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Chapter 12Human Impact on Resources and Ecosystems

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

ENV 301: Environmental Science

A Study of Interrelationships

Discussion notes: Scott M. Graves

Text: Enger • Smith

Ninth Edition

Human Impact on Resources and Ecosystems

Chapter 12

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Chapter Outline

• Historical Basis of Pollution

• Resource Utilization

– Mineral Resources

• Ecosystem Modification

– Forests

– Rangelands

– Wilderness

– Aquatic

• Managing Ecosystems for Wildlife

• Extinction

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Changing Role of Human Impact

• As human population grew, and tools

became more advanced, the impact a single

human could have on surroundings

increased.

• Environmental modifications allowed larger,

dense human populations to arise.

• Nearly all earth’s surface has been affected

in some way by human activity.

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Historical Basis of Pollution

• Pollution—Anything released into the

environment that affects an organism’s

survival and reproduction.

– Two primary factors affect the amount of

damage done by pollution:

Size of the population

Level of technological development

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Historical Basis of Pollution

• When the human population was small, waste

products were generally biodegradable.

– Human-caused pollution is produced when

waste is generated faster than it can be

degraded, especially as people began to

congregate and establish cities.

Throughout history, humans fought

ecosystem degradation with technology.

Short-term solutions.

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Renewable and Nonrenewable Resources

• Natural Resources—Structures and

processes humans can use, but not create.

– Renewable—Can be formed or

regenerated by natural processes.

Soil, Vegetation, Wildlife

– Non-Renewable—Not replaced by natural

processes, or, rate of replacement is

ineffective.

Minerals, Fossil fuels

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Costs Associated With Resource Utilization

• Economic—Monetary costs necessary to

exploit the resource.

• Energy—Energy expended exploiting the

resource.

• Environmental—Environmental effect of

resource exploitation (often deferred).

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Mineral Resources

• Major form of nonrenewable resource.

– Distribution is not uniform.

– Many deposits have already been exploited.

– North America consumes >30% of world minerals.

• Steps in Mineral Utilization

– Exploitation

– Mining

– Refining

– Transportation

– Manufacturing

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Recycling of Mineral Materials

• Many minerals are not actually consumed,

but only temporarily held.

• In many industries, cost of purchasing

recycled raw materials is higher than the cost

of purchasing virgin materials.

– More costly to produce products from

recycled material than virgin materials.

• Historically, monetary cost for energy has

been low, thus no incentive to recycle.

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Utilization and Modification of

Terrestrial Ecosystems

• Natural ecosystems have greater biodiversity

than human-managed ecosystems.

• Impact of Agriculture on Natural Ecosystems

– 40% of world’s land surface converted to

cropland and permanent pasture.

– Most productive natural ecosystems are the

first to be modified by humans.

Pressures to modify the environment are

greatest in areas with high population

density.

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Managing Forest Ecosystems

• 1/2 of U.S., 3/4 of Canada, and almost all of

Europe was originally forested.

• Because of increasing human population

growth, forested areas are under increasing

pressure to provide wood products and

agricultural land.

– Efficient methods of harvest and

transportation are important to reduce

economic cost of using forest resources.

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Economic and Energy Costs

• Major Economic Costs of Utilizing Forests:

– Purchasing or leasing land.

– Paying for equipment and labor.

– Building roads

• Major Energy Costs of Utilizing Forests:

– Harvesting

– Transportation

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Environmental Costs

• Modern forest management practices involve

a compromise that allows economic

exploitation while maintaining some of the

environmental values of the forest.

• Forested areas effectively reduce erosion.

– Loss of soil (nutrients) reduces soil fertility.

– Road building in forests increases erosion.

• Forest areas modify climate, and provide

recreational opportunities as well.

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Environmental Implication of Harvesting

• Clear Cutting—Removal of all trees in an

area. Economical but increases erosion,

especially on steep slopes.

• Patch-Work Clear Cutting—Clear cutting in

small, unconnected patches; preserves

biodiversity.

• Selective Harvesting—Single-tree

harvesting. Not as economical, but reduces

ecosystem damage.

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Plantation Forestry

• Many lumber companies maintain forest

plantations as crops and manage them in the

same way farmers manage crops.

– Plant single species, even-aged forests of

fast growing hybrid trees.

– Competing species are controlled by fire

and insects controlled by spraying.

– Mature rate as low as 20 years (vs. 100).

Quality of lumber reduced.

Low species diversity and wildlife value.

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Special Concerns About Tropical Deforestation

• Tropical forests have greater species diversity

than any other ecosystem.

• Not easy to regenerate after logging due to

poor soil characteristics.

• Deforestation Concerns

– Significantly reduces species diversity.

– Impacts climate via lowered transpiration.

– CO2 trap—Increased global warming.

– Human population pressure is greatest in

tropics, and still increasing.

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Managing Rangeland Ecosystems

• Rangelands—Lands too dry to support

crops, but received enough precipitation to

support grasses and drought-resistant

shrubs.

– Wildlife are usually introduced species.

