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8
worEng oh heather moor, birch and pine wodland and jmiper
scrub in Invmnesa-shire, f'outld much higher dansitf es of self-
sown aeedxnga on soil bared by deer trampling than rm
vegetation-covered soil so perhaps trampling is important
locally in croat ion of niches for now apecies in a closd
c o d t y ,
Crocker (13 3) coneiders th~t
heavy grazing
creates vaccnt niches which are occupied by less palatable
species from within or outside the community and this applies
also to low levels of trampling (~ddls& Greig-Smith, 19~b).
However, Ploate et al., (I 973) and Jonez (4 967) find t kk graaea-
olrt species are not neoessarily replaced by unpalatable species
(FY* 8 - 12).
Published comenta on the effect d trampling
on vegetative reproauction of pasture species are c onflictiq,
Davies (1 938), Pearsall (I 9501, and hwes & Wolch (1 969) state
that treading plus grazing promotes the tillering of grasaes
~herea~l Eamond (I ff8) noted a progressive reduction in
tillering of ryegrass and node f omation by clover as .
at ocking density increased from 0 to 8 aheep ha-' .
. b Effects associated with the cycling of organic matter and
nutrients within the animl-ve~etation-soil systm
On ungrazed hill-land, plant material produced above and below
ground eventually dies and, as it deoays under the influence of
aoil bacteria, f'ungi and animals, the nutrients which it cmtains
are relecse2 and eithzr held in the aoil or re-absorbed by
plants, or loached out of the ndl. . This leaching is moat
pronounced where rainfall is high, as in much of western
Britah, and whore the plant remins produce substances suoh
as aoids and polyphonols which promote movement of materials
down the soil profile. Basos, are amongst the nutrients whioh
leached out, so the plant remins, tond to became