neW urBan environmenTs, C.1860–1950^167the ‘changing location of industry which was taking place in the inter-War
years’ and described how ‘there was in many of the older industrial centres
an increasing degree of decay, as the older factories became obsolescent and
eventually closed down, and were not replaced by new’.^31 Such areas of
derelict land were further increased by bombing during World War II and
by the clearance of slum dwellings after 1950. They were and are complex
environments.^32 Demolition of buildings produces a substrate of brick
rubble, usually rich in lime because of the abundance of fine mortar. This is
initially colonized by species with windborn seeds, such as Oxford ragwort,
groundsel, and buddleia (Buddleja davidii), but fairly minor differences
in the character of the rubble, in terms of structure and alkalinity, ensure
marked variations in the initial communities of plants. After a few years,
the vegetation becomes dominated by tall perennial herbs with leafy
stems, many of which are exotics and garden escapees. Rosebay willow
herb is perhaps the most common but it is accompanied by michaelmas
daisy, golden rod, garden lupin, tansy and Shasta daisy. Native plants are
also present, including a range of thistles (creeping and spear especially),
common mallow, buttercups and mugwort, wood margin plants like hedge
woundwort and bracken, and species of neutral grassland such as yarrow
or cat’s-ear.^33
After eight or so years these various communities develop into rough
grasslands, as plants like false oat-grass, Yorkshire fog and red fescue
obtain a hold, although still with stands of taller herbs, such as yarrow
or michaelmas daisy: at this stage, thickets of Japanese knotweed also
sometimes form.^34 Eventually they develop as scrub and then as woodland,
although the distance of city centres from seed sources sometimes makes this
a slow process. Ash, sycamore, broom, laburnum, hawthorn, rowan, elder
and apple, together with willows, birch, cotoneasters and garden privet are
usually prominent. ‘Such woods are unlike any other self-sown examples in
the country’.^35
What makes these urban wastegrounds particularly interesting was, and
is, their variety. Not only have different substrates generated variations on
these broad successional themes, even on different parts of the same site, but
the availability of seed sources creates radical differences in the character
of communities. Indeed, different cities developed their own distinctive
waste ground flora, the result of idiosyncrasies of geology, soils, climate,
and history. Climate ensured, for example, that buddleia remained rare in
cities in the north of England and that reed and Himalayan balsam came to
dominate waste ground in the west, where there were and are also denser and
more extensive stands of willow herb and Japanese knotweed than in drier
eastern cities. The limestone cliffs around Bristol support large quantities
of traveller’s joy and its seeds are readily blown by the wind into the city,
ensuring that the species became a major component of its wasteground
flora. Oliver Gilbert has described in some detail the distinctive urban
floras of Birmingham, Swindon, Teesside, Bristol, Hull, Leeds, Manchester,