“For diversity, the Ozarks blow the rest of the United States away,” Ladd says. The region supports about 30 species of crayfish, including one that is blind and lives in caves; the Ozark hellbender, one of the world’s largest salamanders, which can attain a length of nearly two feet; the Ozark crocus, found mostly in the Current River Basin; and nearly 150 distinct species of tree. Within the dominant oak-hickory woodlands, one finds a diversity of habitats, from rocky glades inhabited by roadrunners and cacti to wetlands with highly mineralized groundwater—all welcoming spots for lichens to settle in myriad colors and forms. The local diversity and unique geologic history (covered by neither glaciers nor oceans for the past 225 million years, the Ozarks provided refuge for migrating species during the Ice Age) explain the richness of the lichens here: some 600 named species, along with 30 recently discovered ones awaiting their official designation.
Yet for all the diversity of the Ozarks, the region’s natural habitats pale in comparison with the abundance of the past, when more than 4 million acres were covered with old pines, some more than 100 feet tall and almost four feet thick. The forests vanished in the late 19th and early 20th centuries with the settlement of the relatively treeless Great Plains, where houses and fences were constructed largely from those once-grand woods. The Ozarks have continued to change as agriculture and grazing decimate stands of giant cane, impacting animals from swamp rabbits to warblers. Although past scientific ignorance of lichens makes it difficult to determine whether they have been impacted as well, at least one species, Umbilicaria mammulata, has not been seen in the region since the 1920s.
The story of vanishing biomes is now all too familiar, but lichens can issue a warning before destruction occurs; they can also signal an environment on the mend. Many lichen species are exquisitely sensitive to air pollution and other environmental changes, so their absence, presence, or health may be able to tell us what is happening to an ecosystem. In fact, lichens are enlisted in North America and Europe as one of the fastest and cheapest means by which to assess pollution levels. On the other hand, the hardy lichen partnership between fungi and photosynthetic microbes has withstood the vicissitudes of time. Scientists believe lichens were among the first living things to try their luck on dry land some 600 million years ago, 200 million years before the first plants arrived. Lichens are often among the first green things to colonize a harsh territory (as happens frequently after volcanic eruptions in dry climates), and hardy species pioneer damaged environments as soon as conditions allow. During certain seasons in the Arctic, caribou survive by eating reindeer lichens. Other varieties of lichen provide more than 90 percent of the winter and spring diet for northern flying squirrels in parts of Oregon and Idaho. The Northern Parula, a warbler common in the Ozarks, depends on old man’s beard to build its nests.
The significance of lichens probably runs even deeper than these scattered examples suggest. More than 600 organic compounds isolated in lichens have been found nowhere else in nature. Lichen-derived substances have been used as antibiotics and other drugs. Some lichens produce toxins that might serve as natural pesticides; one genus, Vulpicida, was once used in Scandinavia to poison wolves. Although they make up a small fraction of the Ozarks’ biomass, lichens hold a disproportionate number of its nutrients. That is partly explained by the cyanobacteria, which convert atmospheric nitrogen to the nitrate building blocks essential for plant growth and the overall food chain.
Some lichens release a chemical that breaks rock down, helping produce fresh soil. Some can survive drought for more than a year, siphoning moisture and nutrients from the air while clinging to bare rock, vertical expanses of tree bark, desert sand dunes, and even plastic, glass, and decaying cars. Vagrant lichens live loose on the ground, rolling freely with the wind. Other species adhere to specific rocks; Phoebus hydrophobias forms orange patches the size of silver dollars under ledges of dolomite. “You can often tell what kind of rock you’re looking at by the lichens,” Ladd says.
And lichens are forever, or just about. They can live hundreds, even thousands of years, and sometimes they grow so slowly they may advance only a few millimeters a century—an inch or two per millennium. Scientists can therefore use lichens to date ancient rock slides and gauge the pace of retreating glaciers. These techniques form the basis of a little-known way of reckoning time called lichenometry.
It took a while for me to grasp the full significance of my surreal tour through the Ozark woods. Lichens are a part of almost every wilderness scene, hiding in plain sight. Because certain species favor the lee side of a tree, you can sometimes change the color of a forest just by shifting the angle of your gaze. If you look at a landscape dominated by a bluff, you may still be seeing the colors of lichens just as surely as you do in the glimmering trees. Lichens cover the land like paint.
I thought I was taking in the subtle hues of the cliffs along the White River, but I was really admiring the layer of life covering them. Lichens stipple landscapes of granite, blanket the ground like snow, and drip from tree branches as if they were tinsel. Chances are, wherever you look, lichens color your natural world too.