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progressively =ore acid.
This acidity, combined with the
lack of readily-available
.. niltrient; and the low te~erat~s
prevalent in hill areas ~.-e striot s the numbers and activitiaa
of ~econposer -organisms, so deconposition proceeds slowly
wd formation of a mat of plnnt remains and/or of peat occurs,
The imposition of' regular grazing on the system described above
involves defoliation, damga to the plant by trampling and
soil compaction md hence usually lower herbage prduction
(Bryant et al., 1972; Xdmond, .t958; Floate, 1972; h w a
&%lch, t969) and root growkh (~chustor 1964).
This,
toge5her with digeation and assimilation of some material by the
anbal, reduces the mount of organic matter retuned to the
soii. In a paired-plot fence-line study in Scotland, Flmte
(1972) found that imposition of grazing led to a roductiori in
the thickness and amounk of aurface organio matter. Howard
& Ho- (1974). working on A~rosteFes hucetum Fn the northem
Permines, found no ohange in the amount of surface organic
remains with grazing but sug~sted that in the absence of
,gazing much of the dead grass is supported by the live
veget~tion and hence waa not collected 3n their soil cores.
If overstockhg mcurs, herbage m ill be so reduced and
damaged that bare aoil ~ 1 appear, 1 The latter is highly
susceptible to erosion and is also exposed to sxtmmea of
temperature which my, on balance, be unfavourable far
microbiological actlvity although mode rat ely high temperat urea
favour high activity if moi~turo dae~ not become limiting.
Grazing involves channelling sme vegetation tkroue the
and baok to the soil in droppings and urine, The benefioid
effects of dung and urine on soils and vegetation are wellknm
but quantitative evidenoe of their influence on'nutrimt
oyoling is leas well docmente&. Floats (19 72), in