Chapter 10
Sustaining Terrestrial Biodiversity: The Ecosystem Approach
Part 1 – Managing and Sustaining Forests
Photo credit: Cobb, Charles E. 1987. “Haiti: Against All
Odds.” National Geographic , Vol. 172, No. 5: 645-670 .
Photo by James Blair
HUMAN IMPACTS ON TERRESTRIAL
BIODIVERSITY
We have depleted and degraded some of the earth’s biodiversity and these threats are expected to increase.
2005 Millennium
Ecosystem Assessment
85% of earth’s land surface has been disturbed
Figure 10-2
WHY SHOULD WE CARE ABOUT
BIODIVERSITY?
Intrinsic Value:
ethical decision because it exists, it deserves protection regardless of its usefulness to humans
Instrumental Value:
Use Value – humans benefit through economic goods and services, ecological services, recreation, scientific information, and preservation for future uses.
Nonuse Value - humans gain satisfaction through its existence, aesthetics, or bequest for future generations.
Figure 10-3
MANAGING AND SUSTAINING FORESTS
What is a forest ?
Biome with enough average annual precipitation (at least
76 cm or 30 in) to support the growth of tree species and smaller forms of vegetation.
At least 10% tree cover
Cover approximately 30% of earth’s land surface
Three types: boreal, temperate, and tropical
Figure 10-4
DISTRIBUTION OF WORLD FORESTS
TYPES OF FORESTS
Old-growth forest
uncut or regenerated forest that has not been seriously disturbed for several hundred years.
22% of world’s forest.
Hosts many species with specialized niches.
Refuges for biodiversity
Figure 10-5
TYPES OF FORESTS
Second-growth forest
a stand of trees resulting from natural secondary succession
represents re-growth after human activities or natural forces have removed the trees in the area
63% of world’s forest
Second growth forest in Golden Ears Provincial
Park, British Columbia. Photo by Adam Gibbs
TYPES OF FORESTS
Tree plantation
tree farm
planted and managed stands of a particular tree species.
harvested by clearcutting when trees become commercially valuable trees usually of uniform age in a particular tract
5% of world’s forests
Top photo: Olive tree plantation in Morocco. Photo by Alfred
Molon. Bottom photo: Rubber tree plantation on Ko Mook
Island, Thailand © www.traveladventures.com
Clear cut
30
25
15
Years of growth
10
5
Weak trees removed
Seedlings planted
Fig. 10-6, p. 195
WHAT’S HAPPENING TO FORESTS?
WHAT’S HAPPENING TO FORESTS?
Estimated 0.3% - 0.8% of world forests are being cleared or degraded each year.
¾ of old growth forests are found in Russia, Canada, Brazil,
Indonesia, and Papua New Guinea
84% of world’s remaining forests are owned, managed, or otherwise influenced by governments
Modest gains in total temperate forests in North America,
Europe, and China
Some cut areas of tropical rainforest have begun re-growth or cover due to tree plantations.
Exponential worldwide demand for forest products: paper, lumber, and fuelwood
HARVESTING TREES
First step involves building logging roads.
Harmful effects include: increased erosion, sedimentation, habitat fragmentation, loss of biodiversity, exposure to nonnative species, increased accessibility, and disqualification from protection as wilderness.
Figure 10-8
HARVESTING TREES
(a) Selective cutting
•
•
•
•
Intermediate-aged or mature trees are cut singly or in small groups
Reduces crowding
Removes diseased trees
Encourages growth of younger trees and understory plants
Allows for multi-purpose use of a forest
Fig. 10-9a, p. 198
HARVESTING TREES
(b) Clear-cutting
All trees in an area are removed at once.
Fig. 10-9b, p. 198
Fig. 10-10 Clear-cut logging in
Washington State
Figure 10-11
HARVESTING TREES
(c) Strip-cutting
•
•
Strips of trees are cut along the contour of the land
Corridors are small enough to allow for natural recolonization and succession in a short period of time.
More sustainable than clear-cutting
Uncut
Stream
Fig. 10-9a, p. 198
Cut 1 year ago
Dirt road
Cut 3 –10 years ago
Uncut
SOLUTIONS
We can use forests more sustainably by emphasizing:
Economic value of ecological services.
Harvesting trees no faster than they are replenished.
Protecting old-growth and vulnerable areas.
Figure 10-12
PRESSURE ON FORESTS
Worldwide forest biomes are threatened by:
Deforestation
Fuelwood, agriculture, livestock grazing, urbanization
Fires
Demand for wood products
paper, lumber, and furniture
GLOBAL OUTLOOK:
EXTENT OF DEFORESTATION
Human activities have reduced the earth’s forest cover by as much as half.
Losses are concentrated in developing countries.
Figure 10-7
CASE STUDY: DEFORESTATION AND THE
FUELWOOD CRISIS
Fuelwood – wood that is gathered and burned for cooking and heating
usually conducted in an unsustainable manner in developing countries e.g. in Haiti, 98% of country is deforested due to fuelwood demand
– leads to erosion & poor soil quality
Solutions:
Community forestry projects
Providing alternative cooking/heating stoves that are more efficient
Burning renewable fuel sources – e.g. MIT scientist has found a way to make charcoal from spent sugarcane.
