Eating lichens

feeding a diverse group of animals… including humans

Walking along the East Glacier trail one day, I noticed a scattering of gray lichen scraps on the snow next to a small tree trunk whose lichens were the source of the scraps. Some small creature had ripped off much of the lichen, leaving the bits on the snow. A narrow groove led away from the lichens to a small burrow that led down under the snow blanket. That made me think a shrew had been rooting around in the folds of the lichen for insects or spiders, but it was also possible that a small vole had been selectively feeding on the lichen itself.

A few days later, on the Spaulding Meadow trail, I was following some deer tracks, to see where they were going, when my more observant companion called my attention to where the tracks had come from.

There, not far from the trail, there was a noticeable browse line in the arboreal lichens (witches’ hair or Alectoria) hanging from the tree branches, and underneath there was a multitude of deer tracks. All the Alectoria lichens below a certain height, within reach of a foraging deer, were missing from that patch, although they could be found not far away where the deer had not walked.

These observations made me think about lichens as a food source for animals, and I have a very helpful local lichenologist to thank for some great references (as well as instruction on lichen identification). Some lichens are not very tasty, some are actually very poisonous, many have defensive chemicals to deter consumers, and yet a great many critters eat them, often quite selectively.

Somewhere in the world, lichens are eaten by certain snails and slugs, as well as certain kinds of mites and moth larvae; some of these consumers actually specialize on particular kinds of lichen. Although lichen-eating invertebrates have not been well studied in Alaska, we do have a local snail or slug that grazes on the outer layers of leafy lichens. (Recall that a lichen is a composite of a fungus and an alga or bacterium—and some lichens have all three components). Occasionally, if you look closely at the leafy lichens, you might see tiny white trails on the greenish or brownish lichen surface. These meandering trails reveal the white fungal layer below the outer layer, showing where a snail or slug has scraped off the nutritious outer layer that includes the algae or bacteria that also make food for the lichen.

We know a bit more about vertebrates that probably or actually do eat lichens in Alaska.

Caribou are surely the most well-known consumers of lichen all across the North. They use their hooves to dig craters in the snow so they can reach terrestrial lichens, particularly the shrubby, branching ones such as Cladina (reindeer lichens), Cetraria (Iceland lichens), and Stereocaulon (foam lichens), or leafy ones such as Peltigera (pelt lichens). Where there are trees and arboreal lichens, Alectoria (mentioned above) and Bryoria (horsehair lichens) are favorites. Caribou eat lichens all year long, but especially in fall and winter; in spring and summer they consume more willows and herbaceous plants. Apparently, their digestive enzymes change with the seasons, becoming better able to deal with lichens in winter. But lichens are mostly carbohydrate, with low values of protein, so caribou have to find some other source of protein or a means of coping with low levels of nitrogen.

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Reindeer lichen. Photo by Pam Bergeson

Some reports indicate that each caribou has to consume ten or twelve pounds of lichen per day, so a whole herd can make big inroads into lichen populations. Intensive caribou grazing can wipe out whole communities of such lichens, leaving only the low-growing or crust-like ones, and it can take decades for the lichen community to be restored. The most famous example concerns the introductions of reindeer (Eurasian caribou) to St Paul Island in the early 1900s. From just a few animals, the population grew by leaps and bounds, and they ate up virtually all the edible lichens, so their population crashed dramatically. They truly ate themselves out of house and home.

 

In Southeast, Sitka black-tailed deer eat arboreal lichens, as we observed, and so do moose. When mountain goats descend from the peaks into the forest in the winter, they eat arboreal and leafy lichens; in the alpine zone in summer, they may eat branching, terrestrial lichens.

 

There are several species of red-backed voles in western North America and two of them are known to eat both arboreal lichens and branching, terrestrial ones; I found no reports specifically for the species that occurs in Southeast, but it is likely that this species does also. Flying squirrels are important consumers of arboreal lichens (as well as using them to build nests).

 

All these lichen-eating animals are important parts of the ecosystems of Southeast, so it is useful it is useful to consider a few of the ecological interactions that ramify from this lichen base. Some lichens accumulate certain organic pollutants, which are then passed on up the food chain to caribou and deer, and thence to predators such as wolves and humans, where the pollutants become concentrated. Industrial pollution and extensive logging can devastate lichen communities, drastically decreasing the food supply for all of the many consumers. Loss of this important food supply has repercussions in many directions: for example, flying squirrels and voles also eat truffles and disperse the spores when they defecate; truffles are mycorrhizal, making nutrient exchanges with the roots of many trees and supporting healthy tree growth. Caribou, moose, and deer help support predator populations (predators that also prey on other species such as hares and salmon); the browsing of these herbivores can alter plant communities and affect the reproduction of shrubs such as willows and blueberries, which in turn affects bumblebees (that feed on willow and blueberry flowers and go on to pollinate many other kinds of flowers) and birds and bears (that eat blueberries and disperse the seeds).

