An important perquisite for sound decision -making in forest management is accurate information on forest conditions, such as regeneration status, standing timber stock, factors inhibiting growth, prospects for harvesting, etc. Such information is usually derived from a field inventory. From satellite imagery interpretation, virtually the entire project area is classified as Stratum 4. Stratum 4 is defined as ‘very poor’ forests, having 1-4 trees ha-1 greater than 60 cm DBH. Due to poor timber stocking, the project area was considered suitable for forest plantations. This satellite interpretation was subsequently followed by and aerial assessment over the entire project area by helicopter

               In preparing the forest management plan for the project area, a quick field inventory of timber resources was carried out to verify these conditions on the ground. Ten inventory plots were located randomly in the lower part of the project area, south of the designated wildlife corridor. These inventory plots are used in this FMP to describe timber resource conditions for the project area, and are assumed to represent the overall forest condition of the project area. The results represent mean values for the entire project area, with no spatial reference.

 

3.1 Inventory Methods

Ten inventory plots were placed randomly over the designated project area. The inventory method used plots arranged continuously along a 20 m wide and 800 m long linear strip.

               Standing timber stock- All trees > 30 cm DBH were enumerated on 10 x 20 m plots along the strip, whereas trees ≥10 cm DBH were enumerated within 10 x 10 m plots along the same strip.

               Potential crop trees (PCTs)- PCTS > 5 cm DBH were selected within the 10 x 10m plots. PCTs are defined as those commercially valuable trees below the minimum cutting limit (i.e. 60 cm DBH), of good form and vigour, and most likely to form the future crop of harvestable trees. A defective commercial tree does not count as a PCT. Defects were defined as those thought to undermine the future survival, suitability and quality of the tree for timber production (e.g., termite infestation, severe bark damage, leaning bole, poor stem form, multiple leaders, and broke crown). Only 2 PCTs were allowed to be selected within the 10 x 10 m plot, thereby giving a maximum stocking of 200 PCTs ha-1.

               Vines- Vine abundance was also evaluated. They were separated into two groups: woody vines and climbing bamboo. Woody vines and climbing bamboo were counted within the 10 x 10 m nested sub-plots. For woody vines, only 2 stems ≥ 2.5 cm DBH were enumerated. For climbing affected by vines, all trees >5 cm DBH within the 10 x 10 m plots were evaluated for the presence 0r absence of vines, either on their boles or crowns.

3.2 Inventory Results

Standing Timber Stock

The project area is extremely poor in commercial trees greater than 60 cm DBH . Current standards in natural forest management require a minimum of about 9 harvestable trees ≥ 60 cm DBH ha-1 for an economic cut, whereas the commercial stocking of the project area presently stands at 5.7 trees in this size class. Therefore, by current cutting limits, there is limited commercial volume to be extracted from the area for and economic cut. Most trees are in the 20-40 cm size class. Dipterocarps account for only 6% in size class.

               Overall stand basal area of trees ≥ 20 cm DBH is about 25m2ha-1. This is considered very low when compared to a pristine forest, where basal area usually ranges 30-38 m2ha-1. Pioneer trees (mainly Macaranga spp.) and other commercial non-dipterocarp species more than 50% of the total basal area.

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Potential Crop Trees

Only 28% of inventory plots in the project area were found to be stocked with PCTs, i.e. overall PCT stocking is considered low. Of the PCTs recorded, almost 50% fall below 20 cm DBH. The distribution of PCTs towards the lower size classes means that the time required for the area to reach harvesting maturity will be longer. About 18% of plots in the project area were recorded as 'gaps', meaning that the are actually devoid of trees. Such open conditions are likely to have been created by poor logging practices in the past.

Vines

Vines are generally light demanding plats that ascend to the canopy by using tree trunks or other vines as structural support. Their proliferation is usually promoted by an increase in light level, such as caused by logging. Vines can be expected to impede tree regeneration and growth once established in large quantities. Their habit of twining around and scrambling over surrounding vegetation has also been observed to cause stem deformities in the saplings and poles of commercially valuable trees. Climbing bamboo is a serious problem in the project area. Therefore, the suppression of vines is an important practice in production forestry. 

                In the project area, about 68% of all trees ≥  5 cm DBH were found to carry either climbing bamboo or woody vines, or both. When only commercial trees were considered, 58% of trees were found to be affected by vines. Such a high level of vine occupancy on the boles and crown of trees is typical of highly disturbed lowland dipterocarp forests in Sabah. In terms of vine density, the area also showed relatively high level of vine density, when compared with and old growth close-canopy forest.      

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