22
—Lancaster Farming. Saturday. July 20. 1974
The Importance of
by William E. Sharpe
Water Resources Specialist
Pennsylvania State University
Most drinking water comes from the forested watersheds
of Pennsylvania. These watersheds have long produced the
high-quality water necessary for drinking. In addition,
forested watersheds offer a measure of protection against
rapid runoff of precipitation, thus reducing flood hazards.
Erosion and accompanying sedimentation of streams and
reservoirs are greatly reduced by the presence of forests.
These forest influences have long been recognized by man.
In 1215 Louis VI of France instituted an ordinance titled “Hie
decree of waters and forests,” which was intended to protect
forested watersheds from being stripped of trees. In 1608 a
letter was written to the government of Venice enumerating
the effects of deforestation in the Alps on sedimentation in
the lagoon at Venice and the flooding of the Po River.
Unfortunately, these European experiences were soon
forgotten by the early settlers of America. They looked upon
the vast forests covering eastern North America as
inexhaustible and set out to clear the land with uncontrolled
zeal. Such was the magnitude of these forest-clearing efforts
that in 1867 a report was published on the disastrous effects of
deforestation in Wisconsin. This report and other happening*
in those times led to the passage of legislation by Congress to
protect the watersheds of navigable streams. The U. S.
Forest Service was created to administer lands acquired by
the federal government under this legislation.
A great controversy arose at this time over the importance
of forests in flood protection. One result of this controversy
was the establishment nf the first experimental watershed in
the United States at Wagon Wheel Gap, Colorado. Since that
time many more experimental watersheds have been
established throughout the country. Much of what we know
about the relationships of forests and water is a result of
work done at these research facilities.
There is no question that forests are important in in
fluencing the flow characteristics of streams and rivers, but
they do not have much influence on the general climate of an
area. A popular misconception is that more rain falls on
forested areas than on nonforested areas because the forests
contribute more water vapor to the air. We know that such a
notion is false because virtually all of the rain falling on
continental land masses is originally evaporated from the
oceans and transported over the land mass by prevailing
winds.
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__ blanket of dead leaves and humus shields the soil from the
H Awnof/\/l u/nf of raindro P«. which have already had their fall
JT OlcSlCfl Ilr RlfirSilfinS broken by the tree crowns. Soil thus protected is seldom
dislodged and carried into streams to degrade water quality,
The simple observation that it is cooler in the shade tells choke reservoirs, or cover recreation areas with silt,
you that forests are important to the climate near the ground. Forests may affect water quality in many more subtle
One very important aspect of the forest's shading of the ways. Some researchers report that the quality of
ground is its influence on the melting of snow. During winter, precipitation falling through forest canopies differs with
when all the leaves are off of deciduous trees, there is still a forest cover. For instance, precipitation reaching the ground
noticeable shading effect. Slower-melting snow means a less under conifers is likely to be of different quality from that
rapid rise of stream water levels and a reduced flood hazard, falling through an opening in the forest. Similarly, some
Another popular belief is that streams and springs will dry forest species such as alder are able to fix nitrogen in much
up when forests surrounding them are cut. This is not true, the same way as alfalfa does. Streams with alder borders
Research shows that more water is added to streams and tend to have a higher nitrate content. These small increases
springs when forests are cut. This shouldn’t seem surprising in nitrate mean more food for fish,
when you consider the tremendous amounts of water used Shading by forest trees lowers water temperature. Shallow
and evaporated by trees. A single tree is capable of headwater streams are especially influenced by forest
evaporating as much as 10,000 gallons of' water a day. If such shading. Large increases in stream temperature accompany
figures are multiplied by the number of trees in a forest, the the removal of streamside forest vegetation. These tern
tremendous water-using potential of forests is obvious. When perature increases greatly affect aquatic organisms living in
forests are cut, the water that they would have used is the stream and are detrimental to organisms requiring cool
available for streamflow. Thus, streamflows increase waters in which to live. Fortunately, good forest
dramatically for the first few years following forest cutting, management practices prevent this from happening.
Shortly, young trees, growing in place of the ones cut down, Finally, many aquatic organisms, particularly certain
will use as much water as the original trees did. kinds of aquatic insect larvae, require tree leaves, Juts of
Many old root channels in forest soils serve as conduits for bark, tree seeds, and other parts of trees to eat. These
water to enter the soil and underlying rock formations. The stream-bottom dwellers depend upon the accidental falling of
mat of leaves underneath a forest prevents the forest soil a leaf into the water for their existence. In turn trout depend
from becoming compacted by heavy rain droplets. This upon these insect larvae for food. Consequently, a forest can
improves infiltration of water into the soil. All of these things be a vital part of the aquatic food chain,
help to lessen the amount of water runoff, prevent rapid rises Tree leaves can act to lower water quality in some
of stream water levels, and reduce flood hazards. As a result situations. During low-water flows, many streams are
the ground upon which they grow serves as an important nothing more than an intermittent series of pools with very
water storage area. little inflow and outflow of water. Under such conditions a
The value of forests in controlling floods is limited by a heavy-leaf fall may cause a depletion of dissolved oxygen, an
number of factors. The most important of these factors is the increase in water color, and an increase in the acidity of the
amount of rain falling in a given period of time. Amounts of stream. These changes are usually of minor consequence,
rain associated with most catastrophic floods are so great but they do occur.
that the presence or absence of forests matters little. Such Relationships of forests to water may be complex. Despite
was the case with Hurricane Agnes flooding in 1972. some limitations, forests exert strong and continuing in-
However, for lesser amounts of rainfall the influence of fluences on both quantity and quality of water in streams of
forests can be very great. • Pennsylvania. This influence is felt by way of a very intricate
set of interactions involving climate, geology, topography,
soils, and finally the trees themselves. In some ways forests
act to lower water quality and in others they act to enhance
it. The net effect of these complex interactions between
forests and water quality indicates an overwhelming
enhancement of water quality by forests. Forest watershed
research has contributed a great deal to our understanding of
forests and water, but many things are as yet not fully un
derstood.
The next time you walk along your favorite stream,
remember that to a great extent that stream is a mirror of its
surroundings. Trees often are a part of those surroundings.
National Award to
Lancaster Goodwill
The Public Relations
department of Goodwill
Industries of Lancaster
County has received a
national first place award
for a detailed report on
“Outstanding Community
and Financial Support” for
1973. The Lancaster Good
will received the top award
while in competition with 154
other Goodwills throughout
the U.S.
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The award is the result of
community and financial
support to Goodwill last
year; primarily that of the
Goodwill Radiothon held at
the Foodergong Lodge in
October which was
spearheaded by radio
stations WGSA-WIOV and
supported by numerous local
radio and television stations.
Over $BO,OOO was eventually
received as a result of the
Goodwill Radiothon, thanks
to hundereds of hours of
volunteer work.,
Mr. Norman L. Schell,
president of the Lancaster
Goodwill, accepted the
award in New York City this
week at the National
Delegate Assembly of
Goodwill Industries. This
marks the first year the
Lancaster Goodwill has
taken a first place in national
competition.
Forests also influence water quality. Forest soils are held
firmly in place by the extensive root systems of each tree. A
Ye olde
X HUNT
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vice Tips booklet, and an invi- pires July 31, 1974)
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conducting this For-AGH Census Whatever make forage har
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a J? /ester was * n We’ve got a useful premium gift
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The proud owner of "Ye Old- for your HUNT help
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firamelli Farm Service Longenecker Farm Service
Quarryville, Penna. . Rheems, Pa
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Washington Boro, Penna Cochranville, Pa
r *
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