Essentials of Ecology

CONCEPTS 10-1A, 10-1B, AND 10-1C 219

Video 9, at http://www.learner.org/resources/series209.

html), and loss of biodiversity. Logging roads also ex-

pose forests to invasion by nonnative pests, diseases,

and wildlife species. And they open once-inaccessible

forests to farmers, miners, ranchers, hunters, and off-

road vehicle users.

Once loggers reach a forest area, they use a variety

of methods to harvest the trees (Figure 10-6). With se-

lective cutting, intermediate-aged or mature trees in an

uneven-aged forest are cut singly or in small groups

(a) Selective cutting

(b) Clear-cutting

(c) Strip cutting

Uncut

Clear

stream

Cut 3–10

years ago

Dirt road

Clear

stream

Muddy

stream

Cut 1

year ago

Uncut

Figure 10-6 Major tree harvesting methods. Question: If you

were cutting trees in a forest you owned, which method would you

choose and why?

Figure 10-7 Clear-cut logging in the U.S. state of Washington.

(Figure 10-6a). But often, loggers remove all the trees

from an area in what is called a clear-cut (Figures 10-6b

and 10-7). Clear-cutting is the most efficient way for a

logging operation to harvest trees, but it can do consid-

erable harm to an ecosystem.

For example, scientists found that removing all

the tree cover from a watershed greatly increases wa-

ter runoff and loss of soil nutrients (Chapter 2 Core

Case Study, p. 28). This increases soil erosion, which

in turn causes more vegetation to die, leaving barren

ground that can be eroded further, an example of a

harmful positive feedback loop (Figure 2-11, p. 45, and

Concept 2-5A, p. 44). More erosion also means

more pollution of streams in the watershed.

And loss of vegetation destroys habitat and degrades

biodiversity. Figure 10-8 (p. 220) summarizes some ad-

vantages and disadvantages of clear-cutting.

Learn more about how deforestation can

affect the drainage of a watershed and disturb its ecosystem

at CengageNOW™.

A variation of clear-cutting that allows a more sus-

tainable timber yield without widespread destruction

is strip cutting (Figure 10-6c). It involves clear-cutting

a strip of trees along the contour of the land within a

corridor narrow enough to allow natural regeneration

within a few years. After regeneration, loggers cut an-

other strip next to the first, and so on.

Daniel Dancer/Peter Arnold, Inc.