Environmental Encyclopedia

Подождите немного. Документ загружается.

Environmental Encyclopedia 3

Ecosystem

few years by Evelyn Hutchinson, Raymond Lindeman, and

the Odum brothers, Eugene and Howard.

The boundaries of an ecosystem can be somewhat

arbitrary, reflecting the interest of a particular ecologist in

studying a certain portion of the landscape. However, such

a choice may often represent a recognizable landscape unit

such as a woodlot, a wetland, a stream or lake, or—in the

most logical case—a

watershed

within a sealed geological

basin, whose exchanges with the

atmosphere

and outputs

via stream flow can be measured quite precisely. Inputs and

outputs imply an

open system

, which is true of all but the

planetary or global ecosystem, open to

energy flow

but

effectively closed in terms of materials except in the case of

large-scale asteroid impact.

Ecosystems exhibit a great deal of structure, as may

be seen in the vertical partitioning of a forest into tree, shrub,

herb, and moss layers, underlain by a series of distinctive

soil

horizons. Horizontal structure is often visible as a mosaic

of patches, as in forests with gaps where trees have died and

herbs and shrubs now flourish, or in bogs with hummocks

and hollows supporting different kinds of plants. Often the

horizontal structure is distinctly zoned, for instance around

the shallow margin of a lake; and sometimes it is beautifully

patterned, as in the vast

peatlands

of North America that

reflect a very complicated

hydrology

Ecosystems exhibit an interesting functional organiza-

tion in their processing of energy and matter. Green plants,

the primary producers of organic matter, are consumed by

herbivores, which in turn are eaten by carnivores that may

in turn be the prey of other carnivores. Moreover, all these

animals may have

parasites

as another set of consumers.

Such sequences of producers and successive consumers con-

stitute a food chain, which is always part of a complicated,

inter-linked food web along which energy and materials

pass. At each step along the food chain some of the energy

is egested or passed through the organisms as feces. Much

more is used for metabolic processes and—in the case of

animals—for seeking food or escaping predators; such energy

is released as heat. As a consequence only a small fraction

(often of the order of 10%) of the energy captured at a given

step in the food chain is passed along to the next step.

There are two main types of food chains. One is made

up of plant producers and animal consumers of living organ-

isms, which constitute a grazing food chain. The other con-

sists of organisms that break down and metabolize dead

organic matter, such as earthworms,

fungi

, and bacteria.

These constitute the

detritus

food chain. Humans rely

chiefly on grazing food chains based on

grasslands

, whereas

in a forest it is usual for more than 90% of the energy trapped

photosynthesis

to pass along the detritus food chain.

Whereas energy flows one way through ecosystems

and is dispersed finally to the atmosphere as heat, materials

427

are partially and often largely recycled. For example,

nitro-

gen

in rain and snow may be taken up from the soil by

roots, built into leaf protein that falls with the leaves in

autumn, there to be broken down by soil

microbes

to ammo-

nia and nitrate and taken up once again by roots. A given

molecule of nitrogen may go through this

nutrient

cycle

again and again before finally leaving the system in stream

outflow. Other nutrients, and

toxins

such as

lead

and

mer-

cury

, follow the same pathway, each with a different

resi-

dence time

in the forest ecosystem.

Mature ecosystems exhibit a substantial degree of

sta-

bility

, or dynamic equilibrium, as the endpoint of what is

often a rather orderly

succession

species

determined

by the

nature

of the

habitat

. Sometimes this successional

process is a result of the differing life spans of the colonizing

species, at other times it comes about because the colonizing

species alter the habitat in ways that are more favorable to

their competitors, as in an

acid

moss bog that succeeds a

circumneutral sedge fen that has in its turn colonized a pond

as a floating mat. Equilibrium may sometimes be represented

on a large scale by a relatively stable mosaic of small-scale

patches in various stages of succession, for instance in fire-

dominated pine forests. On the millennial time scale, of

course, ecosystems are not stable, changing very gradually

owing to immigration and emigration of species and to

evolutionary changes in the species themselves.

The structure, function, and development of ecosys-

tems are controlled by a series of partially independent envi-

ronmental factors:

climate

, soil parent material,

topogra-

phy

, the plants and animals available to colonize a given

site, and disturbances such as fire and windthrow. Each

factor is, of course, divisible into a variety of components,

as in the case of temperature and precipitation under the

general heading of climate.

There are many ways to study ecosystems. Evelyn

Hutchinson divided them into two main categories, holistic

and meristic. The former treats an ecosystem as a “black

box” and examines inputs, storages, and outputs, for example

in the construction of a lake’s heat budget or a watershed’s

chemical budget. This is the physicist’s or engineer’s ap-

proach to how ecosystems work. The meristic point of view

emphasizes analysis of the different parts of the system and

how they fit together in their structure and function, for

example the various zones of a wetland or a

soil profile

,or

the diverse components of food webs. This is the biologist’s

approach to how ecosystems work.

Ecosystem studies can also be viewed as a series of

elements. The first is, necessarily, a description of the system,

its location, boundaries, plant and animal communities, envi-

ronmental characteristics, etc. Description may be followed

by any or all of a series of additional elements, including:

1) a study of how a given ecosystem compares with others

Environmental Encyclopedia 3

Ecosystem health

locally, regionally, or globally; 2) how it functions in terms

of hydrology, productivity, and biogeochemical cycling of

nutrients and toxins; 3) how it has changed over time; and

4) how various environmental factors have controlled its

structure, function, and development. Such studies involve

empirical observations about relationships within and among

ecosystems, experiments to test the causality of such relation-

ships, and model-building to assist in forecasting what may

happen in the future.

