Growth and productivity of New Zealand kauri (Agathis australis (D.Don) Lindl.) in planted forests

Background

The establishment of even-aged planted stands of New Zealand kauri (Agathis australis (D.Don) Lindl.) for timber has been constrained by a lack of quantitative information on productivity and rotation length on which forest management and investment decisions could be made.

Methods

Stand-level models of height and basal area against time were developed (as well as a stand-volume function to calculate volume from height and basal area) based on planted stands that were up to 83-years old and represented planting sites both within and outside the current natural range of the species.

Results

Planted kauri was shown to be slow to establish with little height growth for the first five years after planting. Similar trends were observed for basal area and whole-tree volume development. A Schumacher equation with local slope parameter and asymptote bounded at 45 m gave the best fit for height, while a von Bertalanffy-Richards equation in difference form with local slope parameter gave the best fit for basal area. For plantations with an average site index (20.4), height was predicted to be 22.3 m in height at age 60, with a basal area of 78.1 m² ha^?1. Whole-tree volume was predicted to be 702 m³ ha^?1. Predicted volume mean annual increment was 11.7 m³ ha^?1 yr^?1for all stands at age 60. From age 20-60 years, stands with a higher site index had a volume mean annual increment of 18.6 m³ ha^?1 yr^?1. The best stand exceeded 20 m³ ha^?1 yr^?1.

Conclusions

This study indicates an opportunity to grow kauri in plantations on selected good-quality sites over rotations of 60-80 years or less.