Tinepits
Pond, Whitchurch Hill
Ecological
Survey and Management Recommendations
August 2009
Rod d’Ayala and Robert Aquilina
Background
This survey and report was
commissioned by Goring Heath Parish Council to establish the nature conservation
value of Tinepits Pond and its surrounds and the management required to
maintain and/or improve the value of the site. The site was visited in May 2009
– and detailed surveys undertaken for both the pond (wetland plants, larger
invertebrates and amphibians) and its surrounds (primarily plants). Incidental
records for other species groups were also made. The report is divided into
sections on general pond ecology, site description, survey results and finally
management and survey recommendations. Full species list are included as an
appendix to the main report.
General Pond Ecology
To ensure that the later sections
of this report, including any specific management recommendations are clearly
understood it is useful to provide summary information about the ecology of
ponds. Major advances have been made in
the understanding of pond ecology in recent years (research by Pond
Conservation) and much of the traditional perceived wisdom about what makes a
good pond and how ponds should be managed has been shown to be at best
simplistic and at worst potentially damaging for their ecological value.
The traditional view of a good
pond for wildlife is often a permanent water body with deep water and some but
not too many water plants (i.e. plenty of open water), perhaps a narrow fringe
of taller water plants around its edge and minimal shade from trees i.e. no or
few trees stopping the sun reaching most of the water. Ducks (or other kinds of
water birds) and/or fish if not pre-requisites are often seen to be desirable
features. The pond surrounds are usually managed to some extent at least, if
not actually kept “tidy” to a greater degree.
In reality this is only one type
of pond – in this case the model for the most useful functional pond that
supplied man with many of his domestic, agricultural or industrial needs.
Ecological research has shown that in reality all ponds can be good for
wildlife, however small or large, permanent or temporary, shallow or deep,
shady or sunny, whatever the quantity or type of silts or pond bottom
substrate. Habitats in ponds that would in the past have automatically been
condemned, such as dead wood or sprawling living trees are potentially good
features - as too are areas that dry out. All of these different habitats can
support different or specialist species.
Under the right conditions the
classic pond described above and much favoured by man, can support a high
number of animal and plant species. It is the many non-standard ponds
(including early and/or late succession ponds) that are more likely to support
the rare, unusual or specialist species.
The three main factors that
control the ecological quality and potential species richness of a pond are as
follows:
clean (i.e. unpolluted) water
(the volume and regularity of supply is less critical)
good (i.e. wildlife friendly)
surrounds which provide both supporting or complementary habitats in their own
right as well as buffering the pond from any damaging external influences
variety of structure or habitat
within the pond, produced by presence of different plants, variable basin shape
and depth, bottom substrate, water chemistry, quantity and type of silt,
density of shade or light levels etc.
Thus many ponds that do not fit
the “traditional” image of a good pond are in fact potentially very good for
wildlife, and their existing ecological value would be destroyed if they were
managed according to the traditional model. Many traditional ponds will in fact
never achieve their maximum ecological potential. Typically for functional
reasons the volume and permanence of water is often more important than its
quality and the most “useful” ponds are often situated in less wildlife friendly
landscapes and/or they have a very simple (but very functional) structure.
A fourth factor that may
influence the number of species in a pond is:
its proximity to other wetland
habitats with an existing wetland fauna and flora
The other key research finding
about ponds is that on a wider scale (i.e. not individual ponds but the whole
range of ponds in any given landscape area) ponds support more species of plant
and macro-invertebrate (two of the better studied groups of aquatic life) than
other freshwater habitats i.e. rivers, streams, lakes and ditches. Ponds also
support up to twice as many rare or uncommon species of these two species
groups than other freshwater habitats, with these rare or uncommon species
being much more likely to be found in early or late succession ponds. The large
number of species found in ponds is perhaps not too surprising as ponds are
extremely variable habitats (every pond is different) and many are small
stand-alone habitats often benefiting from cleaner water than larger freshwater
habitats. Overall, the larger freshwater habitats such as rivers, streams,
lakes and ditches overall tend to have less complexity of habitats and/or being
either large or continuous provide fewer opportunities for specialist species
or species with low tolerance of competition. Being continuous and connected
habitats with much bigger water catchments, they are very likely to suffer from
poor water quality as a result of polluting land management activities within
their catchment area. Ponds however often have small self-contained catchments,
which are or could more easily be relatively immune from outside negative
problems such as chemicals or other run off associated problems.
Survey
Dates, Methods and Personnel
Tinepits Pond and its surrounding
area were visited and surveyed on 6 May 2009. The main species target groups in
the pond were aquatic / wetland plants, larger invertebrates and amphibians.
The pond surrounds were also surveyed, here the survey was primarily botanical
in nature with other species groups being recorded on an incidental basis only.
