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Growth and development of a selectively cut hill dipterocarp forest in peninsular Malaysia Yong, Teng Koon


A Selective Management System (SMS) which emphasizes leaving intermediate-sized trees (30 to 45 cm dbh) was strongly recommended as a viable system for management of the hill dipterocarp forests. Due to the lack of reliable and quantitative data, a growth and yield study was carried out to assess the effects of selective cutting on the growth and development of the residual stand. Prior to harvest, the stem frequency distribution of the hill dipterocarp forest exhibited a reverse J-shaped stand structure, with generally higher variability (coefficient of variation) being observed for trees in the higher dbh classes. The non-dipterocarps were the dominant species, and the application of the various treatments further enhanced the proportion of the non-dipterocarps, by removing a higher proportion of the dipterocarps. Forest harvesting, in general, enhances forest regeneration: five of the replicated treatments exceeded their precut number of stems/ha (5 cm dbh and larger). Results of repeated measures multivariate analysis of variance indicated that there was no evidence of different growth trends among the replicated treatments, in terms of number of stems, basal area and gross volume. The residual stands showed signs of response to the various treatments applied 14 years after harvest. However, the overall increment rates of all trees 30 cm dbh and larger were relatively low, when compared to the rates assumed under the SMS. The overall gross volume growth of all trees 30 cm dbh and larger was 0.80 m3/ha/year, while the periodic annual diameter increment (DPAI) averaged only 0.39 cm/year when compared to 2.0 to 2.5 m3/ha/year and 0.8 to 1.0 cm/year, respectively assumed under the SMS. Though the DPAIs of the dipterocarps were significantly higher than that of the non-dipterocarps, their overall contribution to forest growth was small due to their lower stocking in the residual stand. The overall mean mortality (2.73 %) of all trees 30 cm dbh and larger over the 14 year period was higher than that assumed under the SMS, while the ingrowth of trees (3.35 %) surpassed that expected under the SMS. Besides poorer than average site conditions, the low growth rates could be attributed to the lack of post-harvest silvicultural treatments. Based on these growth rates, anticipating a second cut in 25 to 30 years as stipulated under the SMS, would be overly optimistic for this study area.

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