Page 336 - Environment: The Science Behind the Stories

20

15 Net annual growth
Trees (billions of cubic feet) 10
Net annual removal

5
FIGURE 12.12 Even-aged stands differ from uneven-aged
stands. Even-aged management, with all trees of equal age, can
1 be seen in the foreground in a plantation regrowing after clear-
cutting. Uneven-aged management maintains a mix of tree ages,
National Other public Private as seen in the more mature forest.
forests forests land
Type of land ownership
FIGURE 12.11 As the United States recovers from deforesta- production lack the structural complexity that characterizes a
tion, trees are growing more quickly than they are being mature natural forest as seen in Figure 12.3 (p. 327). Planta-
removed. This is particularly true in national forests and on other tions are also vulnerable to outbreaks of pest species such as
public lands. However, forests that regrow after logging often differ bark beetles, as we shall soon see.
substantially from the forests that were removed. “Private land” here For all these reasons, some harvesting methods aim to
combines land owned by the timber industry and by small landholders. Data are maintain uneven-aged stands, which contain trees of a mix of
for 2006, from USDA Forest Service, 2008. Forest resources of the United States, ages. The greater structural diversity of uneven-aged stands
2007. U.S. Department of Agriculture, Washington, D.C. provides superior habitat for most wild species and, if diverse
tree species are intermixed, makes these stands more akin to
national forests then began to decrease in the 1980s as eco- natural, ecologically functional forests.
nomic trends shifted, public concern over clear-cutting grew,
and management philosophy evolved. By 2006, regrowth was We harvest timber by several methods
outpacing removal on these lands by 11 to 1 (see Figure 12.11).
Note, however, that even when regrowth outpaces removal, When timber companies harvest trees, they may choose from
the character of forests may change. Once primary forest is several methods. In the simplest method, clear-cutting, all trees
replaced by younger secondary forest or by single-species in an area are cut (FIGURE 12.13). Clear-cutting is cost-efficient,
plantations, the resulting community may be very different,
and generally it is less ecologically valuable.

Plantation forestry has grown

Today the U.S. timber industry focuses on production from CHAPTER 12 • FOREST S, FOREST MAN A GEMENT, AND PR O TECTED AREAS
plantations of fast-growing tree species planted in single-
species monocultures (p. 266). Because all trees in a given
stand are planted at the same time, the stands are even-aged,
with all trees the same age (FIGURE 12.12). Stands are cut after a
certain number of years (called the rotation time), and the land
is replanted with seedlings. Such plantation forestry is grow-
ing quickly worldwide, and today fully 7% of the world’s for-
ests are plantations. One-quarter of these feature non-native
tree species.
Ecologists and foresters view plantations as akin to crop
agriculture. Because there are few tree species and little vari-
ation in tree age, plantations do not offer habitat to many for-
est organisms. For instance, stands of red pine planted near
Escanaba, Michigan, host far less biodiversity than the more- FIGURE 12.13 Clear-cutting is cost-efficient for timber
diverse forests of multiple tree species that surround them. companies but has ecological consequences, including soil
Even-aged single-species plantations managed for timber erosion, water pollution, and altered community composition. 335

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