Global
Deforestation
Landsat data show the effects of deforestation
nearthe town of Ariquemes, Rondonia, Brazil
between 1975 and 1992
"Here goes lumber from the Maine woods ... pine, spruce, cedar, - first, second,
third, and fourth qualities, so lately all of one quality, to wave over the bear, and
moose, and caribou..."
- Henry David Thoreau, 1845.
Format for printing
In this lecture period, we wish to learn:

What do we mean by "deforestation"?

How have the old-growth forests been affected by humans?

What are the consequences of loss of forest habitats and ecosystems?

What management strategies are in place
forests?
to preserve, manage and restore
1. Introduction
It is impossible to overstate the importance of humankind's clearing of the forests.
The transformation of forested lands by human actions represents one of the great
forces in global environmental change and one of the great drivers of biodiversity
loss. The impact of people has been and continues to be profound. Forests are
cleared, degraded and fragmented by timber harvest, conversion to agriculture,
road-building, human-caused fire, and in myriad other ways. The effort to use and
subdue the forest has been a constant theme in the transformation of the earth, in
many societies, in many lands, and at most times. Deforestation has important
implications for life on this planet.
Just think, originally, almost half of the United States, three-quarters of Canada,
almost all of Europe, the plains of the Levant, and much of the rest of the world were
forested. The forests have been mostly removed for fuel, building materials and to
clear land for farming. The clearing of the forests has been one of the most historic
and prodigious feats of humanity.
Area of Forest Ecosystems (World
2
total:~ 34 million km )
About one half of the forests that covered the Earth are gone. Each year, another 16
million hectares disappear. The World Resources Institute estimates that only about
22% of the world's (old growth) original forest cover remains "intact" - most of this
is in three large areas: the Canadian and Alaskan boreal forest, the boreal forest of
Russia, and the tropical forest of the northwestern Amazon Basin and the Guyana
Shield (Guyana, Suriname, Venezuela, Columbia, etc.)
Today, forests cover more than one quarter of the world's total land area, excluding
polar regions. Slightly more than 50% of the forests are found in the tropics and the
rest are temperate and boreal (coniferous northern forest) zones.
Seven countries (Russia, Brazil, Canada, the United States, China, Indonesia, and
the Democratic Republic of Congo (formerly Zaire) account for more than 60% of the
total.
For millennia, humankind has influenced the forests, although much of the impact
has been relatively minor. Today, the impact is enormous. Deforestation is
expanding and accelerating into the remaining areas of undisturbed
forest, and the quality of the remaining forests is declining. Today we examine
global patterns in deforestation, assess the human and ecological costs of forest loss,
and discuss some of the steps that can help to rectify this alarming situation.
Frontier Forests of the World
Red = Frontier Forests, 8,000 years ago
Green = Frontier Forests Today
Pink = Current non-frontier forests
Historical trends:
Until quite recently, most of the deforestation occurred in Europe, North Africa, and
the Middle East. By the beginning of this century, these regions had been mostly
converted from the original cover. Now, deforestation in these regions has stabilized
and regrowth is occurring (though second growth forests have quite different
character, see below). In the last few decades, the vast majority of deforestation has
occurred in the tropics - and the pace still accelerates. The removal of tropical forests
in Latin America is proceeding at a pace of about 2% per year. In Africa, the pace is
about 0.8% per year and in Asia it is 2% per year.
The USA has already experienced its wave of deforestation, with the exception of
small areas in the west and Alaska. Our old growth forests were mostly harvested
by 1920, particularly in the East. Pacific Northwest forests and UP Michigan forests
were heavily cut after 1920 until quite recently, and harvest of old growth continues
today in Southeast Alaska. Interestingly, deforestation rates at their peak in the
Midwest were ~2% annually, about the rates now seen in Amazonia. At that rate,
how much of existing forest will remain in 70 years? Just one-fourth. However,
much forest re-growth has occurred in the eastern USA during the 20th Century,
although these second-growth forests differ in structure and composition from their
predecessors.
Area of primary forests in the
United States (lower 48)
(around 1620, top; and 1850 middle;
1920, bottom)
Since 1600, 90% of the virgin forests that once covered much of the lower 48 states
have been cleared away. Most of the remaining old-growth forests in the lower 48
states and Alaska are on public lands. In the Pacific Northwest about 80% of this
forestland is slated for logging.
Some Definitions

Deforestation: The conversion of forest to another land use or the long-term
reduction of the tree canopy cover below a 10 percent threshold.
Deforestation implies the long-term or permanent loss of forest cover and its
transformation into another land use.

