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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2.1.4 VOLUME

Procedures for estimating the volume of individual tree stems vary depending on whether the tree is standing or felled and whether direct or indirect measurement is used. Procedures to follow during measurement include those already listed in Sections 2.1.1 (diameter), 2.1.2 (height) and 2.1.3 (bark thickness). Additional procedures necessary in various situations for deriving reliable estimates of volume and ensuring a safe work environment are listed below.

2.1.4.1 Standing Sample Trees: Direct Measurement

 The following procedures apply specifically to conifers and may need adaptation for hardwoods.

Procedures related to measurement

  • Before measurement commences, clearly mark the breast high position (1.3 m) on the bole and use this mark as the datum for later height measurement (superimpose the 1.3 m marks on the linear tape and tree and read heights above ground directly) . Sometimes a marked point at some other height may be more convenient.

  • If possible, take measurements over the full length of bole distributing them roughly proportional to volume (or value), i.e. concentrate at least one-half of the measurements in the lower third of the bole, e.g. for a tree of dbhob 60 cm, total height 30 m, and 10 points of measurement, an appropriate distribution would be : 0.3 m , 0.7 m, 1.3 m, 2.5 m, 5 m, 8 m, 11.5 m, 15.5 m, 20 m, and 25 m. In some circumstances, e.g. for repeat measurements, fixed length sections may be preferred.

  • Should a sharp reduction in diameter occur at any point along the bole, measure both immediately below and above the point of sudden change in taper.

  • If one's exclusive interest is in the sawn product, confine the points of measurement above breast height to mid-internodes; otherwise, measure at any convenient point along the internode but avoid points with abnormal cross-section due to local swelling, damage, etc.

  • When measuring bark thickness, use the safety belt and branches to move around the tree bole to obtain the most suitable position for using the gauge properly at each of the four selected positions. Do not attempt to measure all four from a single position on the bole.

    Procedures related to crew safety

  • Exclude from climbing persons with a genuine fear of heights or who have an impediment which restricts their climbing ability. Normally this will be considered in crew selection and training.

  • Avoid taking any kind of risk when climbing. Do not skylark.

  • Don't sit or stand under a tree being climbed except when the climber requires a measurement of height above ground; and avoid taking measurements on the lower bole of a tree when another person is aloft.

  • Always wear a safety helmet when on the ground and a safety belt when aloft.

  • Before climbing a tree, thoroughly check the condition of the belt and test it with your full weight on the lower bole. Ensure the buckle is engaged, the belt tongue is secure in its keeper, and the belt itself is not so tight that movement is restricted. Do not climb until you have full confidence in the belt.

  • Ensure that equipment carried aloft (e.g. girth tape, bark gauge) is firmly secured to your person. Should a piece of equipment be dropped or a pine cone or branch be dislodged, shout a warning immediately to those below.

  • Do not deliberately drop equipment from aloft.

    Procedures related to the use of ladders

  • Use them only on the lower bole up to the base of the green crown - unless higher branches are too small to carry a person's weight or the internodes are too long.

  • Don't overdo pruning of the lower branches. These help stabilise the ladders and offer useful footholds when moving around the bole to measure bark thickness. Prune only those lower branches which impede either erection of the ladders or climbing.

  • Climb with caution. Wear light footwear preferably with a non-slip sole.

  • Climb a vertical ladder unsecured at the top by holding the tree bole with the hands.

  • Secure each ladder section firmly to the tree before ascending further.

  • When attaching a new section to an already secured ladder, stand on the second or third rung from the top, secure your safety belt to the tree, and thread the new section of ladder between your person and the tree into the female coupling. If the tree is sinuous, it may be necessary to loosen the chain securing the upper section of ladder before the new section can be engaged.

  • The load limit for an extended set of climbing ladders is one person. Except in exceptional circumstances, do not ascend a tree when another person is aloft. In the exceptional case, ensure that the person aloft is firmly secured to the tree by safety belt and remains motionless while the second person climbs.

  • Climb in the green crown making full use of branch crutches as holds for hands and feet. Test each branch before giving it your full weight. Be extremely wary of dead branches.

  • Disengage a set of ladders one section at a time by releasing the chain of the upper section and retreating to the second upper rung of the section next below. Then secure the safety belt, gain a firm purchase on the lower rung(s) of the section to be removed and with a gentle sideways 'to and fro' motion, disengage the ladder. Release the safety belt, thread one arm through the gap between the two upper rungs, and lower the ladder to ground.

2.1.4.2 Standing Sample Trees: Indirect Measurement

Volumes of standing trees are measured indirectly using either tree volume functions or dendrometry. With tree volume functions, the one or more independent variables appropriate to the function are measured, using procedures described elsewhere in this chapter, and volume is estimated from the function. When using dendrometry, some additional precautions need to be followed as listed below. Remember that :

  • Tree stems are seldom truly circular.

  • Dendrometry involves estimating diameter along the bole generally in the one plane only.

  • A reliable bark function or correction factor is required to derive underbark estimates. Thus, volumes derived from dendrometry cannot be expected to be as accurate or as precise as volumes derived from direct measurement.

