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Hi Nick, David P. & All Jan 11, 2016
I would be cautious about betting the farm on Ca depletion being a major
factor.
One telling passage in the Noseworthy thesis is "To what extent the
apparent luxurious consumption of Ca is beneficial to tree growth remains to
be explored..."
(p. 194).
This is a very complex model as it stands but, so far as I can tell,
makes no allowance for consumption of H+ by weathering of soil minerals so
the effect of acidic ppt. may be overstated to some degree. And, so far as I
can see, it is a balance sheet and consequently does not allow for possible
responses of soils or trees when inputs or outputs change.
Phosphorus was excluded unfortunately. But as the model stands it is I
think an excellent launching pad from which to define questions that need
testing by experiment.
A narrow band of basic soils appears on both sides of most waterways, in
the area most intensively studied (Kejimkujik National Park) suggesting that
the acidity of soil water, as it passes through acidic soil upslope, is
slightly neutralized (weathering effect ?). Whether these bands were a
prediction of the model or an observation of soil survey I am unsure.
One feature of large expensive equipment is that it will tend to be used
regardless of soil conditions. A few passes over soil when it is
sufficiently wet to be compacted may result in damage which will take
decades to reverse. If harvesting by large equipment does in fact reduce
growth of the next generation of trees then it could be due to changes in
soil porosity at 40 cm or beyond and not nutrient removal.
I must become less involved with this question because in less than a
month I have blown a year's allotment of discretionary time and trying to
herd cats up a waterfall is not an efficient use of scarce time.
Yt, DW
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