by Ryan Niemeyer, PhD

Back in 2014, my University of Idaho (UI) research team was doing workshops in Caldwell, Idaho, with a diverse set of stakeholders including ranchers, environmentalists, birders, ATV riders, and state and federal land managers. In one of the discussions, there was a heated argument about the impact of juniper on water between a rancher and an environmentalist. As a doctoral student in water resource at UI, I was the “water-guy.” So these two people brought their argument up with me after the workshop to validate their points-of-view.

The rancher said, “You know those juniper take up a ton of water and have a huge impact.”

The environmentalist said, “You know there is no evidence that juniper impact streamflow.”

I told them both, “You’re right.”  I wasn’t being a spineless scientist, but in fact they were both correct — at that point in time.

I told the rancher he was right based on the research I had conducted in the Owyhees at the USDA Agricultural Research Service Reynolds Creek Experimental Watershed.  My research showed that juniper intercept a lot of snow and rain and take up soil-water later into the summer than sagebrush. And some geophysical surveys we did suggested that some large junipers were extracting water as deep as 30 feet!

I told the environmentalist they were right because there has been multiple catchment studies where juniper or pinyon tree species were all cut down, and there was only a small increase in streamflow after the logging. In most of these studies, the increase in streamflow disappeared in a few years. Some say these studies are a smoking gun about the question of whether juniper impact streamflow. But these studies were mostly conducted in New Mexico, Arizona, and Texas, where much, if not most of the precipitation comes as summer monsoons. This is very different than the winter-dominated precipitation in Southern Idaho and Eastern Oregon. So some question whether we can apply the research from the Southwest to Idaho and Oregon. Nonetheless, as the scientific literature stands, the environmentalist was right.

It was around the time of these workshops when I had an idea. I could conduct a computer modeling study where I could simulate “virtual” catchments and compare how streamflow changes with pinyon-juniper removal across the different climates in the western US, including both the Southwest and Idaho and Oregon. It took several years, but this work was completed and finally published last fall. We found that the computer modeling results are similar to the observed changes in streamflow from the Southwestern U.S. catchment studies and a plot groundwater recharge study in Idaho. This means we can trust the simulation results are reasonable. We found that in simulations in areas with more winter-dominated precipitation (i.e. Southern Idaho and Eastern Oregon), the increase in streamflow with pinyon-juniper removal was much larger. This was also true in areas with more precipitation. It is true that there are many areas in Idaho with either too few juniper or too little precipitation to result in any noticeable increase in streamflow. However, much of the Owyhees has the potential to increase streamflow by two inches of water depth with juniper removal — in a small 20-acre catchment this would increase streamflow by 3.3 acre-feet or more than a million gallons of water! Now this is the median — dry years will probably see little or no increase in streamflow.  And there must be enough subsurface storage to produce this difference. But this research revealed that indeed juniper removal does have the potential to increase streamflow in much of Idaho.

Since this research is important to many Oregonians and Idahoans, I am doing a juniper-water seminar tour in early April. On Tuesday, April 3, I will be speaking at the Harney County Community Center in Burns at 10:30 a.m., and in John Day at the Grant County Regional Airport at 6 p.m.  I will present my research and have time for questions.

This seminar is an opportunity to discuss my doctoral research which focused on “tree-level” and “large-scale” impacts of juniper on an ecosystem’s water budget. I will present some useful resources and tools to help better understand these impacts. Specifically, I have developed a juniper hydrology website for stakeholders and an interactive map where individuals can identify areas of interest and discover potential changes in water resources with shifts in juniper land cover.