Soil Conservation Surveys Guidebook

Table of contents

7 Transect method for areas 10 hectares and smaller

For small areas typically 10 ha or less, the surveyor must establish a series of parallel transects within the survey area, with survey points assessed at defined intervals along each transect. Transects should be laid out to cover the area evenly with approximately 500 points. Two steps are then involved:

7.1 Preparation

Follow the steps below:
 
  1. Walk through the survey area to determine the main orientation of soil disturbance, if any. See Figure 10.
  2. Decide on a transect orientation that will cross the major disturbance at right angles. If the disturbance has no major orientation, locate transects in a convenient direction.
  3. Record the transect bearing on the Transect Survey Field Card (FS 885; see example in Appendix 6).
  4. Using Table 3, determine the transect and point spacing for the size of the survey area. Transect and point spacings are shown for areas up to 20 ha in size. It may be cost-effective to use this method for areas up to 20 ha if they have gentle terrain and a limited slash loading.
  5. Determine the starting distance for the first transect from the point of commencement (POC) by picking a random number from Appendix 3.
To select a random number, first choose a row from 1 to 40 and a column from 1 to 12. The number in the table at the intersection of the chosen row and column is the one to use as a random percentage. (If a number larger than 100 is selected, use the last two digits.) Multiply the selected random percentage by the transect spacing from Table 3 to determine the distance from the POC to the first transect.

Table 3. Transect and point spacings for small area surveys. Survey points established at these spacings will achieve a sample size of 500.


Area (ha)
Transect spacing (m)
Point spacing
within transects (m)

1.0
1.5
2.0
2.5
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
13.0
14.0
15.0
16.0
17.0
18.0
19.0
20.0

5
6
8
10
12
16
20
24
28
32
36
40
44
48
43
46
50
45
48
51
54
57
4
5
5
5
5
5
5
5
5
5
5
5
5
5
6
6
6
7
7
7
7
7

7.2 Field survey layout

Follow the steps below:
 
  1. Establish and label the point of commencement (POC) (see Appendix 5 for marking conventions).
  2. Lay out a baseline perpendicular to the transect orientation and flag the location of each transect. Try to locate the baseline in the middle of the area you are surveying so that you have a reference point to help you accurately locate transects.
  3. For the first transect, proceed along the baseline using the distance calculated in step 5 of the "Preparation" section. Figure 10 shows a typical layout for this small area method.
  4. Sketch a map of the survey strata on the back of the Soil Disturbance Summary Card (FS 889; see Appendix 6). This will help you keep track of your progress and record the survey coverage.

Figure 10. Typical transect survey layout for small areas (<10 ha). The layout shows the transect lines crossing the skidding disturbance. The solid transects are measured first; the dotted transects are added if necessary.

 
  1. Chain along the transects in slope distance. Transects must be chained to ensure that sample points are located without bias. Various methods may be used as long as the points are determined objectively.

    The recommended method is for two people to chain 100-m segments and then make point observations while walking towards each other. A hip chain is not acceptable here, as it is difficult to locate sample points objectively when walking over or around obstacles.

    On uneven terrain, keep the chain near the ground (within 1 m) by hooking it under slash or running shorter distances. Leave flagging to mark the start and end of each transect segment (e.g., each 100-m section) you survey (see Appendix 5 for field marking conventions). Do not move the chain until those measurements are complete.
7.3 Observations along the transect
Tie or stake the chain taut and classify the soil disturbance directly below every survey point on the chain, using the spacing determined from Table 3. Record results on the Transect Survey Field Card (FS 885) using the symbols from Tables 1 and 2.
Measure to the edge of the survey area. Do not sample the zero point and do not count points that fall outside the survey area (e.g., permanent access structures, mapped non-productive areas).

7.4 Locating subsequent transects

At the end of a transect, move over the equivalent of two times the transect spacing. If you wish, mark the additional locations of the transect end points that could be completed in a full survey. Start the next transect.

7.5 Field calculation procedure

Use the Small Area Transect Survey Calculation Card (FS 897) to summarize the results from your preliminary survey. A completed example of this form is shown in Appendix 6.

  1. Add up the number of points classified as counted soil disturbance and the total number of surveyed points. Enter these values in the "Preliminary Survey" column of form FS 897.
  2. Calculate the preliminary percentages for counted disturbance by dividing the total for each by the total number of surveyed points.
  3. For counted disturbance, obtain the confidence interval (CI) from the table on the back of the calculation card.

    "Sample size" on the card means the total number of survey points. The column head "%" means the percentage counted disturbance from step 2.

  4. Calculate the upper and lower confidence limits for the preliminary counted disturbance. To do this, add and subtract the confidence interval to the percentage disturbed and to the percentage displaced.
  5. Using the upper and lower confidence limits as shown in Table 4, determine whether further surveying is necessary.

Table 4. Decision rules for comparing survey results to prescription limits


Case Preliminary percentage Confidence limit (CL) Decision

1 Above Lower CL is above the prescription maximum Stop surveying
2 Below Upper CL is below the prescription maximum Stop surveying
3 Above Lower CL is below the prescription maximum Survey remaining transects
4 Below Upper CL is above the prescription maximum Survey remaining transects

7.6 Finalizing the survey

Follow the steps below:
 
  1. If necessary, survey the remaining transects.
  2. Subtotal the counted disturbance and then total number of points for the additional transects and record these numbers in the appropriate column.
  3. Add these subtotals to the previous subtotals for the preliminary survey above to determine the final survey totals. Enter these survey totals on the FS 897 form in the top "Final Survey" box.
  4. Calculate the final percentages for disturbance, as done in step 2 of the preliminary survey.
  5. For counted disturbance, obtain the confidence interval (CI) from the table on the back of the calculation card.
  6. Calculate the final upper and lower confidence limits for counted soil disturbance.
  7. Calculate the non-compliance percentages for disturbance by subtracting lower confidence limits from the limits stated in the silviculture prescription.
  8. If the final percentage disturbed and the lower confidence limit (cases 3 and 4) are still on opposite sides of the prescription limit, consider the area to be in compliance.

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