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

in terms of soil and stand structure, suggests
that this retention property may be genera l
for Douglas-fir forests west of the Cascade
Range in the Northwestern United States .
Although an explanation for this retentio n
must await the completion of research now in
progress, it appears from the small organic
nitrogen outflow that most of the solubl e
organic substances released from decomposition
of detritus and organism excretions are
rapidly incorporated by the organisms of th e
forest. Nitrate nitrogen outflow is also regulated
to levels much less than the input i n
precipitation. Either nitrification rates are
very low in the soils or the nitrate is retaine d
and rapidly incorporated by the fores t
system. Nitrification is active in the acid soil s
of conifer forests on the Oregon coast (Bolle n
and Lu 1968), but this information is lacking
for soils of the H . J . Andrews Experimental
Forest .
The status of nitrogen capital of a Douglas -
fir forest is the result of a number of processes
including input in precipitation, fixation
by free living organisms such as blue-green
algae and soil bacteria, and fixation by micro -
organisms living in symbiotic association wit h
a host plant. If the forest gains 0 .5 kg/ha
annually, as is indicated by this short perio d
of record, 8,000 years would be required t o
accumulate the 4,000 kg/ha of organic nitrogen
found in the more fertile soils of the
study watershed. Additions of nitroge n
symbiotically fixed by Ceanothus velutinu s
may be somewhat larger . If Ceanothu s
velutinus stands persist for 20 years and fi x
20 kg/ha annually as Zavitkovski and Newto n
(1968) suggest, and if generations of thes e
brush stands are induced by fire at intervals o f
200 years, then 16,000 kg/ha of nitrogen
would accumulate in 8,000 years. From this,
deductions must be made for losses by soi l
erosion and microbial and fire volatilization .
In any case, inputs of nitrogen in precipitation
must be considered of importance compared
with other mechanisms of gain and los s
by the forest .
Phosphorus outflow from the forest wa s
similar to that of nitrogen (table 2) . Loss
occurs as both organic phosphorus and orthophosphorus
. The organic form predominates
in the warm seasons of the year when there i s
a rapid biological turnover of phosphorus b y
the forest. Concentration of the ortho form re -
mains fairly constant throughout the year and
is thought to arise from mineral weathering .
The losses of the cations sodium, potassium,
calcium, and magnesium were large
compared with those of nitrogen and phosphorus
and represent excess amounts of thes e
cations to the annual requirements of th e
forest vegetation (table 2) . These losses are
approximately four times those reported fo r
the Hubbard Brook ecosystem in New Hampshire
except for the potassium values whic h
were nearly equal to those reported her e
(Likens et al. 1970). Cole et al. (1967) also
reported lower losses of potassium and calcium.
The cation and silica losses (table 2) are
estimates of the annual release of these chemicals
by mineral weathering . In this regard, it
is interesting to note that the ratio of
Si :Ca:Na:Mg weathering rates for 1970 ar e
8.9 :4.3 :2.1 :1 .
Another mechanism for nutrient loss is th e
particulate matter that is transported by the
stream. This material may arise from soil
erosion or from organic detritus from the
forest. Losses of suspended sediment fro m
this study (67 and 37 kg/ha-yr) were much
lower than the 12-year annual average of 13 3
kg/ha from another undisturbed watershed in
the Experimental Forest (Fredriksen 1970) .
Although we have not quantified the chemical
loss by this means in this study, previousl y
published annual losses of 0.16 kg/ha for
organic nitrogen represent less than half of
the dissolved component loss (table 2), still a n
important part of the total nitrogen loss
(Fredriksen 1971) . Cation loss was much les s
than 1 percent of the loss in dissolved form .
However, since erosion losses are very sporadic
and dependent on extremes of storm
runoff events, and the results (Fredrikse n
1971) are indicative of the chemical loss during
a relatively quiescent period, they shoul d
be taken as minimum estimates of nutrien t
loss by soil erosion processes .
Biological and chemical processes of th e
forest that control nutrient mobilization an d
retention are undoubtedly closely linked to
environmental factors. The movement of
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