The ultimate in ecosystem studies is a consideration

of the structure, function, and development of the global

or planetary ecosystem, with a view to understanding and

mitigating the deleterious impacts upon it of current human

activities. See also Biotic community

[Eville Gorham Ph.D.]

ESOURCES

OOKS

Hagen, J. B. An Entangled Bank, the Origins of Ecosystem Ecology. New

Brunswick, NJ: Rutgers University Press, 1992.

ERIODICALS

Herbertson, A. J. “The Higher Units: A Geological Essay.” Scientia 14

(1913): 199-212.

Tansley, A. G. “The Use and Abuse of Vegetational Concepts and Terms.”

Ecology 16 (1935): 284-307.

Ecosystem health

Ecosystem

health is a new concept that ecologists are exam-

ining as a tool for use in detecting and monitoring changes

in the quality of the

environment

, particularly with regard

to ecological conditions.

Ecosystem health (and

ecological integrity

)isanin-

dicator of the well-being and natural condition of ecosystems

and their functions. These indicators are influenced by natu-

ral changes in environmental conditions, and are related to

such factors as

climate

change and disturbances such as

wildfire

, windstorms, and diseases. Increasingly, however,

ecosystems are being affected by environmental stressors

associated with human activities that cause

pollution

and

disturbance, which result in many changes in environmental

conditions. Some

species

, communities, and ecological pro-

cesses benefit from those environmental changes, but others

suffer great damages.

The notion of ecosystem health is intended to help

distinguish between ecosystem-level changes that represent

improvements and those that are considered to be degrada-

tions. In the sense meant here, ecosystem-level refers to

responses occurring in ecological communities, landscapes,

or seascapes. Effects on individual organisms or populations

428

do not represent an ecosystem-level response to changes in

environmental conditions.

The notion of health

The notion of ecosystem health is analogous to that

of medical health. In the medical sense, health is a term used

to refer to the vitality or well-being of individual organisms.

Medical health is a composite attribute, because it is charac-

terized by a diversity of inter-related characteristics and con-

ditions. These include blood pressure and chemistry, wounds

and injuries, rational mental function and many other rele-

vant variables. Health is, in effect, a summation of all of these

characters related to vitality and well-being. In contrast, a

diagnosis of unhealthiness would focus on abnormal values

for only one or several variables within the diverse congrega-

tion of health-related attributes. For example, an individual

might be judged as being unhealthy because they had a

broken leg, or a high fever, or unusually high blood pressure,

or non-normal behavioral traits, even though they are “nor-

mal” with regards to all other traits.

To compare human and ecosystem health is, however,

imperfect in some important respects. Health is a relative

concept. It depends on what we consider “normal” at a

particular stage of development. The aches and pains that

are considered normal in a human at age 80 would be a

serious concern in a 20-year old. It is much more difficult,

however, to say what is to be expected in an ecosystem.

Ecosystems don’t have a prescribed lifespan and generally

don’t die but rather change into some other form. Because

of these problems, some ecologists prefer the notions of

ecological or biological integrity rather than ecosystem

health.

It should also be pointed out that many ecologists like

none of these notions (that is, ecosystem health, ecological

integrity, or biological integrity). The reason is that by their

very nature, these concepts are imprecise and difficult to

define. For these reasons, scientists have had difficulty in

agreeing upon the specific variables that should be included

when designing composite indicators of health and integrity

in ecological contexts.

Ecosystem health

Ecosystem health is a summation of conditions oc-

curring in communities, watersheds, landscapes, or sea-

scapes. Ecosystem health conditions are higher-level compo-

nents of ecosystems, in contrast with individual organisms

and their populations.

Although ecosystem health cannot be defined pre-

cisely, ecologists have identified a number of specific compo-

nents that are important in this concept. These include the

following indicators: (1) an ability of the system to resist

changes in environmental conditions without displaying a

large response (this is also known as

resistance

or tolerance);

(2) an ability to recover when the intensity of

environmental

Environmental Encyclopedia 3

Ecosystem management

stress

is decreased (this is known as

resilience

); (3) relatively

high degrees of

biodiversity

; (4) complexity in the structure

and function of the system; (5) the presence of large species

and top predators; (6) controlled

nutrient

cycling and a

stable or increasing content of

biomass

in the system; and

(7) domination of the system by native species and natural

communities that can maintain themselves without manage-

ment by humans. Higher values for any of these specific

elements imply a greater degree of ecosystem health, while

decreasing or lower values imply changes that reflect a less

healthy condition.

Ecologists are also working to develop composite indi-

cators (or multivariate summations) that would integrate the

most important attributes of ecosystem health into a single

value. Indicators of this type are similar in structure to com-

posite economic indicators such as the Dow-Jones Stock

Market Index and the Consumer Price Index. Because they

allow complex situations to be presented in a simple and

direct fashion, composite indicators are extremely useful for

communicating ecosystem health to the broader public.

[Bill Freedman Ph.D.]

ESOURCES

OOKS

Costanza, R., B.G. Norton, and B.D. Haskell. Ecosystem Health. New Goals

for Environmental Science. Washington, D.C.: Island Press, 1992.

DiGiulio, R., and E. Monosson. Interconnections Between Human and Eco-

system Health. New York: Chapman and Hall, 1996.

Woodley, S., J. Kay, and G. Francis, eds. Ecological Integrity and the Manage-

ment of Ecosystems. Boca Raton, FL: St. Lucie Press, 1993.

