out the best way to encourage mahogany to regrow. They used various techniques to clear 24 separate 5000-square-metre patches of forest, and planted 20 mahogany seedlings in each. They also planted seedlings under closed canopy.
After five years, 49 per cent of the seedlings had survived in plots subjected to slash-and-burn-which is a good approximation of a hurricane followed by fire. Meanwhile, 31 per cent survived in plots that had been clear-felled, and only 5 per cent survived under closed canopy. Seedling growth was strongest on slash-and-burn plots, averaging 3.73 metres, compared with 2.69 metres after clear-felling and just 14 centimetres under closed canopy. With green foresting practices, such as selective logging, much of the canopy remains closed. Similar experiments in Belize suggested that mahogany seedlings fare better in clearings of 5000 rather than 500 square metres.
The findings are influencing forestry practice. In Mexico's Yucatan peninsula, Mayan Indians who harvest mahogany are now being encouraged to plant seedlings in their slash-and-burn fields.
Author: Charlie Pye-Smith
New Scientist issue: 1st December 2001
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