Dieback Dynamics

Seth Munson is a plant and ecosystem ecologist with the U.S. Geological Survey Southwest Biological Science Center in Flagstaff, Arizona. His research focuses on how dryland ecosystems respond to drought, wildfire, invasive species, and land-use to assist land management decision-making. Much of Seth’s research aims to understand the dynamics of dryland ecosystems at long temporal and broad spatial scales, and employs a multidisciplinary approach. His work seeks to improve the management of arid and semi-arid lands, including mitigating the impacts of disturbances and determining effective ecological restoration strategies to promote productive ecosystems.

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Science Moab talks with Seth Munson, a plant and ecosystem ecologist with the US Geological Survey, Southwest Biological Science Center in Flagstaff, Arizona.  Seth’s research focuses on how dry land ecosystems respond to drought, wildfire, invasive species, and land use to assist land management decision making. He is currently working with the National Park Service to assess the areas of dieback of Pinyon-Juniper woodlands in the Southeast Utah Parks.

Science Moab: In general, warming temperatures, greater aridity, and pests are killing these pinyon and juniper trees.  Is there anything else that’s adding to the dieback of these trees?

Munson: There are some synergies in the stressors that are playing out.

We do know that 2002 and 2003 were extremely dry years across the Colorado Plateau, so we believe that the shortages of water availability in those time periods is the predominant cause. But of course, there’s wood boring insects and beetles that can act synergistically to cause more stress and even die back in these trees. So it’s a combination of things. I think there’s also the matter of landscape variability where we know that depth to bedrock, the kind of soil the trees are on and their accessibility to soil moisture is also playing a large role.

Science Moab: You and your team have started this study that’s focusing on Southeast Utah parks in terms of trying to understand better the dieback of the pinyon juniper forest. Can you describe the project setup and what you’re trying to figure out?

Munson: We were approached by managers in the Southeastern Utah Group of parks who saw this dieback event in 2017 and 2018. they noticed defoliation or browning of the canopies as they were driving through the parks and some of the sites that they had to access. And so this question came up of how extensive is this dieback?  we had been doing a number of different monitoring based research projects with the parks, and many of them are ground-based. But another tool we have to utilize in monitoring is satellite imagery. so this allows a bigger picture of what’s happening on the landscape.

The project formed into this effort where we’re trying to bring in ground validation of where dieback has occurred based on park observations and on surveys we do. What we’re trying to do is train our ground-based observations to sync with what the satellite has seen so that we can detect dieback across the Southeastern Utah group parks, as well as the surrounding landscape on BLM, forest Service and other lands. So really the goal is just to provide the parks and other land managers with maps of where the dieback has occurred and the intensity to which it’s occurred. We’re also at the same time trying to address the question of what potentially might be causing some of the dieback.  

In our ground-based surveys, we’re doing a tree condition assessment where we go out and determine if the foliage is brown, if there is a noticeable dieback of the tree.  In addition, we also take measurements of the surrounding landscape such as the density of the trees, the size of the trees, information about the soils and the geology of the site. All these things that could potentially help us understand what might be contributing to some of the dieback patterns we’re seeing.

We’ve designed our monitoring to be able to cover different parts of the landscape and different levels of dieback that we’ve seen happen. That’s our general strategy to help the parks understand the degree to which dieback has happened and where it’s been happening.

Science Moab: What do you think the, these, the managers or the parks will do with this information? Or what can they do?

Munson: There’s a lot of interest in understanding the density of these trees within the system.

Across the landscape, there’s different levels of tree densities. You can have everything from an open savanna of pinyon and juniper, sparsely distributed with a lot of grasses in between, all the way to these old growth systems that are quite dense and have a lot of trees in them.

There is the question of whether or not lower tree density reduces the competition among the trees (for water). Of course, there’s elevational differences as well that contribute to some of the balance between grasses and trees, so that remains a question of how do grasses and trees partition the water in these systems and are closed systems more vulnerable than the more open systems?  I think that would be interesting to explore. 

We’re also going to see if some of the maps and tools that we generate for the Southeastern Utah group parks might be potentially expandable to other parks and other parts of the landscape. So that’s another potential way that we could expand this work in the future.