Zion's trees are dying of old age


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ZION NATIONAL PARK — It's a trend that might sadden the hearts of millions who love Zion National Park. One of Zion Canyon's most beautiful features is fading away — and the process may be unstoppable.

The canopy of cottonwood trees that provides a vivid slash of green in many photos of the canyon's famous red-rock may survive only another three to five decades. That's the prediction of Dave Sharrow, a National Park Service hydrologist who's been monitoring the trend in one of the country's most beloved national parks.

"The scenic beauty of these cottonwoods along the stream is tremendous and we would really be a lesser park if we didn't have them," Sharrow said.

That thought was echoed by park visitors armed with cameras.

"The green leaves against the red rocks makes it spectacular," said Vermont tourist Aaron Beaudin, standing on a footbridge that spans the Virgin River in the heart of Zion Canyon.

Flagstaff tourist Brittain Davis, a frequent visitor to the park, said his photos often include the cottonwood trees. "The contrast of colors," he said, "everything's beautiful about this canyon. And the trees add to that."

The cause of the canopy's demise — if it occurs — will be death from old age.

"All we have is the older trees," Sharrow said. "We're not getting the recruitment of younger trees coming in."

As the canopy ages, the older trees are dying. Deadfall litters the ground. But young cottonwoods are not growing up to take their place. In 30 to 50 years, Sharrow said the Cottonwoods could be gone.

It seems contradictory that cottonwood seeds, resembling little fairies, seem to fly all over the canyon in the springtime. The tiny balls of cotton float through the air, carrying seeds that should take root and grow into the next generation of cottonwood trees. But that almost never happens these days in much of the canyon.

With the air so full of cotton, why aren't young trees growing?

The answer is complicated, but it all stems from one thing: People have changed the canyon, beginning nearly 100 years ago.

"We're walking on one of the levees built in the 1930s," Sharrow said as he walked alongside the Virgin River. The levees were designed to protect the paved road in Zion Canyon and to keep Zion Lodge from being damaged by spring floods.


The cottonwoods need soil that's been wetted by the river and is wet when the seed falls on it. That never occurs outside the levees.

–Dave Sharrow, National Park Service


The levees drastically altered the natural flow of the river. Instead of a meandering river that frequently changes channels in the springtime as it floods portions of the canyon, the Virgin River is now straight, fast and especially energetic inside the artificial levees. Cottonwood seeds fall on inhospitable real estate if they land inside the levees.

"So when the river floods, if any cottonwoods have grown, it takes them out," Sharrow said. "It washes away all the young seedlings."

Outside the levees, the story is even worse: Seedlings never get started.

"The cottonwoods need soil that's been wetted by the river and is wet when the seed falls on it," Sharrow said. "That never occurs outside the levees."

One partial solution exists, but it has eluded the National Park Service.

"To take out the levees and armor the road would cost about $7 million," Sharrow said. "The park has asked for the money 10 years in a row, but so far it has not reached the top of the priorities list."

Photo credit: Ravell Call/Desret News

Even if the money were obtained, eliminating the levees wouldn't solve the problem. Even where there are no levees in Zion Canyon, young cottonwoods aren't making it there either.

"There's something else that's causing the young trees to not make it maturity," Sharrow said. "We think it's an overpopulation of deer."

The theory that deer are eating most of the young cottonwood seedlings is not proven. But there is a large deer population because their natural predators are not present here.

"Mountain lions aren't comfortable around a lot of people," Sharrow said. "And in Zion Canyon, we have a lot of people."

Visitation in Zion National Park is now around 3 million people each year. So it's likely that mountain lions will continue to avoid the canyon. Without wholesale slaughter of deer — something the park service is not proposing — there may be no way to prevent the cottonwoods from dying out.

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UtahOutdoors
John Hollenhorst

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