The same day President Bush announced his plan to "continue the journey" into space by colonizing the moon and heading for Mars, I stood in line at the grocery store and thought about space exploration as just another excuse to head ever Westward, another distraction for troubles at home, another frontier to conquer and leave behind.

As I thought, a distinctive odor tickled my consciousness, emitted by a row of votive candles on a nearby shelf. I inhaled the rich, nutty fragrance of roasting chestnuts recalled from my childhood.

"Chestnuts roasting on an open fire," crooned Nat King Cole." When "The Christmas Song" was written, the odor of roasting chestnuts was synonymous with winter, emanating from stands where street vendors sold handfuls of the buttery nuts.

Now, the magnificent forests of American chestnut trees are gone, victims of an accident in the conquering of their particular frontier. A lethal fungus imported with Asian chestnut trees began killing native chestnuts.

The fatal microbe, first noticed at the Bronx Zoo in 1904, eliminated American chestnut trees on 9 million acres of forest in less than 50 years. By the time "The Christmas Song" became famous, the trees that inspired its opening line were gone in a disaster greater than any hurricane or wildfire.

American chestnut trees were the redwoods of the East, with straight trunks reaching 100 feet tall and up to 20 feet across at the base. They dominated deciduous forests from Maine to Alabama and Maryland to Michigan: researchers estimate that one in every four trees was a chestnut.

Their oil-rich nuts fed native wildlife of every sort, fattened domestic livestock, and provided a winter cash crop that rural-dwellers shipped by the railroad-car load to cities across the country. The straight-grained, rot-resistant wood was cut for telegraph poles, fences, railroad ties, paneling, musical instruments and furniture.

Then suddenly, the trees died. The loss of American chestnuts devastated rural economies and destabilized forest ecosystems, causing watershed erosion, loss of soil fertility, and elimination of other native species; it may even have exacerbated global warming by removing the largest source of carbon storage in Eastern deciduous forests.

Here in the West, we have experienced similar accidents of conquest.

In the late 1800s, the U.S. Department of Agriculture touted several species of trees imported from the eastern Mediterranean and East Asia for windbreaks and erosion control in the Southwest and western Great Plains. The thicket-forming trees with their springtime cloud of pink flowers took hold like kudzu: today, tamarisk, also called salt cedar, infests one million acres along Western streams and rivers, crowding out cottonwood trees and poisoning soils with a rain of salty leaves.

The thirst of these trees may be their most devastating economic and ecological effect: Salt cedars out-guzzle the native plants they replaced by an estimated 800 billion gallons of water a year — enough to supply 4.8 million people.

In an arid land perennially short of water; when Kansas is suing Colorado (again) over water not delivered; when California has grudgingly ceded claims to "excess" water it had been sucking from the Colorado River, and New Mexico is scrabbling to find the water it owes to Texas, salt cedar’s thirst has an impact big enough for even Congress to notice. Last year, the Congress appropriated $20 million for research on salt cedar eradication. That’s probably not enough to get rid of the trees in even one Western state.

Then there is cheatgrass, the Eurasian annual accidentally introduced with livestock grazing. A prolific seed-producer and quick germinator, cheatgrass quickly colonized the intermountain West.

Short-lived and intensely flammable, it is proving terrifyingly effective at doing what ranchers have not been able to do in a century of trying: removing sagebrush. Cheatgrass spawns wildfires that have cleared hundreds of thousands of acres of sagebrush just when we are discovering that the once-ubiquitous shrub is critical to the health of the ecosystems where it lives and the economies dependent on those ecosystems.

We have the tools to bring back American chestnuts, and to eradicate salt cedar and cheatgrass. Doing so would enrich the landscapes around us, and the lives we live on them. But such projects require money, lots of it. And money, like water, is a finite commodity: if we spend $1 trillion or so colonizing Mars, there’s that much less for here on Earth.

That’s why I think it’s time for a national vision that is less about heading ever Westward and conquering new frontiers. We need to stay where we are and thoughtfully restore the communities we now inhabit, both human and wild.

Susan Tweit is a contributor to Writers on the Range, a service of High Country News (hcn.org). She is a writer and naturalist in Salida, Colorado.