Ecosystem management

Ecosystem management (EM) is a concept that has germi-

nated within the past 20 years and continues to increase in

popularity across the United States and Canada. It is a

concept that eludes one concise definition, however, because

it embodies different meanings in different contexts and for

different people and organizations. This can be witnessed

by the multiple variations on its title, e.g., ecosystem-based

management or collaborative ecosystem management. The

definitions that have been given for EM, though varied, fall

into two distinct groups. One group emphasizes long term

ecosystem integrity, while the other group emphasizes an

intention to address all concerns equally, be they economic,

ecological, political or social, by actively engaging and incor-

porating the multitude of stakeholders (literally, those who

“hold a stake” in the issue) into the decision-making process.

One usable though incomplete definition of EM is

provided by R. Edward Grumbine: “Ecosystem management

integrates scientific knowledge of ecological relationships

429

within a complex sociopolitical and values framework toward

the general goal of protecting native ecosystem integrity

over the long term.” Ultimately, EM is a new way to make

decisions about how we humans should live with each other

and with the

environment

that supports us. And, it is best

defined not only by articulating an ideal description of its

contents, as Grumbine has done, but also through a rigorous

analysis of actual EM examples.

EM—a new management Style

Between the years 1992 and 1994, each of the four

predominant federal land management agencies in the

United States the

National Park Service

, the

Bureau of

Land Management

, the

Forest Service

and the

Fish and

Wildlife Service

implemented EM as their operative man-

agement paradigm. Combined, these four agencies com-

bined control 97% of the 650 million federally-owned acres

(267 million ha) in the United States, or roughly 30% of

the United States’ entire land area. EM has become the

primary management style for these agencies because of a

fact that became unavoidably apparent in the 1980s and

1990s the traditional resource management style does not

work. It is largely ineffective in addressing the loss and

fragmentation of wild areas, the increasing number of threat-

ened or

endangered species

, and the increased occurrence

of environmental disputes. This ineffectiveness has been at-

tributed to the traditional management style’s focus on

mainly

species

with economic value, its exclusion of the

public from the decision-making process, and its reliance

on outdated ecological beliefs. This explicit acknowledgment

that the traditional management style is inadequate has coa-

lesced within state and federal agencies, academia, and envi-

ronmental organizations, and has been bolstered by advances

in other relevant fields, such as

ecology

and conflict man-

agement.

If we break the traditional management style into indi-

vidual components, we see that each ineffective attribute has

a new or altered counterpart in EM. One of the best ways

to describe what EM actually entails is to explicate this

juxtaposition between traditional and new management

styles.

EM, as its name makes clear, concentrates on manag-

ing at the scale of an ecosystem. Alternately, traditional

resource management has tended to focus only on one or

a handful of species, especially those species that have a

utilitarian, or more specifically economic, value. For exam-

ple, the U.S. Forest Service has traditionally managed the

national forests so as to produce a sustained yield of timber.

This management style is often harmful to species other

than timber and can have negative effects on the entire

ecosystem. In EM, all significant biotic and abiotic compo-

nents of the ecosystem, as well as aspects such as economic

factors, are, ideally, reviewed and the important ecological

Environmental Encyclopedia 3

Ecosystem management

data incorporated into the decision-making process. For ex-

ample, review of a forest ecosystem may include an analysis

habitat

for significant song birds, a description of the

requirements needed to maintain a healthy black bear (Ursus

americanus) population, and a discussion of acceptable levels

of timber production.

A major problem associated with using an ecosystem

to define one’s management area is that boundaries of juris-

dictional authority, or political boundaries, rarely follow eco-

logical ones. This implies that by following political bound-

aries alone, ecological components may be left out of the

management plan one may be forced to manage only part

of an ecosystem, that part which is within one’s political

jurisdiction. For example, the Greater Yellowstone Ecosys-

tem goes far beyond the boundaries of

Yellowstone Na-

tional Park

. Therefore, a large scale EM project for Yel-

lowstone would require crossing several political boundaries

(e.g.,

national park

lands and

national forest

lands), which

is a difficult task because it entails several political jurisdic-

tions and political entities (e.g., state and federal agencies,

and county governments).

EM projects address this obstacle by forming decision

teams that include, among others, representatives from all

of the relevant jurisdictions. These decision-making bodies

can either act as advisory committees without decision-mak-

ing authority, or they can attempt to become vested with

the power to make decisions. This collaborative process in-

volves all of the stakeholders, whether that stakeholder is a

logging

company interested in timber production, or a pri-

vate citizen concerned with

water quality

. Such collabora-

tion diverges from the traditional resource management

method which made most decisions “behind closed doors”

asking for and receiving little public input. These agencies

traditionally shied away from actively engaging the public

because it is easier and faster to make decisions on one’s

own than to ask for input from many sources, there has

often been an antagonistic and distrustful relationship be-

tween state and federal agencies and the public, and, there

has been little institutional support (i.e., within the structure

of the agency itself) encouraging the manager in the field

to invite the public into the decision-making process.

EM’s more collaborative and inclusive decision-mak-

ing style ideally fosters a wiser and more effective decision.

This happens because as the decision team works toward

consensus, personal relationships are established, some trust

may form between parties, and, ultimately, people are more

likely to support a decision or plan they help create. EM

attempts to transcend the traditional antagonistic relation-

ship between agency personnel and the public. Because 70%

of the United States is privately owned, many environmental

issues arise on private land—land that is partially not affected

by federal and state natural resource legislation. EM allows

430

us to deal with these issues on private lands by establishing a

dialogue between private and public decision makers. Finally,

even though the EM decision-making style takes longer to

conduct, time is saved in the end because the decision

achieved is more agreeable to all interested parties. Having

all parties agree to a particular management plan decreases

the number of potential lawsuits which can arise and delay

the plan’s implementation.

