Wood Density and Above-Ground Growth in High and Low Wood Density Clones of Pinus radiata D. Don

Abstract

In Pinus radiata a negative relationship has usually been found between stem volume and wood density. Clones previously found to produce wood of high or low density were used to investigate interrelationships between above-ground partitioning coefficients, carbon gain, and wood density. Cuttings had been propagated c. 5 years earlier, and were 5 m high when the experiment started. Potential carbon gain of the tree was manipulated by using two light environments; one with a light level c. 1.5 times the other. Measurements were of changes in stem, branch, and needle biomass during the 305-day experiment, of rates of photosynthesis, and of wood density by β-ray densitometry and microscopy; densities determined by the two techniques were the same. For all but two trees, wood densities of a stem and its branches were the same; for the other two, stem density was 13% less than that of their branches. Trees in the high light treatment accumulated more above-ground biomass, but there was no simple relationship between wood density and either above-ground growth or photosynthesis. With one exception, partitioning of photosynthate to stem was constant. In most cases, proportionately less photosynthate (30-80%) was allocated to below-ground biomass in the low light treatment than in the high light treatment (60-80%).