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Difficulties were caused mainly by the steepness of terrain in some areas
creating topographic shading on the photographs, and by the large amounts
of bare rock interspersed with some vegetation types. (See Figure 4).
The most widespread types were Calluna-Molinia and Calluna-Molinia/
Tricophorum Eriophorum. Because of the sensitivity of the vegetation to
changes in ground moisture, the degree of wetness of the site often
corresponding to a break of slope was useful in drawing the boundary
between some types.
The greatest difficulties were encountered in identifying Bracken, Deschampsia
Grassland and the mountain top communities of Rhacomitrium-Empetrum with
varying amounts of Nardus and Bare Ground. Bracken could not, on the
whole, be separated from other types of tall shrub understorey. Deschampsia
grassland was easily overlooked, or its extent underestimated, as a result
of its steeply sloping location, but identification of this type can be
aided with the help of a geological map. Rhacomitrium-Empetrum was difficult
to distinguish from Rhacomitrium-Empetrum with Nardus, and Bare Ground,
due to the large amount of bare ground exposed on mountain tops,
interspersed with a scanty vegetation cover, and the nearly white image of
all three types.
Data Collection and Storage
In order for different types of analysis to be carried out on the data,
and to enable comparisons over the area as a whole, it was necessary to
feed the data, comprising 32 parameters, into a computer. This was done
at the 1/4 km? grid level using grid square locations, to allow print outs
in map form. Areas of habitats per grid square were measured by planimeter
and the inter- and intra-habitat variables were measured in lengths or
areas per square according to type of unit. Actual numbers of water bodies
and habitats in each square were counted, and relative relief was estimated
in metres.
The lowland study area - Merseyside
This represents a sizeable portion of the Merseyside Metropolitan planning
region (Figure 5), comprising most of Sefton District and coast, and small
parts of Knowsley and St. Helens Districts. The coastline is dominated
by the Ribble Estuary in the north, with large areas of salt marsh and
mudflats wich gradually give way to the three-to-four mile beaches and sand
dunes of Ainsdale and Formby Point. In the south, the sand dune system
ceases abruptly with spreading urban development at Blundellsands, a
suburb of Liverpool. Eastward of the dune system, the land is flat and
low lying, with isolated patches of improved mossland among permanent pasture
and rich arable land. The area as a whole is semi-rural in character and
much of the coastline is considered to be of outstanding value to wildlife.
Good quality, black and white air photo prints at the scale of 1:10,000,
and flown in May, June and September, 1974, were available for the study.
Mapping categories were chosen according to the ability to identify the
major land use types on the air photos.