Within the vast expanse of Portland’s Forest Park, 200-foot-tall conifers soar above hiking paths. Big-leaf maples shade five types of wildlife habitats. Together, they begin to tell the human history of the area, of logging and urbanization and restoration. Among these radiant trees is an equally revealing yet humbler organism whose appearance can range from sewing pins to tattered rags. This organism—a composite of fungi and algae—is lichen.
Among the highest branches of the park’s tallest trees and along the leafy floor, Hannah Prather, now a post-doctoral research assistant at Portland State University, searched for lichens for several years. She did so because it was an inexpensive way to naturally observe local conditions for her doctoral research. Having been an arborist before she returned to school, Prather also chose to research lichens because wanted to climb trees in urban parks, like other researchers who ascend redwoods in old-growth forests. “Lichens are this fungal tissue and are sponges of the environment—sponges of water and air,” Prather says. They get the necessities for survival by absorbing them from their surroundings. If there are heavy metals or other pollutants in the air, they also absorb these. This feature is an important function of a forest ecosystem: When lichen fall to the ground, they release nutrients they’ve absorbed—which some rooted plants need but can’t get otherwise—into the soil.
A hike through Forest Park can reveal lichens in a range of shapes and colors. These include oakmoss lichen (Evernia prunastri), shield lichen (Parmelia sulcate), and lipstick lichen (Caldonia transcendens). Prather finds Platismatia glauca, also known as tattered rag lichen, particularly fascinating for the range of colors and forms it can take, like a branch or a rag, and this species thrives in the park. These lichens become less common closer to downtown Portland or along the waterfront. This is because theses area don’t meet the habitat requirements of lichens, but also because unlike plants, lichen don’t have mechanisms to defend themselves from pollutants in the air.
They are also bad travelers, or “poor dispersers” in science talk, which means lichen have a hard time relocating to newer pockets of nature from established forests. Luckily, they have clung fast to Forest Park, where they slowly release moisture back into the environment—a critical feature for tree microclimates in this warming era—and retain nutrients, contributing to the overall health of the forest’s ecosystem. In response, the park, with its weaving pathways, density of trees, and vertical range of light and moisture, offers welcome respite for humans and lichens alike.
Explore Forest Park with guided hikes led by the Forest Park Conservancy.
forestparkconservancy.org
Take a tour with Prather at the Hoyt Arboretum.
hoytarboretum.org
Hannah Prather gained intimate knowledge of Forest Park as she searched high and low for lichens to find out how they were being impacted by their urban setting for her doctoral research at Portland State University.
Prather’s tips for observing lichens in Forest Park:
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“The best thing about lichen and mosses—I don’t want to leave out the mosses!—is they are a scavenger hunt,” she says. “You don’t have to look far.”
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Keep a lookout for fallen branches, which can feature a range of lichens and mosses that thrive higher up. “That way, you’re not disturbing them,” she adds.
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Do not pull down branches or lichens, as this is unnecessary and harmful to the ecosystem.
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Enjoy lichens in their natural habitat, and then leave them there. Don’t collect lichens. “They’re an important part of the ecosystem,” Prather says. “There’s so much to observe by what has fallen out or what is on different limbs.”
In Prather’s hand are three species of lichens—tattered rag lichen (Platismatia glauca), tube lichen (Hypogymnia physodes), and oakmoss lichen (Evernia prunastri)—all of which can be found in Forest Park.