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TWO DRYSTONE WALLS IN LANCASHIRE
AN ENVIRONMENTAL APPRAISAL
By Mick Walsh
Summary
This was a study to examine the impact of a drystone wall on its
environment, its role as a habitat and its own response to local conditions. It
is based on two sections of wall of similar age and state of structural decay
and both made of gritstone - an acid rock. The local conditions applying to the
two sites are widely dissimilar, with one section located in a sheltered
position in a wooded valley and the other in an exposed moorland situation on
rough grazing land. In both locations the line of the wall ran roughly, parallel
with the contour on a significantly sloping site.
At both sites the presence of the wall had acted as a restraint to the downward
creep of the land surface and provided a modifying influence on local erosion
patterns. The fallen stone, resulting from the decay of the walls, in both
cases, considerably increased the area directly influenced by the wall and this
area supported species not present elsewhere on the site.
It was found that the wall situated in the wooded valley, in a moist sheltered
situation supported a much richer flora and fauna than did the wall in the
drier, severely exposed, location on the high moor. In both cases wall
restoration which involved the removal of the fallen stone zone would
considerably reduce the habitat diversity and value of the system.
Introduction and background information
For the purpose of this study two sections of wall were chosen. Both would
appear to be in excess of 125 years old and built of mineralogically similar
stone. Both walls were aligned in a, roughly, north south direction . The
physical location and the history of the two sites differ widely.
The first wall examined is now located in dense woodland, in the valley
of the river Roddlesworth [Grid reference SD 6608 2166 ]. The site lies 20
metres east of the river Roddlesworth, at its point of entry into Roddlesworth
Upper Reservoir This wall now forms the western edge of a section of the
Roddlesworth Nature Trail.
The wall was built at some time between 1851 and 1864 to enclose the new
reservoirs, built as part of Liverpool city's waterworks. Walls of this type
were built by full time professional drystone wallers and constructed to a high
standard of workmanship and finish. The woodland which now encloses the site was
planted from 1904 onwards as an erosion protection measure. The area up to this
time was open farmland and the wall's main purpose was, originally, to exclude
farm stock from the vicinity of the river and reservoirs.
The decay of this wall has occurred as a result of large scale land movement,
high flow rates of surface and subsurface drainage water, some stone decay and,
more recently, an element of vandalism.
DECAYED WALL IN WOODLAND AT RODDLESWORTH SITE (Picture above,
cross-section below).
The second wall examined was located on rough pasture on
the high ground dividing the valleys of the river Darwen and Waterside Brook
[Grid reference S D 7100 2280]. This site lies 50 metres north of the bridleway
known locally as Buller's Lane and forms part of the northern boundary of "The
Little Field" of Higher Waterside Farm. The farm itself is shown on the ordnance
survey map of 1841 so it is likely that the study wall was already present at
this date. There is evidence of industrial activity in the field to the eastern
side of the wall. According to information from the landowner this industry
consisted of, small scale, mining of coal, quarrying of clay and a brick works.
These were in operation in the latter half of the 19th century but are believed
to have ceased operations by 1890. It is possible, therefore, that the wall
dates from this, later, change of land use. The wall was built as a field
boundary, probably by farm labour, and does not show the same high level of
skill and finish apparent in the waterworks wall.
The decay of this wall appears to be the result of inadequate foundations and
insufficient taper. Some evidence of stone decay can also be seen and storm
damage may also have contributed to later stages of decay.
DECAYED WALL AT MOORLAND WATERSIDE SITE (Picture above,
cross-section below)
It can be seen from the cross sections illustrated that, in both cases, there is
an accumulation of
material on the up slope side of the wall. This suggests that the walls are
acting to restrain down
slope migration and thus limiting erosion.