Nonequilibrium ecology and EM

A change in the dominant theories in ecology has

encouraged this switch to EM and an ecosystem-level focus.

The idea that environments achieve a climax state of

homeostasis

has been a significant theory in ecology since

the early 1900s. This view, now discredited, was most vigor-

ously articulated by Frederic Clements and holds that all

ecosystems have a particular end point to which they each

progress, and that ecosystems are closed systems. Distur-

bances such as fires or floods are considered only temporary

setbacks on the ecosystem’s ultimate progression to a final

state. This theory offers a certain level of predictable

stability

the type of stability desired within traditional resource man-

agement. For example, if a forest is in its climax state, that

condition can be maintained by eliminating disturbances

such as forest fires, and a predictable level of harvestable

timber can be extracted (hence, this theory contributed to

the creation of “Smoky the Bear” and the national policy of

stopping forest fires on

public land

This teleological view of

nature

has ebbed and waned

in importance, but has lost favor especially within the past

two decades. Ecologists, among others, have realized that

from certain temporal and spatial points of view ecosystems

may seem to be in equilibrium, but in the long term all

ecosystems are in a state of nonequilibrium. That is, ecosys-

tems always change. They change because their ecological

structure and function is often regulated by dynamic external

forces such as storms or droughts and because they comprise

of varied habitat types which change and affect one another.

This acknowledgment of a changing ecosystem means

that predictable stability does not really exist and that an

adaptive management

style is needed to meet the chang-

ing requirements of a dynamic ecosystem. EM is adaptive.

After an EM decision team has formulated and implemented

a management plan, the particular ecosystem is monitored.

The team watches significant biotic and abiotic factors are

watched to see if and how they are altered by the manage-

ment practices. For example, if logging produces changes

which effect the fish in one of the ecosystem’s streams, the

decision team could adapt to the new data and decide to

relocate the logging.

The ability to adaptively manage is a crucial aspect of

EM, one that is not incorporated in traditional resource

management. As stated, the traditional management style

Environmental Encyclopedia 3

Ecoterrorism

emphasizes one or a few species and believes that ecosystems

are mostly stable. So, one only needs to view how a particular

species fares to determine the necessary management prac-

tices little monitoring is conducted and previous manage-

ment practices are rarely altered. In EM, management prac-

tices are constantly reviewed and adjusted as a result of

ongoing data gathering and the goals articulated by the

decision team.

The future of EM

The future of EM in the United States and Canada

looks stable, and other countries such as France are beginning

to use EM. There are many impediments, though, to the

successful implementation of EM. Institutions, such as the

United States’ federal land management agencies, are often

hesitant to actually change and when they do change it

happens very slowly; there are still many legal questions

surrounding the legitimacy of implementing EM on federal,

state and private lands; and, even though we attempt to

review the entire ecosystem in EM examples, we still lack

significant understanding of how even the most basic ecosys-

tems operate. Even given these impediments, it looks as if

EM will be the primary land management style of the United

States and Canada well into the next century.

[Paul Phifer Ph.D.]

ESOURCES

OOKS

Gunderson, L.H., C.S. Holling, and S.S. Light. Barriers and Bridges to the

Renewal of Ecosystems and Institutions. New York: Columbia University

Press, 1995.

Lee, K.N. Compass and Gyroscope: Integrating Science and Politics for the

Environment. Washington, D.C.: Island Press, 1993.

Yaffee, S.L., et al. Ecosystem Management in the United States: An Assessment

of Current Experience. Washington, D.C.: Island Press, 1996.

ERIODICALS

Grumbine, R.E. “What is ecosystem management?” Conservation Biology

8. (1994):27-38.

Ecotage

see

Ecoterrorism; Monkey-wrenching

Ecoterrorism

In the wake of the terrorist attacks on the World Trade

Center in New York City on September 11, 2001, the line

between radical environmental protest (sometimes called

ecoanarchism) and terrorism became blurred by strong emo-

tions on all sides. Environmentalists in America have long

held passionate beliefs about protecting the

environment

and saving threatened

species

from

extinction

, as well as

431

treating animals humanely and protesting destructive busi-

ness practices. One of the first and greatest environmental-

ists,

Henry David Thoreau

(1817–1862), wrote about the

doctrine of “civil disobedience,” or using active protest as a

political tool. The author Edward Abbey (1927–1989) be-

came a folk hero among environmentalists when he wrote

the novel, The Monkey Wrench Gang, in 1975. In that book,

a group of militant environmentalists practiced

monkey-

wrenching

, or sabotaging machinery in desperate attempts

to stop

logging

and mining. Monkey-wrenching, in its de-

struction of private property, goes beyond civil disobedience

and is unlawful. The American public has tended to view

monkey-wrenchers as idealistic youth fighting for the envi-

ronment and has not strongly condemned them for their

actions. However, the U.S. government views monkey-

wrenching as domestic terrorism, and since September 11,

2001, law enforcement activity concerning environmental

groups has been significantly increased.

Ecoanarchism is the philosophy of certain environ-

mental or

conservation

groups that pursue their goals

through radical political action. The name reflects both their

relation to older anarchist revolutionary groups and their

distrust of official organizations. Nuclear issues, social re-

sponsibility,

animal rights

, and grass-roots democracy are

among the concerns of ecoanarchists. Ecoanarchists tend to

view mainstream political and environmental organizations

as too passive, and those who maintain them as compromis-

ing or corrupt. Ecoanarchists may resort to direct confronta-

tion, direct action, civil disobedience, and guerrilla tactics

to fight for survival of wild places. Monkey-wrenchers per-

form sit-ins in front of bulldozers; they disable machinery

in various ways including pouring sand in a bulldozer’s gas

tank; they ram

whaling

ships; and they spike trees by driving

metal bars into them to discourage logging. Ecoanarchists

may practice ecotage, which is sabotage for environmental

ends, often of machines that alter the landscape. In the

early 2000s, radical environmentalists committed arson on

35 sport utility vehicles (SUVs) at a car dealership in Eugene,

Oregon, to protest the gas-guzzling vehicles, and set fire to

buildings at the University of Washington to protest

genetic

engineering

, for example.

