Urban Ecology

Ecology and History

by Diane Boudreau

Cars, power plants, pesticides - these are a few of the things responsible for today’s environmental problems. But long before any of these technologies were invented, people were affecting their environments. In some cases, scientists say they caused the downfall of their own civilizations.

“There’s a tendency to think that the establishment of Earth Day in 1971 was the establishment of all our environmental problems,” says Chuck Redman, an archaeologist and ecologist at Arizona State University. “But ancient people had their own problems. They also dealt with monumental environmental change.”

Redman has written a book about ancient people’s effects on the environment. He says even prehistoric cultures caused environmental problems such as reduced soil fertility, erosion, and deforestation.

“Those problems are not the same as air pollution and global warming, but they are things we still are dealing with. Ancient cultures dealt with them, too. These problems affected people’s productivity and their quality of life.”

When problems got too bad, people would have to leave the area they had changed.

“To us, it seems small - one valley they have to move from. But after generations of living in the same community, people had to leave and find a new home. This doesn’t generally happen today,” says Redman.

The city of Phoenix was built on top of one of these ancient civilizations. More than 1,500 years ago, the Hohokam people settled in this valley. They lived here for as long as 1,000 years - much longer than Americans have lived here.

The Hohokam were irrigation farmers. They brought water to their farms using canals, just like Arizona farmers do today. Redman says the Hohokam may have been the most successful irrigation farmers in all of prehistoric North America.

They were not successful enough to stop their own downfall, however. In about 1350 A.D., the valley suffered a couple of really big floods followed by drought. The Hohokam were using all of their available resources. They were very productive. However, that massive production depended on the climate staying fairly stable.

“But against that background exists a climate that’s naturally variable. There are wet years and dry years,” explains Redman. The Hohokam had developed a very efficient farming system that gave them the most productivity possible. However, their system was geared toward the average rainfall, not to extremes.

“If you really tune yourself to average rainfall, then much more or less than average is bad. Too much or too little water is bad,” says Redman.

The Hohokam society could not withstand the extreme floods and drought, so they had to leave the valley. Nobody knows where they went.

Redman sees parallels between the Hohokam and today’s Phoenicians. In fact, the name Phoenix refers to a mythical bird that lived for 500 years, burned itself to ashes, and was reborn from those ashes to live another 500 years.

Like the bird, the modern city of Phoenix rose from the ruins of a former civilization. Early American settlers found the remains of the Hohokam canal system and used them to build a new irrigation system. The canals made it possible to produce large amounts of food here, which attracted more settlers. Eventually, Phoenicians expanded the canals beyond the old Hohokam system. Farming production increased.

“Our system here parallels the one built by the Hohokam. But they relied solely on the Salt River for water,” Redman explains. “The early Americans dammed rivers for reservoirs, and pumped groundwater. In 1988, Phoenix also got access to water from the Colorado River.”

Like the ancient Hohokam, modern Phoenicians are using their resources to the maximum. They don’t think much about whether they can sustain those resources in the future.

“We are using all available water right now. There’s not a drop more. That puts modern Phoenix in a position it’s never been in,” Redman says. “We have a population of 3.2 million, and we have plenty of water. But if the population doubles to 6.4 million, which it could, we would not have enough water for everyone. We can survive a drought now, but what about in 20 years? What if there’s a longer drought than we’ve ever seen?”

Unlike ancient people, modern humans have the technology to predict their effects on the environment. This allows us to change our behavior so that we don’t destroy our own homes. Redman wonders if human nature allows us to do that. Can people stop their drive to constantly grow, grow, grow?

“Can Phoenix go low-growth? Will rapid growth destroy Phoenix?” asks Redman. “The alternative is longer commutes from home to work, bad air, and bad water. Then again, maybe it’s self-regulating. As the conditions in Phoenix worsen, people will stop moving here. Some might even move away,” he adds.

“But that wouldn’t be good for those of us who live here.”