response of unmanaged ACACIA mangium PLAN TATIONS to delayed thinning in north-east Thailand

The effects of delayed thinning on the survival and growth of residual trees in 14-year-old unmanaged Acacia mangium stands in north-eastern Thailand were studied for 8.3 years. Two types of row-thinning were used: alternaterow thinning and every-third-row thinning plus selective thinning of the remaining two rows. Both types reduced mortality of residual trees to less than 26% of that in the unthinned stand. Both types also increased stand and individual stem volume compared with the unthinned stand. The stimulation of volume increment occurred with 1.2 years of thinning but lasted for only about 3 years. Trees of all sizes responded, although increased volume increment was greatest for larger trees. During the 8.3 years, alternate-row and third-row plus low thinning increased total stand volume increment by 5.8 and 4.2 times above that of the unthinned stand. Both thinning regimes also promoted greater production of merchantable wood volume. Of the two thinning methods, alternate-row thinning was superior to third-row plus low thinning in terms of total stand volume increment and merchantable volume production. Our results indicated that previously unmanaged stands of A. mangium were still capable of responding to thinning with increased volume growth even when the treatment was delayed 10 years, beyond the time normally recommended for the species.