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 