Primary forest: is a forest that has never been logged and has developed
following natural disturbances and under natural processes, regardless of its
age.

Secondary forests: are forests regenerating largely through natural
processes after significant human or natural disturbance, and which differ
from primary forests in forest composition and/or canopy structure.
Disturbed forests: Any forest type that has in its interior significant areas of
disturbance by people, including clearing, felling for wood extraction,
anthropogenic fires, road construction, etc.
Frontier forests: large, ecologically intact, and relatively undisturbed
forests that support the natural range of species and forest functions (WRI
definition).



Forest plantation is one established by planting or/and seeding in the
process of afforestation or reforestation. It consists of introduced species or,
in some cases, indigenous species.
2. Importance of Forests
Forests provide important products for human use and consumption, and they
provide valuable ecosystem services. Let's look at each in turn.
Forest Products

In poor areas where wood is scarce, people, usually women, walk long
distances to gather wood for cooking.

Forests provide useful wood products. Roundwood (whole logs) can be
processed into building materials, or made into plywood products,
furniture, etc. Pulp is used not only for paper and boxes, but for a wide
variety of products (including the sponge you used to wash your dishes).

Forests are the source of numerous non-wood products, including bark,
dyes, fibers, gums, incense, latexes, oils, resins, shellac, tanning
compounds & waxes. Fruits, nuts and berries are harvested as food.
Maple syrup is an example of a unique non-wood product from the sap of
the maple tree.
Ecosystem Services
 Forests influence climate. The within-year fluctuations in atmospheric
CO2 in the temperate zone include a spring-through-autumn decline due
to plant photosynthesis during the growing season, and an autumn-
through-spring rise in CO2 as respiration and decomposition exceed
photosynthetic uptake. At a more regional scale, forests influence local
climate and weather. Rain forests transport great quantities of water to
the atmosphere via plant transpiration. (Water is taken up by plant roots,
bringing dissolved minerals into plant tissues. Plants exchange gases with
the atmosphere through openings in their leaves, and lose water in the
same way. That water loss provides the plant with a means to transport
materials upwards, and so is beneficial, so long as water loss is not
excessive). Much of that transpired water replenishes the clouds and rain
that maintain the rain forest. If the forest is cut, much more of that rain
will become river water, flow to distant seas, and the region will become
permanently drier. No rain forest can regenerate if this occurs. Forests
maintain local climate and strongly influence global fluxes of oxygen and
carbon dioxide. Before green plants appeared, it is believed that there
was very little oxygen in the atmosphere.
 Forests protect the top soil and husband important nutrients. A
famous study of Hubbard Brook, New Hampshire found that, after forest
harvest, summer streamflows greatly increased (because the forest was
no longer transpiring water) and nutrient outflow also increased greatly.
The annual flood crest of the Amazon River has increased over recent
years without any concomitant increase in rainfall, presumably due to
deforestation. Damaging floods are one frequent consequence of
deforestation.
 Forests harbor tremendous biological diversity, and have the potential
to provide us with new crop varieties and medicines. A good example of
medicinal use of tropical rain forest plants is the success of the drugs
vincristine and vinblastine, developed over the past 20 years from a wild
periwinkle found in the forests of Madagasgar. These drugs dramatically
improved the effectiveness of treatments for leukemia and other forms of
cancer, Since fewer than 1% of tropical plants have been screened for
possible use to medical science, ongoing deforestation results in the
permanent loss to science of other species before their value can be
recognized. The winged bean is a new food crop whose value has only
recently has been recognized.
Carbon Sequestration
Tropical deforestation contributes as much as 90% of the current net release of biotic
carbon dioxide into the atmosphere. This change may represent as much as 20% 30% of the total carbon flux due to humans - i.e., rivaling the carbon release due to
fossil fuel burning. Deforestation thus is an important potential source of carbon.
But what if we allow forests to regenerate? As they grow, forests will store or
sequester carbon, and so carbon sequestration has become part of the global
warming debate. What is the current balance sheet? Are the world’s forests a source
or a sink for atmospheric CO2? This is uncertain for three main reasons. We are not
sure how much forest is being burnt, vs the amount of regrowth. We don’t know
enough about the fate of deforested land, ie, how much is reverting to secondary
forest. We don’t know how forest disturbance is affecting soil and forest floor carbon
stores. Still, there is good evidence that the regrowth of previously-deforested areas
in Europe and North America during the 20th century has sequestered considerable
amounts of CO2 from the atmosphere.
Recovery time of a forest after clearing and
a burn. Note that it is only after 100+
years that forest become as they were
before the cut. Forest regrowth sequesters
atmospheric carbon as plant biomass.
3. Tropical Deforestation
The world’s tropical forests are disappearing at an alarming rate. A recent estimate is
that about 100,000 km2 are deforested each year, and another 100,000 km2 are
degraded. Estimates are constantly improving, based on satellite imagery, and
deforestation rates change in response to social and economic conditions, as well as
quality and accessibility of remaining forest. NASA's Landsat (satellite) cannot see
below the forest canopy, and so cannot detect below-canopy clearing, whereas radar
remote sensing can detect, eg, a coffee plantation beneath overstory trees.



