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