 

Humans, too, have made extensive use of lichens as food. Indigenous people of the North ate partially digested lichen from caribou stomachs; this material was mixed with fish eggs to make what was considered to be a delicacy (presumably an acquired taste?). In some parts of the world, lichens have been fed to domestic animals, including pigs, dogs, sheep, and cattle, and humans themselves have used lichens as flavoring, thickener for soups, and emergency food.

 

Historically, the biblical manna from heaven, which is said to have sustained the migrating Hebrews in the desert, could have been one of the so-called vagrant lichens, which grow loosely on the ground and can be blown hither and yon by a wind. Many things have been called ‘manna’, including plant resins, honeydew from scale insects and aphids, and certain mushrooms, but vagrant lichens seem especially plausible as the biblical manna, because they would take up water (and expand) after a rain or morning dew, and they can accumulate in some density after a wind (and dew, rain, and wind are all mentioned in one biblical account or another, in association with the appearance of manna). Lichen-manna is quite edible (to humans, camels, and sheep in the Old World, as well as pronghorns in the Idaho high desert) and can be made into bread, but some reports say that it should be eaten in small quantities.

Although lichens seldom claim much of our attention, it should be clear from these considerations that they should not be neglected!

Lichens

often-ignored beings

Our coastal rainforest is characterized by a rich assembly of lichens. Lichens colonize rocks – including the rocky intertidal zone, logs and fallen branches, and even bare sand. They also adorn the trunks and branches of trees. Some branches support numerous kinds of lichens in a sort of miniature garden, of varied colors and textures, often very beautiful.

What, then, are these often-ignored beings? The traditional view is that a lichen is a happy collaboration of a fungus with one or two kinds of alga: a green alga or what was called a blue-green alga, now known as cyanobacterium. Only certain kinds of algae associate in this way with fungi, and only some fungi make these associations with algae. Lichens have been used as classical examples of natural symbiosis (living together), in which the alga provides carbohydrates (by photosynthesis) and sometimes nitrogen (by the cyanobacteria) to the fungus and the fungus provides a protected habitat, water, and perhaps minerals to the alga.

The reality, however, may not always be quite so bland. When the fungus reproduces by spores, which germinate to form a new individual fungus, the new fungus eventually captures algal cells (thus becoming a lichen) and exploits them until they die. Although most lichenizing fungi can live for some time without algae, the algae apparently can live quite well on their own and getting captured by a fungus may not be entirely beneficial from the algal point of view. Thus, many lichens may be viewed as a sort of controlled parasitism of the alga by the fungus. One researcher even commented that sometimes the algae ‘escape’ from the fungal grasp!

The relationship between fungus and alga may vary with circumstances, but the factors controlling that variation remain to be described, it seems. Whatever the precise relationship between the two (or three) different organisms that constitute a lichen, the ecological roles of lichens are important and widespread.

Lichens are important stabilizers of bare ground; in some situations, they help reduce erosion. Indeed, they are said to be the dominant form of ‘vegetation’ on eight percent of the land surface (think especially of Arctic, Antarctic, and alpine areas). They also—very slowly—break down rocks, mostly by secreting acids that weaken the rock, and thus they contribute to the long-term weathering process that creates soil.

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Crustose lichen on rock. Photo by Bob Armstrong

Ground-dwelling lichens (and mosses) trap wind-blown dust; the dust and associated nutrients, along with nutrients from rainwater, gradually build up soils. Then wind-borne seeds and spores have a good habitat for germination. Lichens containing cyanobacteria can extract nitrogen from the air and make it usable by plants (this is called nitrogen fixation). Foresters in some regions have even encouraged lichens to spread (for example, over a recent burn), in order to improve the soil and make new trees grow better.

Tree-dwelling lichens also extract lots of nutrients from rainwater and fog, and many of our common arboreal lichens are good nitrogen-fixers. Nutrients from these lichens eventually find their way into the soil. For example, we often see, on the ground, fragments of lichens that have been torn from the trees by a stiff wind. When these decompose, their nutrients are added to the soil.

