Santa Fe officials hope fungi will stunt Siberian elms
Mar. 27—An Asian tree brought to New Mexico to supply shade for the drought-parched ground during the Dust Bowl era has overachieved in that mission — turning into an arboreal invader that flourishes at the expense of Santa Fe's native trees.
After years of battling the Siberian elm, a relentless, hardy foe that regrows as fast as it's chopped down, city park managers are trying a new tactic they hope will prove effective.
In what's now a pilot program, managers are inserting several fungi spores, including the white rot strain, into the stumps of felled elms to prevent the trees from regenerating.
Choking off the elms at the base is much more efficient than the current method of having a crew repeatedly cut down the trees — which quickly re-sprout and burgeon — in the same locations until they finally die, a laborious process that can take years, officials say.
"We're looking at how we can reduce and eliminate the elm population in certain places," said Melissa McDonald, the city's park and recreation director. "It's an endless project."
Siberian elms produce and shed a massive amount of seeds, enabling the trees to spread over a large area, she said, which is why they are found throughout the city and region.
The elms thrive in New Mexico because the growing season is longer here than their native Asia, and there are no natural checks in this setting such as pests, pathogens and trees that can outgrow it, McDonald said.
Introducing the fungi is a way to create an organic brake on its otherwise unfettered proliferation, she said. One must be careful when adding a new parasitic organism to the environment, but experts are sure the mushroom spores, which will be embedded inside the stumps, will remain there.
Five fungus species were cultivated on wooden dowels at the University of New Mexico's biology labs and then inserted into holes drilled into the elm stumps, said Reese Baker, owner of The RainCatcher, a company working with the city on the elm-removal project.
"I think it's a fantastic idea," Baker said.
The number of fungi-laden dowels that are required depend on the size of the stumps, Baker said. That means 25 to 30 might be needed on a stump that's 4 inches in diameter, and 50 to 60 required on a 12-inch stump.
A four-person crew plugged 180 stumps in different locations in two days, he said. A larger, more concerted effort could result in a sizable portion of Santa Fe's Siberian elms being treated.
Siberian elms are among the various invasive trees and plants imported to Northern New Mexico generations ago. Others include Russian olive trees, kochia and salt cedar.
But everyone interviewed with experience in combating invasive trees say the elms are especially bothersome because they're so resilient, fast-growing and intrusive, enabling them to dominate wooded areas where they take root.
"It's not so much that they're super plants," McDonald said. "It's just that they have everything they need, and they're super aggressive."
The elms can push their roots deeper than other trees to suck up water, Baker said. In riparian areas, this leads to cottonwoods and willows, which grow along the riverbanks, being deprived of water, he said.
When cut, the elms will sprout shoots exceptionally fast and push out their roots even more forcefully to draw nutrients and water, often damaging nearby walkways, said Skylar Nielsen, city parks operations manager and an arborist.
The elms serve their original purpose of creating shade too well, with canopies that fan out broadly, cutting off sunlight to undergrowth and even other trees, Nielsen said.
"The elms were the worst thing ever introduced," said Michael Smith, executive director of Friends of the Santa Fe River, a nonprofit that also works with the city in eliminating the trees. "They're a complete blight."
In Smith's view, the elms are growing like noxious weeds throughout the city, including along the Santa Fe River, and need to be eradicated.
Smith agreed trying to kill them by chopping them down over and over again is inefficient and labor intensive. It's also costly and can be futile, he said, recalling how he cut an elm stand just to return a short time later and see the trees had regrown to 10 feet in height.
Smith expressed skepticism about the fungi being a solution. He thinks the best way to get rid of the elms is chemical treatments. The state, county, school district and Nature Conservancy use chemicals to kill the pesky trees, but the city won't allow that to be done on its properties, he said.
"That has to change," Smith said.
Baker disagreed, contending an organic method such as the fungi is preferable, given the amount of pesticides and insecticides already in the environment.
Although Siberian elms are nonnative and thus invasive, many people believe they serve a valuable function by providing shade, McDonald said, noting Santa Feans who have weighed in are evenly split on whether to keep the trees or eliminate them.
The city's aim, even with the fungi experiment, is to be selective, removing the elms that are infringing on native trees and leaving ones that offer needed shade, she said. Shade trees like elms that can thrive in an arid place will be essential as the climate grows warmer and drier, she said.
"Climate change is real," McDonald said. "We don't want to deforest our entire urban canopy."
