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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2.4 STEM ANALYSIS
Stem analysis enables the history of growth of a tree stem which exhibits truly annual rings to be reconstructed either partially or completely. Whereas partial stem analysis is applied to one position on the stem and provides information on growth in diameter only at that position, complete stem analysis involves sampling at a number of positions and enables the complete history of growth of the stem in diameter, height, surface area, volume or value to be determined.
The procedure used in sampling a stem for stem analysis differs somewhat depending on whether the tree is standing or felled. Stem cores obtained using an increment borer (bark to pith core) or increment hammer (core of recent growth only) are the basis of analysis in standing trees. For felled trees, the analysis is based on excised stem cross-sections (discs or "biscuits") 2-5 cm thick. For small projects, the data are mostly collected and processed manually as described in Jerram (1939). For large projects, collection and processing of the data are mostly done using sophisticated measuring equipment, data recorders and computers.
Field Procedure for Complete Stem Analysis
The steps in procedure in sequential order are:
- Select the tree for analysis in an unbiased manner. If possible the tree should be sound, straight and round (unless this makes it unrepresentative of its class). Record the date, species, location, and history of the tree if known - otherwise, record notes on the general conditions of growth in the area and whether the tree is predominant, dominant, intermediate or suppressed. Take notes on any observable damage to the tree, malformations, etc.
- Locate the breast-high point (1.3 m) on the tree while it is still standing and mark it using lumber crayon, extending the mark around the full circumference of the bole.
- Fell the tree as near to ground level as possible. Immediately after felling, reconstruct the tip (excurrent trees) or establish the position on the ground of the upper extremity of the crown in a line of continuation with the main stem axis (deliquescent trees).
- On multinodal tree species, locate all the spring whorls and mark them with lumber crayon at the stem junctions. Record the heights above ground of each of these whorls by measuring the distance from the breast-high mark and adding 1.3 m. These heights are accepted as being the heights of the sample discs marked in (5) and cut in (8). In effect, the discs are assumed to be representative of the stem at the spring whorls.
- Also mark the stem with crayon at the point of minimum diameter below each spring whorl. Usually with plantation conifers, this point occurs from 10-20 cm below the whorl. If the lower bole is branch free, make marks at regular intervals at representative points (e.g. every 2 m) depending on the intensity of sampling desired.
- Lop the branches to the tip (excurrent trees) or to crown break (deliquescent trees) to facilitate access to the bole.
- Measure and record the following:
- total height of tree (measure by tape the length to the tip from the breast-high mark and add on the breast height of 1.3 m).
- in deliquescent trees, the height to crown break (as well as to the whorls - see (4)). As before, measure from the breast high-mark and add 1.3 m.
- diameter over and under bark at all the points marked in (5). Before removing the bark for the under-bark measurements, define the points of measurement by using a hand saw to make thin cuts in the wood surface immediately below the points of over-bark measurement.
- Cut a disc 5-10 cm thick from either the top of the stump or from the extremity of the butt of the felled bole and decide which of the two surfaces of the disc is to be used in the analysis. Record the height of this surface above ground (by measuring from ground level if cut from the stump or back from the breast-high mark if cut from the felled bole). On the opposite face of the disc, write identifying information, e.g. 15/1 might signify disc #1, tree #15. If the age of the tree is not known, estimate how long the tree would have taken as a seedling to grow to stump (disc) height and record the estimate.
- Cut discs 5-10 cm thick at breast height and at all points of diameter measurement marked on the bole. As in (8), define which of the two surfaces of each disc is to be used in the analysis. Record the height of this surface above ground (measure from the breast-high mark and add on 1.3 m) and identify the disc appropriately on the opposite face.
- Transfer the discs to the laboratory for analysis. If it is expected that there may be some delay before the analysis can proceed, it may be desirable to protect the discs against splitting from drying out by soaking them in a vat of polyethylene glycol (e.g. see Grimmett (1981).
Preparation of the Discs for Stem Analysis
Procedure is as follows:
- On each disc, plane the surface on which the rings are to be counted.
- Taking each disk in turn, draw axes across its face for measuring diameters. The way to do this depends on the shape of the stem cross-section and the position of the pith, viz.:
- Shape of cross-section approximately circular and pith approximately central. Draw two axes passing through the pith and at right angles to each other.
- Shape of cross-section approximately circular but pith clearly offset from centre. Confine measurements to the single diameter passing through the pith.
- Shape of cross-section approximately elliptical and pith approximately central. Measure on the the long and short axes.
- Shape of cross-section approximately elliptical but pith clearly offset from centre. Measure the length of the long and short axes of the section and average. Then, by trial and error, locate and draw the two axes of average length passing through the pith.
- Shape of cross-section irregular and pith approximately central (not uncommon with stumps of large trees). Measure the average length of four axes passing through the pith (axes oriented 45°ree; to each other). Then, by trial and error, locate and draw two axes of this average length passing through the pith.
- Shape of cross-section irregular and pith clearly offset from centre (not uncommon with stumps of large trees). Measure the average length of a minimum of four axes passing through the approximate geometric centre of the cross-section (the relative orientation of the axes is: four axes - 45°ree;; six axes - 30°ree;). Then, by trial and error, locate and draw through the pith at least one axis (but preferably two axes) of this average length.
Procedures for counting the annual rings and compiling growth information on the tree are detailed in standard texts, e.g. Graves (1906), Jerram (1939), Husch, Miller and Beers (1982), etc.
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