The surveyors were Rod d’Ayala (terrestrial and aquatic habitats) and Robert
Aquilina (aquatic habitats including aquatic invertebrates).
Where applicable standard survey
methods were used. In particular for this survey a standard three-minute sample
was collected from the pond for larger aquatic invertebrates. The sampled
material was taken away for later identification, with individual specimens
being identified to species wherever possible.
It is not possible to identify all specimens caught to species level,
with in particular larval stages of many species being very difficult to
identify. beyond family level. Amphibians were caught during the netting survey
for invertebrates. Pond plants were recorded by walking around and where
necessary wading into the pond. Aquatic plants are also often found during
netting for invertebrates. Simple water chemistry / water quality measurements
were also taken using field meters.
The terrestrial habitats were
surveyed by walking round the site, making note of what species were present
and if relevant notes on their abundance and distribution on site. All other
records were made on an incidental basis. For the purposes of writing the
report, reference was also made to less detailed records made during a previous
visit in March 2007 (Rod d’Ayala only).
Site
Description and Survey Results
Tinepits Pond is located close to
the northern edge of the village of Whitchurch Hill, (pond at national grid
reference SU638792 – OS Map). It is located in a residential area, including
typical density housing with relatively small gardens but also larger
properties with larger gardens.
The pond is approximately oval in
shape – 15 metres wide and 22 metres long. It is set centrally in an
approximately semi-circular shaped piece of land, approximately 50 metres by 40
metres. These surrounds consist primarily of an area of short managed grassland
with regularly scattered trees, some of these trees being large fine specimens.
To the south the site is bounded by a quiet residential road – with the other
boundaries backing onto residential gardens. A public footpath crosses north /
south across the area, to the west of the pond.
There is a high density of trees
on site (at least twelve of significant size), located on all sides of the
centrally positioned pond. In addition to these trees there is a mature thick
managed hedge on the east, north and west site boundaries – thus overall the
pond is shaded to a greater or lesser extent at all times of year. It receives some but relatively little
overhead direct sun.
The
overall shape of the pond basin is rather bowl shaped – with steep near
vertical upper banks (above the high water line) and less but still relatively
steep middle banks on soon grading into a relatively level bottom. This shape
means that there is only a narrow draw down zone – the area of pond that has
very shallow water or is exposed as water levels drop in the spring and summer.
The pond had plenty of water at the time of survey, but is known to be a pond
that either becomes vary shallow or dries out on a regular basis in the summer
months. It is believed that the main sources of water are direct precipitation,
and run off from the immediate surrounds or shallow sub-surface flow derived
from water falling onto the immediate surrounds. The tendency to dry out on a
regular basis would suggest that unlike some other local ponds there is no
perched aquifer or similar structure providing a regular supply of water – or
if there is it is only small. Water
conductivity (a simple measure of relative water cleaness) was low (177
microSiemens) i.e. the water was clean – an important factor in maximising the
ecological quality of a pond. The pH of
the water (relative measure of acidity / alkalinity) was 7.0 i.e. neutral. The
pH value of the water in ponds can vary on a diurnal and seasonal basis and a
pH value of 7.0 does not imply any water quality issues or problems either.
Only
six species of wetland / aquatic plants were recorded. This is well below the
average figure for typical countryside ponds. The most abundant species on site
is Flote Grass Glyceria fluitans, which where
light allows, forms the main dense stand of plants in the pond. Other species
present include Woody Nightshade Solanum dulcamara (apparently
declined since 2007), a plant of damp shady places often growing around the
margins of ponds. The other species include two floating species - the
ubiquitous Common Duckweed Lemna minor and less common
Ivy Leaved Duckweed Lemna trisulca. The last but one
species of plant is Yellow Flag Iris pseudacorus, which has a main
stand on the south side of the pond with another small outlying clump
elsewhere. Soft Rush Juncus effusus grows at the high
water mark of the pond. All the plants on site are common or relatively common
– none are rare. Ivy Leaved Duckweed is probably generally under-recorded. The
primary cause of the scarcity of plants in the pond is probably high levels of
shade. Heavy leaf fall may be playing a
secondary role in suppressing growth of plants in the main part of the basin
itself. Given the high number of mature surrounding trees, heavy leaf falls are
something that cannot be avoided.
For freshwater invertebrates the
number of species in the pond is just below the average for ponds in the wider
countryside, but the list of species recorded in 2009 did contain one
nationally scarce species, a Water Beetle Hydraena testacea. As there
are no (known) equivalent records for the pond it is not possible say if there
have been any significant changes – either for the good or bad. The number of
species may be lower than average, but the relatively simple structure of the
pond may in part at least be a defining factor and the low number not be indicative
of any underlying problem. Compared to what might be “expected” three
observations can be made: there are no Water Slaters Asellus sp., a
normally ubiquitous species in this sort of leafy pond; only one species of
snail was found whereas even in ponds that dry out more would be expected and
there were few True Files e.g. one such family being Crane Flies Tipulidae.