Ecoanarchists do not necessarily view the destruction

of machinery as out-of-bounds, but the U.S. government

views it as terrorism. For instance,

Earth First!

, a radical

environmental group whose motto is, “No Compromise in

Defense of Mother Earth,” takes a stand against violence

against humans but does approve of monkey-wrenching.

The Federal Bureau of Investigation (FBI) defines terrorism

as, “the unlawful use, or threatened use, of violence by a

group or individual ... committed against persons or property

to intimidate or coerce a government, the civilian population

or any segment thereof, in furtherance of political or social

Environmental Encyclopedia 3

Ecotone

objectives.” The FBI reports that an estimated 600 criminal

acts of ecoterrorism have occurred in the United States since

1996, with damages estimated at $43 million. Two groups

associated with these acts of sabotage are the militant

Earth

Liberation Front

(ELF) and Animal Liberation Front

(ALF) groups. In 1998, ELF took credit for arson at Vail

Ski Resort, which resulted in damages of $12 million. The

act was a protest over the resort’s expansion on mountain

ecosystems.

Most environmental groups are more peaceful and

have voiced concern over radical environmentalists, as well

as over law enforcement officials who view all environmental

protesters as terrorists. For instance,

Greenpeace

activists

have been known to steer boats in the path of whaling ships

and throw paint on nuclear vessels as protest, and have been

jailed for doing so, although no people were targeted or

injured.

People for the Ethical Treatment of Animals

(PETA) members have thrown pies in the faces of business

executives whom they found guilty of inhumane treatment

of animals, considering the act a form of civil disobedience

and not violence.

The issues of ecoterrorism and ecoanarchism become

more heated as

environmental degradation

worsens. En-

vironmentalists become more desperate to protect rapidly

disappearing endangered areas or species, while industry

continually seeks new resources to replace those being used

up. Thrown in the middle are law enforcement officials,

who must protect against violence and destruction of prop-

erty, and also uphold citizens’ basic rights to protest.

The most famous ecoterrorist has been Theodore Kac-

zynski, also known as the Unabomber, who was convicted

of murder in the mail-bombing of the president of the Cali-

fornia Forestry Association. On the other end of the spec-

trum of environmental protest is Julia Butterfly Hill, whom

ecoterrorists and ecoanarchists would do well to emulate.

Hill is an activist who lived in a California redwood tree for

two years to prevent it from being cut down by the Pacific

Lumber Company. Hill practiced a nonviolent form of civil

disobedience, and endured what she perceived as violent

actions from loggers and timber company actions. Her

peaceful protest brought national attention to the issue of

logging in ancient growth forests, and a compromise was

eventually reached between environmentalists and the timber

company. Unfortunately, the tree in which Hill sat, which

she named Luna, was damaged by angry loggers.

[Douglas Dupler]

ESOURCES

OOKS

Abbey, Edward. The Monkey Wrench Gang. Salt Lake City: Dream Garden

Press, 1990.

432

Hill, Julia Butterfly. The Legacy of Luna: The Story of a Tree, a Woman,

and the Struggle to Save the Redwoods. San Francisco: Harper, 2000.

Thoreau, Henry David. Civil Disobedience, Solitude and Life Without Princi-

ple. Amherst, NY: Prometheus Books, 1998.

Whitaker, David J. The Terrorism Reader. New York: Routledge, 2001.

ERIODICALS

Chase, Alston. “Harvard and the Making of the Unabomber.”Atlantic

Monthly, June 2000, 41.

Earth First! Journal. P.O. Box 3023, Tucson, AZ 85702. (520) 620-6900.

Richardson, Valerie. “FBI Targets Domestic Terrorists.” Insight on the

News, 22 April 2002, 30.

Ecotone

The boundary between adjacent ecosystems is known as

an ecotone. For example, the intermediary zone between

a grassland and a forest constitutes an ecotone that has

characteristics of both ecosystems. The transition between

the two ecosystems may be abrupt or, more commonly,

gradual. Because of the overlap between ecosystems, an eco-

tone usually contains a larger variety of

species

than is to

be found in either of the separate ecosystems and often

includes species unique to the ecotone. This effect is known

as the edge effect. Ecotones may be stable or variable. Over

a period of time, for example, a forest may invade a grassland.

Changes in precipitation are an important factor in the

movement of ecotones.

Ecotourism

Ecotourism is ecology-based tourism, focused primarily on

natural or cultural resources such as scenic areas, coral reefs,

caves, fossil sites, archeological or historical sites, and

wild-

life

, particularly rare and

endangered species

The successful marketing of ecotourism depends on

destinations which have

biodiversity

, unique geologic fea-

tures, and interesting cultural histories, as well as an adequate

infrastructure. In the United States national parks are per-

haps the most popular destinations for ecotourism, particu-

larly

Yellowstone National Park

, the Grand Canyon, the

Great Smoky Mountains

and

Yosemite National Park

In 1999, there were 300 million recreational visits to the

national parks. Some of the leading ecotourist destinations

outside the United States include the Galapagos Islands in

Ecuador, the wildlife parks of Kenya, Tanzania, and South

Africa, the mountains of Nepal, and the national parks and

forest reserves of Costa Rica.

