There are a number of efforts to bring more shade to the Valley, as we continue to see more and more 100+ degree days. And a big part of those efforts is planting trees. But trees need water, which is in increasingly shorter supply and trees don’t always do so well in this climate. That’s where new research from Arizona State University and the University of Arizona comes in.
Scientists are trying to figure out better ways to water trees, in an effort to both conserve the limited resource and preserve tree health and the shade trees provide. And they seem to have come up with some potential solutions.
Bo Yang, professor in the School of Landscape Architecture and Planning in the College of Architecture, Planning and Landscape Architecture at the UofA and lead investigator for smart tree watering in Arizona’s urban environment on this project, joined The Show to discuss how big of a deal it would be if they could figure out how to plant trees, make sure they thrive and use less water while doing so.
Full conversation
BO YANG: Definitely a very big deal on conserving water and also combat climate change. As you already mentioned, there is a water scarcity issue we are facing as a state. The Colorado River has been really facing climate change, has been shrinking. The water we are getting is becoming less.
But on the other hand, we need trees to provide shade given the heatwaves we have been experiencing and increasing. So there is a dilemma here. There is a need for water to irrigate the trees to provide the shade, but we don’t have that much water to begin with. So the question is: How can we still sustain this urban forestry — but with less water — and still maintain healthy, robust tree growth?
So that’s what this research is trying to tackle.
MARK BRODIE: Right. And this is what you are, as you say, looking into. And it seems as though you found some potentially good ways to water trees more efficiently and effectively, which uses less water, of course, but also make sure that the trees actually grow and survive and provide the shade that we need them to provide.
YANG: Yes exactly, Mark. So the question — actually this set apart from some of the previous work — is this project is to specifically looking at saplings, look at young trees, because that’s where we typically look at this. Starting from young trees, they are very robust. We can make them grow to a more mature size.
So the project emphasizing young tree growth and health and also compare that with mature trees. So there is a focus about general urban forestry, but more focusing on how we grow the trees, really baby them in the establishment period, 1 or 2 years, to see how that data will tell us, how we can scale up this research to public lands and also to even people’s backyards.
BRODIE: Yeah. So how do you try to scale it? Because obviously it’s great if you can keep trees alive in a controlled environment and use less water. But once you get into the city of Tucson or the city of Phoenix or any of the other communities in the Valley, that’s a lot of trees you’re trying to plant and keep alive. So how do you try to scale it up so this has the kind of effect you want it to have?
YANG: So the way we’re doing this is, we at the University Agricultural Center, we are doing the sampling 80 young trees. Those are very controlled experiments. Also, we have locations, different landscape typologies in the city of Tucson. And we purposely choose the tree species, which are desert adaptive and climate resilient tree species.
So to the question how you scale it up. First we choose those species which the cities or counties or municipalities they are trying to use or to promote in their territory. The second thing is we are working with Arizona State University. ASU colleagues are helping us to model these benefits. So they are using machine learning and the AI technology to try to see if this data-validated model can be applied to other locations in Phoenix and Tucson.
BRODIE: Well, how would that work, though? Because if you’re looking at, for example, a neighborhood in Tucson or a part of the Phoenix area, right now I would imagine unless these trees are in someone’s yard, they’re probably not getting watered a ton other than when it rains or if somebody dumps out a bottle of water on them.
So if you’re going to try to implement these new methods of watering these trees, it sounds, at least to a layperson, like that would be an awful lot of work to go around an entire city or community to make that happen.
YANG: Yes, yes. That’s that’s true, Mark. So, again, come back to the original research content. This is trying to develop a methodology for young trees type of establishment. So we’re looking at for now mostly on the public lands. So when those trees establish — that’s what we are doing also — is they will rely on Mother Nature. We rely on the monsoon season so those water can survive, make them sustainable without additional supplementary watering.
So that’s for mature trees. And this work is mostly focused on young trees because when we try to establish them in the first two years, year or two, they do need supplementary water. So how we can use less water but still make them thrive.
So the goal is if we can test this technology — which we have pretty good preliminary findings right now — we can then tell our partners in the city, in the county, in the state forestry department if they can apply this to the public area — rights of way, parks — those are our next steps.
BRODIE: So you have these four watering techniques. You have rainwater harvesting, organic mulch, plastic and cellulose based hydrogels. What is the next step here? What is the next plan for the research? Are you at a point where you can maybe try to scale this up and take it out of a such a controlled environment and put it on the streets of Tucson and see what happens?
YANG: That’s actually what we’re doing right now. So the two things we are doing right now: One is, to your point, we are expanding the basin, rainwater harvesting basin size. So the idea is to mimic a real situation. If we can use purely rainwater harvesting techniques to sustain the tree growth. Right now, it’s already more than a year and a half. So we want to see if the trees can use Mother Nature, just what nature gives us, use that water to thrive without supplementary irrigation. So that’s one.
The second aspect, the next step is to look at the root structure. Because presumably when we do this smart watering technique, our hypothesis is the roots will be developing more robust, stronger. They can promote the lateral growth and deeper to the soil, so they can be stronger compared to conventional treatment.
BRODIE: And as you referenced earlier, I would imagine the ultimate goal is to find sort of the lowest maintenance trees here, right? Like where you wouldn’t have to go and put mulch or hydrogels, where you could just plant the tree and then it would rain and the trees would be fine.
YANG: Yeah, that’s the idea. The maintenance definitely is a very important topic. That’s one of the challenges we have on the side is constant battle with the weeds, the buffelgrass, for example. That’s just a reality. We have to battle with that.
But you’re right. The idea of this technology we’re developing used to minimize the maintenance and minimize people’s labor on this. So if we can use the data to share with people the tree growth, the root growth, the water saving — with those findings, we can confidently tell people how this technology can be applied to other locations.
