Geoscience Reference
In-Depth Information
hydrological processes, erosion, soil compaction, and nutrient loss. Dry forests
may be more vulnerable to conversion than other types of tropical ecosystems for
various reasons. First, warm, dry climates tend to be preferable to hot, humid ones
for both humans and livestock. Second, burning can be facilitated by the dry sea-
son, making the forest easier to clear than rainforests. Third, pest problems are
reduced by a prolonged dry season, enhancing the desirability of dry forest land for
agriculture. Insect-borne diseases such as malaria or dengue fever are less problem-
atic in drier areas. Finally, dry soils are less prone to compaction than the soils of
the rainforest, another desirable characteristic for agricultural land. In addition,
dry forest soils are generally more fertile, less prone to nutrient leaching, and easier
to manage with respect to successional vegetation and weeds. These advantages to
settling in the seasonal forests have produced large population centers. As a result,
the threats to this ecosystem are multiple and complex and deforestation rates
exceed those in tropical rainforests.
Tropical seasonal forests are disappearing at an alarming rate and little undis-
turbed forest remains. As these forests are found in areas of the world with high
populations and persistent poverty, complex social, political, and economic factors
are involved in the process of deforestation. Shifting agriculture is one of the pri-
mary sources of seasonal forest loss, but spontaneous settlers and various govern-
ment projects have also affected deforestation. Cattle ranching plays an important
role in forest conversion in some regions, notably Central and South America.
Road building into and through the forest can also have devastating effects—this is
seen in the building of the InterAmerican and InterAmazonian highways through
Central and South America.
Conversion of cropland for agriculture is considered one of the primary causes
of deforestation in tropical seasonal forests because increasing populations lead to
a dramatic rise in the number of shifting cultivators. Many of the issues discussed
in the rainforest chapters occur in the tropical seasonal forests, but they occur at a
faster rate due to increased population pressure. Sustainable agroforestry systems,
although proven to be almost twice as productive as shifting cultivation, are not
practiced often because many farmers lack the necessary technical knowledge to
succeed at this alternative method.
The second primary cause, large-scale industrial agriculture, is on the rise and
quickly becoming a major threat to survival of the remaining seasonal forests (see
Figure 4.9). In the past, it was once considered no more of a threat than shifting
agriculture, but that belief is quickly changing. Because land is often mistakenly
considered to have little economic value until the forests have been cleared, the
drier forest regions with fertile soil are being heavily targeted for conversion by
large-scale agricultural operations. For example, in the seasonal forests of the
southern Amazon, large expanses of land are being cleared for soybean farming. A
similar situation is occurring near Santa Cruz in Bolivia, where deforestation rates
are some of the highest in the world. The rush to convert land to soybean produc-
tion is so intense that, despite selective logging of commercial species before