  • An appropriate size of crew for forest inventory based on dendrometry is commonly three persons.

  • Check the tree for lean. If leaning, set-up the dendrometer on the ground in a plane perpendicular to the plane of lean (this is vitally important for dendrometers using the optical fork principle to determine diameter, e.g. Relaskop, Telerelaskop). If appropriate, measure and record the lean so that later height (section length) measurements can be adjusted.

  • If log grade is part of the estimation process, ensure that at least one crew member is thoroughly familiar with the grading specifications.

  • Position the dendrometer on the ground such that the sighting angle to the tree tip is 45°ree; or less; the full width of the bole at breast height can be seen through the eyepiece; and a good view is possible of the majority of the bole including the tip. Time spent selecting the best position for viewing is well worthwhile.

  • Measure diameters at breast height and below by girth tape. If underbark volume is required, measure and record bark thickness at breast height.

  • Stand upright to one side of the base of the tree a datum pole 2.5 to 3 m long and brightly painted at the tip. Take the first dendrometer readings of diameter (dp) and height to the top of the pole. Check that dp is either less than the breast high diameter ( i.e. dp < d) or if not, that the anomaly is explainable (e.g. local swelling).

  • Before taking any reading, ensure that the section of bole under observation is sighted in a plane perpendicular to the longitudinal axis of the section.

  • Check that each subsequent reading of diameter and height along the bole is consistent with the reading recorded previously and immediately check any anomalous result. If the reading is found to be correct, seek an explanation for the anomaly and make an appropriate noting on file: this is essential for verifying that the recorded measurements are sound should they subsequently be rejected during processing. A schema of the tree showing the points of measurement, and highlighting any features likely to have influenced measurement, is particularly useful in this process and should be made mandatory.

  • Distribute points of measurement along the full bole roughly proportional to volume (or value) as described in Section 2.1.4.1. Preferably select them well away from the branch nodes on a representative section of the bole.

  • If an estimate of merchantable volume only is sought, dendrometer readings will be required up to the merchantable limit. However, for trees of excurrent habit, this limit is often determined by some specified minimum top diameter. In this case, preferably take the final (upper) reading beyond the expected limit (judged by eye) and subsequently derive the merchantable limit later by linear interpolation during processing. For trees of deliquescent habit (most mature hardwoods), the merchantable limit is often set by crown break. In this case, take the final height reading to the base of the break but record diameter at a representative point below, i.e. at the level of least diameter.

  • In advance of measurement, prepare either an appropriate form (hard copy) or format on a portable data recorder/field computer for recording the data.

2.1.4.3 Felled Sample Trees: Direct Measurement

 Measurements commonly required on felled trees include length, diameter and bark thickness. Instruments mostly used comprise the girth tape and caliper for diameter, logger's (linear) tape for length, and bark gauge for bark thickness. The procedures recommended for measuring standing trees (Section 2.1.4.1) mostly apply to felled trees as well, but owing to the different situation (tree on the ground), some additional procedures need to be followed, viz.:

  • Prior to felling the tree, circumscribe the bole with a clear mark at breast height (or at some other datum on the lower bole at a known height above ground) to enable heights above ground after felling to be read directly.

  • Fell the tree on top of small logs placed at intervals along the expected line of fall and perpendicular to it. This improves access to the underside of the tree for measuring diameter by girth tape and bark thickness by bark gauge.

  • Lay out unused equipment at the stump (e.g. on a small tarpaulin or kit-bag, etc.).

  • Add one or more cant hooks to the equipment list for rolling the tree when required.

  • Trim the branches by axe or chainsaw and move the smaller branches away from the tree so that a clear line of access is established along both sides of the bole.

  • Immediately after trimming the bole, measure and record total and merchantable height and any other heights of interest ensuring that the tape is kept straight and taut during the measurement.

  • Mark the intended points of measurement along the bole with lumber crayon. If bark is to be removed after measuring the overbark diameters so that underbark diameters can be measured directly, make saw cuts into the surface of the wood just below each point of measurement to facilitate later relocation.

  • If underbark volume is needed and time and costs permit, debark the tree either completely or in bands approx 10-15 cm wide at the selected points of measurement. Ensure that the sections of bole to be measured are clear of all bark before measurement.

  • If a caliper is specified for measuring diameter and the underside of the bole is not accessible, measure along two axes lying perpendicular to each other and roughly at 45°ree; to the vertical plane. If the tree is not barked and underbark volume is required, measure bark thickness by gauge at the four points of contact of the caliper arms with the bole.

  • On occasions, the tree bole may be partly embedded in the ground. If a girth tape is specified for measuring diameter, use a small, light crow bar to dislodge the earth beneath the bole and a thin flexible steel probe with a hook at the distal end for 'threading' the tape under the bole. Measure bark thickness at four readily accessible points distributed at roughly 90°ree; intervals around the perimeter of the bole.

  • For measuring diameter at unrepresentative points, follow the procedures described in Section 2.1.1.

  

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