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Tho soil b'cabilizing effect of tree roots is of particular importanoe
on steep slopes. The zone of soil around tree roots is a site of
active miners1 eathe he ring. The importace of the latter effect far
forest in t:w 1,a.k~ District is unclear. The presence of root channels
in aoil rer,dt.rs the latter more permeable to ~vatcx, wh:,reas rod
decomposition adds humus and rat rients slowly throughout the soil profile,
Plant renains on the soil surf~ce buffer the soil against the effects
of clim'ie, part,icul&rly direct insolation and extremes of air temperature
and rainfall,
The rats and type of deompmftion of plant remains
influences tho chemical and physical properties of the underlying soil,
Conifer litter, like _Ca_lLun.n and Erica on moorland, has the rep*tian
of causing physical, chemical and biological deterioration of soil,
'%ilst these effects mmzia sonewhat controversial, and incomplete3y
understoca it is clr;a,r that they vary with soil type, site characteristics
and tree species.
Flelevan'c locsl data a= fen arid indicate tendencies
towards acidity, low n~trierrt cvczilability and podzolization in many
upland soils but no clearly developed podzol profiles.
Evidence from
elset~here indicates that trees, even conifers, will grow well on
aimilur soils to thona f3md in the Lake District without causing
serious aoil degr~cation, although they m y cause the tendencie s
indio~ted 2bove.
The maJdmum dj-rcct eflcct of forerrtry operations on the soil occurs
during site preparation cnd haroastir~g, both of tvbich involve use of
heavy machinery ~:hich coqacts and disturbs soil, partly because of
its om weight, and partly because of its use in ploughing, drt;bing
or logging.
Excegt for light cross-country vehicles and heavy trucks,
such as timber lorries which can exert pmssurt2s ori the soil of up to
-2
about 8 kg ~ rn-~, vehicle pnssurus fall in the range 0.2-4.6 kg om ,
aboat the sme as t h static ~ pressures exerted by anim~ls. One
-2
application of about 0.2 kg cn! can reduce soil pore space by
and 1&2@
of an area can be affected by vehicl~ a during tractor losing.
Data from other aro:ta suggest a that soil cornp~ction by forestry is not
a major problem, but that mrked vegeti-tion changes occur after ploughing,
draining and ro~~liing. Theso chkng~s xi11 ultdtely reflect back
on the soil.