Water from a Tree-tapped Well
Think of Mays as a woman lying on her side, all curves and contours, downy and golden. Think of Jensen as a man, coarse with stubble, brawny and lined. They are opposites, but a pair.
Mays and Jensen are watersheds in the transition zone where central Oregon becomes basin-and-range country and the human population drops from sparse to almost nonexistent. It is an area that gets less than 13 inches of precipitation a year, forcing even drought-adapted plants to battle for moisture. Western juniper has spent the last century creeping down from these hilltops and expanding across the range where it is often victorious in the high-stakes competition for water.
Oregon State University scientists and colleagues from the U. S. Bureau of Land Management are comparing the two watersheds to see just how much water the juniper trees are using. The scientists chose Mays and Jensen because the two watersheds initially had so much in common. Both are located in the Camp Creek drainage, a tributary of the Crooked River, with similar topography and size—about 260 acres each. When the study began in the 1990s, both watersheds were covered with juniper, some spiky and scraggly and some towering and regal. Between the trees were patches of sagebrush and clumps of grasses, many of them dead or dying.
In 2005, after 12 years of study, the researchers removed 90 percent of the juniper growing in Mays while leaving Jensen untouched. The cut opened up the Mays landscape, exposing the hills and valleys; trees greater than 130 years old were left standing on the rocky ridge lines.
Soon after the trees came down, Tim Deboodt, an OSU Extension range management specialist, began measuring a change in the depth to groundwater in Mays. It was too early to say categorically that removing the trees had affected available water, but the spring in the Mays watershed was registering a significantly increased flow after the cut. Into the late summer, the Mays spring continued to flow at a higher rate compared to the spring in Jensen and compared to previous years’ flow data before the cut. In April 2007, Deboodt measured the Mays spring’s flow at about 40 gallons per minute; the Jensen spring, less than a half mile away in the uncut watershed, was running at about 14 gallons per minute.
Previous research has shown that juniper inhibits the soil from retaining and holding water, so there is less groundwater available throughout the growing season. With its wide-reaching roots that can extend more than 40 feet from the tree, and a canopy that can stop more than half of all precipitation from reaching the ground, juniper dominates the landscape where it invades.
“It’s not uncommon to see a landscape of nothing but trees with bare ground in between trunks,” said Deboodt. “The situation leads to increased erosion from storm events and an inability of the land to soak up precipitation for later use.
“The new vegetation coming up in the Mays watershed is capturing precipitation and giving it time to infiltrate into the soil,” said Deboodt. “If we can get water into the soil higher in the watershed, we decrease the chance that soil will wash away in the lower reach, and we save water that can be used by plants and animals later in the season when it’s really needed.”
Overgrazing, fire control, and favorable climatic conditions during the late 1800s and early 1900s are largely responsible for the rampant encroachment of western juniper, which increased ten-fold during the twentieth century, according to Deboodt.
“On its own, juniper isn’t a bad tree,” said John Buckhouse, an OSU scientist in the Department of Rangeland Ecology and Management. “But it is opportunistic, and fire suppression has created a situation that is not natural.”
The “paired” watershed experiment is an attempt to reestablish the landscape of the West’s presettlement era, when wildfire periodically burned the area and controlled the growth of small trees. Intermittent burns kept the juniper in check and helped ensure species diversity in the parched high desert.
“We have learned that management generally works best when we attempt to mimic nature,” said Michael Fisher, an OSU rangeland researcher at OSU’s Cascade Campus in Bend. “In this case we are using a chainsaw as a surrogate for fire; the tree harvest was planned and carried out to simulate a natural burn.”
“Removing the trees results in a more sustainable ecosystem,” said Buckhouse. “Where juniper has been removed, we are seeing the regeneration of sagebrush and grasses; and private landowners are telling us that springs are flowing where none were known before.”