Mistletoe is probably what's up in the tree
What is the pale green moss-like stuff that is growing all over the deciduous trees in the region? I see great swaths of affected trees between Shady Cove and Crater Lake and recently noticed the stuff encroaching on some evergreens, as well. It can also be seen on the hills driving north on Interstate 5. Is it killing the trees or making them more susceptible to fire? If so, can it be stopped?
— Betsy, Ashland
Well, Betsy we at Since You Asked Central have always taken a lichen to answering questions about moss and took your poser to Kristi Mergenthaler, a botanist with the Southern Oregon Land Conservancy, and it was a bit of a stump for her.
Mergenthaler couldn't think of any mosses like the one you described, Betsy, which led her to believe you are likely viewing mistletoe.
Oregon mistletoe, most succinctly. It's a partial parasite — meaning it gets some nutrients from the sun and others from the host tree — that's native to the region, and it certainly grows well here on oak trees.
"People look at it and say, isn't that bad?" Mergenthaler says. "But it's a natural part of our ecosystem. It's just not as beautiful as some other partial parasites like Indian paintbrush and Indian plume."
Besides, Mergenthaler says, mistletoe berries are an important food source for robins and bluebirds in winter.
As for mistletoe's impacts on wildfire? Mergenthaler says there's not much research on the subject, except one laboratory study showed that mistletoe didn't germinate well in smoky conditions.
If it's not mistletoe that you're asking about, Betsy, and that what you describe is moss, well, "don't be worried about moss," Mergenthaler says. "They're a natural part of our ecosystem, too."
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