Environmental Engineering Reference
In-Depth Information
Figure 8-9
Natural capital
degradation:
short (25- to 30-
year) rotation cycle of cutting and
regrowth of a monoculture tree
plantation in modern industrial
forestry. In tropical countries,
where trees can grow more
rapidly year-round, the rotation
cycle can be 6-10 years.
Weak trees
removed
25
15
Clear cut
Seedlings
planted
10
30
Years of growth
5
Highway
Highway
Cleared plots
for grazing
Cleared plots
for agriculture
Old growth
Figure 8-10
Natural capital degradation:
Building roads into previously inaccessible forests
paves the way to fragmentation, destruction, and degradation.
Once loggers reach a forest area, they use a variety
of methods to harvest the trees (Figure 8-11, p. 162).
With
selective cutting,
intermediate-aged or mature
trees in an uneven-aged forest are cut singly or in
small groups (Figure 8-11a).
Some tree species that grow best in full or moder-
ate sunlight are cleared completely in one or several
cuttings by
shelterwood cutting
(Figure 8-11b),
seed-tree
cutting
(Figure 8-11c), or
clear-cutting
(in which all trees
on a site are removed in a single cut; Figures 8-11d and
8-12, p. 163). Figure 8-13 (p. 163) lists the advantages
and disadvantages of clear-cutting.
A clear-cutting variation that can allow a more
sustainable timber yield without widespread destruc-
tion is
strip cutting
(Figure 8-11e). It involves clear-
cutting a strip of trees along the contour of the land,
with the corridor narrow enough to allow natural re-
generation within a few years. After regeneration, log-
gers cut another strip above the first, and so on. This
approach allows clear-cutting of a forest in narrow
strips over several decades with minimal damage.
Science: Harmful Environmental Effects
of Deforestation
Cutting down large areas of forests reduces
biodiversity and the ecological services forests
provide, and it can contribute to regional and global
climate change.
x
H
OW
W
OULD
Y
OU
V
OTE
?
Should conventional clear-
cutting of trees on publicly owned lands be banned except
for tree species needing full or moderate sunlight for growth?
Cast your vote online at http://biology.brookscole.com/miller11.