Lichens provide shelter for numerous tiny animals, such as springtails and mites, which are food for spiders and insects, which in turn are food for shrews and birds. We often see warblers, chickadees, and woodpeckers searching among the lichens on branches for lurking insects or spiders.

Caribou have been called lichen specialists. Lichens comprise much of the caribou diet—as much as ninety percent in winter but even in summer about half the diet is lichens. The ground cover commonly called ‘reindeer moss’ is really a lichen. Caribou were introduced to St Matthew Island in the Bering Sea some decades ago; the herd increased rapidly but eventually ate up most of the lichens, which grow too slowly to compensate for the rate of eating them, and thousands of caribou then died of starvation.

Arboreal lichens provide important food for woodland caribou, elk, black-tailed deer, and moose. Mountain goats in our area eat lichens all year long, including several types that grow on trees. Northern flying squirrels and boreal red-backed voles eat a lot of lichen; arboreal lichens may constitute as much as ninety percent of the winter diet of flying squirrels. The flying squirrels also use horsehair lichens to build their nests inside of tree cavities.

Dozens of species of birds incorporate lichens in their nests. I once found a crossbill nest that had blown out of a tree. The outside was made of lichen-covered twigs; in fact, an expert later identified many kinds of lichen in this nest. Hummingbirds commonly decorate the exterior of the nest with bits of leafy lichens, which help camouflage the tiny nest.

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Rufous hummingbird nest. Photo by Katherine Hocker

Humans in many cultures have found uses for lichens—as food, fiber, medicine and poison, dyes, decoration, and, in some parts of the world, as perfume. Many kinds of lichen can be eaten; only a few are poisonous. However, they are said to be not very flavorful, at best and are better eaten after boiling in several waters to reduce bitterness or with soda to reduce extreme acidity. The lichen known as rock tripe is famous as a survival food for Arctic explorers. Arctic Natives ate the partially digested lichens from caribou stomachs; this stuff is apparently more readily digested than fresh lichen. Mixed with raw fish eggs, it reportedly formed a favorite concoction (an acquired taste, no doubt!).

Over the centuries, lichens have been used as medicines in various ways, both internally and externally. Some of the rationales for medicinal applications seem ludicrous to us now. For example, lungwort was used to treat lung diseases because its lumpy surface reminded people of lung tissue. However, it turns out the lungwort actually does contain substances that work against TB bacteria. The basis for using a yellow-orange rock lichen to treat jaundice, which turns the skin yellow, is still more tenuous.

Beard lichens contain usnic acid, which has some antibiotic properties. So beard lichens have often have been used in ointments to treat skin infections and sores. Indeed, they have been over-collected in some regions, to the point that they are scarce and hard to find. However, some people are very allergic to this acid, so medicines with this as an ingredient must be used with care.

Fibrous lichens were used in clothing by some Native cultures, mixed with bark fiber. Because such garments were not very durable, they were often restricted to ceremonial use. Branching, shrubby lichens are used in floral arrangements and architectural models to represent shrubs and trees.

Lichens have provided dyes for centuries: in our region they have been used to color mountain goat wool and porcupine quills. Prepared in boiling water, certain lichens yield russets, brown, and yellows. Others yield reds and purples when fermented with a source of ammonia (traditionally, this was stale urine—the aroma eventually dissipated).

An unusual use of lichens is directly applicable in our area. Crustose lichens generally grow slowly, less than a millimeter a year. By measuring lichens on dated (and undisturbed) gravestones, one can estimate the average rate of growth. Then if that estimate is applied to the same kind of lichen on rocks near a glacier or a rock slide, it is possible to estimate how long that rock was available for colonization by lichens; that is, how long it has been there.

Humans have a huge impact on lichen populations and communities. The most obvious is habitat destruction through increasing urbanization. Directly relevant to our area is the dramatic loss of tree habitat when old-growth forest is logged. Second-growth stands support only a much-reduced diversity of lichens.

More pervasive is the dramatic effect of air pollution on lichens, many of which cannot tolerate the pollutants poured forth from industrial processes. Sulfur dioxide is an example of a deadly pollutant, but excess amounts of lead or zinc, for example, could also be detrimental. Some of the most pollution-sensitive lichens include the beard lichens and those that contain cyanobacteria (for instance, lungwort and kidney lichens). The trunks of our red alder trees often look white or grayish, but this is actually a white crustose lichen; in areas with serious air pollution, this lichen dies and the trunks show their brown bark. Because of their sensitivity to air pollution, lichens are extremely useful as indicators of air quality.