Finger points to deer

Forest and Bird, Issue 281, 1 August 1996, Page 8

Finger points to deer

A THREE YEAR study into the impacts of deer and possums on a North Island forest has shown that, even at very low densities, deer browsing can shut down the regeneration of many native plants in the sub-canopy. The study was by Wayne Fraser, Graham Nugent and Peter Sweetapple from Landcare Research in Lincoln. They examined relative densities of possums and deer in the podocarp-hardwood forests of the Waihaha catchment west of Lake Taupo, what the animals ate and from where, and how much of each food species was available. Both deer and possums ate about 100 plant species but did not really compete for food. One of the surprising results was the relatively small amount of total foliage eaten. Possums took only 3.3 percent of the foliage produced each year in the forest, and deer only 1.1 percent. Yet in both cases this was enough to have long-term effects on forest health. As deer were targeting seedlings, their impacts were more damaging than possums which mainly eat new growth on mature trees. Few seedlings of deer-preferred species such as broadleaf and lancewood ever

reached more than five centimetres in height, showing that the deer were effectively wiping out future generations of their preferred foods in the shrub layer and sub-canopy. A 1080 aerial drop in 1994 reduced possum numbers in the catchment by 93 percent and deer by 60 percent. The scientists predict that while possum foods will recover, there are still too many deer for their preferred plants to regenerate. The research is continuing. The growing evidence of continuing deer damage to the integrity of native forests is causing a rethink about pest control within the Department of Conservation. To date the department has rarely targeted deer in its control operations, relying instead on recreational and commercial shooting to manage deer impacts. As this policy is patently ineffective, DoC is now in the process of preparing a new deer management plan which will hopefully look at ways of achieving greater reductions in deer impacts in native forests.