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

Forested surfaces are generally considere d
to be effective energy exchange surfaces . Th e
results confirm that this young stand has a
high absorptivity for solar radiation, with a n
albedo of 0 .09 for both clear and overcas t
conditions . This high absorptivity contribute s
to the large net radiation values that wer e
measured under clear skies .
The role of the forest in dissipating the net
radiation is of particular interest. The porous ,
aerodynamically rough canopy is effective i n
transferring sensible and latent energy into
the atmosphere . The large quantity of forest
biomass may also involve an amount of store d
thermal energy that is of significance durin g
short periods, even though the daily totals are
small . Summed over a 24-hour period, evapotranspiration
was about 280 cal/cm 2 min (0 . 5
cm water equivalent) or about two-thirds o f
the net radiation that was transformed unde r
clear skies . Evapotranspiration was relativel y
larger on an overcast day, about three -
quarters of net radiation, although the tota l
amount of latent energy (102 cal/cm2 min, or
0.18 cm water equivalent) was considerably
lower .
These results provide initial estimates o f
the amounts of energy transferred during extreme
conditions under cloudless and unde r
overcast skies . The exchange of energy an d
mass depends not only upon the energy inpu t
to the forest, however, but also upon the
physiological response of the vegetation . No w
that the instrumentation system and the
analysis model have been tested at this site ,
subsequent research will include a range of
environmental conditions . Instrumentation
development and model testing will continue
in cooperation with the lysimeter installatio n
and eddy flux system of cooperating investigators
. Ultimately, analysis and interpretatio n
of the energy transfer studies must include
physiological as well as physical characteristics
of the stand .
Acknowledgments
The work upon which this publication i s
based was supported in part by funds provided
by the U .S. Department of Interior,
Office of Water Resources Research, as
authorized under the Water Resources Re -
search Act of 1964, and administered by th e
Water Resources Research Institute, Orego n
State University ; and the National Scienc e
Foundation Grant No . GB-20963 to the
Coniferous Forest Biome, U .S. Analysis o f
Ecosystems, International Biological Program .
This is Contribution No . 40 to the Coniferous
Forest Biome and Paper 844, Forest Researc h
Laboratory, School of Forestry, Oregon State
University .
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