Fire and Life
Intense heat, smoke, the crackling of
burning grasses, the crashing of flaming
trees—all these characteristics of fire
seem threatening. In recent years, forest
fires have burned huge areas of forest
and have endangered people and
property nearby. But even though fire
can be destructive, it can also be an
agent of life. In fact, scientists are actively
using fire to manage ecosystems—areas
that contain specific groups of living and
nonliving things. Prairies, forests, and
woodlands are examples of ecosystems.
The fear of fire has led people to limit
fires that are a natural part of some
ecosystems. Preventing or putting out
smaller fires in a forest ecosystem can
mean trouble. Occasional small fires burn
small amounts of material and cause only
limited damage. Without these smaller
fires, burnable materials may build up
and lead to the outbreak of a
catastrophic fire.
An astonishing variety of plants blooms in this prairie in Missouri.
The species of living things in some ecosystems have adaptations that
allow them to thrive on fire. In western forests in the United States
trees such as lodgepole pine and jack pine depend upon flames to
release seeds from their cones. Cape lilies lying under the forest floor
blossom almost immediately after a forest fire. On prairies, flowers
such as the rare coastal gayfeather in Texas or the fringed prairie
orchid in Illinois benefit from prairie fires.
On the left, seven months after a
controlled burn, light shines on a
new patch of wild hyacinth growing
at the base of an oak tree.
Observing Patterns
Ecosystems include living things, such as plants and animals, and nonliving things, such as
water and soil. Fires affect both the living and the nonliving. The photographs above show
part of an oak woodland ecosystem. The photograph on the left shows a burn—a fire set
deliberately by humans. The photograph on the right shows the same area seven months
later.
Ashes left from fires add nutrients to the soil. Fire also opens space on the forest floor.
Areas that were shaded by small trees, plants, and dead branches receive light. Over time,
wild hyacinth and other new plants grow around the oak, and new insects and animals
BRINGING BACK THE PRAIRIE
At one time natural events, such as lightning,
along with human activity caused regular
patterns of fire on the prairie. Bison grazed
on tender young plants that grew up after
fires, and the plants that weren't eaten by the
bison had room to grow. In 1989, an
organization called The Nature Conservancy
turned the Chapman-Barnard Cattle Ranch in
Northeast Oklahoma into the Tall Grass
Prairie Restoration Preserve.
Scientists at the preserve are using controlled
fire and reintroducing bison to the area.
Today there are more than 750 species of
plants and animals growing in the preserve.
In tall-grass prairie ecosystems, fire provides
similar benefits. Fire burns away overgrown
plants, enriches the soil, and clears the way
for the growth of new plants. Bison prefer to
graze on these new plants that
appear after a fire.
A New Understanding
Although some of the benefits provided by
ecosystems can't be measured, researchers are
starting to measure the financial contributions
of ecosystems. Ecosystems may help clean our
water, balance gases in the atmosphere, and
maintain temperature ranges.
Researchers today are studying these benefits.
In fact, a new frontier in ecology, called
ecosystem services, is emerging. This new
study is gaining the attention of both scientists
and economists.
Given our growing awareness of the
importance of ecosystems, should humans
deliberately set fire to areas in forests or
prairies? The answer to this question requires
an understanding of interactions among living
and nonliving parts of ecosystems. Forest and
prairie fires can be dangerous, but properly
managed, they provide important benefits to
society as well as to the natural world.
Before, you learned
• Living things need to obtain matter and energy
from the environment
• The Sun provides Earth with light and heat
Now, you will learn
• What factors define an ecosystem
• About living factors in an ecosystem
• About nonliving factors in an ecosystem
VOCABULARY
ecology, ecosystem, biotic factor, abiotic factor
Four Square Diagram = Include: definition,
example(s), picture, description, pronounce,
origin, sentence, synonym, fun fact.
Abiotic Factor
Living things depend on the environment.
You wouldn't find a kangaroo in the Arctic and
you won't see a polar bear in Australia. Each of
these organisms is suited to a certain
environment. The kangaroo and the polar bear
are able to survive despite the harsh
conditions of their surroundings. Ecology is the
scientific study of how organisms interact with
their environment and all the other organisms
that live in that environment.
Scientists use the word ecosystem to describe
a particular environment and all the living
things that are supported by it. An ecosystem
can be as small as a pond or as large as a
desert. What is important in an ecosystem is
how the living parts of the ecosystem relate to
the nonliving parts.
Let's take a look at a pond. A pond ecosystem is more than just water and fish. Plants grow in
and around the water, and animals feed on these plants. A variety of tiny microorganisms in the
water are food for fish and for each other. These are just a few of the living parts, or biotic
factors (by-AHT-ihk), of a pond ecosystem. The nonliving parts, or abiotic factors (AY-by-AHTihk), include the air that supplies oxygen and carbon dioxide, the soil that provides nutrients,
the water in the pond, and the sunlight that plants need to grow.
Biotic factors interact with an ecosystem.
Living things depend upon an ecosystem for food, air, and water, as well as other things they
need for survival. In turn, living things have an impact on the ecosystem in which they live.
Plants, as a biotic factor in land ecosystems, affect other biotic and abiotic parts of ecosystems.
Plants are an important source of food. The types of plants found in a particular ecosystem will
determine the types of animals that can live there. Plants can affect temperature by blocking
sunlight. Plant roots hold soil in place. Even the atmosphere is affected by plants taking in
carbon dioxide and releasing oxygen.
Animals, as biotic factors, also affect an ecosystem. A beaver that builds a dam changes the flow
of a river and so affects the surrounding landscape. Large herds of cattle can overgraze a
grassland ecosystem and cause the soil to erode. In an ocean biome, corals form giant reefs that
provide food and shelter for marine organisms.
Many abiotic factors affect ecosystems.
Abiotic factors include both the physical and
chemical parts of an ecosystem. Physical
factors are factors that you can see or feel,
such as the temperature or the amount of
water or sunlight. Important chemical factors
include the minerals and compounds found in
the soil and whether the ecosystem's water is
fresh or salty. It is the combination of different
abiotic factors that determines the types of
organisms that an ecosystem will support.
List four different abiotic factors that can affect
an ecosystem.
Tip: The word biotic means “living.” The prefix
a– in abiotic means “not,” so abiotic means
“not living.”
KEY CONCEPTS
1. Draw a diagram of an ecosystem near where you live. Label the factors “biotic” or “abiotic.”
2. Give two examples of how plants and animals affect their environment.
3. Describe how temperature, light, and soil affect an ecosystem.
CRITICAL THINKING
4. Predict Think of a forest ecosystem. Now imagine that a large volcanic eruption throws large
amounts of dust and ash into the air, blocking out sunlight. How might the forest ecosystem be
affected if the sunlight is blocked for a day? For a year? (If, then, because)
CHALLENGE
5. Apply Think of how you fit into your local environment. List ways in which you interact with
biotic and abiotic factors within your ecosystem.