Population dynamics of the emergent conifer Agathis australis (D. Don) Lindl. (kauri) in New Zealand. I. Population structures and tree growth rates in mature stands

Abstract

Twenty five plots of mature kauri Agathis australis (D. Don) Lindl., covering the range of the species in northern New Zealand, were sampled for density, basal area, and species composition using a modified point-centered quarter technique. Two increment cores were taken from at least ten trees at most sites, and used to estimate tree ages and growth rates. The density of kauri stems ^ 10 cm d.b.h. ranged from 17 to 416 ha~', and the basal area from 23 to 127 m2 ha~' in the 25 stands. Diameter distributions ranged from highly skewed and unimodal to flat and multi- modal, with all size classes represented in most plots. Combined frequency distributions suggest that two or three kauri generations (cohorts) may be present on many sites. There is only a weak relationship between age and diameter; individuals in the same 10 cm diameter class may vary in age by 300 years, and the largest individual on the site is often not the oldest. Mean annual diameter increments range from 0.15 to 0.46 cm yr~'on different sites with an overall average of 0.23 cm yr~>, equivalent to 8.7 annual rings per cm of core, about half the com- monly quoted figure for growth rate. Periodic mean annual increment and mean annual increment curves are presented. It is concluded that the "normally attainable age" is >600 years. Individuals >2 m d.b.h. probably often exceed 1000 years, but there is no reliable evidence for trees >2000 years in age. individuals in the same 10 cm diameter class may vary in age by 300 yr, and the largest individual on the site is often not the oldest. Mean annual diameter increments range from 0.15-0.46 cm yr-1 on different sites with an overall average of 0.23 cm yr-1, equivalent to 8.7 annual rings per cm of core. The "normally attainable age' is >600 yr. Individuals >2 m dbh probably often exceed 1000 yr, but there is no reliable evidence for trees >2000 yr in age.