Dave Kelly the of University of Canterbury explains why native mistletoes are declining. He also talks about the research that he and Jenny Ladley carry out in Craigieburn Forest Park in the South Island. This includes using observations and measurements to provide a long-term picture and experiments to study pollination.
DR DAVE KELLY
Mistletoes are interesting because they’re declining for various reasons. One reason is habitat clearance. So they grow in forest, and we cut the forest down to make farmland, so that’s bad for mistletoes. The second reason is the birds have decreased so they’re not getting pollinated and dispersed as much as they used to, and also they’re eaten by possums.
Here at Craigieburn, it’s a really good place to work because there’s plenty of mistletoes, and we’re able to find enough to apply our experimental treatments to. And so we’ve just been measuring how good the pollination is, finding out whether it varies from year to year, whether the mistletoes in the tops of the trees are pollinated better than the ones down at ground level. We’re recording how long the mistletoes live and trying to find out if we’re getting enough seedlings coming through to replace the old ones, because the old ones occasionally die. And we’re trying to find out if there’s enough seed being produced, enough pollination, enough fruit dispersal to get new mistletoes on to replace the old ones that are dying.
To find out how long they live, we’ve just got a whole bunch of mistletoes here and we’ve put tags on them, and every year, we come back and say hello and find out if they’re still alive and measure how big they are and whether they’ve grown and are they making flowers this year, and so we’re getting a long-term picture. And then we’ve also got areas where we marked out big 20 x 20 metre plots, and every 3 years, we go through and we search for new mistletoes as well as recording our old ones – we know every mistletoe in those plots – we go back and see if they’re there and so we’re recording deaths, and then we go around searching the canopy with binoculars and we spot new ones and so we’re trying to find out if the new ones are balancing out the old ones.
So to measure the pollination, you run a bunch of pollination treatments, and most of the sites we work on, including at Craigieburn here, the bird-pollinated flowers aren’t doing as well as the hand-pollinated ones.
There’s a bunch of things really to help mistletoes get by. They’ve got to grow in beech forest, and if we cut down all the beech forest, the mistletoes have got nowhere to grow. So protecting habitat and in some places actually planting new beech trees and that gives hosts that the mistletoes can get onto. The second thing is trying to look after birds, so we need more bellbirds and tūī – those are the two most important birds – so anything you can do which will boost the number of these birds locally that will help pollination.
The third thing that helps the mistletoes is getting rid of the herbivores. And in fact, in the North Island where the herbivores seem to be more of a problem, probably getting rid of your possums is the single most important thing, otherwise you’re going to lose the mistletoes locally.