Welcome to Natural Wonders, where I hope to pique your interest each week by sharing some fascinating questions and answers about natural phenomena. If you’re new here or if someone forwarded you this email, you can subscribe below.
Check out past posts by going here and see who I am and what Natural Wonders is about here.
One of the reasons I love being outdoors in winter is the bare nakedness of the forest. Gone is the underbrush, the leaves disguising branches, the shrubs and vines filling the forest floor. Instead, the woods feel expansive, open; just the skeleton of the forest is evident, with the trees and their bare branches stretching above me. It’s now that I notice the differing shapes of trees – some are squat and rounded, some on the edges of fields lean out into the light, most of them stretch their branches upwards, but some curve into bent shapes as a result of some earlier tree-trauma.
In this bare-bones world, anything green stands out. When I study the treetops, that’s when I notice that some trees have clumps of mistletoe growing in their uppermost branches.
Photo by Heather Wall
I have fond memories of hunting for mistletoe around Christmas-time as a child. Because it grows high up in trees, the best and safest way to retrieve clumps of it is to shoot it out of the tree with a small-gauge rifle. Besides the pieces of mistletoe you retrieve from the base of the tree afterwards, there are also the bragging rights to be had from even a tiny bit of success. Of course, this only works in unpopulated areas, of which we had plenty when I was growing up in the Appalachians.
This year, as I’ve noticed the mistletoe in treetops, I’ve found myself wondering how it gets there in the first place – does it have seeds that blow from one tree to another? If so, why does it often seem that one tree has a few clumps while the neighboring tree has none? Some trees seem to be covered up with it while others have just one or two clumps. How does mistletoe survive – is it a parasite? Is it bad for the tree? I realized I needed to find out:
Does mistletoe harm trees?
It turns out that mistletoe is considered a hemi-parasite, meaning it uses its leaves to produce some food for itself through photosynthesis, but it also sends “false” roots through the tree bark into the growth rings to take nutrients from the host tree. It spreads and grows fairly slowly, and it seems that having just a few clumps of mistletoe in a tree’s branches is not considered to be a problem.
However, when a tree is “infested” with mistletoe, that can be a sign that the tree is not healthy and has been weakened or stressed by drought, insects, or damage from winds and storms. Take a look at this tree I found near my house:
Photo by Heather Wall
This deciduous tree almost looks like an evergreen because of the amount of mistletoe. It was able to take hold because the tree was already weakened somehow, and while the mistletoe won’t kill it outright, a heavy infestation of it can continue to weaken the tree to the point that it dies due to drought, insects or disease.
Some folks recommend removing mistletoe to protect the tree, though because of its “roots,” you have to prune off the entire branch to prevent regrowth. However, with an infestation like in the tree above, the amount of pruning you’d have to do would be just as damaging as leaving the parasite.
Not everyone agrees that mistletoe is harmful, however. Some argue that mistletoe is a keystone species, meaning it contributes significantly to the ecosystem in which it lives. Forests with mistletoe appear to be healthier than those without. Birds feed off its berries and some birds rely quite heavily on it as their main food source. The clumps serve as nesting areas for some birds, as well as habitat for insects that are food sources for lizards, birds and bats.
Photo by Heather Wall
One really interesting study showed that mistletoe plants can control the degree to which they use photosynthesis to produce their own food versus feeding off of the host tree. When two unrelated clumps of mistletoe invade a tree, the research showed they “turned on” their photosynthesis in order to draw less from the host as a way of “sharing” resources and preserving the host tree. Scientists aren’t sure how the separate mistletoe clumps communicate with each other, but since trees have been known to communicate with neighboring trees by releasing a scent pheromones, it is possible mistletoe does the same.
Another positive aspect of mistletoe is that while it is poisonous to humans and pets, scientists are discovering it has potential medicinal properties for treating seizures and even cancer. Doctors in Europe have started using mistletoe extract to help with treating colon cancer, though it is not yet an approved method in the U.S.
How it spreads from tree to tree is kind of fascinating: birds eat the white mistletoe berries in the early winter. The seeds are filled with an extremely sticky substance that’s apparently really hard to wash off if you get it on your hands. When the seed passes through the bird, the sticky film helps it stick to tree branches. The seeds also stick to birds’ bills and feathers and so it spreads when the birds wipe their beaks clean against tree branches. Actually, the word “mistletoe” derives from Anglo-Saxon words for “dung” and “twig.”
So, I think the bottom line is that, while mistletoe is a type of parasitic plant, it’s not terribly harmful to trees because of its slow growth and possible beneficial effects for the ecosystem. If anything, an infestation of mistletoe might serve as a “warning signal” to indicate when a tree has become unhealthy for other reasons.
Prompt: Take a look at the trees around your home and on your drive to work – do you see mistletoe up in the branches? Is it just a few or a full-on infestation? If you’re in the western United States, you might look for dwarf mistletoe, which mainly attaches to coniferous trees and looks like this:
What examples of mistletoe have you seen? For those of you outside the U.S., do you have mistletoe where you live? Leave a comment and join the conversation!
Mistletoe controversy: for 114 years, mistletoe was the state flower of Oklahoma. It was chosen in 1893, back when Oklahoma was a territory and not yet a state, because the previous winter had been very hard and when folks who died had been buried, survivors laid mistletoe on the graves, the only bit of color to be found. It was a bit controversial, with residents not wanting their territory and then state to be associated with a parasite, but it remained the state flower until the governor changed it in 2004. Today, it remains the state “floral emblem.”
A highway paved with diapers may change the cloth vs. disposables debate. “You’re not sure what to expect when you turn up to a nappy road,” said Ben Lake, a politician who represents this area in Britain’s Parliament. But, taking a deep breath as he strolled alongside the freshly paved, still glistening road, he pronounced: “It smells like — road.”
If you like to take a peek into other parts of the world, check out these Earth Cams - the 25 most interesting live cams, according to these folks.
Thank you for reading Natural Wonders. This post is public so feel free to share it.
I notice that mistletoe seems to be most prominent in oaks, red oaks to be specific. Did you find anything in your research to support this observation?
I notice that mistletoe seems to be most prominent in oaks, red oaks to be specific. Did you find anything in your research to support this observation?