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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3.1 NUMBER OF TREES
Estimates of the number of trees in a forest stand or per unit area are needed for various purposes, e.g. to assess the success of a regeneration or revegetation programme, to determine the volume of timber in an area using a volume tariff, etc. Most often, the estimates are derived using equal probability sampling methods based on fixed-area plots, quadrats or points. Fixed-area plots are probably the safest to use as problems can arise with the latter two methods when the pattern of occurrence of the trees is clustered or there are gaps in the regeneration mosaic (Greig-Smith, 1964) . An approach to overcome some of these problems was published by Ward (1991). It involves triangular tessellation, uses randomly or systematically located points, and is easy to implement in the field, viz. the sides of a triangle formed by three trees around a sample point are measured for horizontal length and fed into a hand-held computer containing a simple program (listed on p. 289-290 of Ward's paper) which outputs an estimate of stems per hectare. Sampling stops when the cumulative estimate stabilises.
If for some reason an angle-count sample (point sample) forms the basis of the estimate of stocking density (trees per hectare) at a sample point in the forest (e.g. the assessment is just one part of a much broader, multi-stage inventory), the estimation formula is:
where BAF is the basal area factor (m2/ha) of the angle-count instrument used,
n is the number of trees counted 'IN' in the sweep,
and gi is the basal area of the i-th tree counted.