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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2.1.3 BARK THICKNESS

The thickness of bark on trees varies with species, genotype, age, rate of growth and position along the bole. On standing trees, it is measured indirectly by an instrument such as a bark gauge, bark probe, or hammer, nail and graduated scale. Examples of specialised instruments are the Swedish bark gauge and the "handy bark gauge" described by Lewis (1953). The operation is probably the most error-prone of all the operations in forest measurement because it relies heavily on feel. Considerable experience, skill and care are required to obtain reliable results.

Procedures helpful for minimising error in estimating bark thickness on standing trees include:

  • Thoroughly train field crews on a wide range of tree sizes (and tree species if relevant).

  • Use palm and shoulder/forearm pressure only when forcing entry through the bark. Do not twist the gauge at any time or hammer it in. Gauges such as the Swedish bark gauge are easily broken and they are costly to replace.

  • Push the gauge straight in until resistance of the wood is felt, then push the flange firmly against the bark surface and read the scale while the instrument is still embedded. Pull the gauge straight out, firmly and without twisting.

  • Take four measurements at roughly equidistant points around the bole and average to derive the thickness at a given height. Two measurements may be adequate on small diameters.

  • Measurement instructions should indicate whether bark thickness should be measured on the ridges or in the fissures of trees which have furrowed barks.

  • Use a safety belt when working above the ground.

  • On particularly thick and tough barks, use a hammer, nail (10-20 cm long) and a thin metal scale rule and rely on sound and feel to determine when the nail begins to penetrate the wood. On thicker barks, an option is to replace the hammer and nail with a brace and bit.

  • If calipers were used to measure the diameter, measure bark thickness at the points of contact of the caliper arms with the surface of the stem.

On felled trees, bark thickness can be measured indirectly as described above or by measuring the diameter at the specified point on the bole before and after removing the bark. Alternatively, it can be measured directly using a scale ruler either on a cut face perpendicular to the long axis of the stem (e.g. 'v' shaped axe cut) or at the log ends.

 

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January, 1999.