Helicopter-based natural forest management for New Zealand’s rimu ( Dacrydium cupressinum, Podocarpaceae) forests

Abstract

The management of indigenous conifer forests in Westland, South Island, New Zealand has focussed largely on harvest of the Podocarpaceae tree rimu ( Dacrydium cupressinum). Today, key management objectives are to maintain the pre-harvested state of the forest in terms of biomass, tree size ranges (especially old trees), natural spatial patterns, relative proportions of the major tree species, and forest timber quality. This approach to natural forest management is based on utilizing heavy-lift helicopters, pre-empting mortality by harvest of a proportion of single unthrifty rimu trees, and an auditable GPS-based forest record system. A transition matrix model is used to determine the expected natural mortality rate and the sustainable harvest is based on pre-empting a proportion of the mortality over a 15-year felling cycle. Trees with significant wildlife features (e.g. cavities and large epiphyte loads) are not harvested. Even natural forest management can impact ecological processes through loss of senile trees, pre-empting forest tree windfall, altering spatial patterns of forest structure and facilitating pest and weed spread. However, because of the dynamic nature of these forest environments, the impact of forestry should be insignificant over major natural disturbance events. The best way to ensure that key management objectives are realized is to adopt an adaptive management approach that involves regularly monitoring of key forest attributes and frequent recalculation of the sustainable harvest model.