Dear Ask The Naturalist,
How can you tell if a lichen is dead? If it normally is green but patches appear grey, has part of it died?
-Scott Warner, Smithville
Answer: A number of California lichen experts weighed in on this one from the California Lichen Society and the USDA Forest Service. I’m afraid to say there’s no easy answer. You kind of have to be a lichen expert, or very knowledgeable about said species, to notice the living from the dead. Lichen are by nature rather mottled and brittle looking.
“The look of dead tissue really varies by climate, decomposers, and lichen species!” said Sarah Jovan, a lichen expert at the USDA Forest Service. “In my experience, the color of the necrotic tissue can be many colors, black, gray, white, or a much darker shade of the lichen’s color while alive (i.e. in highly pigmented lichens, like Letharia).”
Nevertheless, here are some general rules of thumb for anyone who wants to get to know their backyard lichen REALLY well (we know you’re out there lichen-lovers!). White or yellow-bleached looking is common in hot, dry habitats, said Jovan.
Elsewhere, look for a change in color, especially patches of color that differ from the rest.
“I look for parts of the lichen body (thallus) that are colored differently from the rest of the thallus, especially yellow, blackish or yellow-brown colors in a lichen that is not those colors to begin with,” said Tom Carlberg, vice president of the California Lichen Society. “Often the odd colors are separated by a dark zone line. This may not always work for novices, for obvious reasons.”
Of course, there are complicating factors that can trip up any novice — like what’s causing the unnatural coloration. It could be predation. Shelly Benson, president of the California Lichen Society noted that “whitish-gray patches on a green lichen could be areas where the upper cortex and algal layer have been removed (possibly by something eating the lichen), not necessarily an indication that the lichen is dying.”