Growth response following variable espacement of 28-year-old Alpine Ash regeneration in New South Wales

Analysis of stand growth-response patterns have shown that small increases in sawlog volume resulted from thinning fast grown, fire regenerated alpine ash (Eucalyptus delegatensis R.T. Bak.) from below to a range of regular tree-spacings, at age 28 years. No significant correlation was found between basal area growth response and increased spacing for four treatments that ranged from 3.7 m to 7.3 m.

Rapid natural stocking-attrition occurred in both thinned and unthinned stands during the 31 post-thinning years of measurement. Maximum density diagrams indicated that these alpine ash stands were fully-stocked at lower densities than have been recorded for many other forest species. As a consequence of the propensity to self-thin, little additional stand growth was gained from the thinning treatments. The 150 trees ha^?1 with the largest diameters from all thinned stands averaged a basal area increase of only 0.59 mha^?1 over the 31 year period of measurement (<0.2 mha^?1 yr^?1), when compared with the equivalent stratum from an unthinned stand.

However, the small average nett growth response to spacing was not distributed evenly across the largest 150 trees ha^?1 dbhob. The 50 largest diameter trees ha^?1 in spaced stands showed a significant (α = 0.05) positive response, the trees ranked 51 to 100 showed no significant response and those trees ranked 101 to 150 showed a significant (α = 0.05) negative response when compared with the corresponding strata in the unthinned stand, over the same period.

Thus the overall result of stand spacing on the largest 150 trees ha^?1 was a widening of the stand diameter distribution and a small overall gain in the merchantable volume. For sites of higher quality, the basal area response was larger and predominantly accrued to the largest 50 trees ha^?1.