Conventional wisdom holds that prehistoric villagers planted corn,
and lots of it, to survive the dry and hostile conditions of the
American Southwest.
But University of Cincinnati archaeology professor Alan Sullivan is
challenging that long-standing idea, arguing instead that people
routinely burned the understory of forests to grow wild crops 1,000
years ago.
"There has been this orthodoxy about the importance of corn," said
Sullivan, director of graduate studies in UC's Department of
Anthropology in the McMicken College of Arts and Sciences. "It's been
widely considered that prehistoric peoples of Arizona between A.D. 900
to 1200 were dependent on it.
"But if corn is lurking out there in the Grand Canyon, it's hiding
successfully because we've looked all over and haven't found it."
Sullivan has published a dozen papers outlining the scarce evidence
of corn agriculture at more than 2,000 sites where they have found
pottery sherds and other artifacts of prehistoric human settlement. He
summarized his findings in a presentation last month at Boston
University.
Sullivan has spent more than two decades leading archaeological
field research to Grand Canyon National Park and the region's Upper
Basin, home to the 1.6-million-acre Kaibab National Forest.
When you think of the Grand Canyon, you might picture rocky cliffs
and desert vistas. But the Upper Basin, where Sullivan and his students
work, is home to mature forests of juniper and pinyon trees stretching
as far as you can see, he said.
"When you look down into the Grand Canyon, you don't see any forest. But on either rim there are deep, dense forests," he said.
On these high-elevation plateaus, Sullivan and his students have
unearthed ceramic jugs adorned with corrugated patterns and other
evidence of prehistoric life. Sullivan is particularly interested in the
cultural and social practices of growing, sharing and eating food, also
called a food way.
"What would constitute evidence of a corn-based foodway?" he asked.
"And if experts agree it should look like this but we don't find
evidence of it, that would seem to be a problem for that model."
Like a detective, Sullivan has pieced together clues firsthand and
from scientific analysis to make a persuasive argument that people used
fire to promote the growth of edible leaves, seeds and nuts of plants
such as amaranth and chenopodium, wild relatives of quinoa. These plants
are called "ruderals," which are the first to grow in a forest
disturbed by fire or clear-cutting.
"It's definitely a paradigm-threatening opinion," Sullivan said.
"It's not based on wild speculation. It's evidence-based theorizing. It
has taken us about 30 years to get to the point where we can confidently
conclude this."
Lab analysis identified ancient pollen from dirt inside clay pots
that were used 1,000 years ago before Sullivan and his students found
them.
"They've identified 6,000 or 7,000 pollen grains and only six [grains] were corn. Everything
else is dominated by these ruderals," Sullivan said.
The corn itself looked nothing like the hearty ears of sweet corn
people enjoy at barbecues today. The ears were puny, about one-third the
size of a typical cob, with tiny, hard kernels, Sullivan said.
So if prehistoric people were not growing corn, what were they
eating? Sullivan found clues around his excavation sites that people set
fires big enough to burn away the understory of grasses and weeds but
small enough not to harm the pinyon and juniper trees, important sources
of calorie-rich nuts and berries.
Evidence for this theory was found in ancient trees. Raging
wildfires leave burn scars in growth rings of surviving trees. In the
absence of frequent small fires, forests would accumulate vast amounts
of underbrush and fallen timber to create conditions ripe for an inferno
sparked by a lightning strike. But examinations of ancient juniper and
ponderosa pine trees found no burn scars, suggesting big fires are a
relatively new phenomenon in Arizona.
"To me that confirms there weren't massive fires back then," Sullivan said.
Sullivan also studied the geologic layers at these sites. Like a
time capsule, the stratigraphic
analysis captured the periods before and after people lived there. He
found higher concentrations of wild edible plants in the period when
people lived there. And when people abandoned the sites, the area they
left behind saw fewer of these plants.
But it was only this year that Sullivan found contemporary evidence
supporting his theory that prehistoric people generated a spring bounty
by setting fires. Sullivan returned to the Grand Canyon last spring to
examine forest destroyed by a massive 2016 fire. Touched off by a
lightning strike, the blaze called the Scott Fire laid waste to 2,660
acres of pines, junipers and sagebrush.
Despite the intensity of the forest fire, Sullivan found edible plants growing thick everywhere underfoot just months later.
"This burned area was covered in ruderals. Just covered," he said.
"That to us was confirmation of our theory. Our argument is there's this
dormant seed bed that is activated by any kind of fire."
Archaeologists with the National Park Service have found evidence
that corn grew below the rim of the Grand Canyon, said Ellen Brennan,
cultural resource program manager for the national park.
