Strangers carry dangers when traveling the globe
By Gary Raham
Nature Writer and Illustrator
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I've read about the dangers of exotic plant and animal invasions for many
years, but it was not until my wife and I became "exotic invaders" of Australia
and New Zealand last October that the phenomenon struck home at a visceral
level.
A person quickly learns about his or her suspect status during trip preparation.
Publications admonish travelers to clean hiking or athletic shoe soles
that might harbor clever seeds on a mission of dispersal. Fishermen and
other outdoor enthusiasts must likewise cleanse all equipment of biological
hangers-on.
Invasive plants and animals cause billions of dollars of economic damage
annually worldwide, but damage to biological diversity hundreds of millions
of years in the making may be the longest lasting and most profound insult
– and one with as yet undetermined consequences.
Australia and New Zealand provide maximum contrast for this issue because
both are island refuges for plants and animal lineages long extinct elsewhere.
Both belonged to the ancient supercontinent Gondwana 250 million years
ago. It included what is now South America, Africa, Arabia, Madagascar,
India, Antarctica, Iran, Tibet, fragments of Southeast Asia and New Guinea.
This mega continent began breaking up some 90 million years ago, and Australia
became completely isolated some 60 million years ago.
Because this continental diaspora was during a time when flowers were rapidly
becoming preeminent, and land plants and several mammal lineages competed
for dominance, Australia and New Zealand shelter ancient flowering plants,
mammals that carry their babies in furry pockets, and enough other oddities
to make a stranger's jaw drop.
But humans seem to possess conflicting impulses when it comes to exploration.
They love going "where no person has gone before" (to quote a refrain familiar
to Trekkies), but they soon get homesick for familiar scenery and comfort
foods. Thus, cycads, ferns, conifers and kangaroos now share part of their
space with English oaks and rabbits. Other indigenous plants and animals
disappeared altogether, unable to compete with the more diverse flora and
fauna from the rest of the planet.
Our "Johnny Appleseed" compulsions first expressed themselves before we
realized how intertwined living systems are. Now, they often continue through
ignorance, as when seeds of exotic houseplants like yellow toadflax "go
wild," or as a byproduct of commerce, as when purple loosestrife invaded
New England during the 1800s because its seeds germinated in soils used
as ballast in cargo ships. (See North Forty News, June 2008, "Yard plants:
nurturing natives and ousting aliens.")
"How dangerous can a few misplaced bugs and weeds with wanderlust be?"
a person might ask. The list of problems is robust and expensive.
- Alien creatures, without natural enemies to check their numbers, may
out-compete natives for resources and disrupt ecosystems. Depending on
the ecosystem, this may impede forest regeneration and natural succession
of plant life, alter soil chemistry, which in turn impacts commercial crops,
or change the flow of water and the patterns of fire.
- Aliens may hybridize with natives, changing the genetics of populations.
Altered plant varieties can be unpalatable to humans or their livestock
or become toxic. Genetic changes sometimes aid the spread of diseases.
- Aliens may directly injure or compete with commercial food crops. Invasive
animals can foul shipping lanes or alter fishing and water habitats.
- Ecosystems under siege by aggressive, uncontrolled newbies become simplified
– the core meaning of the phrase "loss of biodiversity." Diversity is nature's
toolbox. If the box contents consist of only a screwdriver and pliers,
those won't help much when a leak makes a pipe wrench and a bucket indispensable.
Good resources for discovering exotic invaders in Colorado include the
Invasive Plant Atlas at www.invasive.org/weedus/index.html and Colorado
Noxious Weed Management Association at www.cwma.org/noxweeds.html. The
Colorado Division of Wildlife site contains information about endangered
or threatened animal species in the state:
wildlife.state.co.us/WildlifeSpecies/SpeciesOfConcern/.
Shortly before we left for Australia, I read about the decade-old discovery
of a tree – the Wollemi pine – thought to have been extinct since the days
of the dinosaurs. I thought a trip north of the Blue Mountains (less than
125 miles from Sydney) where it still grew might be fun, but our schedule
was tight. I've since discovered that to avoid the threats inherent to
frequent visits to the grove of 100 known trees, the Australian park service
and the Royal Botanic Gardens in Sydney have teamed up to promote the propagation
of trees from seeds and cuttings
(www.wollemipine.com/science.php). Ironically,
one effective way to save rare plants is to make them attractive as exotic
captives in distant lands.
This ancient pine doesn't present an "escape threat" like runaway flowering
plants with their advanced methods of growth and seed dispersal. And saving
individual plants doesn't preserve the network of organisms with which
they exist in the wild. I think of the grove of Mesozoic survivors, huddled
near a waterfall in their rainforested canyon, as a kind of biodiversity
insurance policy best left alone for now to carry their extinction-hardy
genetic codes into an uncertain, but always challenging, future.
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