neW urBan environmenTs, C.1860–1950^165of advanced successional stages – such as species associated with ancient
woodland – are thus generally absent. But others flourish, often in unusual
combinations. The ability to tolerate disturbance is the key selective factor
in urban contexts, ensuring that plant species with limited ranges in the
countryside, being out-competed by rivals in most soil or moisture conditions,
can thrive in a much wider range of circumstances, leading in turn to the
development of plant communities of a kind never encountered in rural areas.
Second, disturbed conditions provided good opportunities for introduced
species, large numbers of which came from two sources: gardens, which
accounted for increasing areas of ground; and industry, which sourced many
of its raw materials from around the world. Aliens already present, such as
Oxford ragwort (Senechio squalidus), also flourished. Urban areas were thus
increasingly distinguished from rural districts by having floras comprising a
mixture of indigenous and alien plants.^19 Indeed, the extent to which aliens
have come to characterize the urban flora is often underestimated. Most
dandelions found today in towns and cities, for example, are introduced
species, Taraxacum atacum and Taraxacum exacutum, rather than the native
Taraxacum officinale agg. Lastly, urban and suburban environments are
characterized by considerable variety within a small compass: in Gilbert’s
words, they comprise a ‘varied and small-scale habitat mosaic imposed by
man’.^20 Within a single street, close juxtaposition of paved areas and gardens,
and within the latter of lawns, hedges, flower beds and shrubberies, provided
more diversity than could be found within an equivalent area of farmland
(it should be emphasized that much of this had been true of the towns
and cities of earlier periods: urban environments are considered in detail in
this chapter principally because they now came to occupy a much greater
area than ever before). These three factors together ensured that towns, while
having less total vegetation cover than the countryside they replaced, usually
boasted a higher number of plant species. This was also true of invertebrate
populations; but the situation with higher fauna, unable to cope with high
levels of disturbance and lack of cover, was more variable, and reflected the
spatial organization of towns and cities.
City centre wildlife
As cities grew larger through the later nineteenth and early twentieth
centuries, the density of buildings and the proportion of the ground surface
paved or otherwise surfaced in their central districts both steadily increased,
something that Hudson described, in the case of London in the 1890s, as
the ‘deadly filling-up process’.^21 Fitter, likewise discussing central London
but some 50 years later, noted how ‘the ground is completely covered with
buildings, roads and railway lines and vegetation is almost non-existent.
Yet even in this desert, quite a number of animals, especially birds, have
managed to adapt themselves to the modern environment’.^22 The term