Blanket bogs have developed on the Pennine uplands
and cover vast areas with peat. Development of plant growth is very
much limited by climatic extremes, and by the poorly-drained subsoil.
This habitat is widespread in the Dales and makes up nearly 25%
of the area. There are extensive tracts running down from Langstrothdale
to Fountains Fell, and from Buckden Pike down to Appletreewick Moor
- effectively those moors over 300 metres high within the Yoredale
and Millstone Grit series. Bogs are also to be found in the Millstone
grit moorland areas of mid-Wharfedale.
Species-poor cottongrass bog, overwhelmingly dominated
by hares-tail cottongrass tussocks, usually has some some
bog-moss present, mainly S. capillifolium and S. papillosum.
Dwarf shrubs may be entirely absent but usually some heather or
bilberry can be found. It is found on the Langstrothdale-Ribblesdale
A richer community occurs where the hares-tail
cottongrass is partnered by an ericaceous species, most commonly
heather. Sometimes the heather becomes dominant, particularly if
the moor is managed for grouse. Where the moor is wetter, the bog-mosses
expand and can dominate. On the higher hills this heather-cottongrass
bog is an important habitat for cowberry and cloudberry with good
amounts of other dwarf shrubs. Cowberry is an Arctic-Alpine plant
which is mainly found in Scotland.
Bog-moss-rich bogs are the most diverse of the
bog communities, and also the rarest. Dominant bog-mosses form a
subtle patterning of ridges, hummocks and hollows and these bogs
are usually actively growing. They are a habitat for specialised
bog plants, including cranberry, bog asphodel and round-leaved sundew.
Bog asphodel can form striking golden groups in limited areas, and
round-leaved sundew is a well-known insectivorous plant. Large areas
of these bogs have been destroyed by burning and drainage and atmospheric
pollution reduces acidity and increases fertility.
Peat hags are found where the bog surface has dried
out, with an increase in dwarf shrubs and Cladonia lichens.
Higher up cowberry and cloudberry can become a feature of this habitat.
Lower down, grouse moor management, with its regular disruption
and burning, can produce dessication where heather is encouraged
to take hold.
In upper Wharfedale there is some wet blanket bog
at Oughtershaw and Beckermonds, in the Moss End enclosure. Hare's-tail
cottongrass, purple moor-grass, cross-leaved heath, bog asphodel
and tormentil grow with bog mosses Sphagnum spp., and star
moss Polytrichum commune.
Near Pen-y-ghent, by Churn Milk Hole, there is
a valley bog system which supports bottle sedge Carex rostrata,
white sedge C. curta and the bog moss Sphagnum recurvum.
On the Barden and Blubberhouses moors there are
some deep mires on the higher moorland. Hare's-tail cotton-grass
is dominant, with cross-leaved heath, crowberry, common cotton-grass
and heather. Cloudberry is locally abundant on Henstone Band Side
and Thorpe Fell. The richer vegetation in wetter areas includes
cranberry, bog asphodel, cross-leaved heath, round-leaved sundew
and bog rosemary.
Moorland dominated by crowberry is particularly
extensive on Ilkley Moor, with wet heath containing cross-leaved
heath and cranberry which have developed on the blanket mires.
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