DEFORESTATIONDEFORESTATIONDesign by Joe Naumann

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)

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

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

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

Percentage net NPP (gC/m2/yr) for different ecosystems

70%

3%

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.