(^162) an environmenTal hisTory of Wildlife in england
delicate flowers thrived, have been changed by the deleterious compounds
of coal-smoke into barren deserts’.^4 One Mrs Haweis was moved in 1886 to
pen a book entitled Rus in urbe: or flowers that thrive in London gardens
and smoky towns.^5 In northern towns and cities, trees and shrubs planted
in public parks were frequently killed, or made ill and disfigured, by aerial
pollution and needed to be regularly replenished by the civic authorities. By
the earlier twentieth century smog damage to market garden crops, such
as tomatoes, was one of the factors encouraging the migration of nurseries
northwards, away from London, along the Lea valley; smog could even have
a serious impact on grass, ‘causing a slimy scum and creating acid conditions
that destroy the useful bacteria in the soil’.^6
The decline of lichens in industrial areas had a knock-on effect on certain
kinds of fauna. It was noticed in the late 1840s how a number of species of
moth in northern industrial towns and in London – principally the peppered
moth (Pachys betularia) but also the waved umber (Hemerophila abruptaria),
mottled beauty (Boarmia repandata) and grey dagger (Acronycta) – were
beginning to exhibit significant changes in colour. Dark or black variants
or ‘melanic’ forms, always present in low numbers, now showed a marked
increase. Before industrialization such individuals were highly visible to
predators against the mottled background of lichen-covered trees. But as
lichens were killed off and tree trunks became blackened with soot, these forms
flourished and by 1895 98 per cent of peppered moths in the Manchester
area were of this type, the normal form now being the more vulnerable.
This explanation for the change, often quoted as a powerful contemporary
example of natural selection in action, was first advanced by J. W. Tutt in the
1890s and tested empirically by Kettlewell and Ford in the 1950s.^7 Although
the validity of their work has since been challenged,^8 the theory has largely
been confirmed by subsequent studies and – more powerfully – by the fact
that, with the decline in aerial pollution since 1950, trees have become less
sooted, the proportion of ‘normal’ moth forms has risen sharply and melanic
forms have again become rare.^9 It is probable that pollution had a more
general negative effect on insects in this period. It has thus been suggested that
the marked recovery in the numbers of swifts and house martins in central
London following the passing of the Clean Air Act in 1946 may be due in
large part to the resultant improvement in the number of the insects which
are their prime food source.^10 Some believed that accelerating levels of smoke
pollution – both domestic and industrial in character – had a more generally
deleterious effect on bird life.^11 When John Plant began to record the number
of birds in Manchester’s Peel Park in the 1850s, numbers were still healthy,
with a total of 71 species, of which 34 were breeding. By the 1870s there were
only 19, of which eight were breeding; in 1882 he could find only five species
in the park, and only sparrow and starling were nesting there.^12
All the varied industrial landscapes discussed in Chapter 5 continued to be
created in the late nineteenth and early twentieth centuries – spoil heaps of
great variety, quarries and the like – and on an even greater scale. Most still
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(Elle)
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