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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2.3.1 WIDTH

The width of a tree crown is measured either by projecting its edges vertically to ground or by scalar expansion of the width of its image measured on an aerial photograph.

When defining a tree crown and projecting its edges vertically to ground, ignore very small individual branches and minor crown irregularities. Use either a plumb bob, 'crown-meter' or 'crownometer' (see Weir 1959, Khan 1971, Tihonov 1971, Jackson and Petty 1973), or a similar instrument incorporating two right-angle prisms (penta prisms) which avoids inverting or reversing the image and eliminates any effect of slight movement on the angle of reflection. Once projection is complete, measure by linear tape the horizontal distance between two or more sets of diametrically opposite edges, and average. Record the results to the nearest decimetre (0.1 m).

The accuracy of estimates of crown width derived from aerial photographs depends on the photographic scale, film resolution, ability of the assessor, and the nature and density of the forest canopy. Often, crown widths estimated from aerial photographs are less than those measured on the ground because, with photo measurements, only those parts of a crown visible from above are measured, i.e. parts obscured by the branches of other trees are not seen . Because of the strong correlation existing between crown width and tree dbhob (d), tree volume tables based on crown width (rather than d) can be compiled for use with aerial photographs. The ratio of crown width to d is called the crown ratio. This ratio is of silvicultural interest and is used in photogrammetry to deduce d from measurements of crown width.

If the crown is regular in outline, calculate its sectional area from the average of the measured widths. If irregular, plumb the edges to ground, measure the horizontal distance along several axes, plot the data and determine the area by planimeter.

 

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January, 1999.