Mistletoe: The Kiss Of Life For Healthy Woodlands

In many parts of the world, Christmas and mistletoe are inextricably intertwined. So, as December 25 draw nearer , now is a good time to remind ourselves about what mistletoe is and why we associate it with plum dessert and Santa.

Theres also been some recent discoveries about the role mistletoe plays in boosting biodiversity and improving ecosystem health.

The mistletoe Viscum album from Otto Wilhelm Toms Flora von Deutschland Osterreich und der Schweiz 1885

The whole mistletoe/ Christmas connection predates Christianity, with mistletoe featuring prominently in the Druids ancient wintertime solstice rituals.

With their bright green foliages and complete absence of roots, mistletoes are especially apparent on leafless hosts in the winter, and these sprigs of green in an otherwise lifeless wood inspired a rich folklore. Having harvested a mistletoe sprig from an oak with a golden sickle, the cut was taken back to their temple where it was maintained for three days.

On the fourth day( Christmas Day ), the leaves were distributed to worshippers, signifying the rebirth of the sunshine and ensuring a bountiful harvest in the coming season.

Variations of these rites are still practised today. Mistletoe sprigs variously deter trolls from stables( Sweden ), prevent nightmares( Austria ), welcome loved ones home( Heathrow airport in London ), or devote a sharp-eyed colleague kis privileges at the staff party.

The Good Parasite

In the natural world, mistletoe has long fascinated naturalists and scientists.

As canopy-dwelling parasitic plants, mistletoes are altogether reliant on animals to disperse and plant their seeds on suitable hosts. Until lately, ecologists assumed that most dispersal was conducted by an exclusive group of fruit eatersthe mistletoe fruit specialists.

Eating little else( even feeding the sticky morsels to their chicks ), members of eight groups of birds( including Australias Mistletoebird ), these birds are now known to have very strict habitat predilections, merely visiting areas with abundant mistletoe.

A Mistletoebird carefully extracting a sticky mistletoe fruit from the tough outer scalp. Fourteen minutes later, digestion is complete, the sticky seed is deposited on a perch and dispersal has been achieved Chris Tzaros

So, although important for spreading mistletoe to new hosts, these specialists rarely introduce mistletoe to new regions. That job is performed by a much larger group of occasional mistletoe-munchers, a group were only now starting to learn about.

The more you appear, the more mistletoe mysteries you find. In 2001, I published a review of our current state of knowledge considering mistletoe ecology, demonstrating that mistletoes represent ecological keystones in woods and woodlands worldwide.

As well as direct providers of food( fruit, nectar and succulent foliage ), many animals prefer to nest in mistletoes, and the combined effects of these interactions was a positive effect on biodiversity: areas with more mistletoe have high numbers of animal species living in them.

We cherry pickers to access the canopy for the removal experiment. David Watson

Its All n The Leaf Litter

To test this idea, and work up exactly why it is so, my team conducted a large-scale experimentation. We removed all mistletoes from one set of woodlands, and left all the mistletoes alone in a second set( with a third define of woodlands naturally absence mistletoe for reference ).

The results were as rapid as they were striking. Within three years of removing mistletoe, the number of bird species dropped by over third! But, rather than being the fruit eaters or nectar feeders, it was the insect eaters that indicated the clearest response.

In fact, once insect eaters were gone, there was no further effect of removing mistletoe on the reminder of the bird community. This response was especially true for ground-foraging insect-eaters: the robins, babblers, choughs and their ilk, a group of birds that has undergone widespread deteriorations in south-eastern Australia.

Grey Shrike-thrush, one of the ground-foraging insectivores that declined in woodlands after mistletoes were removed. Tom Rambaut

So, whats the connection between a parasitic plant in the canopy and birds feeing bugs on the forest floor?

Through careful analysis of leaf litter and bird diets, Ive demonstrated that the keystone effect of mistletoe is the result of bottom-up processes, driven by their high volumes of enriched leaf litter.

Unlike most plants that conserve their nutrients, withdrawing them prior to falling their foliages, mistletoes shed their leaves as is, boosting accessibility of a broad range of nutrients and accelerating decomposition.

In turn, this leads to dramatically higher numbers of bugs and spiders on the forest floor, in turn, providing food for insect eaters.

So, rather than the direct effects of food and shelter, this research suggests that the influence of mistletoe on biodiversity is driven by a different impact: the steady stream of leaf litter effectively fertilising the forest and increasing habitat quality for wildlife.

So, while some of you will be hoping for a kiss beneath the mistletoe, next time you assure one in the bush, I foster you to look down rather than up, to appreciate the effect these unsung heroes have on overall ecosystem health.

David M Watson, Professor in Ecology

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