Crown and stand characteristics of Eucalyptus nitens in response to initial spacing: implications for thinning

An experiment was established in a 7-year-old Eucalyptus nitens (Deane and Maiden) Maiden spacing trial, to investigate the effects of initial spacing on crown and stand characteristics. Stocking varied between 500 and 1667 stems per hectare (SPH). Trees from the highest and lowest stocking treatments were harvested to look at aboveground biomass production, biomass partitioning, functional relationships between crown components, individual tree versus stand production and leaf area index. It was found that the lower initial stocking did not affect total aboveground biomass per tree, but increased biomass partitioning to the stem at the expense of branches. Hence stem volume per tree was substantially greater at the lower stocking level. This was a result of greater diameter at breast height (DBH) but not height growth. Trees grown at the lower stocking had greater leaf area per tree, although the relationship between leaf area and sapwood cross-sectional area was not affected by stocking. The only functional relationships that were affected by stocking were those of cross-sectional area and stem volume, tree height, branch dry mass or stem dry mass. Stocking affected these because of changes in stem shape and taper or partitioning to branches. At a stand level total biomass and volume increased with increasing stocking but individual tree size decreased. The relationship between leaf area index and spacing was curvilinear, with no significant differences between stockings above 833 SPH. The results are discussed in terms of the optimal initial spacing and implications for mid-rotation thinning.