"It does appear that the ancient people of the Grand Canyon never
pursued corn agriculture to the extent that other ancestral Puebloan
peoples did in other parts of the Southwest," Brennan said. "In the
Grand Canyon, it appears that there continued to be persistent use of
native plants as a primary food source rather than corn."
The National Park Service has not examined whether prehistoric
people used fire to improve growing conditions for native plants. But
given what is known about cultures at the time, it is likely they did,
Brennan said.
The first assumptions about what daily life was like in the
Southwest 1,000 years ago came from more recent observations of Native
Americans such as the Hopi, said Neil Weintraub, archaeologist for
Kaibab National Forest. He worked alongside Sullivan at some of the
sites in the Upper Basin.
"Corn is still a big part of the Hopi culture. A lot of dances they
do are about water and the fertility of corn," he said. "The Hopi are
seen as the descending groups of Puebloan."
While native peoples elsewhere in the Southwest no doubt relied on
corn, Weintraub said, Sullivan's work has convinced him that residents
of the Upper Basin relied on wild food -- and used fire to cultivate it.
"It's a fascinating idea because we really see that these people
were highly mobile. On the margins where it's very dry we think they
were taking advantage of different parts of the landscape at different
times of the year," Weintraub said.
"It's been well documented that Native Americans burned the forest
in other parts of the country. I see no reason why they wouldn't have
been doing the same thing 1,000 years ago," he said.
The area around the Grand Canyon is especially dry, going many weeks
without rain. Still, life persists. Weintraub said the forest generates
a surprising bounty of food if you know where to look. Some years, the
pinyon trees produce a bumper crop of tasty, nutritious nuts.
"In a good year, we didn't need to bring lunch in the field when we
were out at our archaeological surveys. We'd be cracking pinyons all
day," Weintraub said.
Weintraub recently studied the forest burned in last year's big
Scott Fire. The exposed ground was thick with new undergrowth,
particularly a wild relative of quinoa called goosefoot, he said.
"Goosefoot has a minty smell to it, especially in the fall. We
actually started chewing on it. It was pretty pleasant," Weintraub said.
"It's a high-nutrient food. I'd be curious to know more about how
native peoples processed it for food."
UC's Sullivan said this prehistoric land management can teach us
lessons today, especially when it comes to preventing devastating fires.
"Foresters call it 'the wicked problem.' All of our forests are
anthropogenic [man-made] because of fire suppression and fire
exclusion," Sullivan said.
"These forests are unnatural. They're alien to the planet. They have
not had any major fires in them in decades," he said. "The fuel loads
have built up to the point where you get a little ignition source and
the fire is catastrophic in ways that they rarely were in the past."
The National Park Service often lets fires burn in natural areas
when they do not threaten people or property. But increasingly people
are building homes and businesses adjacent to or within forests. Forest
managers are reluctant to conduct controlled burning so close to
population, Sullivan said.
Eventually so much dry wood builds up that a dropped cigarette or
unattended campfire can lead to devastating fires such as the 2016 blaze
that killed 14 people and destroyed 11,000 acres in the Great Smoky
Mountains or the fires in California this year that killed 40 people and
caused an estimated $1 billion in property damage.
"It's a chronic problem. How do you fix it?" he asked. "The U.S.
Forest Service has experimented with different methods: prescribed
burning, which creates a lot of irritating smoke, or thinning the
forest, which creates a disposal problem."
Fire also seems to increase the diversity of forest species.
Sullivan said vegetation surveys find less biodiversity in forests today
than he found in his archeological samples.
"That is one measure of how devastating our management of fire has
been to these forests," he said. "These fire-responsive plants have
basically disappeared from the landscape. Species diversity in some
cases has collapsed."
Today, federal land managers conduct controlled burns when practical
to address this problem, even in national parks such as the Grand
Canyon.
"The fire management program for Grand Canyon National Park seeks to
reintroduce fire as a natural agent of the environment," the park's
Brennan said. "That is to reduce ground fuels through prescribed fire,
mechanical thinning, and wildland fire."
Scientists also are studying how to adjust forest management techniques in the face of climate change, she said.
"Program managers are working to understand how climate change
affects forest management and how to restore forests to the point where
fire can follow a more natural return interval given a particular forest
type," she said.
Climate change is expected to make wildfires more frequent and
severe with rising temperatures and lower humidity. Meanwhile, public
lands are under increasing pressure from private interests such as
tourism and mining, putting more people at potential risk from fire,
Sullivan said.
"Rather than create more uranium mines or establish more tourist
cities in our forests, it's better to spend our money on addressing 'the
wicked problem,'" Sullivan said. "Unless we solve that, all of these
other ventures will only add to the severity of the risks."
