Height growth of Pinus radiata as affected by stocking

Results from 29 semi-mature trials of New Zealand Pinus radiata D.Don indicate that height growth is positively correlated with final-crop stocking in certain circumstances, and where stockings are less than 800 stems/ha (higher stockings were not analysed). A subsidiary dataset, with ages from planting to 7 years, gave results that confirmed these. Twelve of the trials demonstrated a significant (p<0.05) decrease in annual height increment with a reduction in stocking. For these trials there was an average height loss of 0.13 m/year after thinning to final stockings, or approximately 2 m over one typical rotation, for every halving in stocking. One possibility is that this effect is due to wind: lower stockings incur greater wind turbulence, which reduces height growth. In order to standardise descriptions of stand height, a new equation was calculated to predict Mean Top Height from Predominant Mean Height