Most soil scientists spend their time looking down at the ground, but those at West Virginia University’s Division of Plant and Soil Science are looking up. Research by Jennifer Kane, a post-doctoral scholar, doctoral student Ronald Schartiger, and Ember Morrissey, associate professor of environmental microbial biology in the Davis College of Agriculture, Natural Resources and Design, is adding to what we know about life in the canopy in Washington’s Olympic National Park.
While the idea of soil in the treetops seems contrary, it’s abundant in the park’s old-growth maples.
“The trees that survived a lot of the logging, particularly trees that are in these protected national parks out west, have an accumulation of organic matter in the canopy,” Kane said. “Plants like mosses live on the branches of the tree, and over time they grow and die. A layer of dead organic matter accumulates on the branch that is essentially soil. It becomes a nutrient source for the plants and the tree as well.”
The trees in Olympic are so old, and mosses grow so abundantly, that the soil layer can be up to 10 centimeters deep. This attracts the diverse insects, bacteria and fungi that live in the soil and decompose it. The decomposition process unlocks important nutrients like nitrogen, producing a rich source of sustenance for the tree.
By contrast, the nutrient-poor soils on the forest floor support relatively little life. In response, the bigleaf maples Kane is studying have evolved to grow roots out of their upper trunks.
“These trees have adventitious roots in the canopy, meaning the tree is getting water and nutrients from the canopy soils as an adaptation for the relatively low availability on the ground,” she said. “It’s quite striking to feel the root coming out of the trunk of a tree 50 feet in the air.”
While her colleague, Korena Mafune of the University of Washington, focuses on the nutrient component of canopy soils, Kane said, “My work tries to construct a food web of what insects are up there, what they are eating, how the microbes interact with each other and what it all means in terms of how much diversity is up there and how it affects carbon cycling.”
As one of only a handful of canopy soil scientists, she’s also keeping an eye out for new species of invertebrates.
“There's a good chance—and other papers suggest—that there are undescribed species of invertebrates, specifically in the canopy that we've yet to discover,” Kane said.
According to Morrissey, the canopy functions in different and important ways.
“In addition to harboring biodiversity, it captures a lot of sunlight,” she said. “So that's where a lot of primary productivity in this old-growth forest happens.” New-growth forests, and reforested areas, cannot develop such biodiversity, nor can they act as a carbon sink the way the park’s forest does.
Data collection isn’t simple, as many of the maples are over 150 feet tall. Kane and the team hiked into a private section of the national forest with climbing gear and set up ropes. Climbers took precautions, for their own safety as well as the trees’. Once perched on a sturdy branch, Kane collected soil samples, measured branch diameter and soil depth and recorded the number of different moss species.
“Then we would repel down and talk about how awesome it was,” she said. Branch height ranged from 30 to 80 feet high. While many of the trees sampled were up to 300 years old, others in the forest may be closer to 1,000.
Since returning to WVU, the researchers have been studying the microbial and invertebrate communities in the samples as well as how much nutrient and carbon cycling is occurring.
“We've extracted the micro-invertebrate communities—nematodes and the micro-arthropods like spiders and mites,” Kane said. “We’re seeing interesting trends in how many invertebrates are there and how much nitrogen is in these canopy soils.”
While the trees in Olympic National Park are protected, similar old-growth forests face threats from both logging and climate change, though it’s still unclear how warming temperatures will impact the trees and forest diversity. Kane’s research zeroes in on Olympic National Park’s virgin forest, but it may direct future studies on forest diversity and deforestation. In West Virginia, the extensive history of logging and lack of old-growth trees makes canopy soil an unlikely find, and Kane believes this highlights the effects of deforestation.
“Evidence suggests that there is immense diversity in the canopies of virgin forests,” she said. “The cascading impacts of this diversity loss remain unclear since so few undisturbed areas remain. We want to know how the communities in canopy soil impact carbon cycling so we can better understand what is lost when these trees are negatively impacted by humans. We would love to, in the future, find old trees on the east coast and study the canopy soil there.”
A grant by the Explorer’s Club Washington Group helped fund Kane’s research. The Davis College of Agriculture, Natural Resources and Design envisions a world sustainably fed, clothed and sheltered. To learn more about the Davis College, visit davis.wvu.edu. Keep up with the latest updates and news on Facebook, Twitter and Instagram by following @WVUDavis.
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