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Leave it to beaver

BY BENJAMIN TOWAR | APRIL 21, 2015 5:00 AM

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University of Iowa Facilities Management has formed a unique partnership with local tree-trimming experts — the Iowa River’s beaver population.

Andy Dahl, the Facilities Management arborist, the beavers’ relationship with the university is nothing new. Each year, Dahl and the rest of the department take full advantage of the rodents’ appetite for tree bark to gnaw trees that are unwanted along the Iowa River.

“The damage on campus seems to be cyclical,” Dahl said. “There’s a bit every [winter]. Some years seem to be worse than others, and this year seems to be worse. Maybe there’s more mouths to feed, or they’re hungrier, I’m not sure.”

The beaver-university partnership has been maintained as far back as the 1980s. Facilities Management makes an effort to keep native species thriving along the river’s banks, while whittling down the population of invasive species, such as white mulberry or siberian elm.

“We typically use chicken wire on very large trees, 30 inch diameter or more … on smaller trees, we use woven wire,” Dahl said. “It’s sturdier, so they can’t get through.”

Dahl said that no matter the species, hungry beavers sink their teeth into any desired tree bark. However, he has never seen an instance in which the barriers fail to keep the beavers away from trees that Facilities Management means to protect.

With native and planted species quartered off, the beavers are forced to turn their appetites elsewhere: to the exposed invasive species or over-populated saplings.

Despite their best efforts, the beavers fall short of completely eradicating the trees they feast on by leaving the underground root system intact. Facilities Management then deals with the remains.

Evidence of the beaver’s handiwork can be seen along the Iowa River, with some trees stripped of bark at their bases. Stumps with cylindrical cone tops are also evidence of the beaver’s hefty appetites.

Throughout his 15-year tenure at the UI, Dahl has seen the annual remnants left by the semi-aquatic rodents. However, he has yet to catch one in the act. He said the beavers usually dine in the early morning hours while it is still dark outside.

The nesting grounds of the beaver’s remains up in the air.

“I have a few ideas of where they’d be living,” Dahl said with a smile, “But for their sakes, I think I’ll keep that to myself.”


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