Tropical forests once occupied 16 million km2, today about 8-9 million km2
remain
It is estimated that Latin America and Asia have already lost 40% of their
original forest; Africa a little more than half.
In many countries the rate of deforestation is accelerating. For example, most
of the forested areas of Bangladesh, India, the Philippines, Sri Lanka and
parts of Brazil's rain forest could be gone by the end of the century.
Only in the Congo Basin and some of the more isolated areas of the Amazon Basin
does the forest remain largely intact.
4. Brazil's Amazonian Forests
Brazil contains about 3.5 million km2 of tropical forest.
This is equivalent to 30% of the world's total. Almost
all of Brazil's standing tropical forests are in the
Amazon Basin, a region commonly known as
Amazonia. About half of Amazonia comprises upland
areas in which the original vegetation was tropical rain
forest. Perhaps another 0.5 million km2 consist of
transitional forests. In addition, there are large areas
of savanna in the southern reaches of Amazonia.
Biological Diversity of the Amazon

Amazonia has been characterized as the "single richest region of the tropical
biome."

A single hectare of rain forest near Manaus yielded 235 tree species over 5 cm
in diameter and 179 species over 15 cm in diameter.

There are 2000 known species of fish in the waters of the Amazon Basin. This
is eight times the number found in the Mississippi River system and 10 times
the number found in all of Europe.
Satellite data showing the
amount of land cover classified
as Deforested at 4 dates
between 1975 and 1988. Note
how much higher deforestation
rates were in 1988 compared to
earlier.
Roads
Roads usually accompany timber harvest, in order to move logs to sawmills and
markets. Even when tree harvest is highly selective, and much of the forest
remains, it has been found that the roads themselves have numerous adverse sideeffects. As forests become more open through thinning, they become drier, and
more susceptible to fire. In wet areas roads become pathways for surface runoff,
and carry sediments into streams, destroying aquatic life. Culverts installed where
roads cross rivers often block fish passage, and have devastated salmon populations
in the western USA. In tropical forests, roads allow hunters and poachers much
greater access, resulting in the large and very serious bushmeat trade that is
emptying tropical forests of their wildlife.
Forest fragmentation by roads in Central Africa. This
study shows that 42% of forest area in the six
countries is within 10 km of a road and more than
90% is within 50 km of a road (Source: WRI
Earthtrends).
5. Causes of Deforestation
Deforestation has many causes. Population pressures, profits, and internal social
and political forces can all push up the rate of forest loss. Access to markets,
requiring roads and capital, is an additional powerful force, recently expanded due to
the suite of changes referred to as globalization. Poor countries with expanding
populations, inequitable distribution of wealth and power, and possibly corrupt
governments are especially vulnerable.

In Indonesia, powerful families allied with government rulers control large
and highly valuable timber concessions. These forests are being rapidly
liquidated, at enormous profit.

In Brazil, many of the rural poor are moving to cities for work, and not
finding it. Productive farmland is controlled by a wealthy elite with a long
history of land ownership, and so many of the rural poor are landless. By
opening its frontier – the Amazon forest - to its landless poor, Brazil seeks
to provide a safety valve for what otherwise might be an explosive political
situation.

