A silvicultural evaluation of stand characteristics, pre-felling climber cutting and directional felling in a primary dipterocarp forest in Sabah, Malaysia

This thesis summarises results of four studies. Two studies concern conditions in the primary forest from a silvicultural perspective, one study concerns the feasibility of directional felling, and one study concerns the impact of felling on the residual stand and the influence thereon of pre-felling climber cutting and directional felling. A field experiment was established to evaluate damage on the surrounding stand caused by felling. The experiment had a 2x2 factorial design with the factors climber cutting (or not) and directional felling (or not), and was conducted in a hilly primary dipterocarp forest in Sabah, Malaysia. A total of 88 commercial trees greater than or equal to 60 cm dbh were selected for felling. Before treatment, the surrounding stand was inventoried including trees with dbh greater than or equal to 10 cm and climbers greater than or equal to 2 cm dbh. There was about 400 stems ha-1 (27% dipterocarps) and 189 climbers ha-1 greater than or equal to 2 cm dbh. An average of 23 trees ha-1 with dbh greater than or equal to 60 cm were found (81% dipterocarps). Basal area was 28.4 m2 ha-1. Climber cutting was done one year before felling in squares of almost 2 ha around trees to be felled. Directional felling was done to avoid damage to marked trees. Gaps were defined as areas surrounding trees felled containing no undamaged trees, delineated by undamaged trees with a dbh greater than or equal to 10 cm (Gap10), and dbh greater than or equal to 20 cm (Gap20). Climber cutting significantly reduced basal area destroyed by about 30%, but not Gap sizes. Of trees treated with directional felling, 90% fell wihin 28 deg of the desired lay, and 10 per cent beyond 60 deg. Climber cutting did not affect accuracy of directional felling. Average range of feasible felling directions was 181 deg. Almost no trees marked for retention by directional felling were damaged, but directional felling did not reduce damage levels. Based on stand structure and composition data, damage levels, Gap sizes, and the high commercial stocking, diameter limit felling is cautioned against in favour of more elaborate selection systems.