Publication Type:Journal Article
Source:New Zealand Journal of Forestry Science, Volume 40, p.33-59 (2010)
Kauri (Agathis australis (D.Don) Lindl.) is endemic to New Zealand, where it is the only indigenous member of the Araucariaceae. It has the most southerly distribution of any species in the genus and is currently confined to the warm temperate areas of the North Island. At the time of European settlement, forests containing kauri covered 1 000 000 ha or more in New Zealand. Following uncontrolled logging, land clearance for alternative land use and destruction by fire, only 7500 ha of virgin or primary forest remain, mainly in conservation reserves. An additional 60 000 ha of scrub/shrubland and secondary forest contain varying amounts of regenerating kauri. Kauri is reputed to produce greater volumes of wood from single stems than any other timber tree in the world. Its timber is regarded as one of the finest due to qualities of decay resistance and dimensional stability under moist conditions. A wide range of products was developed by Maori and European settlers. Kauri timber and gum made a substantial contribution to the physical and economic development of New Zealand between 1830 and 1900. Agathis australis shares a number of biological characteristics with lowland Agathis species found in the tropics and subtropics. These include a juvenile form with narrow tapering crown; mature emergent trees with massive, spreading, dome-shaped crowns and upwardly-arched branches; self-pruning in sapling and pole-stage trees; flaking bark; winddispersed, small-winged seeds formed in cones that disintegrate at time of seed maturity while still on the tree; and only a few months of seed viability after shedding. Juvenile trees with taproots and mature trees with wide-spreading lateral roots and descending peg roots are windfirm, assisting longevity. Although surviving trees of massive dimensions (3-5 m diameter) are usually hollow, their life span may be 1500 years or more. Large kauri have a podsolising effect on some acidic soils, making them less fertile. Efficiency in the use of water and nutrients has enabled the species to become dominant on infertile and drought-prone ridge tops. Observations of growth in natural stands indicate mean annual increment of 2.5-6.0 mm in diameter and 0.3 m in height. Interplanting of kauri in scrub and shrubland developed on former kauri forest sites has produced poor results. Mean annual increments of 6.9 mm in diameter and 0.44 m in height have been recorded in young untended plantations. Greater success has been achieved through attention to site selection, improved establishment techniques and silvicultural tending. The most suitable sites for planting are those with fertile, well-drained, light-textured soils, a warm, humid climate, and a history of previous occupation by broadleaved (angiosperm) plant species. Current research suggests that rotation length can be reduced by best-practice management, and that planted stands could be a continuing source of kauri timber in the future.