Three
species of amphibians were recorded, this probably being the actual number of
breeding species. Common Frog was recorded in 2009 only as a juvenile animal –
with no tadpoles being found suggesting the species may not have bred in 2009.
However spawn was observed in 2007, so this species does at least try to breed
though the tendency to dry out early in the year will mitigate against it in
some years at least. The other amphibians were both of the small types of newt
i.e. the very common Smooth (or Common) Newt Triturus vulgaris and in Oxfordshire
as a whole the much more uncommon Palmate Newt Triturus helveticus. The latter
species is only found in areas of acid soils and in Oxfordshire is probably
only common in the Chilterns. In recent years it has been found in many ponds
in this area of the South Oxfordshire Chilterns (e.g. Woodcote, Kingwood,
Nettlebed, Highmoor, Checkendon). Historically there have been few confirmed
records for the county – but this apparent scarcity in the Chilterns at least,
is more an indication of lack of recording effort than true scarcity. The
absence of Great Crested Newt Triturus cristatus is not a surprise.
Though generally common in Oxfordshire it does appear to be much less common on
the more acidic soils covering large parts of the higher ground in the South
Chilterns. Of interest was an “odd” looking Smooth Newt probably infected with
and whose development and appearance was impaired by an internal parasite - a
species of tapeworm (see results spreadsheet for details).
Overall the pond is a good pond
for wildlife. It is small, heavily shaded and receives (unavoidably) a lot of
fallen leaves which tend to fill in the deeper water parts of the pond and
swamp other plants. A technical consequence of the deep leaf layer is to make
netting sampling for invertebrates quite difficult. Overall the habitats and
structure of the pond are rather simple compared to what it might be for a
similar sized and shaped pond in an open habitat – and thus its species
diversity reduced. As long as it is accepted that being different from a
classic open sunny mid-succession pond is OK and in the absence of any major
problems (e.g. contaminated water sources) - there is no known need for any
major intervention.
The best wildlife ponds are
usually located in areas that are generally good for wildlife. The habitats
found around a pond provide other features that pond dwelling organisms (for
all or part of their lifecycle) need e.g. feeding areas or hibernation sites.
The surrounds can protect a pond from potentially damaging influences e.g. by
absorbing potentially damaging chemicals used on adjacent land. The surrounds
can also be good wildlife habitat in their own right. In the case of Tinepits
Pond, though not large the grassland and trees that surround the pond are a
good wildlife site. Except for a few incidental records for other species,
plants were the main species group recorded with a total of sixty nine species
being identified. Most of these are good native species including plants
typical of both woodland and grassland habitats growing together in close
proximity. Most plants are typical of calcareous to neutral soils, but there is
at least one species typical of acidic soils as well (Sheep Sorrel). There are
both damp loving plants and plants of drier habitats. Some
of the larger trees are particularly fine old specimens. Some examples of
plants of note include damp loving plants Cuckoo Flower, Remote Sedge and
Tufted Hair Grass. Typical grassland species include Meadow and Bulbous
Buttercup and Woodrushes. Typical woodland species include Bluebell, Sanicle
and Greater Stitchwort. Perhaps the plant that will draw most attention is the
small patch of Common Spotted Orchids a few metres south east of the pond.
Management
Recommendations
For nature conservation purposes
there is a strong argument to suggest that unless there are real underlying
problems that need to be and can be solved - or other strong reasons to change
a pond, then no management work should be undertaken. Unlike other habitats,
where the effects of particular management are well known and can fairly safely
be carried out without causing problems – the effects of even simple management
on ponds are much less well known and much less predictable. Thus on a
precautionary basis, major management tasks at least are to avoided unless
really necessary. Indeed, often it is best to stagger larger task and monitor
their effect(s) – and then make use of the results of this monitoring to adapt
and inform future management.
Any worthwhile attempts to
significantly increase the levels of light to the pond (either direct and/or
side) and/or reduce the volume of leaves entering the pond would require the
felling of several trees. Most of the trees on site are significant ecological
and landscape features in their own right and to remove them would have a major
impact on the appearance of the site – as well as almost certainly create much
opposition from local residents. Thus no major tree felling tasks are suggested
or recommended.
Thus, three smaller scale
management tasks are suggested, with the idea to try and create a greater
diversity of habitat in the pond and reduce the chance of increased shading
from trees in the future. It has to be emphasised that none of these tasks are
essential to maintain the ponds current ecological interest.