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Environmental Costs of Utilizing Rangelands

• Management techniques and selective

grazing of animals may lead to the

elimination of non-preferred species.

• Important to regulate number of livestock on

rangelands, especially in dry areas.

• Desertification—Process of converting arid

and semi-arid land to desert.

– Over-grazing

– Firewood cutting

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Wilderness and Remote Areas

• Many areas in the world have had minimal

human impact.

– Some are remote and may have harsh

environmental conditions.

Wilderness Act (1964)—Wilderness:

“An area where the earth and its

community of life are un-trampled by

man, where man himself is a visitor

who does not remain.”

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Managing Aquatic Ecosystems

• Aquatic ecosystems divided into:

– Freshwater, Brackish, Marine

• Environmental costs related to utilizing

marine ecosystems fall into two categories:

– Over-fishing

– Environmental effects of harvesting

UN estimates 70% of world’s marine

fisheries are over-exploited.

Capacity should be reduced by 30%.

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Managing Aquatic Ecosystems

• Coastal regions are most productive regions of the oceans.

– Sunlight penetration—shallow—warm

– Nutrient deposition from land

– Wind/wave action stirs nutrients

• Fishing pressure and pollution are greatest in these areas.

– Trawls—nets dragged along bottom.

Large by-catch

Disturbs seafloor

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Environmental Costs Associated with

Utilizing Freshwater Ecosystems

• Two primary human alterations:

– Water Quality —Erosion, toxic run-off

– Exotic Species—Introduced species

Humans have great access to freshwater ecosystems.

Many North American freshwater fisheries are primarily managed for sport fishery.

Fisheries managers must balance:

Sport fisheries

Commercial harvesters

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Aquaculture

• Fish farming is becoming increasingly

important as a source of fish production.

– Currently, about 60% of all aquaculture

production is from freshwater systems.

Problems

Nutrient overloads

Escape into natural waters

Land conversion

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Managing Ecosystems For Wildlife

• Habitat Analysis and Management

• Animals have highly specific habitat

requirements that change throughout the year.

• Once habitat requirements are understood,

steps can be taken to alter habitat and

improve species success.

– Fire to eliminate poor habitats.

Kirtland Warblers—Jack Pine stands.

– Encourage growth of certain plant species.

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Population Assessment and Management

• Wildlife managers use population censuses to

check if populations are within appropriate

levels.

• With suitable habitat and protection, most wild

animals can maintain a sizeable population.

• But high reproductive capacities and/or heavy

protection can cause very large populations.

Whitetail Deer in Eastern U.S.

Elephants in Zimbabwe

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Population Assessment and Management

• Wildlife management often involves harvesting

for sport and meat.

• Hunting regulation is crucial.

– Seasons usually occur in the fall to take

advantage of surplus animals.

• When populations get too small, artificial

introductions can be implemented.

– Native species for augmentation.

– Non-native species for empty niches.

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Managing a Wildlife Population

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Predator and Competitor Control

• At one time it was believed populations of game species could be increased if predators were controlled.

– Still used in some situations.

– But, in many cases, human modification of habitat has a greater impact than natural predation.

– Many species do require refuges where they are protected from competing species or human influence.

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Migratory Waterfowl Management

• Migratory birds can travel thousands of

kilometers.

– North in spring to reproduce.

– South in fall to escape cold temperatures.

• International agreements necessary to

maintain appropriate habitat.

– Canada

– United States

– Mexico

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Extinction and Loss of Biodiversity

• Small, dispersed populations are more prone

to extinction.

– Successful breeding more difficult.

– Local weather conditions can severely

impact population size.

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Human-Accelerated Extinction

• Wherever humans have become the dominant

organisms, extinctions have occurred.

– Food

– Animals Parts

– Pest Status

– Habitat Alteration

Most Important Cause

Habitat Fragmentation

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Why Worry About Extinction ?

• Useful to Humans:

– Medical—Less than 1% of tropical

rainforest plant species have been tested

for pharmaceutical use.

– Food Resources

• Ecological—Species play specific roles in

ecosystem function.

• Ethical—Animals have a fundamental right to

exist.

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Extinction Prevention

• Endangered—Very low populations, could

become extinct in very near future.

• Threatened—Still exist in large numbers in

current range, but are declining in most

areas.

– Could become extinct if a critical

environmental factor is changed.

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Extinction Prevention

• Most extinction prevention interest occurs in

developed countries. Most vulnerable

species already eliminated.

• Less-developed and developing countries

have both highest population growth and the

majority of the world’s species.

– More concerned with immediate needs of

food and shelter than long-range issues

such as species extinction.

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Endangered Species Act (1973)

• Gave U.S. government jurisdiction over

threatened and endangered species.

– Directs that no activity by a government

agency should lead to the extinction of an

endangered species.

– Directs government agencies to use

whatever means necessary to preserve the

species in question.

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Chapter Summary

• Historical Basis of Pollution

• Resource Utilization

– Mineral Resources

• Ecosystem Modification

– Forests

– Rangelands

– Wilderness

– Aquatic

• Managing Ecosystems for Wildlife

• Extinction

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