Surviving desert heat, alpine cold, and meager rainfall each year, two-needle pinyon pines (Pinus edulis) are the backbone of many forests in the southwestern United States. Their stout branches offer shade for bighorn sheep and sagebrush lizards, while their yearly crop of nuts has nourished humans for millennia.
But 150 years of grazing, fire suppression, and other land-use changes have transformed these forests. In many areas, thickets of young trees are choking out woodlands once dominated by widely spaced pines more than a century old.
On the Navajo Nation, some ranchers became concerned that the changing forests no longer have enough of the tender grasses relished by their livestock. To help restore the traditional ecology of these dry woodlands, Arizona researchers worked with undergraduate students to remove the dense growths of saplings on land used by Navajo ranchers.
This project can be “traced all the way back to meetings within the community of how they can address this issue,” said Navajo researcher Lionel Whitehair, a PhD student in forestry at Northern Arizona University (NAU) in Flagstaff and lead author of a recent study in Trees, Forests and People.
Whitehair and his colleagues conducted their experiment on a 10-hectare (25-acre) study plot at Diné College, a tribally-controlled community college in northeastern Arizona. This site, which sits 2,100 meters (7,000 feet) above sea level, receives an average of 29 centimeters (11 inches) of rain annually.
The researchers removed nearly two-thirds of the trees in the forest by thinning most pinyons with a trunk diameter under 25 centimeters (10 inches). They sliced the larger saplings into firewood to donate to the elders of a nearby community, then shredded the smaller bits into moisture-trapping mulch that they spread across the site.
Donating and demolishing the trees also reduced wildfire risk. Previous thinning studies in other locations left felled trees on the forest floor, where they could fuel future fires, Whitehair noted.
But removing pinyon pines can be risky, said Arjan Meddens, a forest ecologist at Washington State University in Pullman, Washington, who was not involved in the research. While thinning benefits understory vegetation like grasses, Meddens said, they also can provide an opening for invasive species to take over: “It needs to be paired with strict monitoring of what happens after the treatment.”
Whitehair noted that his team is working on a companion study to document how the plant community changes after thinning.
During the project, Navajo students and faculty from Diné College traveled about 315 kilometers (196 miles) to NAU to receive training in ecological research methods. “One thing we did was introduce concepts used in Western science, such as taking measurements before and after and seeing what effect this has on the landscape,” Whitehair said.
NAU students also visited Diné College to learn how to prepare wood samples and date tree rings. For many, this was their first trip to the reservation, allowing them to see the Navajo people’s cultural ties to pinyon woodlands.
Another goal of the project was to get tribal students involved in research, said Whitehair. “It took me a number of years to eventually find something that I loved,” he said. “Like many individuals on the Navajo Nation, I [initially] followed in the footsteps of my family, and that was military and construction.”
Whitehair plans to continue involving students and local communities in his research. “I’ve been given these opportunities because individuals gave me the time to share their knowledge and to share their rights and wrongs,” he said. “And I’d like to do the same for others.”
To learn more about Wood For Life, a project that aims to restore forests by reducing the risk of wildfires and flooding and partners to provide firewood to tribal communities, click here.
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