The first of the tasks is to
ensure the shade levels from trees are not increased significantly. There are a
few small Ash seedlings / saplings around the margins of the pond, but being
small they are not and will not increase the levels of shade and fallen leaves
in the near future. The chances are, even if these were left unmanaged, that
these will never come to much. However a task could be organised to remove them
(complete with roots) as a precautionary measure.
The other two suggested tasks are
more speculative and if carried out may produce some benefit – but most
importantly should not cause any actual harm to the suite of species already
present. The first of these suggested tasks is to remove accumulated leaf
litter to a depth of up to 30 cm or the depth of the hard bottom of the pond
(whichever is reached first) over an area of up 10% of the pond surface area
(c. 25 square metres). The second suggested task is more labour intensive and
will need more pre-planning. The steepness of the banks means the pond
currently has a very limited draw down zone and at high water few areas of
continuous shallow water. Thus it is suggested that the up to 10% of the pond
(c. 25 square metres) of the existing basin is dug out to create a shelf
between 10 and 20 cm below normal high water. Another approach to achieve the
same end could be to extend the size of the pond by the creation of a similar
shallow shelf into what is currently the pond bank and surrounding grassland. The latter approach would need to be undertaken with
particular care to avoid breaking through any layer of clay sealing the
existing pond banks. Equally, digging down into the pond needs care to avoid
breaking through a clay layer sealing the pond, should the basin prove to be of
artificial construction. In both cases an investigation of the underlying
geological strata (natural or otherwise) of the pond and its surrounding area
will be needed to ensure the basin will not be breached and any new diggings
will hold water.
The area surrounding the pond is
a good site in its own right and needs to be managed in a sympathetic way for
wildlife not just in its own right, but so it continues to complement and
enhance the pond itself. If the option of enlarging the pond is taken up, care
will need to be taken to which surrounding areas are selected –the best (most
species rich) parts being avoided, or particular uncommon plants on site being
avoided. The main management requirement for the surrounds is some kind of
cyclic cutting. It would be easy to overdo cutting and damage the botanical
richness of the site and any animals it supports. Thus, it is suggested the
bulk of the grassland is cut in late August / early September allowing plenty
of time for most of the plants to flower and set seed. Parts of the site may
benefit from a second cut either in later in the autumn or winter, especially
if they are areas where ranker grasses are more common. The exceptions to the
normal cutting regime are as follows. The margins of the pond are best if they
include some taller rougher growth and these would be best managed by cutting
on a two year cycle i.e. only half or less cut in any given year – suggested
date of early spring (late February or early March) with a high cut (at least
10 cm. above ground level). A variable width strip of grass (up to 3 metres
wide) along the outer margins of the site (alongside the hedges) could be
managed in a similar way – with cutting after the worst of the winter is over
to maximise the amount of over-wintering habitat. Parts of the site may need
cutting more often, especially and most obviously the route of the public
footpath should this grow tall. All cut material should be picked up and
stacked on site, around the margins of the site as one or more ongoing habitat
piles. These should be located away from any notable plants. There is one
existing dump area, which should continue to be used. Shady areas e.g. under the canopy of
trees, with woodland plants may need less cutting, perhaps in some years no cut
at all. The more acid open sunny bank
next to the path could be managed with two cuts to ensure it remains very short
and relatively bare.
The pond supports no problematic
species of plant that need to be controlled. However, the pond surrounds
potentially support one such species of plant, i.e. an introduced population of
hybrid and/or Spanish Bluebells. If after a survey in spring 2010 there is any
doubt as to the nature of these Bluebells they should be dig up and removed
from the site to ensure the continued survival of any real native Bluebells on
site and elsewhere very locally. Spanish Bluebells form hybrids with the native
Bluebell and may in time cause the loss of the native if they spread into large
wild populations of which a feature of the Chiltern woods.
Surveying
and Monitoring Recommendations
Good information now exists about
the ecological value of the pond and its surrounds and the species they
support. Species composition and habitats change all the time, but there may be
particularly marked changes following more interventionist management such as
silt removal or basin extension. Disturbing areas may allow previously buried
seed to germinate. Only by monitoring can any changes in the species present be
ascertained and the positive benefits of any management undertaken proved. A repeat survey of the major species groups
undertaken for this report could be repeated in five years time, to establish
any such changes. In the mean time maintain as many systematic and/or casual
records as possible for the pond and its surrounds. Plant surveys could be
relatively easy as many of the species are familiar and well known. Specific
animal surveys that could be undertaken would include familiar groups such as
amphibians, including searching for spawning Frogs in the early spring and
newts later in the spring and summer. Aquatic invertebrates and most
terrestrial invertebrate surveys would require a greater degree of specialist
knowledge and may have to be sourced from people outside the parish.