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 m 2 ha −1 . Whole-tree volume was predicted to be 702 m 3 ha . Conclusions:This study indicates an opportunity to grow kauri in plantations on selected good-quality sites over rotations of 60-80 years or less.
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Background: A quarter of New Zealand’s land area is currently covered in indigenous forest although only indigenous forests on private land can be harvested. In addition, planted exotic forests (~90% Pinus radiata D.Don) cover a further 7% of the land, and these form the main basis of New Zealand’s forestry industry. However, some landowners are seeking to plant a more diverse range of species (including New Zealand indigenous species) that can be managed in different ways to produce a range of products. Methods: A “cradle-to-gate” life cycle-based economic assessment of three forestry scenarios was undertaken in collaboration with members of Ngāti Porou, an indigenous Māori tribe. The three scenarios were: (1) “business as usual” (i.e. intensive management of radiata pine); (2) continuous-cover forestry management of the indigenous coniferous tree species rimu (Dacrydium cupressinum Lamb.); and (3) intensive production-scale forestry of the indigenous scrub species mānuka (Leptospermum scoparium J.R.Forst. & G.Forst.). Using a 120-year timeframe, discount rates and opportunity costs were applied and a flat- and steep-land comparative analysis was performed (for radiata pine and rimu). Results: The Net Present Value (NPV) was calculated for each scenario and showed that, on flat land, only the mānuka scenario is profitable. However, applications of discount rates can result in a negative NPV, as is the case with the radiata pine and rimu scenarios. On steep land, both the radiata pine and rimu steep-land scenarios have improved NPV returns due to a lower opportunity cost. On steep land, radiata pine is generally profitable with a discount rate of 6% or lower and a stumpage rate of over $100 m3 and rimu is generally profitable with a discount rate of 2% or lower and a stumpage rate of over $650 m-3. Conclusions: This analysis demonstrates the importance of strategically considering what tree species to plant, what slope of land to plant them on, and what forest management technique to utilise. Furthermore, this analysis highlights the importance of choosing appropriate discount rates and the effect of other inherent assumptions, such as opportunity cost.
Background: Kauri (Agathis australis (D.Don) Lindl.) is endemic to New Zealand and is the southernmost species of the tropical genus Agathis. Methods:The growth history of the second southern-most known stand of New Zealand kauri is documented. This stand is located at Wairongoa Springs near Dunedin, approximately 8°of latitude south of the modern natural range of the species. This stand was established in the 1950s and now approximates a natural 'ricker' stand of juvenile kauri. Sample plot measurements of height and diameter growth taken in 2009 were compared to published 1986 data from the same stand, and were used for modelling self-thinning dynamics. An investigation was also undertaken using ring-widths from cores obtained by increment boring to generate a 52-year dendrochronological record that shows a strong common pattern of long-term and inter-annual changes in growth. Carbon isotope analysis of annual rings from 1983-2009 revealed corresponding multi-decadal chemical trends. Segmented linear regression was used to compare the ring-width record with existing kauri growth and self-thinning models.Results: Growth of kauri at Wairongoa Springs was fast, was comparable to other plantations of kauri without silvicultural tending, and was generally faster than that of natural stands. The growth of the stand can be considered as occurring in two apparent phases. The first was a 26-year period of relatively constant rapid growth with ring-widths averaging 3.5 mm while the second phase showed a steady decline in annual growth thought to be indicative of self-thinning due to increasing competition. This ring-width decline was matched by a gradual decline in the ratio of carbon isotope 13 C to 12 C.Conclusions: Ring-width measurements and carbon isotope determinations compared with forestry-based modelling of self-thinning in kauri suggest that this stand is undergoing self-thinning much sooner than other kauri stands. This result highlights other possible influences beyond simple biomass accumulation triggering the onset of self-thinning. The growth rate of the plantation is comparable to others from the North Island, demonstrating that kauri can be grown, albeit in sheltered sites, throughout the length of New Zealand.
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