Tourism is the second largest industry in the world,

producing over $195 billion in domestic and international

receipts and accounting for more than 7% of the world’s trade

in goods and services. There were 693 million international

tourists in 2001, creating 74 million tourism jobs. Adventure

Environmental Encyclopedia 3

Ecotoxicology

tourism, which includes ecotourism, accounts for 10% of

this market. In developing countries tourism can comprises

as much as one-third of trade in goods and services, and

much of this is ecotourism. Wildlife-based tourism in Kenya,

for example, generates $350 million annually.

Ecotourism is not a new phenomena. In the late 1800s

railroads and steamship companies were instrumental in the

establishment of the first national parks in the United States,

recognizing even then the demand for experiences in

nature

and profiting from transporting tourists to destinations such

as Yellowstone and Yosemite. However, ecotourism has re-

cently taken on increased significance worldwide.

There has been a tremendous increase in demand for

such experiences, with adventure tourism increasing at a rate

of 30% annually. But there is another reason for the increased

significance of ecotourism. It is a key strategy in efforts to

protect cultural and

natural resources

, especially in devel-

oping countries, because resource-based tourism provides an

economic incentive to protect resources. For example, rather

than converting tropical rain forests to farms which may be

short-lived, income can be earned by providing goods and

services to tourists visiting the rain forests.

Although ecotourism has the potential to produce a

viable economic alternative to exploitation of the

environ-

ment

, it can also threaten it.

Water pollution

, litter, disrup-

tion of wildlife, trampling of vegetation, and mistreatment

of local people are some of the negative impacts of poorly

planned and operated ecotourism. To distinguish themselves

from destructive tour companies, many reputable tour orga-

nizations have adopted environmental codes of ethics which

explicitly state policies for avoiding or minimizing environ-

mental impacts. In planning destinations and operating

tours, successful firms are also sensitive to the needs and

desires of the local people, for without native support efforts

in ecotourism often fail.

Ecotourism can provide rewarding experiences and

produce economic benefits that encourage

conservation

The challenge upon which the future of ecotourism depends

is the ability to carry out tours which the clients find re-

warding, without degrading the natural or cultural resources

upon which it is based. See also Earthwatch; National Park

Service

[Ted T. Cable]

ESOURCES

OOKS

Boo, E. Ecotourism: The Potentials and Pitfalls. 2 vols. Washington, DC:

World Wildlife Fund, 1990.

Ocko, Stephanie. Environmental Vacations: Volunteer Projects to Save the

Planet. 2nd ed. Santa Fe, NM: John Muir, 1992.

Whelan, T., ed. Nature Tourism: Managing for the Environment. Washing-

ton, DC: Island Press, 1991.

433

A group of tourists visit the Galapagos Islands

(Photograph by Anthony Wolff. Phototake. Reproduced

by permission.)

Ecotoxicology

Ecotoxicology is a field of science that studies the effects of

toxic substances on ecosystems. It analyzes environmental

damage from

pollution

and predicts the consequences of

proposed human actions in both the short and long term.

With more than 100,000

chemicals

in commercial use and

thousands more being introduced each year, the scale of the

task is daunting. Ecotoxicologists have a variety of methods

with which they measure the impact of harmful substances

on people, plants, and animals. Toxicity tests measure the

response of biological systems to a substance to determine

if it is toxic. A test could study, for example, how well

fish live, grow, and reproduce in various concentrations of

industrial

effluent

. Another could evaluate the point at

which metal contaminants in

soil

damage plants’ ability to

convert sunlight into food. Still another could measure how

various concentrations of pesticides in agricultural

runoff

affect

sediment

and

nutrient absorption

wetlands

Analyses of chemical fate (i.e., where a pollutant goes once

it is released into the

environment

) can be combined with

toxicity-test information to predict environmental response

to pollution. Because toxicity is the interaction between a

living system and a substance, only living plants, animals,

Environmental Encyclopedia 3

Ecotoxicology

and systems can be used in these experiments. There is no

other way to measure toxicity.

Another tool used in ecotoxicology is the field survey.

It describes ecological conditions in both healthy and dam-

aged natural systems, including pollution levels. Surveys of-

ten focus on the number and variety of plants and animals

supported by the

ecosystem

, but they can also characterize

other valued attributes such as crop yield,

commercial fish-

ing

, timber harvest, or aesthetics. Information from a num-

ber of field surveys can be combined for an overview of

the relationship between pollution levels and the ecological

condition.

A logical question might be: why not merely measure

the concentration of a

toxic substance

and predict what

will happen from that? The answer is because chemical

analysis alone cannot predict environmental consequences

in most cases. Unfortunately, interactions between toxicants

and the components of ecosystems are not clear; in addition,

ecotoxicologists have not yet developed simulation models

that would allow them to make predictions based on chemi-

cal concentration alone. For example:

An ecosystem’s response to toxic materials is greatly influ-

enced by environmental conditions. The concentration of

zinc that will kill bluegill sunfish in Virginia’s soft waters

will not kill them in the much harder waters of Texas. Most

of the relationships between environmental conditions and

toxicity have not been established.

Most pollution is a complex mixture of chemicals, not just

a single substance. In addition, some chemicals are more

harmful when combined with other toxicants.

Some chemicals are toxic at concentrations and levels too

small to be measured.

An organism’s response to toxic materials can be influenced

by other organisms in the community. For example, a fish

exposed to pollution may be unable to escape from its

predators.

