State of Nature report - RSPB

URBAN
Lichens are sensitive barometers of
air quality: their presence or absence
indicates levels of atmospheric
pollutants such as sulphur dioxide and
nitrogen oxides. In 1970, at the height
of industrial sulphur dioxide pollution,
only nine species of lichen could be
found within a 16km radius of Charing
Cross in central London. Remarkably,
a 2004 study 4 found 72 species of
lichen on oak trees in London parks,
a striking resurgence in response to
decreased sulphur dioxide emissions.
The UK’s urban areas have the potential to hold
a wealth of wildlife, if we give nature a chance.
elatively few species are urban
specialists. Most are generalists
that can be found in greater
numbers in other habitats such as
woodland or farmland. However, a few
species are genuinely associated
with humans, and urban areas provide
substitutes for the habitats they would
have used before modern cities developed.
These include the house fly, several
house spiders, and clothes moths.
In other cases, wildlife occupy the
remaining fragments of natural sites
that have been swallowed up by cities.
During Jennifer Owen’s remarkable and comprehensive 30-year study of the wildlife
in her garden, she found more than 2,600 species, with many more unidentified 5 .
Although we cannot generalise from this one site, her study demonstrates the sheer
wealth of wildlife that can exist on our doorsteps. Worryingly, Dr Owen recorded
substantial declines in five of the six invertebrate groups she recorded throughout
the 30-year study. She put this down to habitat loss within the local landscape.
Index (1972-76 = 100)
140
120
100
80
60
40
hoverflies
macro-moths
butterflies
solitary bees
solitary wasps
ladybirds
All (658)
Invertebrates (434)
Plants (207)
Vertebrates (17)
Strong decrease
Strong increase
0 25 50 75 100
Percentage of species
Slight decrease
Slight increase
For some species, urban areas are
becoming more important due to
the loss of suitable habitat elsewhere
– garden ponds may be refuges for
amphibians such as common frogs,
toads and newts, for example.
Four of the six truly urban birds have
declined, and two – the house sparrow
and swift – have declined dramatically.
Numbers of house sparrows have
plummeted by more than two-thirds
since the 1970s.
However, urban flowering plants
are bucking the trend: more species
have increased their distribution in
recent decades than have declined,
presumably because the amount of
suitable substrate has increased with
the expansion of urban areas and the
transport network. The number of
native plant species associated with
urban areas is, however, much lower
than in other habitats – the exception
being former farmland wildflowers,
such as cornflower and corn cockle,
which are now found only in urban
areas as a result of amenity sowing.
20
0
1972–76
1977–81
1982–86
Recording period
1987–91
1992–96
1997–2001
Relatively few urban species have
been included in national Red List
assessments: only four species (4%)
of urban flowering plant and 19 species
(5%) of urban moss and liverwort have
been classed as Threatened.
54 STATE OF NATURE 2013