deforestation will be forced by increasing global
demand for meat, lumber, and biofuels (soybeans
are used in biofuels). More greenhouse gases will be
emitted by human activities associated with forest
clearance, and accidental fires could increase, in
particular, adding that much more greenhouse gas to
the atmosphere and acting to reduce rainfall.
The combination of forest fires, drought (expected
from global climate change), and logging will combine
to establish a positive feedback such that Amazonian
forests may reach a tipping point beyond which
forests cannot recover. At that point, large areas such
as southeastern Brazil may convert from forest to
savanna- type ecosystems. It has been estimated that
the tipping point will occur with an added 4° C (7.2° F,
within the range of some models of global warming
(see Carlos Nobre, interview in Nature). It is not yet
clear just how Amazonian forests are going to react to
the various drivers that are now altering forest ecology.
Hydroelectric Dams: The Newest
(and Worst?) Threat
It is called the Belo Monte Dam and, as of this writing,
it is scheduled to go into operation within the near
future, though it continues to face court challenges for
its potential effects on indigenous peoples. It is in the
Brazilian state of Pará, and it will permanently alter the
Rio Xingu, displace local populations of indigenous
people, and change the ecology of the region. The
Belo Monte Dam represents one of the largest of its
kind in the world and was designed to provide hydro-
generated electricity, needed to support Brazil’s rapidly
expanding economy. Plans for Amazon- powered
hydroelectric dams such as Belo Monte have existed
since the mid- 1970s, and proposals for damming parts
of the Amazon and its tributaries have continually
generated controversy, including at the international
level. Such dams require enormous capital investments.
Belo Monte, for example, has been estimated to cost
about $18 billion (US dollars), with another $2.5
billion for transmission lines to carry the power. The
complexity of such a project is hard to understate,
and its development and construction have generated
many legal challenges, much debate, and international
protests. But it is being built.
Why should a hydroelectric dam cause such concern?
The dam’s reservoir will flood 400 km^2 (155 mi^2 ) of
forest, and that represents about 0.01% of the Amazon
Basin. It will initiate an ecological cascade of effects that
will result in diminished biodiversity. There is also the
claim that the dam will displace up to 20,000 indigenous
people. For details and references on this immense
undertaking, see https://en.wikipedia.org/wiki/Belo_
Monte_Dam. But there is more.
Dams are also being planned for construction
along the Madeira, Tapajós, and Teles Pires rivers.
Many more Amazonian dam projects are now
under consideration or in the planning stages. The
subsequent loss of forest as well as alteration of the
typical Amazonian flood cycle has the potential to
significantly reduce the Amazon region’s recycling of
water (chapter 2), affecting in particular its capacity
to sustain its annual rainfall. When combined with
climate change, the outlook is concerning, because the
entire region could be subject to frequent and severe
droughts. As the Amazon region becomes drier, it is
likely that plant productivity will decline (chapter 5).
If that occurs it will initiate a bottom- up effect that
will reduce insect numbers, which in turn will reduce
animals dependent on insects, and so on up the food
chain. A friend who resides in Brazil has told me
that Manaus, at the confluence of the Amazon and
Negro rivers, has recently experienced humidity of
below 20%, which is shockingly low. The effect of the
dryness was evident in reduced flowering and fruiting
and obvious changes in patterns of insects and birds.
If such trends continue, and it appears that they will,
the alteration and ecological degradation of the entire
Amazonian region would seem to be inevitable.
There are numerous websites devoted to the various
aspects of Amazonian hydroelectric dam projects
projected to occur in the near future. I have included
some of them after the Further Reading section that
accompanies the chapter. See also a paper by Philip M.
Fearnside (2015) included in Further Reading.Restoration and Rehabilitation
of Tropical Forests: Hope for the
Future?What is the outlook for tropical forests over the
remainder of the 21st century? A research team led by
Britaldo Soares- Filho constructed a model to compare
various scenarios from the present to 2050 for the
Amazon Basin. They examined eight scenarios and384 chapter 18 the future of the neotropics