In many areas, poor people have few options to make income, and forests
have few protectors, and so land is cleared for agriculture and valuable
timber is sold for profit.
6. Forest Management and Recovery
Forest management may have many goals. Under rotation harvest, the goal
typically is to maximize annual harvest while ensuring that the area harvested is
consistent with forest regrowth rates and total area under management. This might
result in a second harvest of the same forest plot after some 60-100 years. The
length of time between successive harvests of a forest is called the rotation length.
Forests on federal and state lands are usually managed according to multiple use
doctrine. This means that in addition to forest harvest, the land is available for
recreation and maintains a healthy forest ecosystem. Managing to protect
biodiversity and to restore pre-settlement conditions are relatively recent goals. In
many parts of the world forests may be used by indigenous people for subsistence
hunting, forest harvest, and as a place to live. These people add yet more
considerations, and more stakeholders, to the challenge of forest management.
Forest restoration may seek to restore the system to a near-natural or completely
natural state, or to restore many aspects of the structure and function of an
undisturbed forest. The latter is usually referred to as rehabilitation, to emphasize
that the desired endpoint is not necessarily that of pre-settlement conditions.
Forest management in the USA often involves the controversial role of fire, and
whether to attempt to direct the course of forest succession. Most forests in the
lower 48 states are relatively young second-growth, and may have developed under
an unnatural degree of fire suppression. In the upper Midwest, for example, aspen
covers much of what was once white pine. Roughly 80 years old, these aspen forests
are at the age when they are likely to die. It is uncertain what type of forest will
replace them. Within oak-maple hardwood forests, the overstory is dominated by
oaks, whereas the seedlings are dominated by maple. To maintain oak forests, some
combination of fire and thinning is needed to favor recruitment by oaks.
Fire plays a major role in many forest types, including some that are highly fire
adapted. The jackpine of Michigan, for example, releases its seeds only after fire
heats its cones. Fire suppression has been US Forest Service policy since some
devastating fires of the 1950s brought calls for fire management. Since then,
fuelwood on the forest floor has accumulated and people attracted by scenic settings
have increasingly built houses in wooded areas. As a consequence, calls for fire
suppression are even stronger, and the human costs of fire are even greater than
before.

Trends in wildlife area burned
in wildfire in U.S.
Iverson, L.R. 2002. Biological trends in the United
States: an annotated on-line review.
Forests often will recover on their own, but perhaps not in the direction or as quickly
as we might prefer. The old growth spruce-hemlock forests of Southeast Alaska
appear to recover toward their original state, but it is hard to say how long this will
take. After all, extensive clear-cuts first took place only some 50 years ago, so there
are no forests that have fully recovered. Best estimates from comparisons of plots of
different ages, some caused by long-ago natural disturbances, suggests 200-400
years. It often is said that tropical forests will never recover from deforestation,
especially if the land is burned and the top soil is disturbed. This may be true in
some instances, but examination of lands abandoned 50, 100, or more years ago
suggests that we should be more optimistic. An ambitious plan to restore a dry
forest (one that sheds its leaves in the dry season) in Guanacaste, Costa Rica, serves
as a good example. Using fire and grazing to control invasive plants, and working
with a detailed knowledge of forest ecology, workers there hope to return this area to
its original forested state. In other regions of the tropics, native seedlings are grown
in nurseries and planted in forest openings to help speed recovery.
Summary

Forest ecosystems provide valuable human products and ecosystem services
§
Deforestation has already removed about half of the world’s forests, and in
your lifetime threatens to eliminate most of the remaining tropical forests.
Many temperate forests are re-growing, however
Forests are managed for multiple uses, to restore as much of possible of
natural ecosystem function, and in some cases to attempt to restore oldgrowth or pre-disturbance conditions
§
Suggested Readings and Links

Forest Patches in Tropical Landscapes, Island Press. John Schelhas and
Russell Greenberg, eds. 1996.

Thomas M. Lillesand and Ralph W. Kiefer, Remote Sensing and Image
Interpretation, Wiley Press, 1994.

Janet N. Abramovitz, Sustaining the World's Forests,in State of the World
1998, Norton/Worldwatch, 1998.

Gurney, R.J, J.L. Foster, and C. L. Parkinson. 1993. Atlas of Satellite
Observations related to Global Change, Cambridge Press, 1993.

"Tropical Forests and Grasslands" World Resources Institute

Extent of tropical deforestation

Tropical Forests in Decline (Canadian International Development Agency)

GC1 Lecture: The Tropical Rain Forest
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