Doreen Fogle: It’s been hot around here!
Summer is finally winding down and I will be so glad to end my constant search for a shaded parking spot. It has been a hot one.
Indeed, NASA announced on Tuesday that it has been the hottest month on the earth, ever, in 137 years of recording.
When a car is parked in the sun, no shade, the car interior can be a good 40 degrees hotter than the outside air. That means that on that 107 degree day, when I got back into my car after a little food shopping, my car was probably close to 150 degrees. I always carry water, thank goodness, in a cooler — otherwise I could be making tea!
Now, that shaded parking space I am constantly searching for: there aren’t many of them. And the few that are there are almost always taken.
There are many good attempts at planting shade trees in parking lots, but the conditions are tough and the shade rarely seems quite enough. The trees are planted into very compacted soil, and it’s subsoil at that.
The planting bed or hole is loosened and amended, but the roots want to reach into the surrounding soil under the pavement, but it’s very compacted. This creates limited soil volumes that confine roots, restrict root growth, reduce anchorage and often supply inadequate soil moisture and nutrients.
Heat reflected from the pavement and from the heat absorbed by the pavement is hard on the trees, too. This can thwart the growth and full development of the trees, leading to a much shorter life expectancy. As a result, we don’t get enough shade.
Much research has been going on to improve this problem. For one thing, trees planted in paved areas need more space. The roots should be able to grow at least out to the dripline of the mature size of the tree. This involves relinquishing some parking spaces, but the result is a cooler, more attractive parking lot and happier people.
Trees can keep things cool in two ways. Shading from the sun keeps things cooler. In fact, we just experienced some celestial shade on Monday. When the moon blocked 80 percent of the sun it was much cooler right away.
The other way is by evapotranspiration which is where water molecules in a leaf absorb heat from the outside and change from a liquid to a gas which is water vapor. This keeps the trees cool, heat is lost from the air and the increase in water vapor feels cool to us.
Parking lots, other paved surfaces, bare ground and buildings contribute to what is called the heat island effect. Sunlight falling on these surfaces is absorbed during the day and released when the ambient temperatures are lower, in the night.
In a city the heat island effect can make the local environment be up to five degrees higher than the rural area around it. This leads to more energy consumption for cooling.
Studies have shown that the shade of trees and vegetation can go a long way to prevent the heating that creates a heat island, even on a small scale in our own backyards. Many of us don’t own parking lots, but we have driveways, parking areas, patios, houses and other structures that could benefit from some shade to keep us cooler and help everything cool down at night.
A large tree shading the west or south side of a house can reduce cooling costs by 10 percent or more. A paved area that has been shaded during the day does not soak up as much sun and heat as it would without the shade. This keeps the surrounding air cooler in the night time, which is so important for the night time cooling that we need. Sun-heated pavement releases heat at night, keeping things warm.
If you have had trees removed because of bark beetle infestation, you may have a new open space and too much sun. Now is a good time to plant a shade tree in a good location. If you have a small paved area, a small shade tree may be appropriate. Or you may live amongst many trees, feeling frustrated about not having a great vegetable garden, in which case, just enjoy the cool shade you have.
When selecting a shade tree, fast-growing is what everyone wants but it is not always the best option. Many fast growing trees have weak wood, resulting in breakage problems.
The Red Maple, Acer rubrum, is a nice fast-growing choice, with beautiful fall foliage. Its wood is somewhat weak, but it is fairly trouble free. I love mature Western Sycamores, Platanus racemosa, a fairly fast-growing native that is an excellent wildlife tree, most suitable for large areas.
The native oaks should not be overlooked. They are slower-growing but yield magnificent trees and support lots of wildlife, again for a large area.
Planting a shade tree can keep you and your home cooler. Higher temperatures seem to be the new normal, so we need to prepare for them.
Doreen Fogle is a Nevada County-based landscape designer with Delightful Gardens. She can be reached at email@example.com. Her website is mydelightfulgardens.com.
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