The air plant niche in North America is occupied by the lichens. Some of these are pendulous – trailing out into the air from the trees. On the foggy Pacific Northwest coast, finely-divided blue-gray Lacy Lichen (1) hangs from the branches like silk draperies. In old growth coastal rainforests, the similarly colored Methuselah’s Beard Lichen decorates the spruces like five meter-long strands of tinsel. These lichens show tints of their green algal symbionts – after they have been revitalized by the rain.
At higher elevations, Wolf Moss occupies the suspended lichen niche. Unlike in the coastal environment, Wolf Moss does not dangle in the breeze. The mountains can experience freezing, gale-force winds. Deeply negative wind chill temperatures can penetrate down to ground level for days on end. That dry mountain air has shaped Wolf Moss far differently than the delicate filaments of the hanging lowland forest lichens.
The mossy texture gives Wolf Moss (Letharia vulpina) its common name (a misnomer, in the same vein as the common name of “Reindeer Moss” – they are both really lichens). Wolf Moss is more accurately known as Wolf Lichen. It grows close on the trunks of the trees, up hundreds of feet into the canopy. It reaches down to the snow line six or ten feet above ground level. Its tight clumps are found in the Sierra and Rocky Mountains, and elsewhere in the Palearctic boreal forests (2). One form of this lichen has “brown eye spots” (spore-forming structures). Brown-eyed Wolf Lichen is a actually related species (L. columbia). Both of these wolf lichens color the shady north sides of conifer trunks chartreuse.
In those forests, the understory is clear. Skylight slanting through the branches falls down the trunks of Jeffery Pine or Red Fir much of the year. At those elevations, the ultraviolet light in the sky is quite bright (UV increases about 20% (cited in: 3) for every mile increase in altitude.)
Wolf Moss contains a pigment that absorbs blue and UV light. The subtraction of blue colors gives this lichen its distinctive yellow hue. The pigment – vulpinic acid – protects the lichen from mutagenic UV radiation (4). The lichen grows very slowly, partly because it commits much of its energy to the synthesis of the pigment. At lower elevations, its slow growth would put the lichen at a disadvantage. Other, faster-growing lichens would out-compete for its space. In the heights, however, where the competitors would be destroyed by temperature extremes and excessive UV light, Wolf Moss fills the niche. It over-flows its space, resulting in a constant yellow-green lichen rain.
Wolf Moss harvests all the nutrients it needs from thin air. Bark and abscised branches sloughed from tall pines carry clumps of lichen foliage down with them. The chartreuse pigment molecules in the lichen are poisonous, so the grounded tangles lie untouched on the forest floor. The bright yellow of their woven strands stands out in the shadows, against the soft browns of fallen bark and pine needles. The lichen tolerates dryness and low light, so it survives on the ground for years – fading only gradually into the humus of the alpine forest floor.
1) The story of Lacy Lichen is told in in depth in chapter 14 of “Between the Rocks and the Stars” (Daubert, S. D., Vanderbilt University Press, 2020, in press)
2) Hogberd, N. et al 2002 Reproduction and molecular genetic variation suggest a North American origin of European Letharia vulpina. Molecular Ecology 11, 1191-1196
3) Flemming, M. 2019 www.weathergamut.com
4) Phinney, N. H. et al 2019 Why chartreuse? The pigment vulpinic acid screens blue light within the lichen Letharia vulpina. Planta 249, 709-718