Inspire Biology

Pioneer stages

Intermediate stages

Mature community

Bare rock

Lichens

Mosses Herbs and

weeds

Grasses

Shade-tolerant trees

Shrubs Shade-intolerant

trees

Ecological Succession

A complex set of interactions within an ecosystem can keep its numbers and types of

organisms relatively constant over long periods of time under stable conditions.

However, ecosystems are constantly changing. They might be modified in small ways,

such as a tree falling in the forest, or in large ways, such as a forest fire. Such changes

might alter the communities that exist in the ecosystem. Forest fires can be good and

even necessary for the forest community. Forest fires return nutrients to the soil. Some

plants, such as fireweed, have seeds that will not sprout until they are heated by fire.

Some ecosystems depend on fires to get rid of debris. If fires are prevented, debris

builds up to the point where the next fire might burn the shrubs and trees completely.

A forest fire might change the habitat so drastically that some species can no longer

survive, but other species might thrive in the new, charred conditions.

The change that occurs in an ecosystem when one community replaces another as a

result of changing abiotic and biotic factors is known as

ecological succession.

There are

two types of succession—primary succession, shown in

Figure 2,

and secondary

succession, shown on the next page in

Figure 3

. Both result in a changed ecosystem.

Figure 2

The formation of soil is the first step in primary succession. Once soil formation starts, there is

progressive succession toward a climax community.

VOCABULARY:

SCIENCE USAGE v. COMMON USAGE

primary

Science usage:

first in rank, importance, value, or

order

A doctor’s primary concern should be the patient.

Common usage:

the early years of formal education

Elementary grades, up to high school, are considered

to comprise a student’s primary education

CROSSCUTTING CONCEPTS

Stability and Change

Over the weekend spend some time outside in

the local area around your school, home, or nearby park. Observe the

biotic and abiotic factors present in the area. Do you think succession

is taking place in the area? What evidence suggests that things are

changing? What evidence suggests that things haven’t changed for a

long time? Use your phone or other video camera to record the

evidence.

Lesson 1 • Community Ecology