EFFORTS to re-establish the world鈥檚 mahogany trees are misfiring. 鈥淕reen鈥�
forestry practices, such as selective logging, are not helping saplings as much
as clearing large patches of rainforest.
鈥淔orest departments around the world have invested millions of dollars doing
something that doesn鈥檛 work,鈥� 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鈥攁 practice known
as enrichment鈥攊s 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鈥檚 failure to regrow successfully in logged areas.
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Part of the reason is that mahogany thrives on natural catastrophes. Snook鈥檚
team has found that it needs events such as hurricanes and fires to survive. 鈥淚f
we are to encourage the regeneration of mahogany,鈥� she says, 鈥渨e need to learn
how to mimic nature.鈥�
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鈥攚hich 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鈥檚 Yucatan
peninsula, Mayan Indians who harvest mahogany are now being encouraged to plant
seedlings in their slash-and-burn fields.