Initial growth response of three early spacing technologies in nine-year-old native Eucalyptus sieberi in East Gippsland, Victoria

Abstract

There is potential to increase productivity from the regrowth forests of East Gippsland, Victoria by investing in more intensive silviculture. A review of literature shows that early spacing of selected stands can increase merchantable volume and decrease rotation lengths which could then increase annual yields and/ or alleviate the pressure to harvest forests with high conservation values. This sub-thesis investigates three early spacing technologies used to space nine-year-old Eucalyptus sieberi in the Cann River Forest District. The three spacing treatments included a non-selective spacing using a mechanical slasher and two treatments that removed trees using a combination of non-selective spacing with either a stem injection of herbicide or a clearing saw that physically removed trees. All treatments were compared to an unspaced control. Stocking and basal area reductions between treatments were found to be different post-treatment in 1992. This was largely due to the proportion of area selectively spaced with the mechanical slasher. There was also natural variation in stocking in the stand, however this could not be quantified due to a lack of replication across treatments. Growth over two years was analysed using Restricted Maximum Likelihood (REML) based on a Mixed Model for unbalanced data. There was a significant (p<O.OOl) growth response in basal area between dominant, co-dominant and intermediate trees in all three treatments compared to the control. The growth response of suppressed trees varied with treatment. The initial relative and absolute growth responses were largely dependent on basal area and the frequency of larger dbhob trees. Basal area and the number of larger trees after treatment were a result of proportion of area selectively and non-selectively spaced. As the selectively spaced area increased there was a more even distribution of larger trees resulting in high absolute growth (m2 ha-1 ). In contrast, the greatest relative growth was associated with treatments that had fewer larger trees. Coppice growth was also considered as an influence on growth rates between treatments. Predominant height lind green height were also measured in the three treatments and control. No significant differences (p<O.OS) were found between treatments and the control. From initial growth analysis and preliminary costing from the literature, a non-selective spacing combined with a stem injection of herbicide was favoured as a feasible spacing method. Show more