The heaviest organism on Earth isn’t a whale or an elephant. It’s a tree — or rather, a system of over 40,000 clonal trees, all connected by their roots. Pando, a six million kg organism in central Utah, is believed to have sprouted toward the end of the last Ice Age.
But after thousands of years of thriving, Pando has run into trouble. A study published in PLOS One this week features the first comprehensive examination of the entire 106 acres of clonal aspen forest, and it concludes that Pando isn’t growing. In fact, the forest has been failing to self-reproduce since at least 30 to 40 years ago.
“People are at the centre of that failure,” said co-author Paul Rogers, the director of the Western Aspen Alliance at Utah State University, who authored a similar study last year on a smaller portion of the Pando.
People have allowed the local deer and cattle population to thrive, Rogers said. Their voracious grazing has resulted in fewer saplings and a whole lot of old, dying trees. During its analysis, the team couldn’t find any sapling-size trees that didn’t have the tops eaten off.
Apex predators such as bears, wolves and mountain lions once kept the mule deer’s population in check, but those are barely around any more because of hunting. Then, there are ranchers who don’t stop their cattle from grazing on the trees.
State and federal officials are the ones who can help remedy this issue, so Rogers blames humans, not animals.
“Humans decide on how many animals are there and how they move around,” Rogers told us. “Because there are people there recreating and having homes in the area and roads in the area, you’re not allowed to hunt. Because of human presence, deer are more safe, which causes a localised overabundance of the animals.”
A survey took place in June 2016 and 2017 where the researchers measured the size, age and health of the trees all across the grove. And they looked at the amount of scat: “We count shit to see what animals are there and what their relative visitation rates are,” Rogers said.
The researchers also looked at two areas of the forest where the trees were protected by fencing and found fences weren’t always all that effective in keeping out wildlife.
What the tree system needs is time free of grazers in order to regrow. The Pando is not like other trees, Roger explained.
“They don’t live as long [as other trees], and they regrow,” he told us. “They send a hormonal signal whenever one of them dies to spread from the roots, not from seed. That’s its survival mechanism. When trees are dying and you don’t see any regrowth, that’s a red flag.”
The Pando’s lack of regrowth became even more evident when the authors’ analysed aerial photos dating back to 1939. Here, other human impacts became obvious, including clear-cutting for homes or campgrounds.
“Nothing ever grew back [in those areas] because of the combination of [people] cutting, and then the deer and cattle browsing,” Rogers said.
While this study tells an important story, there’s more work to be done. There are open questions about how climate change might further impact the Pando. The study also doesn’t get into other clonal aspen ecosystems, such as those in Europe. More research could also be done using cameras or GPS collars to track animals that interact with the Pando.
But for now, the goal is to sound the alarm on this unique organism. What the Pando needs is coordinated action to protect it at the state and federal level. There’s still so much to learn about this forest, but the trees need to be alive in order for those discoveries to happen.