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Although the eWect of tree litter on scil is only partially
understood certain points nrs now clear. Th@ amounts of
bases, polyphenola and other mterials which affect soil
profile development vary not only betvmen species but also
within species depen&ing on the status and type of 3021
on which the trees are gr&g (~ork, 1942; Coulson e'c al.,
t960). This 5uplies that it my be possible to alter the
effect of thc trees on the soil by altt!ring the soil base
st3tus. Some species, for examplebirch, are ofken regarded
as soil improvers (1)5&leb~, 1952; Gardiner, 1368) but this
view has been challeqed and is still controversial (blulie,
1956). One cause of such controversy is the tendency of
some workers to focus thefr attention on the superficid- sail
layera, -here some changes undoubtdly occur (0vh&oa, 1 P~J),
rather than considering nutrient content, nutrierut; availability
and &,her characteristicn of the &ole soil profile in relation
to the +,me's requirements.
Podzolization appears to be unavoidable under conifers on
some sites inEurope. It is rapid and complete under pine on
poor sands or under spruce on fietefiured soils wLch previously
carried deciduous forest whereas on dho r soils it is only
partial with inoreases in the amount of superficial plant
remins, acidity and C/N ratio for humus rich layers
(Faurnier, 7972). Blisck (1974) indicated a similar picture
for Czechoslavakia where 20-4% spruce mixed w%th brmdleaved -
trees caused no adverse effects on moist alluvial soils at
100-200 m altitude and increusing percentages wrt: tolerated
as altitude and rainfall Fnoroased until, at AIOO-1200 TI pum
spruce produced no significant deterioration of brorm f orast
soils. Productivity was roduced significantly if s too high
percentcge of spruce waa plated partly because of soil
degradation physically and inadequate nutrient availability
and also because of high ht orception of precipitation by
spruce dmng the grodg season. G e m v~orkers, in general,