Geoscience Reference
In-Depth Information
thinking about forest ecosystems is less intuitive than
considering the adaptations and relative abundance of
different kinds of plants and animals, as in the previous
chapter. However, ecosystem science enables a better
understanding of the factors determining tree growth,
the development and maintenance of soils that allow
that growth, the amount and quality of water flowing
from watersheds, the effects of disturbances (such as
fires, insect outbreaks, and timber harvesting), and the
effects of climate change. curiously, dead plants and
animals are just as important as those still alive, if only
because they provide microhabitats for various forms of
life. in some cases the dead plant material—the
O hori-
zon
of the soil (commonly referred to as the forest floor,
litter, or debris)—functions as an important mechanism
for erosion control and for conserving nutrients that
may be limiting.
the intrigue of forest ecosystems, or any ecosystem
for that matter, is that the important processes are not
visible. to obtain data, scientists use various instru-
ments to measure processes such as solar radiation (in
the wavelengths used for photosynthesis), the rates of
plant growth and litter decomposition, and the move-
ment of nutrients and water. one's perspective on a
forest changes when such information is revealed. the
late F. Herbert Bormann, eminent ecosystem scientist at
Yale University, wrote:
thousands of gallons of water and tons of chemicals
streaming upward through tree trunks, photons of
energy absorbed by leaves and put to work evaporat-
ing water through leaves and fixing energy in organic
compounds, food manufactured in leaves streaming
to growing points, insect predators quietly nibbling
away, rocks being broken down into useable nutri-
ents, microbes disassembling organic compounds
and freeing nutrients for reuse, all species playing
out their roles in reproduction, the forest ecosystem
grudgingly restocking the forest stream with water,
Energy Flow, Productivity, and Carbon Sequestration
Most of the sun's energy reaching a forest, or any other
terrestrial ecosystem, is used for evaporating water and
heating the environment; a mere 1-3 percent is used for
photosynthesis. in mountain forests, because of high
elevation and a comparatively thin atmosphere with
low humidity, much of the heat gained during the day
is lost at night by radiation back into space. the result is
a relatively cool environment. Also, water is a limiting
factor in many places by mid- to late summer. conse-
quently, because of a cool, relatively dry environment,
tree growth rates are low in the Rocky Mountains com-
pared to rates in other places in north America, such
as the Pacific northwest and the Southeastern coastal
Plain (fig. 12.1). Annual variation in wood produc-
today when i visit a forest, there is . . . a sense of
being surrounded by an enormous dynamism:
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