Being a forest ecologist is not for the faint of heart. Dangling 50 feet above the ground, Dr. Korena Mafune, a researcher at the University of Washington, is attached to a massive tree with only the essentials: a few ropes, a helmet, and the indomitable human spirit. She is on an adventure into the brilliantly green leafy canopy of an old-growth forest. Such adventures are treacherous, one wrong move could send you plummeting on to the unforgiving forest floor. To add to the situation, Dr. Mafune studies soil which is literally the job you can expect to be most rooted to solid ground. But what she and her team of researchers have discovered in the forest trumps any fear of heights.
Olympic National Park in Washington, U.S. is home an impressive array of old-growth trees so massive that they dwarf the hikers passing by. In 2011, a pacific silver fir took home the punny ‘Olympic’ record for tallest tree at a height of 220 feet. These are most definitely not your everyday backyard climbing-trees. So, what is a soil ecologist doing on the end of a rope 50 feet in the air?
When leaves in the top layer of the forest, or canopy, die, the complex network of branches below them traps some leaves before they can reach the ground. As the trapped leaves decompose, a layer of rich, fertile soil forms high above the forest floor. This is known as ‘canopy soil’. Dr. Nalini Nadkarni, a pioneering canopy soil researcher at the University of Utah, was one of the first to realize the potential for this elevated garden bed. In a 2022 interview with the podcast Radiolab, Dr. Nadkarni describes peeling back layers of moss on tree branches and discovering earth that “could be the soil that’s in your backyard garden.” Once Dr. Nadkarni realized the “kaleidoscope of life” that could be found in canopy soil, the research possibilities were endless.
However, all is not entirely well for the trees that house these sky gardens. Droughts, wildfires, and extreme climate events are threatening the survival of old-growth forests in the Pacific Northwest. Even without disturbances at play, the forest floor environment is over-crowded and low in the essential nutrients that trees depend on for survival. But new research is hopeful that trees have found a way to combat threats with the help of their own miraculous canopy soil.
Here, we return to the tree-climbing Dr. Mafune. In a recent study, she and her team of researchers showed that an incredible diversity of fungal species live in close partnership with the tree roots that tap into canopy soil. These roots are smaller than those in the forest floor, growing out of branches as ‘bonus roots’ to take advantage of the rich canopy soil. Fungal species from the same group as your grocery store mushrooms help these roots take in nutrients efficiently, allowing them to be resilient against the tough times on the ground. Think of canopy soil as an ‘emergency snack pack’ for the tree. Dr. Mafune’s team was also able to discover fungal species in the canopy soil that do not exist on the forest floor, opening up new questions about what these species are contributing to old-growth forests.
Standing on the ground looking up into the tree canopy, most hikers or naturalists would never assume a lush garden of life exists way beyond what the eye can see. Yet this environment may be the most important of all for the giants of the forest. In a 2009 TED Talk, Dr. Nadkarni explains that our connection with nature allows us to touch “the most deep and important parts of ourselves.” Third-year biology student Meg Sarty says that learning about something so “old and solid” as an old-growth tree adapting to survive is an “amazing motivator to keep learning[…], the surprising discoveries are always the most special.” A difficult trip up to the canopy to see what was hidden from a perspective on the ground teaches us that growth can come in abundance from unconventional sources. No doubt, this is a feeling Dr. Mafune must have understood when dangling from the tree. There is always something wondrous if we look where we did not expect.
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Cool!