Soil Conservation Surveys Guidebook

Table of contents

8 Transect method for areas larger than 10 hectares

For large areas, typically greater than 10 ha, the surveyor must systematically locate a number of grid centres within the area to be surveyed. To do this, points must be assessed at 1-m intervals along two 30-m transects radiating out from each grid centre. The number of grid centres depends on the size of the area to be surveyed. For areas up to 50 ha, a minimum of 30 grid centres is required. For areas larger than 50 ha, one grid centre for each additional 5 ha must be added. (These are recommended as the minimum number of grid centres.) Refer to Figure 11 for layout.

For a more precise estimate of the soil disturbance, it may be necessary to increase the number of grid centres. It is possible to calculate confidence limits for this survey, but they are wider than those obtained using the small area method. Whenever possible, the small area method should be used. In the case of large standards units, all parties (i.e., Forest Service district staff and license holders for the area in question) may wish to consider agreeing on a representative area that could then be surveyed more efficiently using the small area method.

Figure 11. Transect survey layout for large areas (>10 ha). Establish regularly spaced grid centres on cardinal bearings from a random start. As also shown here, survey points are not established in areas of non-commercial cover greater than 4 ha or permanent access structures. Permanent access structures should be surveyed using the road traverse and landing survey methods.

8.1 Grid centres and grid layout

  1. The first grid centre is located along a random bearing from the POC (selected from the table in Appendix 3). If the random bearing leads outside the survey area, add increments of 90° to the bearing until it leads into it. (See Appendix 4 for grid spacings to cover areas of various sizes.) Locate the first grid centre at one-half the grid spacing distance from the POC.
  2. Flag each grid centre. Number the grid centres with unique numbers for each surveyor (e.g., 1, 2, 3... and 101, 102, 103...).
  3. Use cardinal bearings (north, south, east, or west) to locate the remaining grid centres. Chain between grid centres in slope distance. Fill the entire survey area. This may require more or less than the target number of grid centres. The Transect Survey Field Card (FS 885) provides a space for recording the 45° offset spacing that allows diagonal shortcuts between grid centres on adjacent lines.

8.2 Transects and points

  1. Fill in the random POC bearing on the Transect Survey Field Card (FS 885).
  2. At each grid centre, choose a random bearing (from the table in Appendix 3) for the first transect, and add 90° for the second transect. If a grid centre falls outside the NAR, do not sample any transect points at that grid centre.
  3. Mark the start and end of each transect exactly at the 0-m and 30-m marks with blue flags. If large changes in elevation occur, anchor the transect tape. Do not move the survey chain once it is set in place.
  4. Record soil disturbance at the point directly below each metre mark. Fill in data on the Transect Survey Field Card, using the symbols from Tables 1 and 2.

As shown in Figure 12, do not sample portions of transects that are outside the NAR. Do not survey points on permanent access structures, outside the cutblock boundary or survey area, or within non-commercial cover greater than 4 ha. Do not sample points that land outside the NAR (e.g., if 12 m of a transect falls on a haul road, measure only the remaining 18 of the transect's 30 points; do not measure any of the points on the road). Mark each non-surveyed point with an X on the Transect Survey Field Card.

Figure 12. Omit points outside the net area to be reforested (NAR). Do not measure transect points outside the cutblock or on permanent access structures.

8.3 Calculations

  1. Transfer the data for each grid centre from the FS 885 form to the Transect Survey Tally Card (FS 896). This optional form helps verify grid centre totals before the calculations are done.
  2. Calculate statistics using either a spreadsheet or the Transect Survey Calculation Card (FS 895). The Ministry strongly recommends that a spreadsheet be used. (For more information on spreadsheet programs, contact the Forest Practices Branch in Victoria.)
  3. Copy the lower confidence limit data from the bottom of form FS 895 to the Soil Disturbance Summary Card (FS 889) if the calculations were completed without the spreadsheet.
  4. See Figure 13 for a flow chart of the tally and calculation procedure.

To be in compliance, the lower confidence limit for the proportion of counted disturbance must be less than the maximum allowable soil disturbance limit.

Figure 13. Flow chart for forms recording large area transect surveys.


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