Environmental Engineering Reference
In-Depth Information
complex ecosystems can change frequently over short distances, relatively minor
disturbances, like logging, can cause species extinction. This is one of the reasons why
ecologists and conservationists are so concerned about uncontrolled exploitation of the
rain forest.
ENVIRONMENTAL CHANGE
The history of the rain forests appears to be more complex than was once thought. The
diversity of species in tropical rain forest was for long believed to be the result of
environmental stability. It was thought that the impact of the Pleistocene glacial periods,
which had been dominant in temperate and polar regions, had not extended into the
equatorial areas. Indeed, there is still controversy over the amount of change which has
occurred. Some scientists believe that the wet tropical regions of Earth have been stable
for at least the last 40 million years. In that case the rain forest development should have
taken place over a long period of time. The idea is that this period of uninterrupted
development has allowed rain forest plants and animals to evolve and adapt. Hence there
is a richness and diversity of forest species to exploit the resulting ecological niches.
Other experts believe that the forests should no longer be considered ancient biomes
that have survived since the Tertiary. Instead it is argued that they
did
experience
dramatic changes during the Quaternary period, and probably owe much of their present
diversity to the periods of isolation they experienced at that time. This isolation led
Figure 28.6
Pleistocene refugia of the
African rain forest.
Source: After Maley (1987).
to the development of many endemic species, each found exclusively in the area in which
it speciated (Figure 28.6).
It is also clear that distinct variations related mainly to climatic and geological factors
occur within these biomes. An idealized picture of these patterns is shown in Figure 28.7.
Enhanced greenhouse impacts are not believed to produce major impacts in the humid
tropics. GCM predictions suggest an increase in both mean annual temperature and in
mean annual rainfall, but the change is smaller than in temperate parts of the globe. It
would seem that natural change of the tropical forest environment in the near future
should not be large, though human-induced changes may generate further impact on the
forest.
