Welcome to the Homogocene
The snow has started to melt off the pasture behind our house, revealing an emerald-green carpet of grass. It’s a welcome sight, but how, you might wonder, could the grass already be green in mid-February? Because it is cheatgrass, an exotic Eurasian species that springs up and matures faster than any of the West’s native grasses. Cheatgrass likely made its way to our continent in a grain shipment from Europe in the late 1800s, and it now covers more than 40 million acres of Western rangelands, an area larger than California.
Cheatgrass is hardly the only exotic on our place. Along the back fence, a dense monocrop of Russian knapweed thrives in an unirrigated area trampled by the hooves of exotic cows and horses. Russian olive trees have sprung up in thickets alongside the irrigation ditch, right next to the Chinese elms. European starlings nest in the old cottonwood trees, using holes formerly occupied by native woodpeckers. And no doubt the West Nile virus, first identified in northern Uganda in 1937, lurks in the patch of wetlands below the house; some scientists speculate that it made its way to the U.S. in the late 1990s via an airplane that harbored an infected mosquito.
The urge to spread into new habitats and bring along our own menagerie of plants and animals is as old as the human species. As Yvonne Baskin notes in her wonderful book on exotic species invasions, A Plague of Rats and Rubbervines, neolithic travelers undoubtedly brought dogs and plants with them as they moved from continent to continent. Hieroglyphs reveal that the Queen of Egypt sent ships to collect foreign trees for her gardens at least 3,000 years before Columbus.
But because of modern transportation systems and an ever more global economy, our biotic mixing — intentional and unintentional — has increased at a frightening pace. Some scientists have dubbed the current era the Homogocene, a time when weedy generalist species will take over large portions of the globe, pushing out the specialist species that developed in isolation.
The subject of this issue’s cover story, the quagga mussel, is one of those weedy winners. It has taken to North American waters — and within the last year the lower Colorado River — as if it always belonged here.
So why should we care about yet another species flexing its muscle in the New World? First, as they multiply and clog aqueducts and pipes, the quagga, and its relative, the zebra mussel, could cause an immense and expensive headache for Western water managers. Second, and perhaps more important: Michelle Nijhuis’ quagga story shows how difficult it is to stop the movement of just one invasive species, even when you have decades to prepare, and you mount extensive education campaigns.
It’s too late to return the West to its pre-Columbian state. But if we want the region to support a large proportion of its native flora and fauna, we’ll need a much higher level of societal commitment to exotics control than we have shown to date. Otherwise, the West, long seen as a region isolated by its vast distances and harsh climate, will support ecosystems that look no different than any other semi-arid place on Earth.