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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2.1.1 DIAMETER
The most common and most important measurement made on forest trees is that of the diameter of the stem. The measurement is usually derived indirectly using a linear tape calibrated in π units to allow diameter to be read from a girth measurement. Diameter can also be read directly using a caliper as described later.
The universal convention is to measure the diameter of trees at a fixed height above ground called breast height (BH). This fixed height is 1.4 m in many countries of the world including New Zealand and 1.3 m in many other countries including Australia.
Recommended procedures for measuring diameter at BH under Australian conditions are:
- Check that the instrument (diameter tape , caliper) is in perfect working condition, viz.,
- tape: not kinked (steel) and calibrations easy to read.
- calipers: sliding arm firm (no play), straight tips on both arms, arms coplanar, and calibrations easy to read.
- Identify the zero mark (origin of measurement) on the girth tape.
- Displace loose mounds of soil and litter around the tree base and remove any vines, lichens, moss and loose bark at breast height (BH).
- Measure at 1.3 m above ground.
- On sloping ground, measure on the uphill side of the tree irrespective of its disposition, i.e. vertical or leaning.
- On level ground, measure leaning trees on the under side of the bole.
- Locate BH using a stick cut to length (assuming the point of measurement is not already marked on the tree, e.g. paint or scribe mark). In some applications, such as when measuring small sized material and recording the data in 2-3 cm classes, the point of measurement may be determined from a position on one's person known to be 1.3 m above ground.
- Measure in a plane perpendicular to the longitudinal axis of the bole irrespective of whether the tree is vertical or leaning. Minimise the diameter measurement at that point.
- Keep the tape comfortably taut at the moment of measurement.
- Measure coppice stems at 1.3 m from ground level, not from the level of the stump or stool.
- Treat as double stems (B2), triple stems (B3) or multiple stems (Bn, where n indicates the number of forks) trees which breach or fork below BH, and record a diameter for each fork locating the BH points from ground level.
- Treat trees forking above BH as single stems. Code these as double leaders (D2), triple leader (D3) or multiple leaders (Dn).
- For trees forking at or just above BH, measure the diameter below the fork at the point of minimum bole diameter.
- Measure buttressed and fluted stems at a representative point above BH. Should the unrepresentative condition extend well up the bole, specify an arbitrary height for measurement, e.g. 3 m above ground.
- With calipers, record the diameter along two axes perpendicular to each other and average the result (arithmetic mean). Ensure that the caliper arms rest firmly against the tree or log surface and that its long axis lies perpendicular to the longitudinal axis of the object at the moment of measurement.
- If measurement of a single axis by caliper is acceptable (e.g. when the data are being grouped into, say, 5 cm diameter classes, or when measuring a large number of trees), take special care when measuring noticeably eccentric trees. In such cases, take the measurement on an axis approximately mid-way between the long and short axes.
- To derive underbark diameter from caliper measurements made on standing trees, record bark thickness at the points of contact of the caliper arms and the tree surface.
- If the BH point is unrepresentative (due to some malformation, e.g. branch whorl, fire scar, mechanical damage, etc.) , take two measurements equidistant above and below the nominal point of measurement and average the two diameters. However, if the diameters differ appreciably in size, average their sectional areas and derive the diameter equivalent. Alternatively, choose for measurement a point on the bole judged by eye to be representative of the diameter at the nominal point of measurement had the malformation not been present.
- Should the BH point on a tree in a permanent sample plot or experimental plot be unrepresentative, follow the procedure outlined next above and then locate by trial and error a point of equivalent diameter on the stem. Mark this second point permanently on the bole (paint mark, soft nail, scribe mark, etc.) and confine subsequent remeasurements to it. Alternatively the height of measurement from the ground should be recorded (e.g., for smooth-barked trees).
- When measuring diameter at points along the bole other than BH, check that the point of measurement is representative. If unrepresentative, apply the same procedure as described above for an unrepresentative BH. If the point resides on or near a whorl at the upper extremity of the merchantable stem, measure the diameter at the position of smallest stem diameter below it (but record height to the unrepresentative point).
- In periodic (repeated) measurement, mark the BH point permanently on the stem with a scribe or paint mark.
- Trees of dbhob less than a certain specified minimum diameter, e.g. 10.0 cm, may be ignored in some inventories or may be recorded only as number of stems.
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