Many southwestern communities in the Mountain West are looking at importing specific kinds of trees in the battle against extreme heat. What they learn could be a model for other communities in our region.
“This is Maverick, he’s a Canadian Goose” said Tara Pike, pointing to one of many animals at her All Friends Animal Sanctuary, a petting zoo in a Las Vegas residential area.
She went on to list the variety of animals at the sanctuary which includes cows, pigs, and
All Friends Animal Sanctuary has just about every living thing – except trees.
But that changed when the sanctuary received its first trees during the Clark County give-a-ways. She received the first one during last year’s fall give-a-way and another during the county’s spring give-a-way this year. And Pike has applied for a grant to get 30 more.
“Yeah it’ll be gorgeous when all these trees and once they get big,” she said.
There is a concerted effort across cities in the southwest to plant more trees.
For example, Phoenix has launched a “Trees Are Cool” initiative. And Albuquerque has a "Let’s Plant ABQ” program.
Las Vegas has plans to plant nearly 60 thousand new trees by 2050.
That means the urban-desert landscape could change significantly in the next 50 years – as the city moves away from palm trees and cacti – to trees that provide shade, can survive harsh summer heat and winter freezes as well.
Brad Daseler is the city of Las Vegas’ Urban Forester. While walking through the city’s nursery, he described the diversity of trees.
“Behind you, we have a Burr Oak. So those would be trees that we would use more in our park spaces,” he said.
Aside from well known desert trees like the Palo Verde and Mesquite, the city is also looking at a variety of trees that can survive the desert city’ the tough climate.
Looking at the Indian Rosewood tree, Daseler said: “We would think about being more adaptable to our streetscapes and parking lots on streets where they're surrounded by asphalt and concrete and all this heat load that not every tree is prepared to deal with.”
The city is also looking to other parts of the world for trees that may be good candidates to withstand the challenging environment.
“We have a variety of eucalyptus trees here that are incredibly tough and tolerant of the heat...and obviously those are predominantly from Australia.”
And, the nursery is training trees to adapt by getting used to using less water.
“So that's the elm tree. Not native to here,” he said. I would probably put it in like a turf grass park type situation. Something a little bit softer, like a little bit cooler. When asked if temperature, location and other factors are important, Daseler replied:
“Absolutely, I think there's a lot of nuance in making the correct decision with tree planting.”
He continued by explaining what can happen if the wrong tree is planted in the wrong place.
“It kinda stifles its growth. There's no benefit to the citizens, there's no benefit to the community. We have to get that part of it right and then give it the time to mature and grow.”
How do trees cool the air?
Cheyenne Ingel, a scientist with the Desert Research Institute, says there’s a lot going on in a tree. She explains that trees help cool the environment through their own evaporative cooling process.
“So just like a swamp cooler, trees will release water through the leaves and through that process, just like sweat from your skin–You feel the evaporative cooling,” she said.
But, Ingel points out that these trees can also struggle in extreme heat.
“A lot of trees in our urban arid environments are shutting down their mechanisms during the day and doing the work at night. So we actually are getting less daytime cooling.”
So scientists are studying the qualities in trees that can be leveraged for cooling, down to the diameter of the leaves.
“We have a little project this summer that we call the Leaf Area Index. So it looks at the overlap of leaves throughout a canopy. And which trees have a greater complete leaf coverage and which have less.”
And, if arid environments reduce evaporization, what more can be done?
There is a study in Tucson that looked into the distribution of trees throughout the city. Their placement is key as they compare an even distribution vs. clusters. Distributed, “they may have a greater effect on cooling the city of Tucson than clustered in parks. However, we also know that trees clustered have a greater effect than sort of the sum of the individuals.”
There’s still more to learn–but what is known is that trees are a natural and effective way to mitigate heat—and strategic steps today can make a difference in the future.
