Plot layout

Each sampling unit consists of a cluster of five plots. The plot design employs a combination of variable plots (point sampling) and fixed plots (Figure 2). Trees with a dbh equal or greater than 15 cm are enumerated in the variable plots while the smaller trees (less than 15 cm dbh) are enumerated in fixed circular plots. The variable plot samples, proportional to the size of tree and therefore the same sampling intensity, are allowed for small and larger trees. In other words, the larger trees that contribute significantly to the standing volume are given better chances of being tallied compared to fixed plots (with samples being proportional to the frequency of stems within the plot). This allows for better estimates of basal area and volume. In addition, the point sampling does not require the demarcation of plot boundaries. This reduces costs and also avoids sampling errors normally associated with poor boundary demarcation in fixed plot methods. However, for the smaller trees, the point sampling method is not efficient and thus a fixed plot design is adopted to obtain reliable estimates. Details of the plot design and parameters measured are given in Table 4.

The inventory also collects data on the presence of bamboo, rattan, palms and other non-timber forest products (NTFPs). Such information is useful and can indicate the degree of disturbance, as usually the abundance of bamboo and rattan is associated with large canopy openings due to logging.

Table 4. Plot design and parameters measured

Plot shape/size	Tree sizes sampled	Parameters measured
Variable plot	All trees ³ 15 cm dbh	Species, dbh, crown condition, illumination class, wood quality and weed infection
Quarter circle	Estimate of non-timber product distribution e.g. rattan, bamboo, palms	Estimated extent and species
Fixed circular	All saplings ³ 5 cm and < 15 cm dbh	All saplings ³ 5 cm and < 15 cm dbh
Fixed circular	All seedlings < 5 cm dbh and >1.5 m height.	Species, counts