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Life on logs

The loss of Minnesota’s largest white pine opens opportunities for researchers to talk about its afterlife, an often ignored, yet rich chapter of its story.

Pine tree in center of frame surrounded by smaller other trees with blue sky in background

Clipboards, vials and cameras in hand, a small team mills around the carnage as steam rises from recent rain. They place specimens into bags, and rather than shake their heads at the loss, they marvel at what’s to come. Although a couple of suspects come to mind, questions remain. Who was to blame for this?

While all the makings of a crime scene, 911 wasn’t called.

Instead, a newly penned notebook entry details a 41-foot-long section of a white pine — formerly Minnesota’s largest — brought down by a strong summer storm in 2019. In the widest section, even two people can’t reach around for a hug.

IBSL Director Jonathan Schilling, who is a professor in Plant and Microbial Biology, studies wood rot and was just a few miles away during the storm. News of the toppled tree spread fast and Itasca State Park staff called Schilling to alert him. Schilling and lab members — including undergraduate researcher Lauren Otolski and lab technician Molly Moran — headed over to the tree. The team collected samples that morning and frequently returned to collect more.

“One way or another, every tree is going to die,” says Schilling. “I’m fascinated by what happens when that tree hits the ground. The microbial battles that play out and dictate what happens next have massive implications.”

Uncertain afterlife

When the white pine segment hit the forest floor, it joined a slew of other logs, stumps and branches. These woody fragments make up 80% of the total carbon that comes from plants. Fungi and other decomposers feast on these woody delicacies, and different fungi specialize in breaking down different structures. Sometimes, carbon is released into the atmosphere and other times it is sequestered in the soil.

Despite the prevalence of woody material, it was long ignored in climate models because all evidence showed it’s breakdown was slow, relative to other processes that release carbon to the atmosphere. However, in the past decade researchers have learned more about fungi driving decomposition. It turns out that the rate of decomposition isn’t as predictable, and neither is the carbon’s ultimate fate.

Brown rot fungi and white rot fungi are the two primary players in wood rot and key culprits of what brought down the white pine. Their diets are different and the “waste” they leave behind can either head to the soil or the atmosphere.

If brown rot fungi made its home on the white pine, about a quarter of the decomposing white pine would end up in the soil off Wilderness Drive. In years to come, hikers would meet new plants nourished, in part, by the former giant.

If, on the other hand, researchers discovered white rot fungi on the white pine, the “waste” products from the fungi’s meal would instead be released as a gas and float into Wilderness Drive’s canopy — and beyond.

“A key uncertainty for climate models is the type of fungus responsible for the decay. If we become a ‘white rot world’, all indications are that more carbon is going to end up in the atmosphere rather than sequestered in the soil,” says Schilling.

Beyond logs

Researchers used both long-standing and relatively new techniques to sort out what fungus brought down the beloved white pine. They tested the density and chemistry of the wood (Schilling calls this “crime scene” investigation) and sequenced DNA (the “criminal” investigation).

Ultimately, they identified a brown rot fungus known as “The Train Wrecker” — named for its knack of degrading railroad ties — as responsible for weakening the tree’s trunk to a snapping point.

For Schilling and lab members, the white pine’s loss and thriving fungal life to follow opened up new opportunities to engage with park visitors. Schilling recently led a walk on the site as part of Itasca State Park’s Science in Nature series detailing the investigative work on the white pine. State Park staff are interested in building out permanent signage on the site.

Paying more attention to life on logs — and what it means for climate models — has broad implications. For one, planting trees is a go-to solution for offsetting carbon emissions. However, this doesn’t take into account a tree’s afterlife.

“We need to know the balance of rot types and what might make it tip,” says Schilling. “The tease of (planting) trees to offset our emissions is very popular right now, but there is a Train Wrecker out there just waiting to derail it.” —Claire Wilson


About the article | This article originally appeared in the Fall 2021 edition of Upstreama biannual publication by Itasca Biological Station and Laboratories.

About the image | A white pine standing off Wilderness Drive, formerly known as Minnesota’s tallest. Photo: Jonathan Schilling

 

Posted 
November, 2021