The next time you find yourself with no sense of direction in any city, just ask a street tree! Seek out a thin skinned tree planted in a park row or boulevard next to a street or sidewalk. Cherries, Maples, Plums, and Ashes are most helpful. Check the bottom 5’ or so of trunk, and more often than not, you will see a longitudinal injury running up and down the stem. This will be the west/southwest direction from the trees location. With extremely few exceptions, this almost NEVER happens to native trees in the wild. This damage is from direct and reflected solar radiation, sunburn, if you will. I didn’t have to look hard to find a sun damaged trunk or two to photograph for this month’s column!
With no protection offered by lower branches or some type of trunk guard, thin skinned trees are often doomed from the get go. The cambium that produces wood toward the center and bark to the outside of a tree is only about one cell thick, and easily damaged. Without the insulation offered by thick, corky bark, the sun’s direct rays and the reflected blast bouncing off the street and sidewalk will cook this delicate layer just under the bark, like putting a match to a sugar cube. Put your hands around a young tree’s trunk exposed to the direct sun on the fourth of July and feel the temperature difference between the shaded side, “Ouch!”
When this layer dies, there is no longer vascular conductivity, and an open injury often results, a prime court for infection. Boring insects and fungi love to set up shop in these locations!
Until the canopy of a young tree gets big enough to shade the trunk, this area needs to be protected. Shop for trees with branches that run all the way down the trunk if you can find them (good luck)! Anything that will block the sun from the stem is what you are looking for, a sacrificial shrub, sprouts or suckers from the root stock, shade cloth stretched between two stakes, or ANYTHING that casts shade on the west/southwest facing side will do. Avoid wrapping anything non porous that will trap unwanted moisture against the trunk. The black plastic “buck guards” that have 1” squares are about the best thing going and do double duty as well! I don’t care for painting the trunk white as I think it looks tacky, but you gotta do what you gotta do…
I’m not quite ready to jump on the global warming bus just yet, but the sun burns my skin way faster than it used to and I know it’s not just my imagination ‘cause I’m not getting any older (wink)!