WELCOME TO AMERICA - The New Wild: Why Invasive Species will be Natures Salvation - page 37

rivals by germinating early in spring. That also makes it a valuable fodder crop. The downside is that
it dries out by mid-June and burns well. Its dense growth also means that fires travel much faster than
in the days when sagebrush dominated. “In Idaho they have million-acre burns,” says DiTomaso. After
the fires, cheatgrass recovers first and takes over more land. Thus cheatgrass encourages fires, and fires
encourage cheatgrass.
Other old-world grasses that have done well include couch grass, foxtail, and meadow-grass ( Poa
pratensis ). A principal reason why all four have prospered is that they were well matched with the graz-
ing animals that they accompanied westward. European cattle are much more voracious grazers than
the bison they mostly replaced. Native sagebrush could not cope. European cattle required European
grasses. Only their dense growth could withstand the assault of a million teeth. Cheatgrass domination
is often described as a step toward desertification, but almost certainly it held back the soil erosion and
desert spread that would have followed long-term grazing of sagebrush by European cattle. Americans
probably have reason to be thankful for the foreign grass.
When it comes to nature, we are all fickle. We forget that much that appears loveably native is ac-
tually foreign. Some vagabond species that we like can become so much part of the landscape that they
get local names and even become adopted Americans. Old-world meadow-grass was renamed Kentucky
bluegrass. “Tumbleweed” sounds quintessentially American—a metaphor of ghost towns in western
movies as it rolls across the landscape in the wind. But the most common tumbleweed species is not
native to the United States. Salsola tragus , Russian thistle, was brought by nineteenth-century Ukrainian
immigrants in flax seed.
Likewise few would regard the humble and helpful earthworm—“nature's little farmer,” plowing
and fertilizing soils—as an alien from the Old World. But it is. Canada and the northern states of the
United States had no earthworms until Europeans showed up. There are several species around now,
including the most numerous, the litter-dwelling octagonal-tailed Dendrobaerta octaedra , and Europe's
favorite, Lumbricus terrestri . Alien they may be, but they are perhaps only replacing worms wiped out
before the last glaciations scraped away the soils in the North—the final piece in the reconstruction of
post-glacial soil ecology.
Not everyone accepts the rise of European worms. Some forest ecologists say that before their
takeover of American soils, forest floors were thick with leaf litter. Now that worms eat this litter, soils
are exposed and species have disappeared, including some salamanders and ground-nesting birds. 22 One
lifelong worm enthusiast, Paul Hendrix of the University of Georgia, thinks it is worth trying to hold
back their advance. 23 Time, at least, is on his side. Typically, invasion fronts advance by less than a
mile a century, says Cindy Hale of the University of Minnesota, a fanatic who started a worm farm as
a kid. 24 So, despite many introductions, their conquest is far from complete. Outside urban areas, they
are mostly found near roads and lakes—suggesting introductions on vehicle tires and as fishing bait. In
Alberta, Canada, 90 percent of boreal forests remain worm-free.
Another unexpected alien is the European honeybee ( Apis mellifera ). The species had been domest-
icated in the Old World for four millennia before British settlers brought fully stocked hives to North
America in the seventeenth century. Some ecologists see the European arrivals as an ecological disaster.
But on a continent where the main source of sweetener had previously been maple syrup, honey from
the aliens was welcome. And while there were pollinators in North America before, the European bees
have assumed a major role, especially for crops. Today they do an estimated 80 percent of the pollina-
tion carried out by insects on US farms and in orchards—and a third of all pollination.
Most Americans today see the European honeybee as fully naturalized. Twelve states list it as
their state insect. When nearly a third of honeybee colonies died in 2012, from a mysterious disorder,