Effects of green pruning on growth of Pinus radiata

Pruning of plantation trees is completed to produce knot-free timber and veneer logs, thus increasing the value of the plantation. A long-term study (11 years) was established to investigate the effects of selective pruning on radiata pine (Pinus radiata D. Don) stem growth. The 175 stems selected for the experiment had been pruned to 2.4 m at 6 years of age. At ages 8 and 10, the trees were pruned to 45%, 60%, or 75% of tree height and growth was compared with a control (first lift pruned only). Pruning to 45% of tree height had no effect on growth to age 13 years. Responses to the other treatments were apparent soon after pruning and continued until measurements ceased at 17 years of age. Pruning to 60% or 75% of tree height at second lift reduced diameter increment, and increment decreased as pruning severity increased. There was a further separation of the growth curves following third-lift pruning to 60% or 75% of tree height. The results suggested that maintaining a live crown ratio of 55% would minimize effects of pruning on diameter growth. The effect of severe pruning on diameter increment was greater for subdominant trees than for dominant stems. Pruning had less effect on height than diameter increment, but all treatments involving pruning to 75% of height at third lift resulted in trees that were approximately 10% shorter than unpruned trees at 13 years of age. More severe second-lift pruning resulted in smaller diameter over stubs at the time of third-lift pruning. Second-lift pruning to 60% of total height produced acceptable diameter over stubs. Implications for management are discussed.