Originally Published: January 28, 2018 6:03 a.m.
Something is rotten in the American and Liberty elm trees downtown, their colleagues are stressed, and the concrete is cracking up.
But Yavapai County Facilities Director Kenny Van Keuren doesn’t find the state of the courthouse plaza, and its trees, funny.
The nearly 4.5-acre plaza contains 164 trees, most planted 90 to 100 years ago, Van Keuren said. The large elms are not native, and while they can live to 150 to 300 years in their natural habitat, overcrowding and the compacted soils of the plaza reduce their lifespan to about 100 to 120 years.
“They were all planted at the same time; they all die at the same time. We gotta’ get moving on this,” Van Keuren said.
The heart rot that is occurring is a result of a popular pruning method of the 1980s and 1990s where groundskeepers topped the trees. Today this practice is considered harmful.
To survive, the tree produces branches from the cut section. Water collects in the crotch between the new branches and begins to rot the tree trunk from the inside out.
Van Keuren put together a committee to inspect the trees, made up of two arborists with International Society of Arboriculture certification, University of Arizona Cooperative Extension Director Jeff Schalau, and Dr. Ursula Schuch, UofA Coop professor and horticulture specialist. Schuch won’t start until March, but the others have looked closely at every tree.
They have identified 19 diseased trees, two of which have been removed, and three trimmed severely to decrease the chance of toppling over; they will be taken out in the next month or so. All have heart rot.
In order to determine how much of the inner wood is damaged, Van Keuren used a sonic tree decay detection device that sends sonic waves from one side of the tree to the other via prongs. The faster the wave moves through the wood, the more solid the tree is.
The sonic device identifies where the decay begins as workers move it up the tree. Van Keuren kept one section taken from 30 feet up the trunk where three-quarters of the center was honeycombed with rotten wood, something no one could have seen from ground level.
He hopes to remove 10 of the 17 sick trees before summer. The plan, he said, is not to go too fast but to balance the use of the plaza with public safety.
“We are trying to be sensitive, but there are liability issues. This can cause catastrophic issues if a tree falls,” he said, adding that he expects resistance from the public. “The work will continue for the next five to 10 years so that there’s not a huge change in the atmosphere of the courthouse plaza.”
Mature replacement trees can be planted any time of the year. Right now, however, tree farms are low on stock, he said.
Ideally, the trees should have been planted 50 to 70 feet apart; instead, they are within 20 feet of each other causing the canopies to grow together and block out sunlight, which affects the health of the lawn underneath. The thick canopies also contribute to the spread of another, less serious, disease.
European elm scale, an infestation that causes branch dieback in healthy trees, looks like grayish powdery mold. Birds can spread the disease from tree to tree as well as branches on one tree contacting another.
The county will use an injection system at the base of tree trunks to apply an insecticide the tree draws upward to the upper branches that kills the scale.
Replacement elms will be species resistant to elm scale and other diseases.
“Elms were favored because of their shape which enhances the architecture of the courthouse,” Schalau said, remembering this from reading an old document written by a landscape architect who worked for the Forest Service.
The last time the sidewalks around the courthouse were redone was in the 1970s. Cracks and shifts are now causing a safety hazard.
“It has nothing to do with the trees,” Van Keuren said.
The plan is to replace much of the broken concrete areas this spring and check the “I” paver bricks. “We are constantly monitoring as the ground is always shifting,” he said.
Schalau said there may be some educational outreach in the spring to answer the public’s questions.