Heat sends Southwest climate back in time

The pika, a high-elevation rabbitlike creature, could also disappear locally, although they’ll probably persist in the northern Rockies.

But the story is not all doom and gloom, says Allen. Juniper- and pinyon-dotted mesas come to mind when we imagine the Southwest. But in many areas, their dominance is an artifact of human interference. Now, prompted by more intense extremes, the ecosystem has come full circle, returning to something approximating its original state. The new landscape – grasslands with a much lower density of juniper and pinyon – will be more resilient, and better able to recover from future droughts, he says.

“For a while we went through this ‘woodification’ trend,” says Allen. “Now that excess is being squeezed back by dieback and by fire. In a structural sense, it’s actually somewhat restorative.”

Scientists at Bandelier are trying to speed along the restoration. Much of the area’s nutrient-rich topsoil, itself a remnant of cooler, wetter conditions that prevailed here during the last Ice Age, which ended 10,000 years ago, has eroded away. But scientists have found that simply strewing the now-dead tree branches across the land can mitigate, and perhaps reverse, this desertification.

The pine needles and woody matter slow down running water so that it seeps into the ground rather than flowing off.

“You’re sort of redistributing organic material,” says Brian Jacobs, a botanist with the National Park Service in Bandelier. They also shade the earth from the sun, lessening evaporation and helping grasses to establish themselves.

“We’re trying to hold on to the soils,” he says. “And we’re using the least invasive methods for doing that.”

Ancient lessons in adapting to dry climate

When the Spanish arrived in what is now the US Southwest in the late 1500s, they found a settled, agricultural people throughout the river valleys of the area. They dubbed these native Americans “Pueblo” (“village”) Indians. But ruins of an earlier people – the Anasazi – dotted the mesas and hilltops of the region. To the arriving Spanish, the settlements already stood abandoned. What had happened?

Archaeologists are quick to correct several widespread misconceptions in this story. First, the Anasazi didn’t vanish at all. The Tewa-speaking Pueblo Indians are, in fact, their descendents. They didn’t disappear; they simply moved into the river valleys.

Second, don’t call them “Anasazi,” Navajo for “ancestor of our enemies.” They’re “ancestral Puebloans.” ("Navajo," for that matter, derives from a Tewa word meaning "fields adjoining an arroyo," a reference to the tribe's agricultural practices. The Navajo call themselves "Diné" – "the people.") [Editor's note: The original story misstated the origin of the word "Navajo."]

Why did the ancestral Puebloans move? One theory: climate change. A megadrought coincided with the abandonment of the Four Corners region of the US in the late 1200s, where they’d lived for perhaps 1,000 years. The drought link is less clear in settlements like Bandelier in north-central New Mexico, abandoned by 1550. But soil exhaustion from centuries of farming and deforestation may have also played a role, says Rory Gauthier, archaeologist at Bandelier National Monument in New Mexico.

As today’s inhabitants contemplate a changing climate in the Southwest, they could probably learn a few things from the successes and failures of the ancestral Puebloans, Dr. Gauthier says. Foremost among them: the art of conserving water: The Pueblo’s ancestors developed intricate irrigation systems and terraced hillsides to better conserve water. They designed their gardens rather like waffles: a series of raised ridges created sunken squares that trapped and held water for crop use.

“I’m hopeful,” says Gauthier. “If we take the Pueblo people as a model, they’ve survived for a long time. They’ve made social adjustments. And they’ve been able to meet that challenge.”

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