All about the birds and the bees — and the overworked trees

Press, 15 January 1986, Page 17

All about the birds and the bees — and the overworked trees

By

TESSA WARD

A “sticky problem” could be emerging in South Island beechforests between the honeydew and the birds and the bees that feed on it. While the gleaming globules of sap dangling on beech trees . are an abundant source of high energy food, two researchers want to find out if a growing share by apiarists’ bees of this sweet nectar of nature could seriously affect the native birds. Dr Henrik Moller, a Nelson scientist, and Ms Shaarina Boyd, an Auckland science student, hope that their studies will also provide a guideline for setting aside sufficient South Island beech forest for the future conservation of native birds. They have chosen 10 hectares of beech forest harbouring many native birds in the middle of Baigents pine forest, inland from Nelson, as their study area. Mr Peter Gaze, a technician with Dr Moller’s D.S.I.R. Ecology Division in Nelson, says that an excess of bees in the forests is likely to affect bird numbers and cause deterioration of the beech trees. As more bees feed on the honeydew, or excreted sap, the trees will have to provide more replacement sap. Taken to extremes, that could be more than they can cope with, he adds. “Hopefully, a satisfactory balance can be reached between the bees and birds feeding on the honeydew and the health of the beech trees. I think there is another factor here of effectively controlling the number of bees so that we don’t reach a state of imbalance. “This is the amount of pollen oailable to the Jor building ffieir hives which Ts relatively

scarce in the beech forests. The bees tend to have to resort to pollen from plants on the perimeter of the forests, such as broom and gorse.” The apicultural advisor for the Ministry of Agriculture and Fisheries in Christchurch, Mr John Smith, says that so far surveys have shown that the 15,000 apiarists’ beehives are not having any drastic effect on the birds or beech trees.

“I would suggest that the accidental introduction of exotic wasps to the forests is probably having a bigger effect on the forest ecology than the bees,” he adds. “These wasps are very efficient at preying on many kinds of insects in the forest which affects the foodchain.”

Beech trees, mainly in Canterbury between Mount Somers and Kaikoura, and some parts of Westland and Nelson, are studded with dewey droplets at the end of tiny silvery wax tubes. This honeydew is the “mountain of surplus sap” produced by each sucking scale insect which burrows inside beech tree bark to feed and excrete.

All this industry perfumes the forest air with a distinctive heady sweet smell. It also provides key building blocks for the bees’ dark strongly flavoured honey , a valuable source of income to apiarists, and possibly a crucial component of several native birds’ diets.

A sooty mould that lives on, infected trees also depends on it, and any honeydew that eventually manages to fall unconsumed to the forest floor increases the number of valuable nitrogen-fixing bacteria in the soil. Lucrative overseas markets have developed for the popular honey, particularly over the last five years, several million dollars for each year,

Mr Smith says. “There has been a build-up in the number of hives in response to this but a major hindrance to the number rising much above 15,500 hives is the shortage of suitable sites for them. Finding a lot more suitable sites could well involve using a helicopter to transport the hives, which becomes a completely different commercial ball game.” To measure how important honeydew is to native birds, the two researchers say they will try to monitor what individual birds do each day. Dr Moller is particularly interested in findng out how many trees covered with honeydew that native birds are prepared to defend.

Mr Smith says that another factor to consider in assessing the value of apiarists’ bees in the forests is the apiarists destruction of wasp nests wherever they find them.

“First, this helps to control the predation of the introduced wasps on other insects in the forest, and it also helps the public to enjoy a relatively wasp-free visit to the forests. Farmers in some areas, on the other hand, would like the wasps to continue to prey on. blow .Hies.”

Conservation groups have generally supported the introduction of apiarists’ bees to the beech forests, Mr Gaze says. “These groups feel that the introduced bees help to keep the forests in their untouched state while becoming valuable export earners.” Dr Moller expects his honeydew research to keep him “busy” for at least three years. “While we are hopeful that beekeeping has little impact on the beech forest ecology we may find that at a certain level it does,” he says. “Then people will have to decide what is more important — the birds or the bees.”