Genetic variation in growth curve parameters of Konishii fir (Cunninghamia lanceolata (Lamb.) Hook. var. Konishii

Cunninghamia konishii is the island race of the species complex C. lanceolata, and is native to Taiwan. It is a valuable timber species. A comprehensive provenance family test was established in 1973. Height and diameter were measured periodically until age 26, which was close to the species' harvest age of about 30. These data offered an opportunity to examine the species' growth characteristics by fitting asymptotic growth functions. We adopted the concept of repeated measures data analysis, i.e., a combination of variance component analysis and growth curve fitting, the latter involved fitting the individual tree height and diameter data to a Weibull-based function. A severe typhoon in 1996 caused serious damage to the plantation, mostly to tree heights. To prevent this damage from influencing our results, we limited the analyses to those trees judged relatively free of typhoon damage, and focused on the diameter growth data. Fitting a Weibull function with parameters a, b, and c was statistically successful (e.g. the mean R2 for diameter was 0.98). Both analyses indicate substantial variation among provenances and families, and thus opportunities for genetic selection and breeding. We particularly expound on the practical applications of growth curve fitting as an analytical tool for elucidating the mechanistic process of tree growth to assist decisions on the age for selection, even retrospectively, and modeling the response of tree growth to future climate.