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Flo, a century-old pecan tree at Barton Springs, is diagnosed with fungal disease

A pecan tree by a pool is surrounded by barricades and supported by scaffolding.
Michael Minasi
Flo, an iconic pecan tree at Barton Springs, was diagnosed with a wood decay fungus known as brittle cinder fungus.

Yes, the crisp, cold water is undoubtedly Barton Springs' main attraction. But the lush shade trees surrounding the watering hole in Zilker Park play an important role in its enduring allure. And one of the watering hole's most treasured trees is struggling.

Austin Parks and Recreation learned last week that "Flo," the century-old pecan tree arching over the northside of the pool tested positive for brittle cinder fungus, or Kretzschmaria deusta, a potentially fatal fungal pathogen. The fungus eats away at tree roots and bases causing otherwise healthy-looking trees to collapse. The testing came as part of regular inspections by the parks team in July. Staff sent the fungal sample to a lab at Texas A&M, which confirmed the diagnosis.

Joshua Erickson, manager of the City of Austin Urban Forestry Program, says this type of fungus is common in Texas, but it's particularly insidious.

"Kretzschmaria is unique in that it does not just feed on dead tissue, like some other wood decay fungus, it actually will compromise live tissue as well," Erickson said. "So with a tree that has Kretzschmaria, the leaves can look fine, the canopy is not affected, but at the same time, the structure of the cells are being broken down and it's actively compromising its structural stability."

Flo's future is now being analyzed by a group of independent arborists certified by the International Society of Arboriculture. The Parks Department expects recommendations from the arborists by early September. In the meantime, Flo has been blocked off from the public and reinforced with rope as a safety precaution. Once the arborists' recommendations are returned, the city will weigh the options of preservation and public safety.

Flo with Steam Shovel, March 1926. Photo Courtesy of Austin History Center
Austin History Center
Flo arches over Barton Springs in 1926.

According to the Parks Department, Flo dates back to at least 1925. Archival photos from that time show the native nut tree well-established and arching toward the springs. The city speculates the tree's pronounced lean was intensified by a 1935 flood, which may have also caused a large cavity in the tree's trunk. Shortly after, around 1940, the city built the existing concrete support wall for the swooping tree.

In the mid-'70s, Flo received more treatment when its cavity was filled with cement, a common practice at the time, but no longer used. Since then, the tree has received additional fortification including fencing around the roots to protect them from foot traffic and steel support saddles. Understanding Flo's vulnerability, a nearby pecan tree was planted to create a canopy if Flo were to ever decline.

"The efforts that have been taken to preserve [the tree] in its current location are pretty remarkable," Erickson said. "It's absolutely an asset to the pool and to our park system."

Flo is surrounded by barricades and supported by scaffolding on Tuesday. Aug. 22, 2023, in Austin. Flo has been diagnosed with a wood decay fungus known as brittle cinder fungus, and Austin Parks and Recreation is awaiting analysis on treatment or removal of the tree. Michael Minasi / KUT
Michael Minasi
Flo is surrounded by barricades and supported by scaffolding on Tuesday.

The city says if it must completely remove the massive tree, it will offer opportunities for the public to honor and memorialize Flo through ceremony and creative reuse of the tree's healthy wood.

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