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BCD Special Report
Historic Gardens 2010
7
Action Plan,
‘
Priority Habitats’.
5
Its website
lists more than 50 priority species that are
associated with ponds for conservation
action, either because of significant declines
in recent times, or because they are rare and
threatened by extinction. Ponds are also
used for breeding by all three European
protected
6
amphibians that occur in
Britain including the great crested newt
Triturus cristatus
, the pool frog
Rana lessonae
and the natterjack toad
Bufo calamita
.
What makes a good pond
for wildlife?
It is difficult to be specific about what defines
a ‘good’ pond for wildlife because different
types of ponds will support characteristic flora
and fauna dependent on their origin and local
environmental factors such as substrate, water-
source and surrounding habitat. However,
there are general features that, if present,
are likely to encourage ecological interest.
Water quality is important. Ponds with a
high ecological interest are usually associated
with water that is free of pollutants and has
low levels of soil nutrients such as nitrogen,
phosphate and potassium. High nutrient
loads in ponds have become increasingly
problematic in the British lowlands, largely
as a result of agricultural intensification.
This can encourage algal blooms which
have a severe impact on both biodiversity
and the ornamental value of a pond.
An isolated pond is usually of less
ecological value than one that is located
in a cluster of others, because the risk of
species extinction increases as pond density
declines.
¹
Recolonisation of ponds that have
lost populations of species becomes less likely
with increasing isolation, because the more
uncommon species associated with ponds
often have poor dispersal mechanisms.
Ponds with structural variation are
more likely to provide opportunities for a
higher number of species than ponds with
a more uniform structure. For example,
small variations of pond-bed topography
allow a greater number of dragonfly
species to co-exist with each other. In
a more uniform environment, smaller
less-competitive dragonfly species will
be less able to hide and avoid predation
by the larger dragonfly species.
Native plants are preferable to
ornamental ones because they support a
greater diversity of animal species, but in
an ornamental setting, native plants may
not be appropriate. In this situation, some
degree of invasion by native species should
be tolerated as these plants can be helpful
to wildlife: even the most heavily managed
ponds can support wildflowers in the margins
and the submerged plant community will
usually contain some native species.
To some extent, a lack of native species
in a garden environment can be offset by
complex plant architecture. In general, the
more diverse the plant structure, the greater
the range of opportunities that organisms can
exploit. In the case of a pond this can mean
that a diverse range of emergent, floating-
leaved and submerged aquatic plants is best.
The pond above is located in the grounds of Walton Manor, a 16th century building at Milton Keynes. It is a plastic-lined pond set
within a formal landscape of paving, mown lawns and ornamental shrubbery that is approximately 4m in diameter and 0.75m in
depth. This pond contains medium-size populations of great crested newt (peak count of 29 adults) and smooth newt (peak count
of 45 adults) and common frog has also been recorded; most importantly the pond does not contain any fish species. The newts lay
their eggs on the water-lily
(
genus
Nymphaea)
pads and strands of filamentous algae. (Photo: Natalie White, BSG)
The photograph above shows a pond in the latter stages of natural succession at Cotswold Wildlife Park, a process whereby
standing water-bodies gradually infill with silt and debris, and change to wetland, then ultimately to terrestrial habitat.
The pond shown is now dominated by bottle sedge
Carex rostrata
in the centre, with hard rush
Juncus inflexus
and marsh
bedstraw
Galium palustre
on the margins, and could be classified as a wetland rather than aquatic habitat.
Although ponds such as this can support amphibians, they are sub-optimal for breeding purposes, because of a lack of
open water for display. Unless there is good reason, ponds with a complete cover of wetland rather than aquatic plant species
should not be restored by removal of vegetation and silts because wetlands are often as valuable as ponds and will support a
different biological community to that which is typically associated with ponds. In all cases, a survey should be carried out
before any management is implemented. (Photo: Helen Evriviades, BSG)
Water-lilies are a familiar site in ponds, lakes, canals and slow-flowing rivers, but most populations of white water lily
Nymphaea alba in Britain are not native. However, stands of any water-lily species in a pond can provide excellent habitat for
pond fauna including great crested newts. However, the ecological value of a pond will decline, if the majority or the entire pond
surface is covered by water-lily pads. This is because the heavy shade will suppress the growth of other plant species. In addition,
dense stands of water-lily can reduce the area available for male newts to display and attract females. Therefore, management of
aquatic plants is usually essential to maintain the long-term ecological interest of a pond. (Photo: Helen Evriviades, BSG)