It’s monsoon season here in Arizona, when we see the clouds building on the horizon in the afternoons and watch the storms roll in at night. At least we hope that’ll happen. So far this year, the Valley hasn’t seen a lot of rain.
But when those storms come, there’s also storm damage: trees downed, branches on the ground, sometimes flash floods or worse.
When we lose trees to the monsoons, what should they be replaced with? And what trees can survive the storms best?
For answers, The Show sat down with our resident tree expert: the City of Tempe’s urban forester, Richard Adkins. He began with some of the biggest trees in the Valley: the eucalyptus.
They lose a lot of branches when the storms hit, and lots of people assume the non-native trees are bad for the Valley. But Adkins says they’re not.
Full conversation
RICHARD ADKINS: I don’t think they’re bad at all. There are some large, older eucalyptus that are growing throughout the Valley, and a lot of those branches do break and they will fall in the monsoon storms. But a lot of those are just very old. And some of the newer species that we’re planting, they don’t have that problem.
LAUREN GILGER: I’ve heard they have been referred to in the past as widowmakers because of those branches falling.
ADKINS: Yeah, the large branches, they get stuck up in the tree sometimes and then they'll shift as people are walking under and unsuspecting. And thus widowmaker.
GILGER: OK, so tell us about the history here of these. Because there are not a lot of like 100-foot-tall trees in the Valley. But eucalyptus are certainly some of them. And you see them all over the place, but they’re not local, right? They’re an Australian tree. How did they end up here?
ADKINS: They are Australian trees. There’s actually over 700 species of eucalyptus, and they all are from the Australian, Tasmania and the islands that surround that continent there. They first came to California in like the mid 1800s, mid-late 1800s, when they were planted there and they started moving across the United States. The first recorded ones that we know here in Arizona were in the 1920s at the Boyce Thompson Arboretum out in Superior.
They were planted for windbreaks, and people thought they were going to be good timber. And they ended up not having very good timber qualities. So basically the essential oils, firewood and firebreaks.
GILGER: So they do well in the desert. I can see that. Lots of Australia is desert, right? That makes sense. Why do they do so well here?
ADKINS: They do well here because they are very drought tolerant and they can really deal with the heat that we have.
GILGER: And not a lot of trees can do that, right? So let’s talk about trees that do well or not so well when it comes around this time of year and we start to get these monsoon storms. We’ve gotten a few here in the Valley, a lot down in Tucson this time of year.
When the winds come, you get those microburst, you get these very super-specified monsoon storms. Is a eucalyptus tree a good tree to have near your house?
ADKINS: Now it would depend on the species, and I guess it would depend on your property. It always goes back to you have the right tree for the right space, depending on the benefits that you’re really looking for for that tree and the site conditions that you have.
Now, if you have a small patio home, one of the larger Eucalyptus camaldulensis in the backyard is probably not your choice of tree. But one of the smaller, like the bookleaf mallee gets up to about 25 feet. It’s a very beautiful tree. Be fantastic for that. No problem with the storms.
GILGER: That’s a great title, by the way, bookleaf mallee. What other trees do well in the monsoon season, or maybe not so well?
ADKINS: Well within the monsoon season, you’ve got to be very specific because again, it depends on the site. So there’s a number of trees that we want to look at that are climate adapted here in the Valley. So a lot of our elms will do well. Some of the acacia species do quite well. Fruitless olive, tipu — just a few trees that actually do quite well here, there are very nice big shade trees.
GILGER: Yeah. Are there parts of the monsoon season that are good for trees, that will help them out, make them stronger and maybe benefit from those deluges that will get here and there?
ADKINS: Whenever we do get that deluge — we haven’t had much rain so far up here in the Valley — but that good rain is always helpful. But a little bit of wind, trees have a natural dampening effect with the way that they’re structured, so they can generally handle a good windstorm. It’s the way that we maintain and prune them sometimes that really throws off that balance. And the tree can’t handle it, and the wind comes and grabs the branches and it actually ends up breaking them off.
GILGER: So we need to trim them up. How do you do that? Well, does it depend on the tree too?
ADKINS: Actually, I would say we might need not to trim them so much because people tend to overthin them. You always hear, “Well we need to thin the tree so the wind can blow through.” No, the tree wants to work with the wind. And like I said, it’s a dynamic dampening process.
So you want to get them so they’re not in your face or hitting your building or your home, but you want to be sure not to overthin them too much during the monsoons, because the wind can just grab those long branches that are hanging out there with tufts of growth at the end. And it’s like a lever arm is how it works, and it just snaps those branches off.
GILGER: OK, so let’s talk a little bit about what this all means for what trees do well here, not just in the monsoon season but beyond that. Because every year in the monsoons, we’re going to lose some trees, especially older ones — some of the really big ones, which you want to be careful of. As you’re replanting, how do you choose what to replant?
ADKINS: Well, it kind of depends. I’m going to work with the property owner. And if it’s with the city, I’m going to work with the municipality. If I’m coming over to your home, I’m going to work with you to see what benefits and values you’re looking for in a tree. Are you looking for something that flowers? Are you just looking for shade? Are you looking for something that’s going to provide you some food products? So I want to see what you’re looking for in your benefits and value needs and then look at your site. And then I’m going to try to site the right tree for you.
GILGER: How do you approach that on a sort of a mass scale, like in the city of Tempe for example?
ADKINS: Well, I’m looking for diversity for one, because we want not just a monoculture of species. We want different species to work with as well as different age classes of species, so that we have a continual sustainable forest.
GILGER: Are the kinds of trees that live and survive well here changing as climate change takes hold and things get hotter and hotter?
ADKINS: I think that’s something that we need to expect. The trees that we were planting in the ’60s, in the ’70s, we’re no longer going to be planting those coming up in the ’30s, in the ’40s. I mean, we always like the native trees, and everybody likes the native mesquites and ironwoods and palo verdes, desert willows. Fine stock, but they’re not for every location.
So I try to work with the native palette first, and then there’s some other introduced species that do quite well here that are drought tolerant, low water use, can maintain up into the storms and not break in the winds, and still provide benefit and value for the community.
GILGER: We had you on the show last year to talk about the Aleppo pines, these beautiful big old trees that are starting to really die off here, largely because of the heat, but partially because of age and being attacked by insects when they’re weak, that kind of thing. And you said at the time that you thought that the tree cover in the Valley — and you’re very involved in creating this in Tempe — would look different in the future as shade becomes more important. But as the city becomes more extreme, what do you think it will look like?
ADKINS: This is my opinion from just working here in the Valley for over 25 years. We’re going to go to smaller-stature trees, back to what the native desert structure looks like. If you go out into the Sonoran Desert, you’ll see your ironwoods, your mesquites, your palo verdes. They’re very low to the ground, full canopies going all the way down. And we plant them here in the urban space and we lift them all up, and we want them to be tall and provide us shade.
So I think we’re going to have a restructure of that and go back to smaller-statured species, the taller pines and eucalyptus like you see now are probably going to be a thing of the past.
GILGER: So is that like a loss in some ways? You can still get shade out of these. But it’ll feel different, right?
ADKINS: It’s going to feel different. It’s going to look a little bit different. We have to be more intentional on our siting of where we’re putting the trees, not just, “Oh, we’re going to plant a tree here and plant one there, and everybody is going to have shade.” Now we have to really look at our resources in the way that the cities and municipalities are developing with the urban form, and it’s really going to drive the decisions that we need to make.
GILGER: How important is shade going to be in our city’s future?
ADKINS: I think for livability here as well as for just human health, extremely.
