Transcript Global Deforestation

GLOBAL DEFORESTATION
The Fate of a Renewable Resource
Deforestation
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Deforestation is the net reduction of forested area
on our planet
One of the greatest forces of global environmental
change (mainly over the past 200 years)
Reduced forest cover by human action has a huge
impact on global biodiversity
Why We Deforestaion occurs
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Forests are cleared, degraded and fragmented by:
Timber harvest
Conversion to Agriculture
Road building
Human caused fire
Removal for heating and cooking fires
Urban development
How Much Forest Do We Have
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Originally, almost half of the United States, threequarters of Canada, almost all of Europe, the plains
of the Levant, and much of the rest of the world
were forested
Currently about
34 million Km2 of
forest remains
What’s Left?
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About ½ of our original forests are gone
Each year another 13-16 million hectares are
removed (approximately the size of Panama)
22% of the world’s old growth forest remains
About ¼ of the world’s land area is still forested
Seven countries including: Russia, Brazil, USA,
Canada, China, Indonesia, Dem.Rep. Congo, account
for 60% of the world’s forested land
Frontier Forests of the World
Red = Frontier Forests, 8,000 years ago
Green = Frontier Forests Today
Pink = Current non-frontier forests
How Fast is it Disappearing?
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Most developed Countries currently have close to zero
net deforestation
Deforestation in Europe was largely completed before
the end of the 1800s
Most current deforestation currently occurs in the tropic
and most severely in poor countries
In Latin America and Asia deforestation rates are about
2% per year
At this rate by 2080 we will have only ¼ our current
forested area
Key Definitions
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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.
Importance of Forests
Forest Products
 In many poor areas wood is still commonly used for cooking.
 Building materials
 Furniture
 Pulp and paper products (including cardboard and
cellulose)
 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
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Influences climate: captures carbon, reduces
atmospheric CO2, involved with hydrologic cycle
Where forests are cut increased erosion and
flooding may be issues and may result in ultimately
a drier climate
Protection of soil and nutrients
Foster biodiversity (loss of potentially valuable
species for medicine or agriculture)
Tropical Deforestation
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about 100,000 km2 are deforested each year, and
another 100,000 km2 are degraded
Estimates are constantly improving, based on satellite
imagery
Causes of deforestation in the Amazon
Cattle ranches 65-70%
 Small-scale, subsistence agriculture 20-25%
 Large-scale, commercial agriculture 5-10%
 Logging, legal and illegal 2-3%
 Fires, mining, urbanization, road construction, dams 1-2%
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The State of Tropical Forests
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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.
Brazil contains about 3.5 million km2 of tropical
forest. This is equivalent to 30% of the world's total
Biodiversity and the Amazon
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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.
The Impact of Roads
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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 side-effects
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
roads allow hunters and poachers much greater access, resulting in
the large and very serious bushmeat trade
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
Forest Management and Recovery
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
Results 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
Forest Management and Recovery
Multiple Use:
Forests on federal and state lands are usually
managed according to multiple use principles
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 presettlement conditions are relatively recent goals
Forest Management and Recovery
Indigenous Use:
Forests may be used by indigenous people for:
 subsistence
hunting
 forest harvest
 as a place to live
Forest Management and Recovery
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If left to nature forests will re-establish themselves
This process is called Succession and typically takes
from 50-200 years depending on tree growth rate
Tropical forest are very vulnerable as they are
difficult to rehabilitate. Soil is quick to be leached
of nutrients and may be lost through erosion
Restoration Vs Rehabilitation
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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 and Fire
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Fire is suppressed in many forest ecosystems to:
Protect valuable commercial wood
 Protect human homes in or adjacent to forest
 Protect old growth ecosystems
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In many cases fire is positive to a forest ecosystem
Some trees require fire to reproduce (jack pine)
Other trees require thinning of the understory to
repopulate (Oak)
Fire suppression created a build up of dry fuel
This increases the intensity of a forest fire and may
cause greater ecosystem damage