Mistletoe has suffered from a split reputation: either the decorative prelude to a sweet Christmas kiss or the tree-killing parasite that must be mercilessly excised for the good of the forests.
Now an Australian study has come up with a surprising new understanding of the evergreen plant: It is a key to keeping forest life healthy. Not only should it not be cut out of the forests it affects, but it could also be introduced in injured woodlands to restore them to health.
The mistletoe makeover stems from an experiment started in 2004 in a small woods surrounded by farmland in the upper Billabong Creek area of Australia’s New South Wales. David Watson, an ecologist at Charles Sturt University in New South Wales, reasoned that the only way to discern the role of mistletoe was to remove it from 17 woodlands and compare them with 11 woodlands where the mistletoe remained and 12 woodlands naturally devoid of the plant.
It was a herculean task to eradicate the parasitic mistletoe, involving cherry-pickers, loppers, a dozen people and two seasons of work, made all the tougher because the Australian mistletoe mimics the trees it takes root on. Moreover, while mistletoe, with its 1,400 species in five families, lives on every continent except Antarctica, it is sparse within each forest. Watson said he found only a few plants in every acre in the woodlands he worked on.
In all, his team members removed more than 40 tons of the plant, leaving it on the ground for livestock to consume. Then they waited for three years.
Watson had supposed that creatures that fed or nested on mistletoe would be affected by its removal. Instead, he found that the whole woodland community in the mistletoe-free forests declined.
Three years after the mistletoe vanished, so had more than a third of the bird species, including those that fed on insects. Bird diversity is considered an indicator of overall diversity. Where mistletoe remained, bird species increased slightly. It was a similar story for some mammals and reptiles, but, in another surprise, particularly for those that fed on insects on the forest floor.
“It’s a bit of a head-scratcher,” said Watson.
Analysis showed that species of mistletoe play an important role in moving nutrients around the forest food web. That has to do with their status as parasites.
Nonparasitic plants suck nutrients out of their own leaves before they let them fall, sending dry containers to the ground. But because the vampiric mistletoe draws water and nutrients from the tree stem or branch it attaches to, it is more nonchalant about leaving that nutrition in falling leaves. That means the fallen leaves still contain nutrients that feed creatures on the forest floor.
Not only that, but mistletoes make and drop leaves three or four times as rapidly as the trees they live off of, said Watson. As evergreens, they also do it throughout the year, even when trees are dormant. It is like a round-the-calendar mistletoe banquet.