DEFORESTATION
Design by Joe Naumann
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 myr
Flowering plants 100 myr
(Angiosperrms)
Unit XI. Deforestation and the role of forests in
the climate system.
A. History of forests
• First land plants short…..<0.5 m (100 myr)
• As competition for light increased, they
grew taller. Required support (trunks).
• Tall forests for ~300 myr, but dramatic
changes in composition.
• Only last 100 myr would look familiar.
Less than 2% of Earth history.
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)
NPP: Net Primary Productivity
What is the net annual production of organic
matter 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.
Characteristics of Earth’s Forests
Forest
Type
Boreal
Where?
Area
Rainfall
(km2)
High N
Latitudes 12 M
(50-60 °N)
Soil
BiodivNPP
gC/km2/yr ersity
Immature, but
Low abundant
300 M
20-50 minerals yet
cm/yr to be released
Low
MidModerate Rich, fertile,
Temperate Latitude 12 M 50 to 100 abundant
500 M Moderate
(30° - 50°)
nutrient
cm/yr
reserves
Poor, highly
Low
High
Tropical Latitude
leached. Most
2
to
10
17
M
1000 M High
Rainforest (0 - 30°)
nutrients
m/yr
recycles
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)
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.
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.
Percentage
area covered
by different
ecosystems
NPP (gC/m2/yr)
for different
ecosystems
70%
3%
Percentage net
NPP
(gC/m2/yr) for
different
ecosystems
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.
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.
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
Unit XI. Deforestation and the role of forests
in the climate system.
D. The role of forests in the climate system.
How a geologist
views a tree.…Key
variables:
Leaf area index
Rooting depth
Water-holding
capacity of the soil.
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 vapor
to the atmosphere.
Two effects:
• landward migration of rainfall
• water vapor fuels more storms
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.
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 the
forested catchment. Rainfall similar in the
two basins, so difference is decreased
evapotranspiration.
Forested
Deforested
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 abandoned
due to lower rainfall, less humidity and more
extreme summer temperatures.
Similar example in India where rice production fell
after rainforest removed.
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.