Mistletoe has a mixed reputation. On the one hand, we associate it with the Christmas folk tradition of obliging those who stand beneath it to be kissed. But foresters have always considered it a parasite that sucks the life from the trees in which it lives. Today we have the pleasure of reporting the result of a study in Australia which exonerates mistletoe of this crime.* It’s our Christmas gift to our readers.
David Watson, an ecologist at Sturt University in New South Wales, Australia, had long suspected that his favorite plant, mistletoe didn’t deserve its reputation as a harmful plant. In 2004 he set out to prove his hunch. He removed all the mistletoe from 17 woodlands and compared them with 11 woodlands in which the mistletoe remained and 12 woodlands in which there was no naturally occurring mistletoe.
Removing the mistletoe was a huge task which took two years. A dozen people, using cherry-pickers and clippers removed 40 tons of mistletoe. They waited three years to study the differences in the three types of forest.
They found that there were more birds, mammals, and reptiles in the forests where the mistletoe remained. But the most significant difference in the three types of forest was that the number of insects on the forest floor where the mistletoe remained was much greater.
There are more insects on the forest floor where mistletoe resides because the leaves of the mistletoe contain more nutrients than the leaves of the tree that it occupies. The tree uses the water and nutrients in its leaves before the leaves fall, whereas the fallen leaves of the mistletoe are both more abundant and contain more nutrients. The leaves of the mistletoe also fall throughout the year when many of the trees are dormant. Hence, there’s more food on the forest floor occupied by mistletoe for the insects that live there.
Mistletoe is found everywhere in the world except Antarctica. There are 1,400 species of mistletoe in 5 families. Fossil pollen grains indicate that mistletoe has existed in North America for millions of years. Although a controlled experiment has not been done in North America, some scientists have noticed the benefits of mistletoe to forest life. David Shaw, at Oregon State University, has noticed that the endangered northern spotted owl nests in mistletoe.
Science tests our assumptions
This study of mistletoe is a nifty little example of the power of science to test our assumptions. Our assumptions are often mistaken. We should keep an open mind about any assumption that has not been tested empirically.
Native plant advocates assume that native plants are inherently superior to non-natives and conversely, that non-native plants are not beneficial to wildlife. Their assumptions are not supported by scientific studies. In fact, when their assumptions are tested empirically, they are often proven to be wrong. The native plant movement is an ideology that is not based on science. It is a horticultural preference which should compete in the marketplace of ideas with all other horticultural preferences.
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*Alanna Mitchell, “Beyond the kiss, Mistletoe Helps Feed Forests, Study Suggests,” New York Times, December 17, 2012. Available here.
Conservation Sense and Nonsense 
I love the phrase “horticultural preference,” as it so clearly captures what is going on.
I don’t understand,however, why mistletoe does not use up the water and nutrient in its leaves, as trees do?
Webmaster: Thank you for this excellent question. We wondered the same thing but the explanation in the NY Times article didn’t make sense to us, so we didn’t quote it. Your question prompts us to do our homework.
Here’s the explanation from the study (David Watson, “Parasitic plants as facilitators: more Dryad than Dracula?” Journal of Ecology, 2009, 97, 1151-1159):“…nutrient return and plant growth all increased near the hemiparasites [mistletoes] in both cases…In addition to reallocation of nutrients from host tissues, some of the additional nutrients may be excreted by other organisms, such as visiting pollinators, seed dispersers, herbivores and members of below-ground decomposer communities.”
I have often found it bewildering if not completely contradictory when native plant enthusiasts castigate non-native plants as inferior to the natives (which are said to be better adaprted to local conditions) and then bemoan the fact that aggressive non-native plants are invading and taking over native plant communities. Both of these assumptions can’t possibly be true for all species. But such protestations bounce off hardened assumptions. And just to be completely honest here: I prefer native plant communities to those composed of tansy, valerian,and canary grass (three major weeds in my area). But these non-natives do extreemly well in the disturbed soils of “wild” urban landscapes and only a superhuman amount of pulling or spraying will make them go away.
Finally, about mistletoe. There is a dwarf species here in the Great Lakes region that grows on black spruce. It is about 2 to 5 mm tall and causes the spruce to develop brooms and stunts the trees. Bad right? Only from a logging perspective. Form the perspective of many birds these brooms are great places to nest. Just a personal observation of mine but one which might deserve some real study.
Webmaster: Excellent observations! Thanks for your visit.