Environmental Engineering Reference
In-Depth Information
comer humans prospered, as did many of the species they had brought. When the English adventurer
Captain James Cook first visited in 1778, there were several hundred thousand Polynesians there.
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Europeans brought many more alien species, like cats and mongooses to hunt down rats; pigs and
giant African land snails for food; deer for hunting; and guava and other useful trees. Out went a num-
ber of the islands' unusually large range of bird species, including the Hawaiian rail, last seen in 1884.
Nonetheless, each new invasion added biodiversity, since many more species arrived than were made
extinct. Hawaii contains some fifteen hundred species of flowering plants found nowhere else, but also
more than a thousand new plants have arrived. There are only seventy-one known extinctions. The es-
timated twenty-five hundred introduced insect species have added 50 percent to the native component.
The avian tally is sixty-six bird species lost and fifty-three gained, though most of the losses were spe-
cies hunted to extinction by Polynesians before Europeans arrived. Some of the introductions, like the
worm-eating mynah from Asia, were made to combat pests. Others, such as songbirds and the American
northern mockingbird, a notorious mimic, probably won passage for the sheer joy of their company.
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Whether adornments or not, most newcomers also provide ecological services. Alien birds such as
the Japanese white-eye and the red-billed leiothrix, introduced from India a century ago, are today the
mainstays for dispersing the seeds of native shrubs. “Introduced mangroves are straining sediment and
building habitat that native fish utilize,” says Mascaro. Most ecologists do not spot these important ser-
vices, he says, because they dismiss ecosystems containing alien species as damaged and degraded.
Thus, they are beneath the attention of those who are searching for the truth about nature. This, he says,
is a big mistake, because much of the truth about nature is bound up in these novel and disrupted ecosys-
tems.
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Getting rid of the alien birds would leave the understory of many native Hawaiian rain forests
bare, says Jeffrey Foster, now of the University of New Hampshire.
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Most controversial is the case of
Morella faya
, a myrtle tree sometimes called the “fire tree.” It was
brought to Hawaii by Portuguese migrants a century ago from Atlantic islands like the Azores. It enjoys
the sometimes harsh volcanic conditions and is the first plant to colonize newly created lava flows in the
Hawaii Volcanoes National Park. It fixes nitrogen from the air and uses it to turn the lava into soil, which
no native plant can do. Many ecologists nonetheless think this skill is a bad thing. Princeton's Andrew
Dobson concluded in 1998 that by colonizing the lava flows, the myrtle “shuts out natives species and
leads to their subsequent extinction.”
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Ecologist Peter Vitousek, who has spent a long career at Stan-
ford University and is famous for his work on the nitrogen cycle, has taken the same view, though he
has agreed that their nitrogen-fixing skills might eventually turn the lava into soils fit for native plants.
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I thought that more than a decade after these pronouncements it would be interesting to know what
happened. Did the fire tree pave the way for other species, or crowd them out? But there is a dearth
of published data. Nobody, it seems, has bothered to research the question. When I checked the Global
Invasive Species Database of the International Union for the Conservation of Nature (IUCN), it had no
references to research into the impacts of
Morella faya
on Hawaii since 1991.
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Mascaro told me that
from what he saw, the myrtle appeared to be receding from lava flows as native species have colonized
the soils it has created. He said the case was a perfect example of how conservationists can, through their
love of native species and ecosystems, simply fail to recognize the services that aliens often provide to
the wider environment.
Odd things happen on islands because their simple ecosystems have weak spots and tipping points bey-
ond which dramatic changes can take place. Sometimes the arrival of outsiders triggers these tipping
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