Units of measurement, symbols, significant digits and rounding off
1.1 Units of measurement and symbols
1.2 Significant digits
1.3 Rounding off
1.4 Bias, accuracy and precision
Individual Trees and Logs
2.1 Bole characteristics
2.1.1 Diameter
2.1.2 Height
2.1.3 Bark thickness
2.1.4 Volume
2.1.5 Stem form and taper
2.2 Log characteristics
2.2.1 Diameter
2.2.2 Length
2.2.3 Volume
2.2.4 Weight
2.2.5 Allowance for defect
2.3 Crown characteristics
2.3.1 Width
2.3.2 Depth
2.3.3 Surface area
2.3.4 Volume
2.3.5 Biomass
2.4 Stem analysis
Groups of Trees (Stands)
3.1 Number of trees
3.2 Diameter
3.3 Basal area
3.3.1 Fixed-area plots
3.3.2 Angle count sampling
3.3.3 Advantages and disadvantages of angle count sampling
3.4 Height
3.4.1 Mean height
3.4.2 Predominant height, top height, dominant height
3.4.3 Stand height curve
3.5 Volume
3.6 Crown closure
3.7 Crown biomass
3.8 Growth and increment
References
Appendix 1: Checklist of equipment and materials
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3.3.3 ADVANTAGES AND DISADVANTAGES OF ANGLE COUNT SAMPLING
Advantages
- Relative ease and speed of estimating G. Theoretically, the estimates are exact.
- For periodic assessment, only the sample points (angle count spots) need be marked in the field. However, for ease of location, more identifiers may be required, e.g. blazed or banded trees.
- The method estimates G from a sample so the estimate is subject to sampling error. In a series of estimates, the precision of estimate of G depends on:
(a) the size of sampling unit, i.e. BAF of the angle gauge,
(b) variation of G in the area under study,
(c) the experience of the operator.
- The stocking density (N - number of trees per hectare (or per size class)) is not given directly. However, this information can be derived by having an assistant measure the diameter at breast height of each tree counted in the sweep. The stocking density is then given by:
where F = basal area factor (m2/ha) of the angle count instrument used,
n = number of trees counted 'in',
and gi = basal area (m2) of the i-th tree counted.
An alternative is to lay out a temporary circular plot with its centre at the sample point and count the trees within the plot boundary .
- It is sometimes difficult to obtain a clear unimpeded view of particular trees in unpruned stands or in stands with heavy undergrowth. Using an instrument of higher BAF and moving sideways from the sample point while keeping constant the radial distance to the tree under observation can overcome many of these sighting problems.