Evaluating inter-specific competition on individual radiata pine trees in Canterbury, New Zealand

An investigation was carried out on the effectiveness of vegetation management regimes, including one which is commonly used by managers in Selwyn District of the South Island of New Zealand. A neighbourhood study approach with four randomised blocks and eight weed intensity treatments was used. Results from initial measurements and 3 remeasurements showed that there was a strong correlation between the amount of weeds measured and crop tree growth than between treatments and tree growth. Moreover, the conventional control regime (1 m band spraying along tree rows) was shown to lead to suboptimal tree growth. Mean diameter growth under herbaceous competition could be described with a decay function of the form. Y = alpha + beta*exp(-gamma*hpc), while for mean height growth the equation was Y=alpha+beta*exp(hpc); where Y=tree growth, hpc=herbaceous percent cover index and alpha, beta and gamma were estimated non-linear regression coefficients. Under woody competition the function was Y=alpha+beta(wci) for both mean diameter and mean height growth (wci=woody abundance index as expressed by crown foliage density*height*proximity/H). Managers in the area therefore, need to redefine their non-crop vegetation reduction standards so as to improve tree growth and to use available resources more efficiently.