Lichens are a composite organism created from a symbiotic partnership between a fungus and an alga or cyanobacterium. The fungus provides the physical structure and protection, while the alga, through photosynthesis, produces the food for both partners. This cooperative arrangement allows them to colonize some of the most extreme environments on the planet. The Arctic tundra, with its harsh winds and freezing temperatures, is one such place where these organisms are a fundamental part of the landscape.
Survival in Extreme Conditions
One of the most significant adaptations of lichens is an ability known as poikilohydry. This allows them to endure long periods of drought by losing nearly all their cellular water and entering a dormant, dehydrated state. When liquid water becomes available again, from melting snow or rain, they can rehydrate within minutes and resume metabolic functions.
This resilience is complemented by their capacity for low-temperature photosynthesis. The algal partner within the lichen is capable of producing energy in very low light conditions and at temperatures just above freezing. This is an advantage in the Arctic, where the growing season is short and sunlight can be weak. Photosynthesis can occur even when the lichen is frozen, as long as there is sufficient light and the internal temperature rises slightly.
Their slow growth is a survival strategy. In an environment where nutrients are scarce and the window for growth is brief, lichens conserve energy by growing at a glacial pace. Some Arctic species grow less than a millimeter per year, an adaptation that allows them to persist for centuries or even millennia in a landscape where faster-growing organisms cannot gain a foothold.
Key Arctic Lichen Species
Among the lichen species in the Arctic, a few are prominent and illustrate the different ways lichens grow. One recognizable species is Reindeer Lichen, known scientifically as Cladonia rangiferina. It forms extensive, pale, sponge-like mats across the tundra floor. This species has a three-dimensional, branching structure that resembles a small shrub, a growth form categorized as fruticose.
Map Lichen (Rhizocarpon geographicum) exemplifies the crustose, or crust-like, growth form. This species appears as a bright, yellow-green stain growing tightly against rock surfaces. Its appearance is characterized by distinct black lines that separate adjacent colonies. These lines, which are the edges of the fungal body, create patterns that resemble the borders on a map, giving the lichen its common name.
Role in the Arctic Ecosystem
Arctic lichens are foundational to the region’s ecosystem. Their primary role is as a food source, particularly during the harsh winter months. Caribou and reindeer depend almost entirely on lichens for sustenance when other vegetation is buried under snow. These animals use their hooves in a behavior called “cratering” to dig through the snowpack and access the nutritious lichen mats below.
Lichens also function as pioneer species, initiating the process of soil formation on bare, rocky ground. They are the first organisms to colonize such inhospitable surfaces. The weak acids they secrete over time begin the slow work of breaking down rock. As older lichens die and decompose, they contribute the first layer of organic material, paving the way for mosses and eventually other plants to establish themselves.
Because lichens absorb water and nutrients directly from the atmosphere, they are highly sensitive to airborne contaminants. This sensitivity makes them effective bioindicators of air quality. The health, abundance, or disappearance of certain lichen species in an area can signal the presence of pollutants like sulfur dioxide and heavy metals. Their condition provides a direct measure of environmental change in the otherwise remote and vast Arctic.