Appendix 1-A. Decision rules for determining the number of plots required for a green-up survey

Unless the maximum number of plots has been established, a separate statistical analysis must be carried out for each stratum for both the number of commercially valuable trees per hectare and green-up height.

A. Statistical tolerances for adequate stocking

A minimum of 10 well-distributed plots should be established per stratum. More plots (up to a maximum of 1.5 per hectare) may be required to meet the 90% confidence interval (CI). Use the following decision rules:

1. If the estimate of total countable trees per hectare and its 90% lower confidence limit (LCL) are greater than 800 total trees/ha on the coast and 1000 total trees/ha in the interior, the area is considered adequately stocked for the purposes of a green-up survey (Figure A-1a). No further stocking plots are required. The area must meet a three metre green-up height before it is considered greened-up.
2. If the estimate of total countable trees per hectare is greater that 800 total trees/ha on the coast and 1000/ha in the interior, but its LCL is less (Figure A-1b), then:

• sufficient plots must be established and measured to ensure that the desired sampling precision has been achieved. The area must meet a three metre green-up height before it is considered greened-up, or
• no further plots are required. The area must meet a 3.5 metre green-up height before it is considered greened-up.

3. If the estimate of total countable trees per hectare and its LCL are less than 800 total trees/ha but greater than 500 total trees/ha on the coast, and less than 1000 trees/ha but greater than 700 trees/ha in the interior (Figure A-1c), the area meets the default stocking levels set in the legislation. No further stocking plots are required. The area must meet a 3.5 metre green-up height before it is considered greened-up.
4. If the estimate of total countable trees per hectare is greater than 500 total trees/ha on the coast and 700 trees/ha in the interior, but its LCL is less (Figure A-1d), then:

• sufficient plots must be established and measured to ensure that the desired sampling precision has been achieved; and the area must meet a 3.5 metre green-up height before it is considered greened-up, or
• no further plots are required. The area must meet a 3.5 metre green-up height and requirements that satisfy the district manager before it is considered greened-up.
5. If the estimate of total countable trees per hectare is less than 500 total trees/ha on the coast and 700 trees/ha in the interior, no further plots are required. The area must meet green-up requirements specified by the district manager before it is considered greened-up (Figure A-1e).
6. Sampling precision (e) is acceptable when the confidence interval (CI) is less than or equal to e where:

• e = +/- 100 stems/ha, if the estimate of total countable trees per hectare
  is less than or equal to 1000 stems/ha,
• e = +/- 10% stems/ha, if the estimate of total countable trees per hectare is greater than 1000 stems/ha,
• CI = t(n-1) _ Sx _ 200, (Sx = standard error of mean)




Figure A-1. Relationship between adequate stocking levels, minimum stocking levels and green-up height requirements.

Note: These scenarios would differ accordingly if the district manager specifies an increased green-up height requirement or the district manager/designated environmental official has specified a reduced green-up height.

7. Compare confidence interval (CI) to e:

(i) if CI is less than or equal to e, the area is considered to be adequately stocked or above the minimum stocking level as the case may be; no further plots are required,

(ii) if CI is greater than e, more plots are required to meet statistical precision and to be considered adequately stocked or above the minimum stocking level as the case may be.

8. Where more plots are required, use the following formula:

    n = t2 x s2 ÷ e2

where: n = the estimated number of sampling plots required to meet sampling precision

t2 = the student "t" value (refer to FS 1138B)
s2 = the standard deviation squared
e2 = the square of the desired sampling precision

This estimates the total number of plots required to achieve the required statistical precision. However, the maximum number of plots for an area is limited to 1.5 plots per hectare (minimum of 10 per stratum).

Additional plots (up to a maximum of 1.5 plots per hectare) should be established systematically along a pre-defined line or randomly.

Once additional plot information has been collected, recalculate statistics and make the decision based on a direct comparison between your estimate of total countable trees of per hectare and 800 trees/ha or 500 trees/ha on the coast and 1000 trees/ha or 700 trees/ha in the interior, as the case may be. DO THIS ONLY ONCE - do not establish any more plots or do any further calculations.