Environmental Engineering Reference
In-Depth Information
FIG
43
. Hoary rock-rose, a rare plant with a discontinuous distribution on the limestone of western Britain. (David
Painter)
the Estate of Evan Evans for Figure
Areasoflimestoneheatharedominatedbygorse,sometimeswithbellheather
Erica cinerea
orbrack-
en,andcontain alargenumberofassociated calcicole andcalcifuge species inanintimate mixture. Gorse
(Fig. 44) is one of the most highly structured plants, the tight cluster of rigid stems forming an ideal
framework for web-spinning spiders such as
Theridion sisphium.
While gorse bushes usually occur as a
more or less complete cover, the more open forms of heath in which it occurs as a mosaic with patches of
grassland are probably a response to grazing. Anthills are common and support a different flora in which
wild thyme
Thymus polytrichus
and common rock-rose
Helianthemum nummularium
are abundant. The
mostfrequentspeciesassociatedwithgorseareribwortplantain
Plantago lanceolata
,commondog-violet
Viola riviniana
, glaucous sedge
Carex flacca
, salad burnet
Sanguisorba officinalis
ssp.
minor
, cat's-ear
Hypochoeris radicata
and red fescue.
Away from the typical thin limestone soils, in places where glacial drift deposits have accumulated
and there are thicker, more acid soils, the flora is dominated by bracken or purple moor-grass
Molinea
caerulea
, with bramble and sometimes common and western gorse
Ulex gallii
. Some of the most
frequent associates are Yorkshire-fog
Holcus lanatus
, sweet vernal-grass
Anthoxanthum odoratum
, tor-
mentil
Potentilla erecta
and wood sage
Teucrium scorodonia
. This community is often subject to fire.
