ECOLOGICAL CLEANSING - The New Wild: Why Invasive Species will be Natures Salvation - page 60

salt marshes, and other wetlands. 25 As part of this program, the Army Corps of Engineers began plant-
ing rewetted marshes with a cordgrass native to the eastern United States ( Spartina alterniflora ).
This new grass began to interbreed with its close relative, the local California cordgrass ( Spartina
foliosa ). The result was a new hybrid grass that colonized much more aggressively than either of its
forebears. It spread to areas no one had intended, blanketing previously open mudflats, clogging chan-
nels, getting in the way of oyster farmers, and—worst of all, for many—spoiling million-dollar views
and damaging the value of upscale waterfront properties. 26 So a decade ago, authorities launched a
multimillion-dollar project to rid the bay of both the alien from the east and the hybrid.
But that went wrong too. It turned out that one of the bay's most totemic and endangered birds, the
chicken-sized and largely flightless California clapper rail ( Rallus longirostris obsoletus ), had grown
partial to the new hybrid grass. The grass grew more densely than the local version and didn't die back
during the winter, providing better cover and nesting habitat for the secretive bird. During the 1990s,
as the hybrid spread, the rail population had soared. But after 2004, as the eradication got underway,
the bird's numbers crashed. There was no mistaking the cause. In time and space, the bird population
declined following the eradication of the alien grass.
Conservationists now face a dilemma. Should they carry on with the eradication and hope the birds
eventually recover? Or should they walk away? In 2013, nobody seemed sure what to do for the best. 27
The website of the California-based bird conservation group Point Blue Conservation Science still
backed removing the grass, saying “invasive non-native plant species” are a primary threat to the rail,
and that the hybrid “may reduce channel and mudflat areas important for foraging rails.” 28 But bay man-
agers had banned further removal where there are nesting rails. The rail must be as confused as the rest
of us.
Eradication can take many forms. In South Africa, ridding the land of alien trees and shrubs has gen-
erally involved chain saws and machetes and human sweat. Muskrats faced traps. Reindeer were shot.
Rats and other rodents generally suffered bombardment with brodifacoum or some other poison. But
an increasingly popular idea is deploying biological weapons such as insects or diseases. Dick Shaw at
CABI, Britain's chief biocontrol practitioners, reckons there have been some 140 releases of biocontrols
in Europe alone.
The idea is simple. Aliens often prosper because they come alone, unencumbered by the predators
and other natural enemies they encountered back home. Nothing in their new environment has learned
to eat them or inflict diseases on them, much less evolved to do that. In most cases this does not secure
their success, however. Something gets them. Few predator species will forego a free meal, even if the
prey is novel. By the same token, the new arrivals have no honed defenses against what they may find
in their new home. So the stakes are high in the early days. But if the newcomers do not succumb to
some native species that takes a liking to them, then they can have a free run for a while. Under those
circumstances, if you want to be rid of them, the logical way to fight them is to track down and import a
predator or some disease from their homeland as their nemesis in the new land. Set an alien to catch an
alien.
Among practitioners, Australians are regarded as the masters. Their reputation lies mostly with erad-
icating the prickly pear cactus ( Opuntia monacantha ), an introduction that goes as far back as English
settlers in Australia. When Captain Arthur Phillip was on his way to set up the first European settlement
at Botany Bay in 1788, he stopped off in Brazil to pick up some prickly pears. He wanted the cochineal