The secret world of lichen

lichen

A lichenologist’s extraordinary photographs reveal the sublime colours and unexpected configurations of one of earth’s oddest life forms

by Kevan Berg

Sprawl
Lichens typically require bare, undisturbed surfaces and highly specific levels of temperature and light, each of which depends in part on the shape of the host tree. The sparse canopy of the jack pine allows sunlight to pour in, creating suitable habitat for a great diversity of lichen species. More than 10 species of lichens flourish on the jack pine branch here. In contrast, little light penetrates the thick foliage of black spruce trees, but they retain more and longer dead branches in the lower canopy. Here, lichen grows in almost equal abundance but with less diversity. Age is also a factor. Due to painfully slow growth rates, particular bark and habitat preferences, and inefficient methods of dispersal, certain lichens will thrive only on older trees.

From antibiotics to soup
For centuries, people from diverse cultures have used lichen for medicines, dyes, poisons, fibre for weaving clothing and blankets, and food. Pictured here is monk’s hood lichen (Hypogymnia physodes), stretching out above several lobes of variable wrinkle lichen (Tuckermannopsis orbata). Monk’s hood lichen is a common species in the boreal forest of northern Ontario, and was used by the Potawatomi people of Wisconsin as an ingredient in soup and as a cure for constipation. In Scotland and Scandinavia, monk’s hood lichen was used as a brown dye for wool. Today, the lichen is used for its antibiotic properties and is regarded as an important indicator of air quality.

Lichen as sponge
Lichens are highly efficient in the uptake from and exchange of substances with their surroundings. They lack the waxy coating found in leafy plants and therefore can rapidly absorb water and other molecules through any part of their surface. In areas such as this black spruce stand in the boreal forest, where epiphytic lichens are particularly widespread, this sponge-like capability makes lichens essential to nutrient cycling. Lichens absorb large quantities of nutrients from rainwater, thereby influencing the distribution and availability of nutrients in the soil and, in turn, affecting the growth of surrounding plants. Through the release of the absorbed rainwater, lichens can even affect the levels of humidity within the forest.

Family tree
Lichens vary greatly in size, form and colour. Here, the olive-brown variable wrinkle lichen (Tuckermannopsis orbata) holds out its disk-shaped fruiting bodies like horns, trumpeting its supremacy on a black spruce branch. What is the story behind this diversity in appearance? Where do lichens fit on the evolutionary tree of life? Biologists suggest that lichens have not all evolved from a common ancestor, but rather that lichenization – the synthesis of algae and fungus – has occurred independently several times. Lichens are therefore united not by ancestry but through their unique means of acquiring nutrients.

The domino effect
Threats to lichens brought on by climate change will have a cascading effect. In the boreal forest, deer, elk, moose and especially woodland caribou depend heavily on lichens for food. Ungulates forage on stringy and shrub-like lichens, such as pitted beard lichen (Usnea cavernosa) and boreal oakmoss lichen (Evernia mesomorpha), both pictured here on a jack pine branch. Rodents such as the boreal red-backed vole feed on the lichens attached to fallen branches. Insects, spiders, slugs and snails eagerly consume epiphytic lichens. Birds such as gnatcatchers, flycatchers and hummingbirds collect lobes of hammered shield lichen (Parmelia sulcata) and carefully attach them as camouflage to the outside of their nests.

Fool’s gold
Although you would never know it from its name, powdered sunshine lichen (Vulpicida pinastri) is saturated with poisonous acids that are toxic to animals. It was once used in some parts of Europe to dye wool green. Here, a small lobe of V. pinastri stands tall and bright, ringed in the brilliant yellow of tiny reproductive granules.

I am standing within a curtain of jack pine branches in the boreal forest north of Beardmore, Ontario, a small town northeast of Thunder Bay. It is daybreak, and the sky is flecked with the pink and blue brushstrokes of a crisp June morning. At my fingertips is a species of lichen true to its name, the powdered sunshine lichen, or Vulpicida pinastri. Wrapped tightly on a crooked branch of jack pine, the lichen emits a fierce greenish yellow glow, its lobes ruffled and dissolving into powdery clusters as bright as the sun.

