Native mistletoe’s bad rap as parasite plant put to rest

Mistletoe has long been seen as one of two things - something to stand under at Christmas-time for a kiss, or a parasitic plant that grows on other trees.

However, University of Otago researchers have now found native mistletoes on introduced deciduous trees act as great refuges for invertebrates during the colder months because they are evergreen, and the finding has prompted the researchers to call for New Zealand’s native leafy mistletoes to be protected.

Some frown upon mistletoe because it is a parasite plant that grows and survives on host trees, and mistletoes are perceived as depriving host trees of nutrients and stunting their growth.

Research co-author Associate Prof Janice Lord said it was a myth that mistletoe killed trees.

"Very rarely do they cause damage to a healthy tree.

"I get frustrated when people start chopping mistletoes off when it’s actually a native plant and it’s actually really important for birds, insects, spiders, moths and butterflies and all sorts of things."

She said Dunedin was home to six species, including the leafy green mistletoe Ileostylus micranthus, the focus of the study, and the endangered white mistletoe Tupeia antarctica.

She said researchers collected foliage samples of 19 host trees and 19 mistletoes living on them, from a mix of rural and suburban areas in summer and winter in the greater Dunedin area.

Summer samples harboured 1335 arthropods with no overall differences between mistletoes and their hosts, whereas winter samples had 60 arthropods mainly found on mistletoes.

Lead author and Otago botany PhD candidate James Crofts-Bennett said native invertebrates, such as arthropods, were more likely to survive in urban and suburban habitats if mistletoe was present.

"Arthropods - which include hexapods, chelicerates, crustaceans and myriapods - make up the vast majority of animal species.

"They provide a vast array of ecosystem functions and are crucial to maintaining the world as a whole.

"The classic example is bee pollination, but moths, flies, beetles and even some arachnids can be important pollinators.

"Likewise, oribatid mites are crucial to forest soil cycling, similar to earthworms in agricultural systems.

"All these animals were found in mistletoes we examined."

Department of Conservation information showed native mistletoe populations had declined since the early 1900s, mainly due to possums, vegetation clearance and the decline in native bird species that acted as pollinators and seed dispersers.

It said if this decline continued, more local populations might disappear and, in the long term, species could go extinct nationwide.

One species, Trilepedia adamsii (Adams’s mistletoe), was last seen in 1954 and was presumed extinct.

john.lewis@odt.co.nz