Ecotoxicologists use all three kinds of information:

field surveys, chemical analyses, and toxicity tests. Field sur-

veys prove that some important characteristic of the ecosys-

tem has been damaged, chemical measurements confirm the

presence of a toxicant, and toxicity tests link a particular

toxicant to a particular type of damage.

The scope of environmental protection has broadened

considerably over the years, and the types of ecotoxicological

information required have also changed. Toxicity testing

began as an interest in the effects of various substances on

human health. Gradually this concern extended to the other

organisms that were most obviously important to humans—

domestic animals and crop plants—and finally spread to

other organisms that are less apparent or universal in their

importance. Hunters are interested in deer, fishers in fish,

434

bird watchers in eagles or pelicans, and beachcombers in

loggerhead turtles. Keeping these organisms healthy requires

studying the effects of pollution on them. In addition, the

toxicant must not eliminate or taint the plants and/or animals

upon which they feed nor can it destroy their

habitat

. Indi-

rect effects of toxicants, which can also be devastating, are

difficult to predict. A chemical that is not toxic to an orga-

nism, but instead destroys the grasses in which it lays eggs

or hides from predators, will be indirectly responsible for

the death of that organism. Protecting all the

species

that

people value, along with their food and habitat, is a small

step toward universal protection. An ambitious goal is to

prevent the loss of any existing species, regardless of its

appeal or known value to human society.

Because each one of the millions of species on this

planet cannot be tested before a chemical is used, ecotoxicol-

ogists tested a few “representative” species to characterize

toxicity. If a pollutant could be found in rivers, testing might

be done on an alga, an insect that eats algae, a fish that eats

insects, and a fish that eats fish. Other representative species

are chosen by their habitat: on the bottom of rivers, mid-

stream, or in the soil. Regardless of the sampling scheme,

however, thousands of organisms that will be affected by a

pollutant will not be tested.

Some prediction must be made about their response,

nonetheless. Statistical techniques can predict the response

of organisms in general from information on a few randomly

selected organisms. Another approach tests the well-being

of higher levels of biological organization. Since natural

communities and ecosystems are composed of a large number

of interacting species, the response of the whole reflects the

responses of its many constituents. The health of a large

and complex ecosystem cannot be measured in the same way

as the health of a single species, however. Different attributes

are important. For example, examining a single species like

cattle or trout might require measuring

respiration

, repro-

duction, behavior, growth, or tissue damage. The condition

of an ecosystem, on the other hand, might be determined

by measuring production, nutrient spiralling, or colonization.

Since people depend on ecosystems for food production,

waste processing, and

biodiversity

, keeping them healthy

is important.

[John Cairns, Jr.]

ESOURCES

OOKS

Carson, R. Silent Spring. Boston: Houghton Mifflin, 1962.

, R. P., and P. G. Wells. Controlling Chemical Hazards. Boston: Unwin

Hyman, 1991.

Levin, S. A., et al., eds. Ecotoxicology: Problems and Approaches. New York:

Springer-Verlag, 1989.

Environmental Encyclopedia 3

Effluent

Wilson, E. O. Biodiversity. Washington, DC: National Academy Press,

1988.

Ecotype

A recognizable geographic variety, population, or ecological

race of a widespread

species

that is equivalent to a taxonomic

subspecies. Typically, ecotypes are restricted to one

habitat

and are recognized by distinctive characteristics resulting

from adaptations to local selective pressures and isolation.

For example, a population or ecotype of species found at

the foot of a mountain may differ in size, color, or physiology

from a different ecotype living at higher altitudes, thus re-

flecting a sharp change in local selective pressures. Members

of an ecotype are capable of interbreeding with other ecotypes

within the same species without loss of fertility or vigor.

Ectopistes migratorius

see

Passenger pigeon

Edaphic

Refers to the concept that soils have influence on living

things, particularly plants. For example, soils with a low

will more likely have plants growing on them that are adapted

to this level of

soil

acidity. Animals living in the area will

most likely eat these acid-loving plants. The more extreme

a soil characteristic, the fewer kinds of plants and animals

are able to adapt to the soil

environment

Edaphology

The ecological study of

soil

, including its role, value, and

management as a medium for plant growth and as a

habitat

for animals. This branch of soil science covers physical,

chemical, and biological properties, including soil fertility,

acidity, water relations, gas and energy exchanges, microbial

ecology

, and organic decay.

Eelgrass

Eelgrass is the common name for a genus of perennial grass-

like flowering plants referred to as Zostera. Zostera is from

the Greek word zostermeaning belt, which describes the dark

green, long, narrow, ribbon shape of the leaves that range

in size from 20 to 50 cm in length, but can grow up to 2

m. Eelgrass grows under water in estuaries and in shallow

coastal areas. Eelgrass is a member of a group of land plants

435

that migrated into the sea in relatively recent geologic times,

and is not a seaweed.

Eelgrass grows by the spreading of rhizomes and by

seed germination. Eelgrass flowers are hidden behind a

transparent leaf sheath. Long filamentous pollen is released

into the water, where it is spread by waves and currents.

Both leaves and rhizomes contain lacunae, which are air

spaces that provide buoyancy.

Eelgrass grows rapidly in shallow waters and is highly

productive, thus providing habitats and food for many ma-

rine organisms in its stems, roots, leaves, and rhizomes.

