Download Clear-cutting

Do Now: Movie Clip
• While watching the clip answer the following:
1) Identify and describe at least 2 causes/impacts of
deforestation in the Amazon.
Turn and Talk
• Why is it important to preserve natural lands and
sustain Earth’s biodiversity?
Aim: What are the major threats to
forest ecosystems?
Forests Vary in Their Make-Up,
Age, and Origins
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Make up 30% of earths land surface.
What are the three types of forests?
½ are tropical rain forests.
Classified based on their age and structure
Old Growth or Primary Forests
• Represents 36% of all forested land
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Uncut or not disturbed for several hundred years
Rich in biodiversity
Niches for many animals
Top 5: Russia, Canada, Brazil, Indonesia, and Papua New
Guinea.
Redwood Forest
Natural Capital: An Old-Growth Forest
Washington State
Olympic National
Forest
Fig. 10-2, p. 219
Second Growth Forest
• Represents 60% of forested land
• Trees in an area were removed. Ex: clear cutting,
forest fires, hurricanes, volcanic erruptions.
• Secondary ecological succession:
- naturally or when trees are planted
Tree Plantation
• Tree farm, commercial forest represent 4% of
forested land
• 1-2 species all the same age.
• Violates sustainability and biodiversity
• Depletion of nutrients from topsoil
• Harvested by clear cutting when trees are
commercially valuable. Then replanted.
• May supply most industrial wood in the future.
• Top 5: China, India, US, Russia, and Canada
Rotation Cycle of Cutting and Regrowth of
a Monoculture Tree Plantation
What are two ways in which this process can degrade an ecosystem?
Fig. 10-3, p. 219
Weak trees
removed
25 yrs
Clear cut
30 yrs
15 yrs
Years of growth
Seedlings planted
5 yrs
10 yrs
Fig. 10-3a, p. 219
Forests Provide Important Ecological
Services
• Support energy flow and chemical cycling
• Reduce soil erosion
• Absorb and release water
• Purify water and air
• Influence local and regional climate
• Store atmospheric carbon
• Habitats
Forests Provide Important Economic
Services
• Wood for fuel
• Lumber
• Pulp to make paper
• Mining
• Livestock grazing
• Recreation
• Employment
• Medicine
Natural Capital: Major Ecological and
Economic Services Provided by Forests
Fig. 10-4, p. 220
Read A Loud
• Science Focus: Putting a price tag on natures ecological
services.
Science Focus: Putting a Price Tag on
Nature’s Ecological Services
• Forests valued for ecological services
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Nutrient cycling
Climate regulation
Erosion control
Waste treatment
Recreation
Raw materials
• $4.7 trillion per year
Pause…Write…Discuss
• Some analysts believe that we should not try to put
economic values on the world’s irreplaceable
ecological services because their value is infinite? Do
you agree with this view? Explain. What is the
alternative?
Deforestation Step by Step
• Step 1: Build roads to access and remove timber
• Problems:
- Increased erosion
- Sediment runoff into waterways
- Habitat fragmentation
- Loss of biodiversity
Natural Capital Degradation: Building Roads
into Previously Inaccessible Forests
Fig. 10-5, p. 221
Deforestation Step by Step
• Step 2: Timber Harvesting; 3 methods
• Selective cutting
• Clear Cutting: All trees in an area are removed. Most
efficient/most harm.
• Strip cutting: removes a narrow strip of trees.
Selective cutting: middle aged/mature trees are
removed individually or in small groups.
Clear
stream
Fig. 10-6a, p. 222
Clear-cutting: All trees in an area are removed. Most
efficient/most harm.
Muddy
stream
Fig. 10-6b, p. 222
Strip cutting: removes a
narrow strip of trees
Uncut
Cut 1 year
ago
Dirt road
Cut 3–10
years ago
Uncut
Clear
stream
Fig. 10-6c, p. 222
Clear-Cut Logging in Washington State
Fig. 10-7, p. 222
Trade-offs: Advantages and Disadvantages
of Clear-Cutting Forests
Fig. 10-8, p. 223
a) Selective cutting
Summary:
(b) Clear-cutting
Clear stream
Muddy
stream
(c) Strip cutting
Uncut
Cut 1 year ago
Dirt road
If you were cutting trees
In a forest you owned,
Which method would
You choose and why?
Cut 3–10 years ago
Uncut
Clear stream
Stepped Art
Fig. 10-6, p. 222
Fire, Insects, and Climate Change Can
Threaten Forest Ecosystems (1)
• Surface fires
• Usually burn leaf litter and undergrowth
• May provide food in the form of vegetation that
sprouts after fire
• Crown fires
• Extremely hot: burns whole trees
• Kill wildlife
• Increase soil erosion
Fire, Insects, and Climate Change Can
Threaten Forest Ecosystems (2)
• Introduction of foreign diseases and insects
• Accidental
• Deliberate
• Global warming
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Rising temperatures
Trees more susceptible to diseases and pests
Drier forests: more fires
More greenhouse gases
Surface and Crown Fires
Fig. 10-9, p. 223
Nonnative Insect Species and Disease
Organisms in U.S. Forests
Figure 10, Supplement 8