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 �
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 |
