People have been dangling mistletoe at holiday gatherings ever since the earliest days of Christianity. But the plant also gotten a bad rap due to its parasitic nature (it attaches to other trees and shrubs and sucks water and nutrients from their branches).
The hypothesis is based on an experiment that a New South Wales ecologist began in 2004. David Watson decided to remove all the mistletoe (40 tons of it) from 17 woodlands and compare them with 11 woodlands where mistletoe still grew and 12 woodlands where it never grew.
Within three years, over a third of the bird species had disappeared in the woodlands that had the mistletoe removed. In the control woodlands, bird species slightly increased. Mammals and reptiles followed suit.
The researchers realized that mistletoe leaves contain nutrients that the leaves of nonparasitic plants don't — and mistletoe drops leaves more often. Forest creatures scurry about to collect the leftover nutrients in the mistletoe leaves; when it's not there, they can't find it elsewhere. Thus, Watson came up with the idea of introducing it to forests in poor health.
In Europe, mistletoe extracts have been used in the fight against cancer. In the U.S., people are also realizing that the plant isn't just a pest — or a holiday decoration. Still, no one is purposely reproducing it just yet.