Geoscience Reference
In-Depth Information
Given that the world's population is predicted to continue to increase, it seems
unlikely that firewood needs will be able to meet the growing demand. One option
to help alleviate the demand is the creation of plantation forests that can grow tree
species with higher wood production yields. While promising, this alternative is
limited by water and irrigation available to enhance growth. Irrigation can increase
growth up to four times more than in naturally rain-fed plantations, but it is fre-
quently too expensive to be feasible. Having to pay for fuelwood from plantations
would be incredibly difficult for families that still rely on subsistence agriculture for
survival.
Fire is a natural but relatively rare occurrence in most tropical seasonal forest
types. The most vulnerable dry forests are those adjacent to savanna vegetation,
although even those are not affected too negatively given the sparseness of vegeta-
tion under the tree canopy. If fire is frequent and seeds and seedlings are destroyed,
however, the forests are unable to regenerate, and over time will become savannas
or scrublands. Today, fire is commonly used by people to clear forests, control
weeds in pastures, and burn logging debris. Both intentional and unintentional fires
are growing in size and frequency throughout the tropics. Logged seasonal forests
are more prone to fires, especially during droughts. Exposed forests dry out quickly
and piles of woody debris are easily ignitable by lightning strikes, as well as by
ranchers and farmers that practice shifting agriculture, who start fires to clear the
forest floor. Fragmented forests are also more predisposed to fire because edges
become desiccated and forest patches are often adjacent to fire-prone pastures and
farmlands. Low-intensity fires, able to penetrate large distances into fragmented
forests, can kill numerous trees and create canopy openings that further add to the
forest's susceptibility to future catastrophic wildfires.
Small changes in the structure of a forest's ecological conditions, in combina-
tion with logging, slash-and-burn activities, and drought can increase the potential
for fire. Droughts occurring during El Ni
no events have brought huge wildfires that
swept through forests, destroying vast areas, particularly in Asia.
Finally, deforestation is not a random process, and not all forest types are
equally threatened. Regions most vulnerable are those that are accessible with gen-
tle slopes and productive, well-drained soils suitable for farming or ranching, such
as the seasonal forests in Asia. Thus, one of the regions of greatest concern is
Southeast Asia, because its tropical forests are smaller in area and are exposed to
the highest relative rates of forest clearing and logging.
Tropical seasonal forests are the most threatened biome in the world. More
than 80 percent of these forests are destroyed or degraded in Central America and
Madagascar, while at least 60-80 percent has been converted in Africa and South-
east Asia. The two most contiguous areas of seasonal forest left are found in South
America, but they too are at risk. In most other areas and regions, they are severely
fragmented and scattered over extensive areas.
A great deal is left to learn about the ecology of tropical seasonal forests and its
inhabitants. Increasing interest in the biology, function, and value of tropical
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