Early-age and later-age thinning affects growth, dominance, and intraspecific competition in Eucalyptus nitens plantations

Abstract

High-intensity thinning treatments were applied to young Eucalyptus nitens (Deane and Maiden) Maiden plantations aged 6 (early-age thinning), 8, and 9 years (later-age thinning). Thinning treatments were an unthinned control plus final density levels that ranged from 100 to 600 trees/ha, representing between 14 and 72% of pretreatment stand basal area. Initial planting densities were between 1143 and 1430 trees/ha. Cumulative basal area increment was significantly reduced after both early- and later-age thinning if more than 50% of the standing basal area was removed. When select groups of trees in the thinning treatments were compared with the equivalent groups of trees in the unthinned control, there was a significant response to early-age thinning in the best 100-400 trees/ha and to later-age thinning for the best 100-600 trees/ha. Height increment was not affected by thinning. However, mean live crown ratio increased with time in thinned treatments. Dominant and codominant trees showed the greatest growth response to thinning. From the data presented in this study, a final density in the range of 200-300 trees/ha is recommended. This density would improve the growth of individual trees during a rotation length of 20 to 25 years without seriously under utilizing site resources.