It’s part of Christmas – hanging up the mistletoe and stealing kisses beneath it. But as we think more about green issues, can we still justify this? Mistletoe is not a common plant in most parts of Britain, so is the annual custom of picking it to kiss under sustainable? Is it threatening this unique parasite of tree branches?
A new paper published in the Journal of Ecology confirms that the surprising answer is that there is no risk. Mistletoe, though only abundant in its stronghold areas of Herefordshire, Worcestershire and Gloucestershire and into the edge of Wales, is not an endangered species. Indeed recent evidence suggests it is thriving, in both those stronghold areas and within local colonies scattered across the rest of the country.
The annual harvest for Christmas, mainly from mistletoe in Herefordshire and Worcestershire apple orchards, has been ongoing since the 19th century, when the kissing custom was popularised, like so many other Christmas customs, by the Victorians. That harvest helped keep the apple orchards sustainable, as too much of mistletoe – which parasites the tree by connecting into the host vascular system – will weaken the host trees.
The balance has shifted in recent years, as those old orchards decay and become less managed. Mistletoe has boomed in many of them, with its viscous seeds (the plant’s scientific name is Viscum) glued onto new branches by wintering birds. This is causing problems for the remaining old apple trees. Mistletoe is a hemi-parasite, with its own green leaves and photosynthesis and, until recently, it was thought that it just steals water and nutrients from its host tree. But there is growing evidence that mistletoe also steals sugars from its hosts, gradually weakening a tree with a heavy load of mistletoe. This adds to the known problem of mistletoe’s extravagant use of water which can lead to the host becoming very short of water in a dry summer.
So hanging up the mistletoe each year is certainly sustainable – it helps balance the parasite’s impact on any host tree, but especially for the old apple trees in those midland orchards. Kiss on – it helps the tree (and also the mistletoe) survive.
More details in Journal of Ecology: Biological Flora of Britain and Ireland: Viscum album Peter A. Thomas, Monika Dering, Marian J. Giertych, Grzegorz Iszkuło, Dominik Tomaszewski, Jonathan Briggs