California is home to several native species of mistletoe (Phoradendron spp. and Arceuthobium spp.), which are not to be confused with the few unfortunate occurrences of the non-native European mistletoe (Viscum album) found in Sonoma county. European mistletoe was introduced to Sonoma county around 1900, ironically by the great horticulturist, Luther Burbank. It is not terribly host-specific, meaning it will grow happily on a wide variety of plants, but it seems to be relatively contained to one small area north of the San Francisco Bay. The vast majority of the mistletoe across California is exactly where it is supposed to be, contrary to what most of us have heard.
With that bit of confusion out of the way, my aim today is to dispel the myth that mistletoes - our native Californian mistletoes - are bad, and to hopefully make a convincing argument for their great value in the ecosystem. (Aside: the same can be said for poison oak. Marvelous plants all around!)
American mistletoe (Phoradendron leucarpum) is the species of mistletoe you're most likely to encounter in California (outside of the deserts and high Sierra, where you will encounter desert mistletoe (P. californicum) and juniper mistletoe (P. juniperinum), respectively). One noteworthy subspecies of American mistletoe found in California is oak mistletoe (P. leucarpum tomentosum), a plant of great importance in our oak woodlands.
Clumps of mistletoe provide food and shelter for a number of species and oak mistletoe is so valuable it may be considered a keystone species in oak woodlands. (Keystone species are defined as those that have a disproportionately strong effect on the rest of the ecosystem, relative to their abundance.) Mammals, birds and insects rely so heavily on mistletoe that according to Kate Marianchild's book, Secrets of the Oak Woodlands (a book I highly recommend to all Californians!), removing mistletoe from an ecosystem results in the loss of one third of the ecosystem's animals.
Winter is the ideal time to scout for mistletoe, since the large, dense clumps are the only leaves left on bare, dormant trees, and beginning in December, bright white berries ripen. Winter is when this plant really shines!
It is true that mistletoe does grow on trees. Seeds are planted on branches by animals, and root-like structures (called haustorium) grow into the tree. Mistletoe takes some minerals and water from host trees, but also produces some of its own food through photosynthesis, like any other respectable plant. As such, it is considered hemiparasitic, much like paintbrushes and owl's clovers (Castilleja spp.). And yet, none of us complain about those cheery wildflowers!
But, as you are beginning to learn, there is much to love about mistletoes as well! The benefits these plants have on entire ecosystems are immense.
Wildlife feeds voraciously on the nectar, fruit and leaves of mistletoe (which are all toxic to humans). When few other food sources are available, the small white-ish berries provide a source of winter food for nearly thirty species of birds, as well as squirrels and ringtails. (A handful of those birds are: western and mountain bluebirds, phainopeplas, cedar waxwings, robins, quail, flickers, scrub jays, thrushes, thrashers, warblers, juncos and goldfinches.)
Bullock's orioles and phainopeplas sip nectar from inconspicuous mistletoe flowers, alongside great purple hairstreak butterflies which lay their eggs exclusively on the leaves of our native mistletoes.
Squirrels, mice, chipmunks and porcupines eat nutritious mistletoe leaves directly from the plants high in the canopy, while deer, elk and pronghorn browse beneath mistletoe-bearing trees for fallen leaves.
Dense clumps of mistletoe provide shelter for birds and mammals, and some species, like white-tailed kites, black-throated gray warblers, wrens, chickadees and bushtits, build their nests in them. Spotted owls also nest in these "witches' brooms," as the thick, tangled masses of mistletoe branches and leaves are sometimes called. I have read that nifty, seldom-seen critters like porcupines, martens and flying squirrels can be found curled up in mistletoe balls during the winter, seeking shelter from the cold.
|An American Robin sits on its nest constructed in a "witches' broom," or clump of mistletoe, one rainy spring day along|
the Stanislaus river (San Joaquin county)
Research indicates that mistletoe is not as harmful to healthy trees as once believed. The growth rate of mistletoe is quite slow, so it steals negligible amounts of water and minerals from host trees. However, during extended drought (a familiar thing in California) trees may become stressed if they are losing water to multiple clumps of mistletoe. This may result in the death of trees that are genetically weaker and less tolerant of dry conditions, improving the gene pool over time - a benefit in disguise. I'm also surmising that our imported ornamental trees, so often planted in city landscapes and victims of mistletoe infestations, don't get along well with our native mistletoes, not having "grown up together," so to speak.
Additionally, let us remember that standing dead trees and snags, cavities left behind where dead limbs have broken off, and fallen logs on the ground are all essential parts of the ecosystem, providing valuable habitat for cavity nesting birds (swallows, bluebirds, screech owls and the like) as well as mammals, reptiles and amphibians. One National Wildlife Federation source I read stated that a forest with mistletoe, and therefore branches and trees killed by mistletoe, supports three times as many cavity-nesting birds than a forest devoid of mistletoe.
If you find yourself beneath a sprig of mistletoe this Christmas, may it remind you of the amazing, awe-inspiring ecosystems that are all around us.