Climate Change Action: Nurturing Urban Trees
The heat dome that has settled over the southern tier of North America during this very hot summer of 2023 is serious business. The heat seems relentless and brutal. We are breaking records left and right. As I write, Phoenix, Arizona is into the 21th consecutive day of temperatures at or above 110oF. Is there anything we can do?
To tackle the global greenhouse gas issue, these books are a helpful place to start: The Story of More: How we Got to Climate Change and Where We Go From Here, by Hope Jahren and The Future Earth by Eric Holthaus.
We also need to address conditions in cities. Expanses of tree-less asphalt and concrete make temperatures even hotter. Dense urban forests provide shade and sequester carbon. Read the science here if you wish –
Carbon storage and sequestration by urban trees in the USA - ScienceDirect
One action you can take is to nurture the old-growth trees around you and make sure more aren’t cut down or ruthlessly pruned. In addition to befriending trees and becoming their protectors, you could also plant new ones.
This essay from Bringing Home the Wild: A Riparian Garden in a Southwest City gives you my take on the importance of nurturing trees in your own backyard.
Chinaberry: A Solid and Helpful Citizen
Before we purchased our two-story Spanish Colonial, its tenants were derelict in their duties. Rock pigeons, rock squirrels, roadrunners, and coyotes were among those who squatted there, for a year, without performing basic maintenance or irrigating the orchard trees. Nor did anyone else. One tree who did survive was chinaberry (Melia azedarach), near the leakiest part of the irrigation system. Maybe I am biased- the Mahogany family have a reputation as solid and helpful citizens- but I liked those trees from the start. There was that peculiar incident involving Alfie, our blue merle cattle dog, and the vet. Alfie had gorged on her fallen berries- technically, drupes- and become inebriated, but our country-style doctor advised him to sleep it off and all would be well. Which it was. Other than that, chinaberry has indeed proven helpful. Besides providing perches for western kingbirds and entertaining us with percussion music when she drops her drupes on the metal roof, she is a warrior in the ‘battle’ against the rapidly changing climate. I should have led with that; it is so important.
Air temperature within our hot city can vary from one neighborhood to another by more than ten degrees Fahrenheit depending on the density of trees. The trees are not equitably distributed; the wealthier neighborhoods have denser canopy. To empirically determine how much relief our forest provides, I bought an infrared sensor and was having great fun taking the temperatures of plants in our garden, and of bare ground, too. The temperature was twenty degrees lower in the chinaberry/cottonwood patch! You can feel the temperature drop when you walk into the woodland, and you can see how the leafy branches shade us from solar rays, but what my new toy confirmed was that each living plant, be she tree, shrub, or herb, is cooling the air through a process invisible to our eyes. Even the layer of dead annuals, left over from last year, buffers the temperature for those living in the soil underneath.
My favorite subject in school was not thermodynamics but for some reason the concept of latent heat of vaporization thrills me to the core. The notion of a water molecule transitioning from fluid to gas, and cooling the air in the process, seems like a gift from the gods. Chinaberry and her large-leaved friends cottonwood, elderberry, and velvet ash (Fraxinus velutina) transpire gallons of fluid over a course of a day, cooling us and connecting us to the mountains afar. A flake of snow that landed in the White Mountains, say, wended its way into an aquifer and now finds its way skyward in a xylem stream that extends from chinaberry’s root to her leaf. As chinaberry opens the little pores in her leaves- the stomates- the water exits, transitioning from liquid to gas and cooling the air in the process. The carbon dioxide enters her body, and she fixes the carbon into sugars and then sequesters some into yet more complex compounds, helping minimize the atmospheric greenhouse effect and delaying, incrementally, the warming. Shade, evaporative cooling, and carbon sequestration: a three-for-one deal that’s hard to pass up.
There are more than 300 trees in our forest garden. I just got back from counting them. It was a quick and dirty count, as it is very hot; I will conduct a more accurate survey come winter. Some of the trees are Southwestern in origin; others evolved elsewhere. Certain leaf traits are known to allow for greater capture of carbon and greater transpiration, and these traits do not differ inherently between those classed as aliens vs. natives. All are playing a role. Our tree density is on par with that of John Marzluff, the author of Welcome to Subirdia, who went to the trouble of estimating the carbon storage in his forest and calculating his household carbon use to arrive at this conclusion: “Our yard is a carbon sink!”. I am guessing our yard is, too.
Look for the helpers, they say. She is one. Chinaberry is our refuge in the summer heat.
