Incorporation of climatic indices into models of growth of Pinus radiata in a spacing experiment

Abstract

Schumacher models incorporating climatic indices are used to describe stand height, basal area and volume growth in an initial spacing trial with Pinus radiata. Annual photosynthetic carbon fixation estimated with a process based model, BIOMASS, was a better climatic index than annual rainfall. Incorporation of the growth index derived from BIOMASS into the time function in the Schumacher equation led to path invariant models which improved the fit compared to the basic equation by 13, 22 and 31% for mean tree height, stand basal area and stand volume respectively. Inclusion of the growth index into the asymptote function improved the fit for basal area and volume to 33 and 35% respectively but these models can only be fitted when annual growth data are available and growth estimates are restricted to annual time steps. The new models improve the descriptive power of the Schumacher model and open the avenues for wider interpretation of experimental results. The models should also prove useful for updating forest inventories.