PE EIE[R-Rg RESEARCH ON - HJ Andrews Experimental Forest

spiration are being conducted, cuvettes will b e
installed at various locations within the crow n
to monitor the spacial variation of transpiration.
In addition, the rates of transpiration ,
determined with the cuvettes, will be compared
with the lysimetric transpiration rate t o
determine how representative the cuvett e
technique is for determining transpiration o f
the tree .
Test Meteorological Methods
Meteorological methods such as energy balance,
aerodynamic, and eddy correlation techniques
have been used to determine evapotranspiration
from agriculture crops. The
methods need further testing in forestry be -
fore they can be utilized on a wide scale . Th e
evapotranspiration rates from the lysimeter
tree, if representative of other trees, can b e
utilized for testing the meteorologica l
methods .
Profiles of meteorological parameters suc h
as radiation, temperature, humidity, carbo n
dioxide, and windspeed will be monitored .
These parameters will be utilized to calculat e
the transfer coefficients (eddy diffusivities) o f
sensible heat, latent heat, momentum, an d
CO 2 . In addition, transpiration and photo -
synthesis by layers will be calculated fro m
these parameters .
Canopy Interception of Precipitatio n
Interception of precipitation either as rain ,
dew, or snow will be represented as a weigh t
increase by the lysimeter . The amount of
precipitation intercepted by the crown of th e
tree can be studied by providing a waterproof
cover for the soil surface to prevent th e
throughfall from being recorded as a weigh t
increase . The throughfall will. be measure d
separately . If stemflow is measured, then th e
rest of the weight increase can be attribute d
to canopy interception . It is obvious that thi s
method can be utilized to determine th e
amount of rainfall and snowfall interceptio n
in relation to intensity, duration, and previou s
wettings .
However, this technique may be more useful
in determining the amount of moisture
extracted from the atmosphere as dewfall-at
present, an unknown quantity. During the
summer months, energy budget calculations
demonstrate that Douglas-fir trees, under the
conditions of the site, would be stresse d
within 2 to 3 weeks after the last rainfall if
they transpired at a potential rate, unless transpiration
is supplemented by evaporation of
dewfall. Dewfall may be a very important
parameter in the survival of these trees .
Fertilization and Irrigation
At the present time considerable interest i s
being expressed in using forested areas for disposal
of sewage sludge . The benefit of irrigation,
sludge, or other fertilizers to tree growth
could be tested with the lysimeter installatio n
by comparing the photosynthesis and transpiration
of the tree being studied with th e
adjacent trees .
Summary
During the summer of 1970, a lysimeter
container (366 cm in diameter and 122 c m
deep) was built around the root mass of a
28 m Douglas-fir tree at the Cedar Rive r
Watershed near Seattle, Washington . This container
was placed on top of the hydraulic
transducer which is capable of weighing th e
tree, soil, and container, a mass of 28,900 kg ,
with a sensitivity of 630 g or 0 .06 mm of
water . A weather station was located on a
33 .5 m tower adjacent to the lysimeter tree .
The proposed uses of this installation are :
(1) as an evapotranspirimeter, (2) as a standard
for testing cuvettes, (3) as a standard for
testing meteorological methods, (4) to stud y
evapotranspiration in relation to soil moisture
potential and atmospheric evaporative demands,
(5) to study the shrinking and swellin g
of the plant tissue in relation to evapotranspiration,
(6) to determine interception of
rainfall, snow, and dewfall by the crown, an d
(7) to study the effects of irrigation and fertilizer
upon the growth of the tree .
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