Unit10 Deforestation

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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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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/yris the (net) grams of carbon fixed

over each square kilometer in an average year.


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Characteristics of Earths 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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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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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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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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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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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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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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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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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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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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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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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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Examples: Ivory Coast, India

Proving cause and effect is difficult, but first

principles provides a reasonable mechanism

to explain these observations.

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Unit10 Deforestation