Researchers at Washington State University are using tree ring data try to answer the question of how localized climate change in the Southwest contributed to the depopulation of the southern Colorado by Ancestral Puebloan people in the late 1200’s.
Professor Tim Kohler and post-doctoral researcher Kyle Bocinsky used tree ring data, along with the growth requirements of traditional maize, a main food source of the Southwestern peoples, and analytic computer programs to create a detailed mapping of the ideal Southwest growing regions for the past 2,000 years. They used over 200 tree-ring chronologies, which use the annual rings of ancient tree to reconstruct climate patterns over time. Pine trees at lower elevations have their growth limited by rainfall, making good indicators of precipitation, while higher elevation tree tend to be limited by cold season, making good indicators of temperature. Both can be used to get a picture of overall climate in a region.
The most dramatic changes in the Southwest took place near the end of what is known as the Medieval Warm Period, the warmest in the Northern Hemisphere for the last 2,000 years. This period is actually a smaller change than is what is being seen currently with climate change.
The shifting patterns of rainfall and temperature let Bocinsky and Kohler isolate to a few square kilometers the areas that would receive just under a foot of rainfall a year, the minimum needed for ancestral maize varieties still farmed by contemporary Pueblo people.
The area in what is now southwest Colorado’s Mesa Verde National Park ended up being one of the best places to grow maize, with good conditions more than 90 percent of the time. The Pajarito Plateau ended up being highly suitable as well, with slopes that would shed cold air and precipitation levels suited to rain-fed agriculture.
Bocinsky noted that it was very important to note that when people moved out of southwest Colorado they move to another area that had the same niche, allowing them to preserve their traditional agriculture of maize farming. Also the research indicates how local climate can be and even micro changes can have major effects.
[quote_center]“When we are looking for ways to alleviate human suffering, we should keep in mind that people are going to be looking for places to move where they can keep doing their type of maize agriculture, keep growing the same type of wheat or rice in the same ways,” he said. “It’s when those niches really start shrinking on the landscape that we start having a major problem, because you’ve got a lot of people who are used to doing something in one way and they can no longer do it that way.”[/quote_center]