The effect of understory pasture species on branch size and tree sinuosity in Pinus radiata at the Lincoln University agroforestry trail

Abstract

Branch size and sinuosity affect wood quality in the pruned and unpruned logs which is reflected in the economic return to the grower. Measurements were made at the Lincoln University Agroforestry experiment to test the effects of understorey competition on branch size and sinuosity in Pinus radiata (D. Don). Four clonal varieties and one seedling of radiata pine were tested in six pasture treatments. The pasture treatments were ryegrass/clovers (Lolium perenne/Trifolium spp), cocksfoot/clovers (Dactylis glomerata/Trifolium spp), phalaris/clovers (Phalaris aquatic/Trifolium spp), ryegrass only, lucerne (Medicago sativa) and bareground. Branch index measurements were undertaken by averaging the diameter of the largest branch in each of 4 quadrants of the tree (N,E,S,W). Sinuosity was defined as the maximum deviation of the tree from straight.

Branch index was significantly affected by understorey competition. Smaller branches were located in the more competitive treatments of phalaris/clovers, cocksfoots/clovers and lucerne. Branch index was not significantly affected by tree type, but the interaction of understorey competition and tree type was significant. This was due to one clone having very much larger branches than the others in the bareground treatment.

Sinuosity was not significantly affected by the understorey, though seedlings were found to be more sinuous than clones. There was a poor relationship between sinuosity and toppling at age 2 for those trees remaining after thinning at age six. This study has shown that sinuosity is not significant when thinning of more sinuous stems is undertaken. This has been possible with the initial stocking rate at 1000 sph and the final stocking rate at 200 sph. Agroforestry design needs to incorporate thinning to gain these advantages.