Survey methods
The method of survey, in both cases, was as detailed :-
1. A cross sectional elevation was prepared at right angles to the sample wall.
sectioning was achieved by setting up a horizontal line, across the wall line,
supported by a pair of vertical posts driven into the ground at each end of the
section length. The vertical distance from the ground surface to the fixed line
was measured at fixed intervals along the section. From these measurements a
cross section drawing was prepared for each site
2. Ground vegetation in the immediate vicinity of the wall was assessed and
recorded.
3. The area of fallen stone was examined and vegetation recorded.
4. The fallen stone was carefully cleared from a 1 metre length and samples of
all animals found were taken. Evidence of animal tracks and signs was also
recorded.
5. The cleared I metre length of wall was closely examined and samples of all
surface growth were taken.
6. The cleared length of wall was carefully dismantled and samples taken of all
animals encountered. [Specimens which could be positively identified on site
were immediately returned to a closely adjacent section of wall and those not
immediately identifiable were removed for later determination, after which these
were also returned.]
Results for woodland wall
The plant and animal population of the woodland wall was sampled in mid-December
and the following species were detected:
ON GROUND WITHIN 2 METRES OF
WALL
GRASSES
Glyceria fluitans
Deschampsia caespitosa
Agropyron sp.
Poa sp.
2 unidentified ssp.
Creeping rhizomes - unidentified
BRAMBLE
Rubus (Eubatus) sp.
RUSH
Juncus effusus
(Soft rush)
FUNGI
Laccaria bicolor
Stereum gausapatum
MOSSES
Brachythecium plumosum
B. rivulare
B. rutabulum
Dicranella heteromalla
Eurynchium praelongum
Plagiochila asplenioides
Polytrichum commune
P. formosum
Rhytiadelphus loreus
R. squarrosus
FERN
Dryopteris sp.
ON WEST FACING WALL FACE
FERNS
Cryptogramma crispa
Cystopteris fragilis
LICHENS
Lepraria incana
L. membranacea
MOSSES
Brachythecium rivulare
B. rutabulum
Eurhynchium praelongum
Nardia scalaris
Orthotrichum diaphanum
Plagiothecium denticulatum
Polytrichum commune
Rhytiadelphus squarrosus
R. triquetrus
R.
undidentified sp. (Similar to R.
triquetrus but branches much more widely spaced on primary stem)
Tritomaria quinquedentata
ON WALL TOP
GRASS Holcus lanatus
MOSSES Hypnum cupressiforme
Polytrichum formosum
Rhytiadelphus squarrosus
ON EAST FACING WALL FACE
LICHEN
Platismatia glauca
MOSSES
Atrichum undulatum
Dicranella heteromalla
Polytrichum commune
Rhytiadelphus squarrosus
Spagnum sp
ANIMALS IN WOODLAND AND WALL
(Wall section dismantled for sampling)
COMMON FROG Rana
temporariu 1 specimen hibernating at base of west face
COMMON TOAD Bufo bufo 1 specimen in east face of wall,
0.5m below surface level
NETTED SLUG Agriolimax reticulatus Several specimens
CENTIPEDES Lithobius fbrficulus Frequent
L. duboscqui Frequent
Haplophilus subterraneus 4
specimens
MILLIPEDES Polydesmus angustus 3 specimens
Polydesmus sp 1 specimen
Tachypodoilicus sp Frequent
WOODLOUSE Oniscus asellus Frequent
BEETLES Coccinella punctata 3 specimens
Nebria sp Frequent
Bembidion sp Frequent
Family Clambidae 1 specimen, 1mm
Elateridae Part specimen
only, thorax & abdomen with elytra
Cryptophagidae
<lmm golden coloured, frequent in moss cushions
Campodeiform larvae 1 specimen 15mm
1 specimen 6mm
1
specimen 2mm
FLIES Many, unidentified, dipterous larvae
Ceratopogonidae 1 specimen
Tipulidae 3 species Frequent
WORMS Lumbricus terrestris
Octolasium lacteum
Unidentified, immature, specimen
HEMIPTERA Heteroptera unidentified, 1.5mm, specimen
Homoptera
Aphididae 4 species, frequent in roots
GARLIC GLASS SNAIL Oxychilus
acliarius 2 specimens
MITES
Several, unidentified, species frequent
PROTURA 3
species
COLLEMBOLA 6 species
HARVESTMAN Nemustomu
bimaculutum 2 specimens
SPIDERS
Segestria 3 species
Araneus sp 1
specimen
NEMATODE WORMS Frequent
POTWORMS 3 specimens
Results for moorland wall
The plant and animal populations of the moorland wall were sampled at the
beginning of March and the following results obtained:
ON GROUND WITHIN 2
METRES OF WALL
[The entire area is subject to intense grazing pressure from a large rabbit
population.]
