Post on 25-Feb-2016
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Island Biogeography Islands have fewer species than
continents– The smaller the island the fewer the
species– The farther away from a continent
the fewer the species– Theory of island biogeography
Island Biogeography Small islands tend to have fewer
habitat types A small population easily wiped
out by a storm, flood, catastrophe or disturbance.– The smaller the pop the greater the
risk of extinction The farther an island is from the
mainland the harder it is to reach.
Island Biogeography Islands tend to maintain
consistent number of species over time.– Result of the rate at which species
added– Minus rate at which they become
extinct Concept applies to ecological
islands– A comparatively small habitat
separated from a major habitat of some kind.
Biogeography and People People alter biodiversity by
– Direct hunting– Directly disturbing habitats– Introducing exotic species into new
habitats Introductions have mixed results
– Food sources, landscaping, pets– Disastrous ecological consequences
Earth’s Biomes Rules of moving species
– 1st less harmful if moved w/in biotic province
– 2nd moving a specie into a new biome from a different biotic province likely to be harmful
– 3rd local moves less likely to be harmful than global moves
Chapter 13: Forests and Parks
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. Figure 10-5
Types of Forests
Second-growth forest: a stand of trees resulting from natural secondary succession.
Tree plantation: planted stands of a particular tree species.
Figure 10-6
Tree Niches Each species of tree has its own
niche and adapted to specific environmental conditions– E.g., water content of the soil– Tolerance of shade– Some adapted to early succession,
others to later stages
Harvesting Trees
Building roads into previously inaccessible forests paves the way for fragmentation, destruction, and degradation.
Figure 10-8
Fig. 10-8, p. 197
Old growth
Highway HighwayCleared plots for grazing
Cleared plots for agriculture
Harvesting Trees Trees can be
harvested individually from diverse forests (selective cutting), an entire forest can be cut down (clear cutting), or portions of the forest is harvested (e.g. strip cutting).
Figure 10-9
Fig. 10-4, p. 193
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
Provide numerous wildlife habitats
ForestsNatural Capital
Fuelwood
Lumber
Pulp to make paper
Mining
Livestock grazing
Recreation
Jobs
EconomicServices
EcologicalServices
Fig. 10-9a, p. 198
(a) Selective cutting
Fig. 10-9c, p. 198
Uncut(c) Strip cutting
Stream
Uncut
Cut 3–10years ago
Dirt road
Cut 1year ago
Fig. 10-9b, p. 198
(b) Clear-cutting
Effects of Harvesting Trees
Fig. 10-11, p. 198
Higher timber yields
Maximum profits in shortest time
Can reforest with fast-growing trees
Short time to establish new stand of trees
Needs less skill and planning
Good for tree species needing full or moderate sunlight
Disadvantages
Reduces biodiversity
Disrupts ecosystem processes
Destroys and fragments wildlife habitats
Leaves large openings
Increases water pollution, flooding, and erosion on steep slopes
Eliminates most recreational value
Trade-OffsClear-Cutting Forests
Advantages
Types and Effects of Forest Fires
Depending on their intensity, fires can benefit or harm forests.– Burn away flammable ground material.– Release valuable mineral nutrients.
Figure 10-13
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.
Approaches to Forest Management
Managing forests can involve – removing poorly formed and
unproductive trees to permit larger trees to grow
– Planting genetically controlled seedlings
– Controlling pests and diseases– Fertilizing the soil
Sustainable Forestry A sustainable forest is one from
which a resource can be harvested at a rate that does not decrease the ability of the forest ecosystem to continue to provide that same rate of harvest indefinitely.
What is Sustainability and How is it Applied to
Forests Two basic kinds of ecological
sustainability– Sustainability of the harvest of a
specific resource w/in an ecosystem (harvest of timber)
– Sustainability of the entire ecosystem (forest as an ecosystem)
Lack scientific data to demonstrate that either type ever achieved in forests
Fig. 10-12, p. 199
• Identify and protect forest areas high in biodiversity
• Grow more timber on long rotations
• Rely more on selective cutting and strip cutting
• Stop clear-cutting on steep slopes
• Cease logging of old-growth forests
• Prohibit fragmentation of remaining large blocks offorest
• Sharply reduce road building into uncut forest areas
• Leave most standing dead trees and fallen timber for wildlife habitat and nutrient recycling
• Certify timber grown by sustainable methods
• Include ecological services of forests in estimating their economic value
• Plant tree plantations on deforested and degraded land
• Shift government subsidies from harvesting trees to planting trees
Sustainable Forestry
Solutions
A Global Perspective on Forests
Vegetation of any kind can affect the atmosphere in four ways– 1. By changing the color of the
surface and therefore the amount of sunlight reflected and absorbed.
– 2. By increasing the amount of water transpired and evaporated from the surface to the atmosphere.
A Global Perspective on Forests
3. By changing the rate at which greenhouse gases are released from Earth’s surface into the atmosphere.
4. By changing “surface roughness”, which affects wind speed at the surface.
World Forest Area, Global Production and Consumption of
Forest Resources Countries differ greatly in their
forest resources– Potential of their land and climate
for tree growth– History of land use and deforestation
Forest Area
World Forest Area, Global Production and Consumption of
Forest Resources Developed countries account foe
70% of world’s total production and consumption of industrial wood products
Developing countries produce and consume about 90% of wood used as firewood
90% of world timber trade– Construction, pulp and paper– NA is the dominant supplier
World Forest Area, Global Production and Consumption of
Forest Resources In recent years world trade in
timber has not grown substantially.
The fundamental questions are– Whether forests can continue to
produce at least this amount of timber for an infinite period
– Whether they can produce even more as the population grows