Weeding the Salmon Patch

Every time I pick up another scientific journal, I find something to remind me that Mother Nature has a wicked sense of humor. Mind, that's not the way scientists see it. They'd talk about things like balance and interconnectedness, observation and logic.

Foo. I know a practical joker when I see one, and nature does set up humans for pratfalls when we least expect them. Take, for example, the explanation of how a thriving Eurasian weed helped make for some flat wallets from Haines to Ketchikan.

The August 26 issue of the journal Science devoted a few pages to the 1994 meeting of the American Institute of Biological Sciences. This year, presentations of the gathered life scientists concentrated around the theme of science and public policy. Among the papers discussed was one delineating the dangers of alien invasion.

Of course, the aliens of concern aren't bug-eyed monsters. They're green, leafy, and greedy, and they're taking over the American West.

Several species of Eurasian weeds have immigrated to the Americas, either because human immigrants wanted them to come, or because they found ways of hitching along unnoticed. The problem has been recognized in agriculture almost since the Pilgrims put plow to stony New England soil, but now the aliens have left the farms and moved onto undisturbed ground.

They're moving quickly, too. Bureau of Land Management research coordinator Jerry Asher put together data gathered from scientists and agency officials to draw an alarming conclusion: On BLM lands, alien plants are expanding their territory by 14 percent a year. Put in other terms, he said, that means the foreign weeds take over 2300 additional acres every day.

Some of the land they've invaded is acreage most Americans would consider to be virtually pristine wilderness. Grand Teton National Park now hosts thriving populations of invaders such as spotted knapweed from central Europe, musk thistle from Eurasia, and Dalmatian toadflax from near the Adriatic Sea.

A likely first response from someone reading such a list might be, "So what?" It's a big country, and the exotic weeds might just as well be seen as so many dandelions in a lawn, a nuisance, perhaps, but hardly deadly. Yet surely dandelions can choke out the grass in an abandoned lawn, and similarly, the exotic weeds can out compete native plants upon which whole ecosystems may depend. Just as human immigrants left Old World feuds and debts behind, the immigrant plants usually came away without their pests and predators. That means they have an edge up on the locals. Asher calls the alien weeds' success "an explosion in slow motion."

Like other explosions, the weedy one can do spectacular damage. Species diversity drops, erosion increases, and once healthy ecosystems become "a patchwork of undesirable species."

Consider, for example, what has happened in the Sellway/Bitterroot Wilderness in Idaho. Riverbanks there wear an increasing blanket of spotted knapweed, a homely cousin of the handsome garden flower known as bachelor's buttons. Between the knapweed plants the silty earth is bare, and some of that soil washes into the streams whenever it rains. The silt settles onto the gravels of the riverbed, smothering any eggs that the few remaining endangered salmon of the region might have been able to lay there.

Now, remember how protecting Idaho's almost-extinct salmon runs has cut into southeastern Alaska's fishable stocks of salmon? The risk of snaring one of the precious few left in a severely endangered stock meant that our still healthy supply of fish had to be left more undisturbed than otherwise necessary, and far more than Southeasterners or their visitors liked. The Idaho salmon have had to survive past overfishing, dams blocking their way up- and downstream, and now they have to cope with spawning beds spoiled because of invading knapweed.

See? Mother Nature plays rotten jokes, though the fish (and fishermen) aren't laughing.