unit10 deforestation.ppt
TRANSCRIPT
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DEFORESTATIONDEFORESTATIONDesign by Joe Naumann
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Unit XI. Deforestation and the role of forests
in the climate system.
A. History of forests
Earth 4.6 byr
Life >3 byr
Multicellular Life 600 myr
Plants on land 400 myr (green algae)
Ferns, etc. 200 - 70 myrFlowering plants 100 myr
(Angiosperrms)
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Unit XI. Deforestation and the role of forests in
the climate system.
A. History of forests
• First land plants short…..
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Unit XI. Deforestation and the role of forests
in the climate system.
B. Forest types
• Boreal Forests (conifers)
• Temperate Forests
(mixed deciduous hardwoods)
• Tropical Rainforests
(conifers and hardwoods)
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NPP: Net Primary Productivity
What is the net annual production of organicmatter by a particular ecosystem,usually
measured in the amount of Carbon fixed as
organic matter.Net means the total fixed minus the total
respired.
gC/km2 /yr is the (net) grams of carbon fixed
over each square kilometer in an average year.
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Characteristics of Earth’s Forests
Forest
Type
Where? Area
(km2
)Rainfall Soil
NPP
gC/km2 /yr
Biodiv-
ersity
Boreal
Temperate
Tropical
Rainforest
High N
Latitudes(50-60 °N)
Mid-
Latitude(30° - 50°)
Low
Latitude
(0 - 30°)
12 M
12 M
17 M
Low
20-50
cm/yr
Moderate
50 to 100
cm/yr
High
2 to 10
m/yr
Immature, but
abundant
minerals yet
to be released
Rich, fertile,
abundant
nutrient
reservesPoor, highly
leached. Most
nutrients
recycles
300 M
500 M
1000 M
Low
High
Moderate
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Unit XI. Deforestation and the role of forests in
the climate system.
B. Forest types
• Boreal Forests: slow growing, cold, 1/2
year low light, shallow, immature, but
mineral-rich soils. Low plant and animal
diversity.
Capable of sustained harvest, but low yield
(slow growth)
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Unit XI. Deforestation and the role of forests in
the climate system.
B. Forest types
• Temperature Forests: Mixed deciduous
hardwoods and evergreens, fertile soils.
Resistent to disturbance: if cleared, rapid
recolonization.
Sustained yield OK in most regions.
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Unit XI. Deforestation and the role of forests in
the climate system.
B. Forest types
• Tropical Rainforest: Closed canopy, high
rainfall. Most in Brazil (Amazonia),
central West Africa (Congo, Zaire),
Indonesia and Madigascar. Also Central
America, Angola, Peru, Bolivia, India and
scattered outliers.
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Percentage
area coveredby different
ecosystems
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NPP (gC/m2 /yr)
for differentecosystems
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Percentage net
NPP
(gC/m2 /yr) fordifferent
ecosystems
70%
3%
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Unit XI. Deforestation and the role of forests
in the climate system.
B. Forest types
• Tropical Rainforest are the lungs of the
world. They inhale CO2
and exhale O2
through the process of photosynthesis.
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Unit XI. Deforestation and the role of forests
in the climate system.
B. Forest types
• Tropical Rainforest: The risky bit…..
Soils: Ancient, little rock, highly leached
(high rainfall), and few sources of new
nutrients. Almost all nutrients are
recycled.
Incapable of sustained high harvest.
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Unit XI. Deforestation and the role of forests
in the climate system.C. Deforestation: why we should be
concerned.
• Loss of biodiversity
• Global warming (burning releases CO2)
• Climate impacts
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Unit XI. Deforestation and the role of forests
in the climate system.
D. The role of forests in the climate system.
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How a geologist
views a tree.…Key
variables:
Leaf area index
Rooting depth
Water-holding
capacity of the soil.
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D. The role of forests in the climate system.
Amazonia: Estimated that 50% of the rainfall
over the Amazon Basin is recycled water.
During a rainfall event, leaves intercept rainwater,
and organic-rich soil absorbs rainfall. Leaf
evaporation and transpiration returns water vaporto the atmosphere.
Two effects:
• landward migration of rainfall• water vapor fuels more storms
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D. The role of forests in the climate system.
Amazonian Paradox:
Amazon rainforest requires heavy rainfall to
exist, but half the rainfall is itself depedent on
the rainforest being present.
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D. The role of forests in the climate system.
Examples:
Two adjacent catchments…. One clear cut,
the other left forested. Stream runoff in the
deforested catchment was 4 to 10 times theforested catchment. Rainfall similar in the
two basins, so difference is decreased
evapotranspiration.
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Forested Deforested
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D. The role of forests in the climate system.
Examples:
Ivory Coast: Replacement of rainforest by cropland
over last 5 deacdes,; runoff increased 8-fold.
Areas formerly suitable for cocoa now abandoneddue to lower rainfall, less humidity and more
extreme summer temperatures.
Similar example in India where rice production fell
after rainforest removed.
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D. The role of forests in the climate system.
Examples: Ivory Coast, India
Proving cause and effect is difficult, but first
principles provides a reasonable mechanism
to explain these observations.