Plot layout consists of a single georeferenced stake around which a modified basal area sweep is performed. Trees which are counted as 'in' in the sweep have their structural characteristics measured and recorded.
Basic data required
The following is essential data required for data management purposes:
Geographic coordinates (easting, northing, zone OR longitude, latitude);
Operators: who collected the data;
Date: consistent time format (dd/mm/yyyy);
Time: consistent format (hh:mm) - this is necessary for data management reasons;
Plot name - reference to star transect plot.
Wedge factor used
Additional attributes required are listed in the field data collection sheet and detailed on the metadata page.
Data collection process
Field equipment checklist
GPS - preferally differential
Basal area wedges or prisms or angle gauges
Digital camera (if taking photos)
Laser range finder
Diameter breast height (DBH) tape (or standard tape measure if DBH tape not available)
3 x 100 m tape measures
flagging tape and marker
Plot selection and setup
Select centre point for sweep, hammer in stake and get geographic coordinates of stake location.
Record initial details on field sheet (date, time, plot name, geographic coordinates, prism factor, tape used, and field operator's names). If data is being collected in conjunction with a SLATS star transect, use those detail.
Determine which trees will be measured
Trees to be measured are determined with a 360 degree sweep, with an optical wedge prism or an angle gauge, around a georeferenced stake (the centre stake of a star picket if collected in conjunction with that data), as follows:
Select an appropriate prism or gauge factor for the site. Larger factors will require greater trunk diameters before a tree is included as 'in'. Ideally, the factor selected should include about 10 trees. Some experimentation may be required to determine the ideal factor. Record the selected basal area factor on the field sheet.
Stand at the stake
Hold the prism at arms length and look through it. Be sure to turn the wedge/prism to line up with the angle of the stem.
Slowly rotate clockwise, If a tree trunk appears to overlap the tree viewed without the wedge prism (Figure 1a) or just touches (Figure 1c) the tree is counted as 'in' and is measured. If the trunk does not overlap the tree is not counted (Figure 1b). If using the basal area wedges, count the tree as 'in' if the tree cannot fit in the wedge or just fits in.
Figure 1. Using an optical wedge prism. a) an ‘in tree’—with overlap; b) an ‘out tree’—space between tree and offset image of trunk; c) a borderline tree—slight overlap between tree and offset image of trunk (Source: http://en.wikipedia.org/wiki/Wedge_prism )
Figure 2. Using an Angle Gauge.
Unlike the wedge prism, which is held over the plot center, the surveyor's eye is kept over plot center when using an angle gauge. When using an angle gauge the user must count trees that are larger than the width of the angle gauge, as viewed from the center of the plot. The angle gauge is held a set distance away from the eye of the surveyor. Most angle gauges have a string or chain that lets the user know the set distance. (Source: http://en.wikipedia.org/wiki/Angle_gauge )
If a tree has multiple stems at breast height, then each stem should be checked. Flag all stems which are 'in' with flagging tape and label sequentially.
Any stems that converge at 30 cm or above are considered to be the same tree. This is important for crown measurements. If multiple stems converge from a lignotuber below 30 cm, these are considered seperate trees and their crown measurements should be considered and measured seperately.
Record structural details
For each tree recorded as 'in' measure the following attributes and record on field sheet:
Record if the tree is live or dead on the field sheet
Diameter at Breast Height (DBH) and at 0.3 m (units - cm)
DBH will measured at 1.3 m (breast height) and at 0.3 m using a DBH tape. If a DBH tape is not available, use a standard tape measure. Ensure you mark on the field sheet the type of tape measure used. If trees are distorted (e.g., branches or large swelling) at 1.3 m, a measurement at equal distance above and below 1.3 m will be obtained and these two derived diameters will be averaged and recorded. Any stem at the 0.3 m is considered a tree. If the trees split into two or more stems above 0.3m, each stem will be measured and each measurement recorded separately on the field sheet but as the one tree. In species prone to branching low down, it can be difficult to distinguish between a stem and a branch. In these cases, a stem will be defined as the section of the tree that extends to form part of the upper crown of the tree (Figure 3) (Australia Greenhouse Office, 2002).
Figure 3. Measuring stem diameter at breast height. Source: Australia Greenhouse Office, 2002. Page 60.
Crown Diameter Major Axis and Crown Diameter Minor Axis (units - m).
Determine the major crown axis (axis a crown's greatest width). Use two people and a tape measure to determine the diameter of this axis. Have one person stand under the the canopy border one side of the tree, and one on the other. Measure the distance between them.
Bark Description (smooth, rough)
Record if the bark is rough or smooth.
The tree height, which is defined as the vertical distance from ground level on the high side to the uppermost point, will be measured using a laser range finder, hypsometer or clinometer and tape.
Laser range finder/clinometer
It is important to measure from some distance from the tree so that the top of the tree can be identified.
If not using an automated tool, at least 3 measurements are taken and recorded on the field sheet to determine the tree height (Figure 4):
the horizontal distance to the tree;
the angle/height to the base of the tree; and
the angle/height to the top of the tree.
Ideally, all 5 height measurements should be taken (2 angles and 3 distances), to ensure measurements are correct. From these measurements the height of the tree can be calculated.
Figure 4. Using a laser range finder to measure tree height on flat ground. Source: Australia Greenhouse Office, 2002. Page 68.
Height to first branch
In a similar manner to the method described above, it is possible to determine the height to the canopy, or 'first branch', by measuring the distance to the bottom of the canopy with the laser range finder (Figure 5). Measure to the first "significant" branch, that is, one that is live and clearly contributing to the canopy structure. Record this measurement on the field sheet for each tree.
Figure 5. Using a clinometer to determine height to first branch.