San Bernardino Mountains, CA, June 7, 2014 – According to an old Scandinavian Christmas custom, a couple who meets under hanging mistletoe is obliged to kiss. But mistletoe’s function in the forest is actually less romantic: as a parasite, it attaches to the branches of a host tree or shrub, and absorbs water and nutrients from the host plant.

There are six different species of mistletoe in the San Bernardino Mountains. Its presence is spotty in the Big Bear area, but hikers have noted species-specific mistletoe on Western Junipers near Onyx Summit and along the PCT. Experts say this “background level” is acceptable; it’s when it becomes epidemic that it’s a problem–and that’s the case just outside Big Bear. In fact, there’s a dedicated group of volunteers calling themselves the Mistletoe Warriors who remove overly dense clusters of mistletoe from native Black Oaks in the Keller Peak region near Snow Valley resort, to maintain and improve forest health.

If it flourishes too much, mistletoe can devalue natural habitat, but it’s not all bad. It’s been recently recognized as an ecological keystone species. Its dense branching stems provide roosts and nests for owls, and its juicy berries feed winter birds. Three different kinds of butterflies are completely dependent on the mistletoe, and bees find it an important source of pollen and nectar. And although its toxic to humans, other mammals–squirrels, chipmunks and even deer–can eat its leaves and shoots.

So does this parasite have a good relationship with it’s fellow forest dwellers? It’s complicated. While too much of the moocher can kill trees, a study of mistletoe in junipers showed that more juniper berries sprout in stands where mistletoe is present, since it attracts berry-eating birds that also eat and spread juniper berries.  Interactions like this can dramatically influence diversity, showing that one organism’s parasite is another’s provider.