Wednesday, November 29, 2006

Mistletoe


On the park's southwest edge, the sycamore sticks out like a sore thumb. With all the leaves gone, the infestation of mistletoe high in the sycamore's canopy is evident. Long held to be a true parasite, a destroyer of trees, mistletoe is a welcome sight in southeast Missouri.

Last winter when I saw the first plant, I called my boss, the Chief of the Natural History program, to let him know it was here. He was delighted and asked me to take pictures for documentation. It's an obligate plant in the southeast U.S. and its presence here represents Missouri's southeast U.S. heritage. Mistletoe is actually a hemiparasite, a plant that uses the host tree for water and minerals but manufactures its own food by photosynthesis. It doesn't necessarily kill healthy trees, but when the root system of mistletoe weakens high canopy branches, it causes leaf loss, which is incidentally what Chief wants to see: breaks in the canopy that allow light to hit the forest floor. Phoradendron flavescens is only known from a few counties in Missouri. It's range is the embayment, east to Virginia, then west to the Current River drainage along the Arkansas border. Worldwide there are roughly 1400 different species of mistletoe.

Mistletoe, named after the Anglo-Saxon words "mistel," meaning dung and "tan" meaning branch, is spread by birds. Waxy white berries borne on the female plants are particularly tasty to thrushes and cedar waxwings. As birds feed on the berries, they excrete the seed in tact onto another branch, where it attaches with slight, sticky hairs. The root system of mistletoe breaks through the tree bark and pierces the living tissue where it derives water and minerals to help the plant grow. Agencies concerned with timber harvest and fruit production describe terrible "outbreaks" caused by mistletoe. The plant only grows on certain species of deciduous trees, including elms, tupelos, sycamores and, in Florida, pecan trees.

Research has shown that infestations tend to occur in monoculture plantations, where all the trees are of the same size and age class, and in areas that have been clearcut but for a couple of trees. In healthy woods with a developed midstory and understory, birds have plenty of perching sites and the chances are slim that all of the perch sites will be the trees that mistletoe requires. Mistletoe is a lot like poison ivy: people hate it because they think it kills forests, but both plants are integral parts of a healthy forest. Mistletoe and poison ivy produce high quality food for wintering birds and we probably wouldn't have as many thrushes without them.

Every year around Christmas, Daddy and I used to head out to the woods to blast mistletoe out of the oaks with shotguns. We'd distribute bundles of the evergreen plant to neighbors to hang above their doorways. This tradition is only loosely based in Scandinavian culture, wherein Vikings represented the goddess of love, Figga, with bundles of mistletoe hung above their doors. The plant represents eternal life and love because it remains green throughout the year. Nevertheless, Daddy and I never really thought about the impact we were inflicting on the mistletoe population when we shot it down in large clumps. But, in fact, we weren't making an impact at all. Even without the green parts of the plant, mistletoe lives in the tree until the host branch dies. And that probably explains why we went back to the same place every December with a box of shells.

2 comments:

Anonymous said...

Just spotted some in Hollister, MO along Tablerock Lake

Allison Vaughn said...

I wrote this post over ten years ago, long before the major effects of climate change were availing themselves. To find mistletoe at Table Rock is certainly notable--used to be relegated to the bootheel, but must be moving up from Arkansas. Thanks for the notification. I wonder what species it is? Just across the border is the southeast Louisiana species--if that's in Missouri now, it can also explain why I saw a Forsythia in bloom today at Lake of the Ozarks and my daffodils coming up. Sad times.