Environmental Engineering Reference
In-Depth Information
Horticulturalists share a list of the same “big four” foreign plant invaders in Britain: Japanese knotweed,
Himalayan balsam, rhododendron, and giant hogweed. All four got their start with Robinson and the
other Victorian wild gardeners. All four do best in disturbed land around people, so they are frequent in
suburbia and along footpaths and riverbanks. That makes them highly visible to casual observers, but
they are not widespread in the countryside at large. In different ways, all four are victims of the kind
of hostile treatment that no native species would receive. Like crossed lovers, gardeners seem to relish
hating what they once loved.
Giant hogweed (
Heracleum mantegazzianum
) first came to Britain from the Caucasus in the early
nineteenth century. It looks like giant cow parsley, and Victorian Britons loved its height. In Norway,
they still do. There, it is known affectionately as the Tromso palm, after the Arctic town where it grows
widely. But Britons have learned to fear the hogweed. Legend has it that it strayed from respectable gar-
dens into the wild a century ago by escaping from Buckingham Palace into London's parks. From there
it reached the canal system, and its floating seeds spread to the rest of the country.
It has colonized riverbanks like those of the Wye and Usk in Wales. Even so, nobody thought much
about it until the 1970s, when reports emerged of children getting blisters after touching it while playing.
Doctors discovered that the sap from its stem sensitizes skin to sunlight, causing it to redden alarmingly.
Cases are rare but can be serious. Hogweed juice could, theoretically at least, cause blindness. The me-
dia thenceforth called it a triffid, after the botanical menace in John Wyndham's 1950s science fiction
classic
The Day of the Triffids
, which took over the world after humans were blinded. In 1981, giant
hogweed joined Japanese knotweed as an officially “noxious weed.” It is an offense both to plant it and
to throw it away.
11
Naturalists such as Dickson say that once again an ecological case against a nonnative plant species
is overblown. Hogweed may stand tall, but it does not, as often claimed, obliterate any other plants in
its midst. In Glasgow, there are famous “hogweed forests” on the banks of the River Clyde near Kelvin-
bridge, he wrote to me in an e-mail. “But it's not true that everything else vanishes. You get spring flor-
as, a bit like a woodland, with smaller plants such as lesser celandine growing beneath the hogweed.”
is working on a rust fungus to deploy against the menace.
Joining hogweed in the doghouse are rhododendrons. London gardener Conrad Loddiges brought
the first samples of
Rhododendron ponticum
to Britain, probably from Spain, in 1764. Later, Kew's le-
gendary plant explorer Joseph Hooker added a host of new species after a trip to Sikkim in the Indian
Himalayas. In 1853, he had enough to plant a grotto called Rhododendron Dell at Kew that still attracts
visitors today.
13
The various species soon showed a penchant for interbreeding to create hybrids. They
were an instant hit with gardeners. The plants love Cornwall's china clay pits. The Eden Project, an
ecological theme park constructed in one of the former pits, sells what it proudly calls the Trewithen
Hybrid.
14
While still liked in gardens, rhododendrons are feared in the wild because, though not widespread,
they sometimes crowd out other plants. But rhododendrons “can be surprisingly good for many wildlife
species including winter roosts for birds, breeding nightingales and cover for deer, badgers and otters,”
says Ian Rotherham, an urban ecologist at Sheffield Hallam University.
15
Their dense leaf canopy pro-
tects native wood mice from predator birds. Mice numbers increase where the alien evergreen lives, and
there is also a measurable rise in the number of weasels lurking in the hope of finding those mice unable
to take refuge.
16
Search WWH ::
Custom Search