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

Abstract

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.