I was taking a lunch walk around Capitol Lake in Olympia a couple of weeks ago. It was a nice walk even though the 85 degree heat was a bit warm for my taste–72 degrees is about warm enough for me. Even with a breeze, heat rose up off the gravel and paved walkway, reminding me how warm the sunshine in May can be.
Then came a distinct pattern of hot, cool, hot, cool, as I walked in and out of shade cast by trees located on the south and southwest side of the path. With the addition of shade the breeze was cooling and the temperature quite pleasant. I noticed then that all along this side of the lake folks were enjoying the natural ‘air-conditioning’ of shade trees: picnicking, snoozing or sitting and chatting in almost each spot of shade. The trees here are still quite young, but they are already being appreciated for that wonderful summertime benefit, shade.
Radiant energy from the sun is absorbed and stored by built surfaces, sidewalks, roads and buildings. Trees shade and reduce this heat absorption, which helps cool our cities and homes. Trees transpire, or release, water vapor into the air from their leaves cooling the air, much like old fashioned swamp coolers. Temperatures can be 5 to 10 degrees cooler in the shade than in nearby areas without shade.
Did you know that shade can be quantified? Shaded streets require less maintenance than trees in full sun, resulting in cost savings to our public works departments. According to Dr. Greg McPherson, 15-year-old trees on the west side of a building can reduce energy bills by nearly 12 percent (the savings are somewhat less in cooler climates). Older trees provide even greater benefits.
With a climate that is warming, it is a wise investment to strategically plant trees now. Shade trees planted on the west and southwest of homes provide the greatest benefit. Tall deciduous trees will shade roofs in the summer, and allow sunshine to penetrate in the winter.
As you plan for planting, make sure to select the right tree for the right location. Look up (for overhead powerlines), down (get a locate for underground utilities), and all around (plant with the mature size of the tree in mind). Finally, have a plan in place to water and care for your tree as it grows into a benefit-providing asset in your landscape.
Enjoy the summer!
By Linden J. Lampman, program manager, DNR Urban and Community Forestry Program