CASE STUDY: TROPICAL DEFORESTATION
Large areas of ecologically and economically important tropical forests are being cleared and degraded at a fast rate.
Figure 10-16
CASE STUDY: TROPICAL DEFORESTATION
At least half of the world’s terrestrial plant and animal species live in tropical rain forests.
Large areas of tropical forest are burned to make way for cattle ranches and crops.
Figure 10-17
WHY SHOULD WE CARE ABOUT THE LOSS
OF TROPICAL FORESTS?
About 2,100 of the 3,000 plants identified by the National Cancer Institute as sources of cancer-fighting chemicals come from tropical forests.
Figure 10-18
CAUSES OF TROPICAL DEFORESTATION
AND DEGRADATION
Tropical deforestation results from a number of interconnected primary and secondary causes.
Figure 10-19
Solutions
Sustaining Tropical Forests
Prevention
Protect most diverse and endangered areas
Educate settlers about sustainable agriculture and forestry
Phase out subsidies that encourage unsustainable forest use
Add subsidies that encourage sustainable forest use
Protect forests with debt-for-nature swaps and conservation easements
Certify sustainably grown timber
Reduce illegal cutting
Reduce poverty
Slow population growth
Restoration
Reforestation
Rehabilitation of degraded areas
Concentrate farming and ranching on already-cleared areas
Fig. 10-20, p. 207
ENVIRONMENTAL INVESTIGATION AGENCY
A large contributor to the loss of forests worldwide, particularly in the undeveloped world, is the international wood trade.
U.S. major driver of this market.
Revision of the Lacey Act of 1900 now enables U.S. government to regulate wood trade, pending resources.
The Lacey Act: Closing Down the Illegal Wood Trade
Part 1 Part 2
TYPES OF FOREST FIRES
1.
Surface fires – burn undergrowth and leaf litter on forest floor
Kill seedlings/small trees
Spare mature trees
Allow animals to escape
Help to release mineral nutrients
Removes flammable material that helps prevent more destructive fires
Release seeds/ enhance germination
Contribute to succession
Maintain animal habitats
2.
Crown fires – burn whole trees and ignite other trees
Destroy vegetation, kill wildlife, and increase soil erosion
May damage human structures
Figure 10-13
TYPES OF FOREST FIRES
3. Ground fires – smolder or creep slowly through the organic humus and leaf litter layers
May burn for extended periods of time
Expose minerals and underlying rock that is prone to erosion
Remove valuable topsoil
Kill large and small trees due to prolonged high temperatures
Destroy small organisms and fungus
Consume stored seeds in the leaf litter
Kill roots in all but deep soil layers
Leave a baked and hardened seed bed behind that prevents revegetation.
If they occur in wetlands or during less dry periods, such fires may actually be favorable.
TYPES OF FOREST FIRES
Depending on their intensity, fires can benefit or harm forests.
Burn away flammable ground material.
Release valuable mineral nutrients.
SOLUTIONS:
CONTROVERSY OVER FIRE MANAGEMENT
To reduce fire damage:
Set controlled surface fires.
Allow fires to burn on public lands if they don’t threaten life and property.
Clear small areas around property subject to fire.
SOLUTIONS:
CONTROVERSY OVER FIRE MANAGEMENT
In 2003, U.S. Congress passed the Healthy
Forest Restoration Act :
Allows timber companies to cut medium and large trees in 71% of the national forests.
In return, must clear away smaller, more fire-prone trees and underbrush.
Some forest scientists believe this could increase severe fires by removing fire resistant trees and leaving highly flammable slash.
CONTROVERSY OVER LOGGING IN U.S. NATIONAL
FORESTS
There has been an ongoing debate over whether U.S. national forests should be primarily for:
Timber.
Ecological services.
Recreation.
Mix of these uses.
Figure 10-14
SOLUTIONS:
REDUCING DEMAND FOR HARVEST TREES
Tree harvesting can be reduced by wasting less wood and making paper and charcoal fuel from fibers that do not come from trees.
Kenaf is a promising plant for paper production.
Figure 10-15
AMERICAN FORESTS IN A GLOBALIZED
ECONOMY
Timber from tree plantations in temperate and tropical countries is decreasing the need for timber production in the U.S.
This could help preserve the biodiversity in the U.S. by decreasing pressure to clear-cut old-growth and second-growth forests.
This may lead to private land owners to sell less profitable land to developers.
Forest management policy will play a key role.
CASE STUDY:
FOREST RESOURCES AND
MANAGEMENT IN THE U.S.
U.S. forests cover more area than in 1920.
Since the 1960’s, an increasing area of old growth and diverse second-growth forests have been clear-cut.
Often replace with tree farms.
Decreases biodiversity.
Disrupts ecosystem processes.
