It’s time for another Benefits of Trees blog post. This time, I won’t be drawing from someone else’s list. Instead, I’ll share one of the top benefits from my own personal list. But before I dig into the benefit, I need to set the stage for you.
As I write this, it is the week after Labor Day weekend.
I can already feel the shortening of the days, and the heat of the sun seems lessened from this time last week. But, while the summer holiday may be over in the culture of America, the summer season still has almost a month left on the calendar. And here in the south, the summer comes on strong and holds on tight. So, while the mornings may be blessedly cool and the evenings refreshingly low humidity, we still need an ally to thwart the midday malice of the not-yet-northerly sun.
That’s where trees come in, and that’s why I consider shade to be a key benefit. If you look at the lists I posted in the last blog entry, you’ll notice there are multiple benefits that are a consequence of the shade a tree casts, things like: “Trees cool the streets and the city”, “Trees conserve energy”, and “Trees shield children from ultra-violet rays”. These are good benefits, and we will give them their due at a later date. But, for now, let’s talk about shade in a more specific sense.
As you may know, when I’m not sitting at my desk writing about how much I love trees and how important I think they are as allies in solving human-environment interface problems, I run a tree service in Knoxville, Tennessee. And while I have good crew who help share the labor, there’s no getting around the fact that on most days, tree work is hot, dirty work. We start at 7 am, and by 7:30, I’m typically covered in sweat, and I stay that way until I get home for the day (although it often doesn’t end there since I typically have farm chores or a workout to dig into). Basically, the summer is a hot and sweaty time, and the shade of the trees under which I have the privilege to work make it bearable.
According to the U.S. Department of Energy, the shade from trees can cool the air nearby by as much as 6 degrees Fahrenheit, and the air directly underneath by a whopping 25 degrees Fahrenheit.
In case that’s somehow not clear to you how big a deal it is, consider that, in my humble opinion, 65 degrees Fahrenheit is the most pleasant outdoor temperature, so on a 90 degree day, pretty typical in the southeastern U.S. summers, all you need is one tree to rest under and you can pretend, aside from the humidity, that it’s already fall.
The benefits of resting directly underneath are pretty obvious, but if you think the 6 degree decrease for the surrounding area is not sufficiently significant, consider that the worst predictions of current climate change models have the global average rise over the next hundred or so years at just over 6 degrees Fahrenheit. I don’t know how much you watch the news, but people are pretty concerned about this much change. This cooling action is one of the many reasons that urban tree planting has become a big part of the climate action narrative.
But I, as an outdoor laborer, am not the only one in need of cooling shade. With the numbers above in mind, just about anyone living in the southeast (or the rest of the country for that matter) who gets a bit of that summertime covid cabin fever is going to want some shade in which to recreate, picnic, or just spread out and unwind.
And here’s another one, your car likes the shade, or perhaps more accurately, you like your car better when it’s been in the shade. My pickup truck is black, so in the summer, it gets crazy hot in there. I know this problem is solved by many with a garage, but at my house, our driveway wraps under some lovely sugar maples, so when it’s really hot, my wife and I park our cars under the trees.
And speaking of my wife, she made some new friends this summer… Two baby deer decided to take up residence in our yard/forest edge, and while she doesn’t feed them, she makes sure they have water, and she talks to them so they don’t find her frightening. As a consequence, one can quite regularly walk out into the yard and find them resting in the shade, not even a stone’s throw from the door.
The deer bring me to another example of the importance of shade. The canopy, which casts the shade in the first place, also provides quite a lot of habitat. Specific numbers can be hard to pin down, but consider this for a moment, when I was working in California, almost 10 years ago now, I spent a lot of my free time with some folks who were rather accomplished naturalists, and I learned a lot about birds and animal tracking and native plants and more. One thing that was said, that stuck with me, was that when you walk through the forest, for every pair of eyes that you can see trained upon you, there are ten, or a hundred pairs, that you cannot see.
Birds, in particular, are very good at hiding from prying eyes when they choose, and in fact, the auditory mechanics of their calls and whistles are often pitched in such a way that makes them very difficult to locate, even though the sound itself comes to our ears so clearly. Ask yourself next time you see a bird hopping around the shaded branches of your neighborhood tree, “How many other creatures are here right now that I don’t see?” Expand that out even further, and ask yourself, “How many will pass through this space in the course of a day?” Once you start looking at trees in this dynamic fashion you realize that under their shade lie bustling highways teeming with living creatures.
If you aren’t familiar with the naturalist’s technique of the “sit spot”, I encourage you to look it up. In a brief, you pick a spot, and you go there every day (or as often as you’re able) and you sit still for 5, 15, 30, 90 minutes, however long you’re willing and able to commit, and while you are there, you do nothing, simply observe, maybe write down your observations if you’re motivated. You will be amazed by what’s been going on in the shade of your own tree that you’d never noticed before.
We’ve well established that shade is cooling, and so far, I’ve made the case that mobile creatures appreciate being able to move into the shade when it’s too hot in the open.
But what about the more sessile living things? For plants, shade creates microclimates. If you’ve ever gardened or done any landscaping, you know that many plants have specific growing conditions. Some like full sun, some part sun, and some, full shade.
One of the simplest ways to see the tangible consequences of these preferences is the tendency of a plant to exhibit scalding of bark or bleaching of leaves. I have two Japanese maples on the north side of my home, and early in the year they have beautiful red foliage, but by this time in late summer, it has gone to greenish gray, because, while they are on the north of my house, it isn’t tall enough to cast appreciable shade. Those same trees, planted in partial shade can keep their deep red until the leaves fall off in November.
Let’s dig into these microclimates a bit further.
Imagine you have just one shade tree in your yard and it is well enough away from any structures that there is usable space on all sides of it. On the east side of the tree, you will get morning sun which is gentle on fragile but sun-loving plants. On the south side you will get the most direct midday sun, suitable for hardy plants. On the west side you will get the evening sun, not as intense as the midday sun, but it comes coupled with the hottest part of the day, so its impact can be easily underestimated. And last, on the north side, you will get dappled sun throughout the day. Each of these 4 light regimes comes with associated increases and decreases in average and peak heat as well as increase or decrease in available moisture throughout any given day. Add multiple trees to the equation, and you will see how the overlap of these 4 zones creates even greater nuance and variety.
For the savvy urban gardener, these microclimatic variations are the keys to success in having lush gardens that can produce from the very earliest depths of spring all the way until the first frost and perhaps beyond. And in case you’re thinking microclimates only matter with gardens, consider this. At my home in east Knox County, we have a patio that wraps around the south, east, and north sides of the house. Additionally, adjacent to the east side patio, we have 4 large sugar maple trees. The changing patterns of sun and shade throughout the day (and throughout the seasons) means that if you were to come visit me, you’d likely find me outside, but exactly where would depend on the when.