Mistletoe Branch

For Healthy Woods Mistletoe Is The Kiss Of Life

There have been some recent discoveries about the role the plant 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 winter solstice rituals.

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

On the fourth day( Christmas Day ), the foliages 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 practiced today. Mistletoe sprigs variously deter trolls from stables (Sweden), prevent nightmares (Austria), welcome loved ones home (Heathrow airport in London), or dedicate a sharp-eyed colleague kissing privileges at the staff party.

The Good Parasite

In the natural environment, mistletoe have all along fascinated naturalists and scientists.

As canopy-dwelling parasitic plants, mistletoes are altogether reliant on animals to scatter and plant their seeds on suitable hosts. Until lately, ecologists assumed that most dispersals were conducted by an exclusive group of fruit eaters the 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 skin. 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 areas. That undertaking is performed by a much greater group of occasional mistletoe-munchers, a group were only now starting to learn about.

The more you seem, the more 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 woodlands 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 define (with a third define of woodlands naturally without mistletoe for reference ).

The outcomes were as rapid as the latter are 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 bug eaters that indicated the clearest reaction.

In fact, once insect eaters were run, 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, what the connection between a parasitic plant in the canopy and birds eating insects on the forest floor?

Through careful analysis of leaf litter and bird diets, I’ve 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 leaves, mistletoes shed their foliages as is, boosting availability of a wide range of nutrients and accelerating decomposition.

In turn, this leads to dramatically higher numbers of insects 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 river of leaf litter effectively fertilizing 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 watch one in the bush, I encourage 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

Read more: www.iflscience.com

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