Eelgrass communities (meadows) provide many important

ecological functions, including:

anchoring of sediments with the spreading of rhizomes,

which prevents

erosion

and provides stability

decreasing the impact of waves and currents, resulting in

a calm

environment

where organic materials and sedi-

ments can be deposited

providing food, breeding areas, shelter and protective nurs-

eries for marine organisms of commercial, recreational, and

ecological importance

concentrating nutrients from seawater that are then avail-

able for use in the food chain

serving as food for water fowl and other animals such as

snails and sea urchins

detritus

(decaying plant matter), providing nutrition to

organisms within the eelgrass community, in adjoining

marshes, and in offshore sinks at depths up to 30,000 feet.

Eelgrass growth can be adversely impacted by human

activities, including

dredging

logging

, shoreline or over-

water construction,

power plants

oil spills

pollution

, and

species

invasion. Although transplantation projects de-

signed to restore eelgrass meadows have been initiated on

both coasts of the United States, creation of a large-scale

meadow with the complex functions and relationships of a

natural eelgrass system has not yet been achieved.

[Judith L. Sims]

ESOURCES

THER

Gussett, Diana.Eelgrass.Port Townsend Marine Science Center. [cited May

27, 2002]. <www.ptmsc.org/html/eelgrass.html#lore>.

Effluent

The etymological meaning of this term is “flowing forth

out of.” For geologists, this word refers to a wide range of

situations, from lava flowing from a

volcano

to a river

flowing out of a lake. However, effluent is now most com-

monly used by environmentalists in reference to the

Clean

Environmental Encyclopedia 3

Effluent tax

Water Act

of 1977. In this act, effluent is a

discharge

from a

point source

, and the legislation specifies allowable

quantities of pollutants. These discharges are regulated under

Section 402 of the act, and these standards must be met

before these types of industrial and municipal wastes can

be released into surface waters. See also Industrial waste

treatment; Thermal pollution; Water pollution; Water

quality

Effluent tax

Effluent

tax refers to the fee paid by a company to

discharge

to a sewer. As originally proposed, the fee would have been

paid for the privilege of discharging to the

environment

However, there is presently no fee structure which allows a

company, municipality, or person to contaminate the envi-

ronment above the levels set by

water quality

criteria and

effluent permits, unless fines levied by a regulatory agency

could be deemed to be such fees.

Fees are now charged on the bases of simply being

connected to a sewer and the types and levels of materials

discharged to the sewer. For example, a municipality might

charge all sewer customers the same rate for domestic sewage

discharges below a certain flowrate. Customers discharging

wastewater

at a higher strength and/or flowrate would be

assessed an incremental fee proportional to the increased

amount of contaminants and/or flow. This charge is often

referred to as a sewer charge, fee or surcharge.

There are cases in which wastewater is collected and

tested to ensure that it meets certain criteria (e.g., required

level of oil or a toxic metal, etc.) before it is discharged to

a sewer. If the criteria are exceeded, the wastewater would

require pretreatment. Holding the water before discharge is

generally only practical when flowrates are low. In other

situations, it may not be possible to discharge to a sewer

because the treatment facility is unable to treat the waste;

for example, many hazardous materials must be managed in

a different manner.

Effluent taxes force dischargers to integrate environ-

mental concerns into their economic plans and operational

procedures. The fees cause firms and agencies to re-think

water conservation

policies, waste minimization, pro-

cessing techniques and additives, and

pollution control

strategies. Effluent taxes, as originally proposed, might be

instituted as an alternative to stringent regulation, but the

sentiment of the current public and regulatory agencies is

to block any significant degradation of the environment. It

appears to be too risky to allow

pollution

on a fee basis,

even when the fees are high. Thus, in the foreseeable future,

effluents to the environment will continue to be controlled

by means of effluent limits, water quality criteria, and fines.

436

However, the taxing of effluents to a sewer is a viable means

of challenging industries to enhance pollution control mea-

sures and stabilizing the performance of downstream treat-

ment facilities.

[Gregory D. Boardman]

ESOURCES

OOKS

Davis, M. L., and D. A. Cornwell. Introduction to Environmental Engi-

neering. New York: McGraw-Hill, 1991.

Peavy, H. S., D. R. Rowe, and G. Tchobanoglous. Environmental Engi-

neering. New York: McGraw-Hill, 1985.

Tchobanoglous, G., and E. D. Schroeder. Water Quality. Reading, MA:

Addison-Wesley, 1985.

Viessman, W., Jr., and M. J. Hammer. Water Supply and Pollution Control.

5th ed. New York: Harper Collins, 1993.

Eggshell thinning

see

Dichlorodiphenyl-trichloroethane

A measure of the oxidation/reduction status of a natural

water,

sediment

soil

. It is a relative electrical potential,

measured with a potentiometer (e.g., a

meter adjusted

to read in volts) using an inert platinum electrode and a

reference electrode (calomel or silver/silver chloride). E

reported in volts or millivolts, and is referenced to the poten-

tial for the oxidation of

hydrogen

gas to hydrogen ions

). This electron transfer reaction is assigned a potential

of zero on the relative potential scale. The oxidation and

reduction reactions in natural systems are pH dependent

and the interpretation of E

values requires a knowledge of

the pH. At pH 7, the E

in water in equilibrium with the

oxygen in air is +0.76v. The lowest possible potential is -

0.4v when oxygen and other electron acceptors are depleted

and

methane

carbon dioxide

, and hydrogen gas are pro-

duced by the decay of organic matter. See also Electron

acceptor and donor

Paul Ralph Ehrlich (1932 – )

American population biologist and ecologist

Born in Philadelphia, Paul Ehrlich had a typical childhood

during which he cultivated an early interest in entomology

and zoology by investigating the fields and woods around

his home. As he entered his teen years, Ehrlich grew to be

an avid reader. He was particularly influenced by ecologist

William Vogt’s book, Road to Survival (1948), in which the

author was the outlined the potential global consequences