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Hungry herbivores and human impacts threaten world's largest organism

Trees in the Pando aspen stand, the world's largest organism.
Paul Rogers
Trees in the Pando aspen stand, the world's largest organism.

Pando, the world’s largest organism by weight, is a stand of aspen trees located in south-central Utah. The massive stand is thought to be thousands of years old and has become a destination for sight-seers and researchers alike.

Paul Rogers, an adjunct professor in USU’s Environment and Society Department, explained how this aspen grove claimed the title of largest organism.

“Pando is a 106-acre individual. It's a tree that is a forest. And what makes it that is its connection in the root systems. And even more importantly, that all those elements of a forest, which we might think of as trees, are really stems that are genetically identical,” Rogers said.

Despite being such a large organism, Pando’s size doesn’t protect it from outside attack. Herbivores, like native deer and elk, and human-introduced species like cows, browse the new aspen growth through the summer, before heading down slope as colder temperatures roll in. This constant attack by hungry animals stymies new growth, preventing new trees from thriving after older trees die, ultimately spelling trouble for Pando.

“I've used this analogy many times. We have whole communities that are full of senior citizens...and we're like, where are all the babies? Where are the teenagers? Where are the middle aged ones? They're missing and we have a very vulnerable system,” Rogers explained.

Rogers’ recent research suggests that not only is Pando’s health at risk, but that installation of fencing around parts of Pando to keep hungry herbivores out may be causing the ecosystems in these areas to grow in diverging ways, and that unfenced areas are suffering.

“It's clear that Pando is developing two or three clearly different pathways, because we put up these fences and then we put up a fence that didn't work well, and we tried to repair it and it seems to be working better…and then we still have about half of the total 106 acres that's not fenced. And it's no doubt that it's on a downward spiral,” Rogers said.

According to Rogers, Pando’s health comes down to how we manage cattle and native herbivores. He said we’ve done a poor job of keeping herbivore populations at sustainable levels, leading to severe over-browsing happening within Pando. However, it’s not as simple as reducing herbivore populations. Pando’s future depends on who we’re managing the aspen stand for, and at what point do we consider Pando a man-made organism as we continue to alter the aspen grove through fencing and management practices.

“We've essentially created a vegetative zoo,” Rogers said. “People are coming from around the world now, as well as across Utah and the West to see this…we have recreationists, we have hunters, we have livestock managers, we have ecologists and scientists and simple leaf watchers, people who are interested in aesthetics and photography, and so on. All these different interests that are diverging…but these are doable and fixable issues, but we all got to kind of come to the table.”

To manage Pando in the most scientifically-sound way possible, Rogers called for an increase in what’s known as “process-based management”, which allows managers to assess their progress and course-correct if needed, with the latest scientific tools available. He said we’ve historically done a poor job of assessing how well ecological management initiatives are actually working on the ground.

“The whole idea is to understand the ecology and work with the system as opposed to our long history of trying to engineer systems to do what we want them to do,” Rogers explained.

With the issues Pando is facing, Rogers said the grove is a poster child for the many ecological issues aspens are facing globally.

“These forests of aspen support a high level of biodiversity. Unfortunately, the corollary to that is when they start to fall apart, a lot of species start disappearing and falling off the landscape,” Rogers said.

Rogers was recently featured in the IMAX film Into America’s Wild, which highlights America’s natural wonders and inclusivity in the outdoors, and in USU Today.

Aimee Van Tatenhove is a science reporter at UPR. She spends most of her time interviewing people doing interesting research in Utah and writing stories about wildlife, new technologies and local happenings. She is also a PhD student at Utah State University, studying white pelicans in the Great Salt Lake, so she thinks about birds a lot! She also loves fishing, skiing, baking, and gardening when she has a little free time.