pruning mistakes that leave the tree susceptible to disease and decay while preventing it from proper healing. Stub cuts occur when the pruning cut is made too far outside of the branch collar. In other words, too much of a stub is remaining aer the cut. This prevents a tree from developing the callus tissue and wound wood needed to seal the surface of the cut. Because compartmentalization is de- layed, a tree is open to decay for longer periods of time, according to Gilman. Exposure to oxygen can stimulate the growth of bacteria and fungi. “It gives the fungi and bacteria more time to work on the tree’s natural bar- riers,” says Gilman, “compared to mak- ing a cut at the right spot, which en- courages closure of the wound sooner and therefore cutting off the oxygen.” Conversely, flush cuts occur when the pruning cut is made too close to the primary branch and the second- ary branch collar is removed. This can damage the tree’s natural de- fense mechanisms and permanently removes the natural barrier of the branch protection zone. “There are four different ways trees compartmentalize decay that can come in from a pruning cut,” says Dr. Gilman. “The only thing le when you make a flush cut is the weakest barrier and that’s plugging, which is the weakest process or defense the tree has. So, a flush cut removes that capacity that the tree normally would have if you made the cut at the right spot.” PRUNING LARGE BRANCHES Arborists should only cut large branches on trees as a last resort when no other pruning methods can help resolve the issue with the tree or help it to meet its objective. “You’re making this huge wound, and the tree has very weak defenses against that type of wound,” Gilman says. “That’s got implications, and
Lion's tailing involves the excessive removal of inner branches, which leaves tufts of foliage at the end of large branches.
In general, however, topping a tree un- necessarily exposes it to disease, pests, decay, and other structural risks, which can create larger problems than simply having a tall tree. “Trees do grow tall, and they could be at a low risk relative to their size,” Buell says. “But once you’ve cut that tree in half, now you’ve predisposed it to branch attachments that are very poor as well as decay.” Topping can also disrupt the natural growth and development of a tree, leading to the need for far more restor- ative work down the road, according to Buell. That’s because topping activates the tree to respond by rapidly growing weak, thin branches that will require intensive pruning and management. “In order to restore trees from top- ping cuts, you need to come back over time and really make some strategic cuts that will regain the tree’s natural form," he says. LION'S TAILING Lion’s tailing involves the excessive removal of inner branches, leaving tus of foliage only at the ends of large branches. If pruning isn’t prioritized on a tree while it’s young, this can lead to
the growth of large, low branches.
Eventually, these branches could be- come hazardous or create clearance is- sues on paths and streets below them. That’s why arborists sometimes resort to lion’s tailing and simply remove all of those low branches. However, this practice is actually count- er-productive to creating a safe environ- ment around the tree, says Gilman. “It forces the tree to grow even taller and puts a lot of stress on the mechanics of the tree’s connections,” he says. “It ul- timately makes the tree somewhat un- stable, and that gets worse over time.” Buell adds that the practice of lion’s tailing is also detrimental to a tree’s health and growth, since it reduces the tree’s ability to photosynthesize effectively. “Lion’s tailing is a horrible prac- tice, and it’s a very inappropriate approach to pruning,” he says. STUB CUTS AND FLUSH CUTS How well a cut is made can significant- ly impact how well a tree heals from the wound. Unfortunately, poor cuts — like stub and flush cuts — are common
32 | ArborTIMES Winter 2024
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