Saturday, 28 November 2015

Mistletoe - friend or foe?

One of the most fascinating group of plants growing in the Australian bush is mistletoe, and they are often found growing on native trees throughout the country. These plants are sometimes perceived as worthless parasites that weaken trees prior to their death. While this is partially true their value to our environment has been underestimated. Recent research on these highly evolved native plants has led to a reappraisal of their importance to the ecosystem.

The nectar from this mistletoe flower attracts 
a diverse range of birds, bees and butterfly's

Mistletoe's are a world-wide group of plants which are found in many different habitats. Most early settlers would have known the European Mistletoe (Viscum album), a commonly seen plant culturally associated with pagan fertility rights.

Australia has 85 species of mistletoe, mostly from the Loranthaceae plant family. Most mistletoes are found growing on open forest and woodland trees such as eucalyptus, wattles and she-oaks. While most mistletoes photosynthesise from their own leaves they are usually dependent on the hosts sap for water and nutrients.

Mistletoes are often seen growing on trees near the edge of woodland along roads or near cleared land. A 2004 study by ecologist David M Watson near Albury in New South Wales found that 80% of trees growing along habitat edges carried mistletoe compared with fewer than 5% in the interior.The reason for their preference for habitat edges was, according to Watson, related to increased light, decreased fire frequency, increased run off from roads and decreasing numbers of mistletoe eating animals such as possums and gliders at habitat edges. These environment factors have subsequently led to these plants being abundant on the edges of woodland.

While the presence of mistletoe can have a negative affect on the health of the host tree these plants certainly attract a wide range of animals. Associate Professor Watson found that the presence of mistletoe increased the abundance of bird species by 20% or more when compared to similar bush where the mistletoe had been removed. Watson is of the view that the presence of these well adapted plants is 'one of the key factors allowing our woodland-based animals to survive in what's left of their habitat.'

A drooping mistletoe growing on eucalypt
Many birds, animals and insects feed on the flowers, fruit and leaves of mistletoe. Birds birds found feeding on mistletoe include parrots, Eastern-Spinebills and of course the tiny Mistletoebird which feeds on the sticky fruit of the plant. The spreading of the sticky seed by the Mistletoebird is the principal way that new mistletoe plants grow on other host trees. These plants are also important food plants for bees, butterflies and Christmas beetles and are a popular nesting site.

References and further reading

Misunderstood Mistletoe by David M Watson, published in the March 2004 issue of Wingspan magazine

Mistletoes of Southern Australia by David M Watson, CSIRO publishing 2001 (highly recommended)

The Australian National Botanic Garden in Canberra has a fascinating mistletoe web site which will be of interest.

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