THINNING INCREASES SAW-LOG VALUES IN FAST-GROWING PLANTATIONS OF <em>ACACIA</em> <em>HYBRID</em> IN VIETNAM

Abstract

BEADLE CL, TRIEU DT & HARWOOD CE. 2013. Thinning increases saw-log values in fast-growing
plantations of ^{Acacia hybrid} in Vietnam. High stockings at plantation establishment of fast-growing species
can lead to rapid compromise of individual tree growth. This study examined the possibility of early
thinning for Acacia hybrid to realise saw-log potential defined as log volume > 15 cm small-end diameter
under-bark at harvest. A 2.5-year-old Acacia hybrid plantation located near Dong Hoi in Central Vietnam
and established at 1000 stems ha^-1 was subjected to four thinning treatments, namely, an unthinned
control (871 stems ha-1 at time of thinning) and 600, 450 and 300 stems ha^-1. Significant diameter
responses to thinning were observed after 6 months and sustained until at least 2 years after thinning and
these were associated with significant differences in total basal area between treatments during the same
period. However, by 18 and 25 months after thinning there were no significant differences in periodic
basal area increment between treatments. This experiment showed that sites supporting mean annual
increment (MAI) > 25 m³ ha^-1 and thinned to 600 stems ha^-1 when the trees had mean diameter at breast
height of 9 cm led to about 20% of the commercial log volume reaching minimum saw-log size within 5
years from planting. Our results support the view that thinning Acacia hybrid in these environments can
rapidly realise saw-log values and increase the value of these plantations to smallholders.