I have been studying and photographing the unique world of lichens for about two years. What I find endlessly fascinating about these organisms is the surprising degree of diversity in size, shape and colour, as well as the tremendously complex coexistence of lichen species in so-called lichen communities. I specialize in lichens that grow on trees, and am interested in the factors responsible for the arrangement and abundance of lichens on conifer branches in the boreal forest. I have discovered that if you look very closely at the branch itself, the entangled lichens bear a striking resemblance to the architecture of the host forest.

On the branch of the jack pine, I can see that V. pinastri is only one of many species rooted down within the peeling bark. Fantastically shaped miniature life forms cover the branch. Fishbone beard lichen (Usnea filipendula) towers above the others, its slender, bone-like tendrils twisting upwards and arching with limbs of ragged beard lichen (Usnea diplotypus). Beneath, the thorny and almost impenetrable gorse-like rampart of burred horsehair lichen (Bryoria furcellata) tumbles across the surface of the branch, a spiny barricade through which the thick spongy stems of boreal oakmoss lichen (Evernia mesomorpha) push skywards. Variable wrinkle lichen (Tuckermannopsis orbata) hunkers down at the centre of the array, lobes tough and leathery. And, not unlike the hidden plants of a forest understorey, hammered shield lichen (Parmelia sulcata) carpets the branch base and fans outwards, enveloping the hollow, hooded lobes of monk’s hood lichen (Hypogymnia physodes).

Another lichen oddity: the branch on which this colourfully tangled congregation occurs is dead. How can something grow without a fertile surface? Lichens are “fungi that have discovered agriculture,” writes lichenologist Trevor Goward. It works like this: A lichen is a partnership between two or more non-plant organisms, one of which is a fungus that acquires water and nutrients from rain and dust. The other half of the partnership is a colony of algae (or sometimes cyanobacteria) that produces food through photosynthesis. In working together, the algae and the fungus create a tiny self-sustaining ecosystem. The fungus is the dominant partner and architect in this relationship, and constitutes the external structure of the lichen within which it shades and protects the algal cells and provides them with water and nutrients. In exchange, the fungus receives a steady supply of sugars and other carbohydrates from its algal partner, sometimes drawing so much that the algae barely survive. The lichen endures only because algae reproduce more quickly than the fungus can starve them – an arrangement that, from the vantage point of the algae, could be characterized as a kind of “controlled parasitism.”

As calamitous as this arrangement may seem, the partnership has been a remarkable success. There are some 14,000 species of lichens worldwide, inhabiting almost every kind of surface and occurring in almost all terrestrial environments. The lichens under scrutiny on the pine branch are classified as epiphytic lichens, meaning that they grow primarily on trees. Epiphytic lichens flourish in Ontario’s boreal forest, a landscape that is wet but cool, and thick with spruce, fir and pine. This unique life form plays an important role in the functioning of the ecosystem. Lichens constitute a significant proportion of the biodiversity of the forest, aid in the cycling of nutrients and provide an abundance of food and habitat for birds, mammals and invertebrates. Certain epiphytic lichens also serve as some of the most sensitive indicators of environmental change in the forest. Due to almost imperceptible rates of growth, as well as fastidious habitat and dispersal requirements, lichens are extremely susceptible to both incremental and sudden changes in their surroundings. For example, clearcutting produces dramatic and instantaneous changes in temperature, moisture, humidity and exposure to light, thereby weakening many lichens growing along the perimeter of a clearcut.

Incremental changes to lichen habitat occur as the forest adjusts to fluctuations in moisture and temperature associated with climate warming. As the range of boreal tree species shifts northward with climate change, lichens specific to these trees will likely decline in health and occurrence if their slow growth and dispersal limit their ability to keep pace with the northward shift of their host trees. Close monitoring of these changes will make lichens increasingly valuable as indicators of the rate and direction of climate change.

More about lichen
So common they are often overlooked, lichens are one of the most remarkable life forms on earth. To learn more about the mysterious ways of these organisms, visit the websites Lichens of North America at www.lichen.com or Lichenland at ocid.nacse.org/lichenland. Through the Toronto Lichen Count website at www.citizensenvironmentwatch.org/tlc, you can take part in a research project that uses lichens to monitor air pollution and climate change.

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