Demarcation of the felling block

1. The location of the felling block is determined from a 1:50,000 scale map. The UTM co-ordinates are read for each corner of the compartment and an assessment is made to determine the point of easiest access.

2. This starting point is found in the field using a GPS unit. A search is made to determine whether the felling block boundaries can be found. If not, the boundaries are re-established by a cut line, with the cut line direction maintained by compass sight. This line is cleaned so that it is well-defined and easy to walk along. Trees up to 5 cm dbh that lie along the line are felled. Clearly marked off-sets are made around large trees. A slope correction is made whenever the angle of slope exceeds 5 ^o for more than 20 m.

3. The directions of the block boundaries are usually given on the 1: 50,000 scale topographic map. Most boundaries follow the UTM grid system and are aligned on the cardinal bearings. This gives magnetic bearings of 14 ^o, 104 ^o, 194 ^o and 284 ^o, after allowing for magnetic variation (14^o W). At each corner of the block the UTM position is confirmed using the GPS unit.

4. Survey stakes are placed at 100 metre intervals along the northern and southern boundaries of the block. The interval between each stake is measured using a 30 m Land Chain. On the eastern and western boundaries stakes are placed at 20 m intervals, with double stakes set at every 100 metres.

5. Cut lines are then made within the block from the southern to the northern boundary linking the 100 m stakes. The cut line direction is maintained by compass sight. The lines are lightly cut, yet opened sufficiently to allow easy access. Survey stakes are placed at 20 m intervals, with double stakes at 100 m intervals. The harvesting block is thus defined by ten parallel transects of 1,000 x 100 m.

6. During the field survey each transect is divided into fifty 20 x 100 m measurement units. Yellow flagging ropes are laid out to indicate the north and south limits of each unit. Booking is closed every fifth unit, making 10 survey units per transect, as indicated in Figure 1.

7. The survey team consists of two groups working closely together. The first group consists of four people who are responsible for laying out the flagging rope between successive measurement units. A second group of three carries out the tree measurements. At least three 100-m flagging ropes are laid out at any one time connecting the marker posts set at the west and east boundaries of each measurement unit.

8. The survey team begins in unit one and works north following the sequence indicated in Figure 1. On completion of the first transect the team then work southwards down the next transect (i.e. from units 20 to 11). This method of working continues until the whole block has been surveyed. The expected output per measurement team over reasonable terrain is one transect per day (i.e. 10 ha).

1 2 3 4 5 6 7 8 9 10 Transect number

A standard form is used to record all the information (see below).

11. For the commercial species (see species list), those trees above 30 cm dbh without a buttressed stem are measured to the nearest centimetre at the standard measurement height of 1.3 m above ground level. A 5 m fibre-glass diameter tape is used to measure dbh. For trees with buttresses the measurement is made immediately above the buttress, using the diameter tape or, where the buttress height is very high, preventing the use of the tape, by eye. These ocular estimates are recorded to the nearest 5 cm. They demand that the field crews are well trained and continually re-assessed to ensure that consistent and accurate stem diameter measurements are taken.

12. For non-commercial species, trees above 60 cm dbh are measured to the nearest centimetre. All other mensuration procedures are the same as above.

A visual inspection is then made to record evidence of logging damage (caused by either felling or skidding), using the following codes: