By PAUL HETZLER
It’s heartening that many county highway department and state Department of Transportation (DOT) jobs include funds to plant trees to replace the ones that have to be removed to make way for large road construction projects.
However, I can’t help but notice how often these DOT replacement trees all live to a certain size—in the eight- to ten-inch diameter range—and then decline and die as a group, sometimes in the course of just a few years.
When a tree has survived for 15 or 20 years, it may come as a surprise that its demise is due to shoddy planting. A sugar maple can easily live to be 100, and some even manage to survive a lot longer. One that expires at 20 because it was planted “fast and dirty” is a waste of effort and expense. You might as well consider such a tree a rental rather than a purchase.
Given their druthers, tree roots would like to extend two to three times the length of its branches, also known as its drip line. When a good-size tree is dug in the nursery, between 80 and 90 percent of its roots are cut off by the tree spade that digs them. The term transplant shock refers to this catastrophic loss of roots.
Obviously, trees can and do survive transplanting, but they need to get their roots back. Initially, a good deal of root re-growth happens within the root ball. Fibrous roots will proliferate in the original soil plug, and for a time the tree survives much like a potted plant even though it may look like it has all the room in the world.
When a transplanted tree begins to send out roots from the root ball, it’s essential they be able to penetrate into the soil around it. Any barrier, no matter how slight, induces the root to turn aside in search of an opening. Barriers include compacted soils—a common condition in road rights-of-way—as well as heavy clay soils, stones and other buried objects.
Even the burlap around the root ball has been shown to cause roots to circle around inside the fabric. To make matters worse, much of the burlap used today contains synthetic material which does not break down. Wire cages surrounding the burlap can last 30 years or more, and often cause further problems as roots enlarge.
Over time, tiny circling roots become large circling roots. As they increase in diameter they often constrict one another. If the wire cage is left on the root ball, roots more frequently encounter wires as they thicken and lengthen, which cause further cutting and constriction.
Circling roots near the surface often become “girdling roots” and strangle the trunk, either partially or wholly, below the soil line. This cuts off the flow of water and nutrients to part or all of the crown. Then stress symptoms like early fall color and twig dieback begin to appear.
As troubles pile up for the congested root system, the tree has become larger and more “expensive” to maintain. Its roots need to send ever increasing amounts of water and nutrients to the crown at a time when its ability to do so is decreasing.
The cost of wholesale trees is roughly the same no matter what contractor bids to plant them. Any cost savings will mostly come from keeping labor costs down. It takes time to dig a planting hole of appropriate size. (Cornell recommends it be three times the width of the root ball.) Removing the burlap and wire cage from the root ball in the planting hole is also time-consuming. The fastest crew can bid the lowest.
As it stands, the process is not so bad. We are protected from excess cost, and we get the benefit of a tree-lined road for a decade or two. Perhaps observing this “tree rental process” may serve to help educate the public about the importance of good planting practices.
Paul Hetzler is a forester and Cornell Cooperative Extension of St. Lawrence County horticulture and natural resources educator.