Utah ghost tree offers centuries-old 'climate archive'
While on a walk with his wife near Utah's Indian Creek last fall, Barry Baker discovered a 13-foot juniper hovering like a ghost, embedded in a towering cutbank several feet above a creek bed.
The limbless trunk, which radiocarbon dating indicates died 350 years ago, stood perfectly upright, its roots clinging to the gravelly strata.
This piece of wood is like a searchlight beam into the past, revealing what the landscape southeast of Canyonlands National Park looked like centuries ago, according to Baker, an ecologist who directs the nearby Canyonlands Research Center. Sediments had completely entombed the tree, which was exposed by arroyo cutting during the past century.
Its growth rings reflect precipitation levels and its scorched bark tells the story of a fire that swept an Indian Creek tributary in San Juan County.
"The unique position of the tree found in the arroyo will be of great value in helping us better understand and document past climatic and sedimentation regimes within the North Cottonwood drainage," Baker wrote in a March 18 letter to the Bureau of Land Management (BLM), seeking permission to remove the juniper for scientific study.
The center, which The Nature Conservancy operates in partnership with various state and federal agencies, explores the interplay between various land uses and the Colorado Plateau's changing climate.
The Bakers found the tree in a part of Beef Basin where The Nature Conservancy helps manage a grazing allotment on BLM land associated with the 5,000-acre Dugout Ranch.
BLM officials granted the request, but asked researchers to leave the root collar at the tree's base in place. The rest was to be sent to Utah State University for tree-ring analysis.
Under the direction of geology professor Tammy Rittenour, USU students studying paleoclimatology pulled the tree out in April using a ladder, chainsaw and rope, then sliced the trunk into 2-inch-thick "cookies." The team counted 130 rings, one for each season of growth in light and dark striations. Variations in ring widths record variations in the factors that influence tree growth, creating what Rittenour calls a "climate archive."
"We have 130 years of tree ring variability," she said. "We can find living trees that we can link to this tree and expand the chronology further."
But it was scorched bark that really sparked her interest.
The bark facing away from the cutbank had been weathered away, but when the students freed the tree, they discovered the protected side had been burned. Rittenour believes the tree died in a wildfire because there is little evidence of post-burn growth or scarring.
The tree provides conclusive evidence of the time frame for how sediments piled up here and then eroded away.
"What's amazing is the fire burned the tree more than 350 years ago, and around early 1900s the creek entrenched it into its current from," Rittenour said. "So it took 200 years to deposit four meters of sediment. That's pretty fast."
To further understand the rate of arroyo cutting at this site, she has gathered sediment samples from various points around the old juniper's location and subjected them to a test called optically stimulated luminescence, or OSL. This science can determine when grains of sand were last exposed to light, determining the date when they were deposited.
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