become more frequent. Forests become so degraded
by fire that the land becomes, in effect, deforested. This
forest fire feedback loop is exacerbated in El Niño years,
when there is less rainfall. Indeed, heating and drought,
both forecast to increase in the future due to climate
change, are expected to greatly increase occurrence of
serious fires in areas of humid tropical forest. Though
natural fires do occur in Amazonia, the time between
fires at a given location is historically in the hundreds or
thousands of years. That has changed.
Logging
Logging is practiced routinely throughout the global
tropics (plate 18- 3). This activity may take various forms,
ranging from clear- cutting to more selective removal.
In many parts of the temperate zone, particularly in
North America and Europe, sustainable logging is well
established. In its most basic form, sustainable logging
is based on removal of trees of economic value that
have not yet reached senescence, which is the point
at which plant growth is slowed essentially to a stop.
Thus harvesting when the trees are still vigorously
growing is, in the economic sense, logical. The logged
area is reseeded or replanted with tree species that
attain harvestable size relatively rapidly. In many
cases, temperate- zone forests may be clear- cut in 40-
to 50- year (or shorter) cycles. Sustainable logging is,
in a sense, much like basic agriculture, with trees as
the crops. Debatably, sustainable logging in much of
the temperate zone has not resulted in major species
reductions or loss of ecosystem function, though this
is not true in such places as Germany and Scandinavia.
Logging in the tropics is not as straightforward
as it is at higher latitudes. Some forests are largely
clear- cut. But in many cases valuable trees must
be removed individually because they are widely
separated, a general characteristic of tropical forest tree
distribution. Loggers make trails to access trees whose
timber is deemed of value, and logging roads penetrate
deeply into forests. Trees are cut and subsequently
dragged over skid (also called snig) trails to the road
to be loaded on to large trucks. Trucks carry logs from
forest to central locations where they can be shipped to
urban areas for further processing (plate 18- 4).
Intensive logging activity in the tropics results in
forest degradation. Logging roads, skid trails, and
human activities associated with logging impose
damage to plants other than the target species, reduce
forest biomass, permit greater light penetration, create
damage to soils, and increasing potential for serious
fire. Conservation biologists distinguish between
deforested areas, as are typical in areas of agriculture,
and degraded forest, where logging is practiced.
Another question focuses on the impact of logging
on wildlife. Logging roads and skid trails permit
hunters to penetrate areas that would otherwise be
difficult to access and have therefore contributed to
increasing wildlife harvest.Deforestation in AmazoniaExtensive deforestation has occurred in many areas
of the Amazon Basin, particularly in Brazil, which
occupies the majority of the region. The Brazilian
Amazon contains about 40% of all remaining tropical
rain forest; because of this massive area, the future of
the Brazilian Amazon has been a focus of concern for
many years. Most deforestation has been associated
with the growth of soybean production and cattle
ranching (plate 18- 5). Some years ago, for example,
there was much discussion about the “hamburger
connection,” having to do with the exportation of
inexpensive South American beef, raised in pastures
that were once rain forest, to North America for use in
fast- food restaurants (plate 18- 6).
Brazil has been the focus of attention for many
years, though other Amazonian countries have also
experienced major deforestation of lowland forest. In
Brazil, forest clearance has been most extensive in the
states of Mato Grosso, Pará, and Rondônia. Much of
the rest of the country remains deeply forested.
While much of the forest clearance in Brazil has been
for cattle ranching and soybean production, logging
has also been a major activity. A comprehensive review
of logging in the Brazilian Amazon by Greg Asner and
colleagues showed that from the years 1999 to 2002
between 12,075 and 19,823 km^2 (4,662– 7,654 mi^2 ) were
logged per year, figures that were somewhere between
60% and 123% greater (depending upon which study it
was compared with) than those that had been reported
previously. The study employed large- scale, high-
resolution, automated sensing analysis, using Landsat
Enhanced Thematic Mapper Plus satellite data, to detect
previously undetectable logged areas. The researchers
found that, in general, such protected areas as national
parks, reserves, and lands belonging to indigenous
people were not subject to illegal logging, with the378 chapter 18 the future of the neotropics