GROWTH EFFICIENCY OF PINUS RADIATA STAND ELEMENTS: IMPLICATIONS FOR STAND GROWTH MODELLING STRATEGIES

Individual tree growth rates and growth efficiencies were assessed for different stand elements from Pinus radiata D. Don pruning trials in New Zealand. Growth rates were higher for non-crop elements, but crop elements had significantly higher rates of efficiency (basal area increment per unit of crown length or per unit of sapwood cross-sectional area at crown base (as a representation of leaf area)). Sapwood basal area was more strongly related to tree basal area increment than to measured crown length, indicating it may be a better measure of crown size in growth models and in measures of crown growth efficiency. Weak correlations between plot basal area increment and average crown length per tree indicated that the primary effect of crown length per hectare on basal area increment was through its relationship to stocking density rather than crown length. Inclusion of a growth efficiency variable in the EARLY growth model resulted in some minor improvements to the model for productive farm sites, but not for less-productive pumice forest sites. Future modifications which may enhance the EARLY model might include adding calliper cross-sectional area at crown base as a production variable to represent leaf area