deforestation
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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 Life600 myr Plants on land400 myr (green algae) Ferns, etc.200 - 70 myr Flowering plants100 myr - PowerPoint PPT PresentationTRANSCRIPT
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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 byrLife >3 byrMulticellular Life 600 myrPlants 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…..<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.
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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 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.
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Characteristics of Earth’s Forests
ForestType
Where? Area(km2) Rainfall Soil
NPP
gC/km2/yr
Biodiv-ersity
Boreal
Temperate
TropicalRainforest
High NLatitudes(50-60 °N)
Mid-Latitude(30° - 50°)
LowLatitude(0 - 30°)
12 M
12 M
17 M
Low20-50 cm/yr
Moderate50 to 100 cm/yr
High2 to 10 m/yr
Immature, butabundant minerals yet to be released
Rich, fertile,abundantnutrientreserves
Poor, highlyleached. Mostnutrientsrecycles
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 covered by different ecosystems
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NPP (gC/m2/yr) for different ecosystems
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Percentage net NPP (gC/m2/yr) for different 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 vapor to 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 the forested 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 abandoned due 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.