GRASSES 2
species, unidentifiable, heavily grazed.
SHEEP'S SORREL Rumex
acetosella
MOSSES
Hypnum cupressiforme
Plagiochila asplenioides
Racomitrium lanuginosum
Rhytadiadelphus squarrosus
Drepanocladus uncinatus
FERN
Asplenium adiantum mgrum
ON WESTERN FACE OF WALL
Small areas of unidentified green
algae on lowest, sheltered, 10 cm. at wall base. Remainder of
wall face with no detectable
plant life.
WALL TOP
No detectable plant life.
ON EASTERN FACE OF WALL
Abundant green algae of two
unidentified species on lower, 50cm, of wall. Higher section barren
LICHENS
Lepraria incana
Stereoauulon evolutum
Parmelia sp
1-2mm specimen only
Cladonia sp one,
3mm specimen only
ANIMALS IN MOORLAND WALL
Note - the standing portion of
the wall yielded only 3 spiders and 1 centipede. All other specimens were taken
from the fallen stone zone.
EARTHWORM
Allolobaphora sp
BEETLES Leistus spinibarbis
Chalsoides sp
2mm
Stenus sp
2mm
Myctloporus sp
4mm
Tachyporus sp
4mm
Philonthus sp
15mm
Unidentified circulionoidae larvae
COLLEMBOLA Entomobryoidae 3 species <lmm
1.5mm
grey
1.5mm strongly opalescent
HEMIPTERA - HOMOPTERA
Aphididae one, 2mm specimen
CENTIPEDES Lithobius forficatus
L. dubosqui
SPIDERS 3 unidentified
specimens
PSEUDOSCORPION Dactylochelifer sp 2.5mm
Within the fallen stone zone
small mammal runs were observed. Separate observation sugests
that these runs are generated by the field vole Microtus agrestis.
Comparing the two sites
The following table shows the comparisons between the two test sites.
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LOCATION
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WOODLAND
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MOORLAND
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ENVIRONMENT
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Valley,
Wooded,
Sheltered |
High ground.
Rough grassland,
Exposed |
|
MOISTURE STATUS |
Wet, percolating water |
Dry, no free water |
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GENERAL CONDITION
|
Wall spaces with much
particulate and organic matter |
Wall spaces open voids
without organic material |
|
FALLEN ZONE |
Partly buried, heavily
overgrown |
Resting on surface, no
overgrowth |
|
VEGETATION COVER |
Heavy |
Sparse
|
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ALGAE SPECIES
|
0 |
2
|
|
FERN & GRASS SPECIES
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3
|
0
|
|
LICHEN SPECIES
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3
|
4
|
|
MOSS SPECIES |
16 |
0 |
|
TOTAL PLANT SPECIES |
22 |
6 |
|
TOTAL ANIMAL SPECIES |
55 (Present in standing
wall) |
17(4 Only in standing
portion) |
It can be seen that the wall in the damp, sheltered situation supports a much
more diverse
population than the exposed moorland wall.
Since a significant number of species are present in the fallen stone zone,
particularly in the case
of the moorland wall, restoration which includes the removal of all fallen stone
will reduce the
habitat value of the overall system.
Mick Walsh can be contacted at 123 Cranberry Lane, Darwen, Lancs BB3 2HL.
Tel 01254 702845
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