B. Statistical tolerances for green-up height

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 green-up height and its 90% lower confidence limit (LCL) are greater than three metres, 3.5 metres or the green-up height specified by the district manager or by the DM and DEO, as the case may be, the area has achieved green-up height. No further height plots are required.
2. If the estimate of green-up height is less than three metres, 3.5 metres or the green-up height specified by the district manager or by the DM and DEO, as the case may be, the area has not achieved green-up height. No further plots are required.
3. If the estimate of green-up height is greater than three metres, 3.5 metres or the green-up height specified by the district manager or by the DM and DEO, as the case may be, but its lower confidence limit is less, sufficient plots must be established and measured to ensure that the desired sampling precision has been achieved.

Sampling precision (e) is acceptable when the confidence interval (CI) is less than or equal to e where:

• e = +/- 40 cm if the estimate of green-up height is less than or
  equal to four metres.
• e = +/- 10% of the green-up height, if the estimate is greater than
  four metres.
• CI = t(n-1) _ Sx

4. Compare confidence interval (CI) to e:

(i) if CI is less than or equal to e, the decision is made that the area has achieved green-up height; no further plots are required,

(ii) if CI is greater than e, more plots are required to meet statistical precision for green-up height

Where more plots are required, use the following formula:

n=t2__ s2 ÷ e2

This states 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).

In a systematic manner, additional plots (up to a maximum of 1.5 plots per hectare) should be established evenly spaced along a pre-defined line.

Once additional plot information has been collected, recalculate statistics and make the decision based on a direct comparison between your estimate of green-up height to three or 3.5 metres or the green-up height specified by the district manager. DO THIS ONLY ONCE - do not establish any more plots or do any further calculations.

Note: Where a statistical analysis indicates that sufficient plots have been established to meet the statistical precision for density, but there are insufficient plots established to meet the statistical precision for green-up height, additional 5.64 m radius plots ONLY (green-up height plots) need to be established. Where a statistical analysis indicates that sufficient plots are established to meet the statistical precision for green-up height, but insufficient plots are established to meet the statistical precision for density, additional 3.99 metre radius plots ONLY (density plots) need to be established.

Example #1

A 20 hectare coastal block. Walk-through indicates area is a single stratum and is likely greened-up. Minimum of 10 plots is established.

Statistical calculations

Stocking M=6	Green-up height
Estimate=1060 trees/ha	Estimate=3.1m
N=10	N=10
S=0.949	S=0.269
T=1.833	T=1.833
Sx=0.300	Sx=0.085
CI=110 trees/ha	CI=0.2m
LCL=950 trees/ha, therefore the block is adequately stocked.	LCL=2.9m LCL is not greater than 3m, however, sampling precision is acceptable, CI < 40cm. Therefore, decision is that green-up height of 3.0m is achieved.

Green-up status: Greened-up

Example # 2

An interior pine stand. The stand is not adequately stocked but density exceeds the minimum density level of 700 countable trees/ha and therefore requires a green-up height of 3.5 metres to be considered greened-up.

Statistical calculations

Stocking M=7	Green-up height
Estimate=960 trees/ha	Estimate=3.8m
N=10	N=10
S=1.816	S=0.268
T=1.833	T=1.833
Sx=0.573	Sx=0.085
CI=210 trees/ha	CI=0.2m
LCL=750 trees/ha, therefore the block is adequately stocked, but meets the minimum stocking level	LCL=3.7m LCL is > 3.5 m. The block has achieved a green-up height of 3.5 m.

Green-up status: The area exceeds minimum stocking levels and has a green-up height greater than 3.5 m, therefore, it is greened-up.

Example # 3

A stocked 4-5 m tall Douglas-fir, larch, pine stand. The minor amount of 2 m tall spruce and western white pine contributes to stocking, but does not meet the green-up objective to provide critical winter wildlife habitat. The district manager has issued a written variance increasing the green-up height requirement of adequately stocked stands to 5 m.

Statistical calculations

Stocking M=7	Green-up height
Estimate=1280 trees/ha	Estimate=4.6m
N=10	N=10
S=1.075	S=0.874
T=1.833	T=1.833
Sx=0.340	Sx=0.277
CI=125 trees/ha	CI=0.5m
LCL=1150 trees/ha this block is adequately stocked	LCL=3.7m LCL is > 4.1 m. green-up height requirement is not achieved.

Green-up status: This block is not greened-up. The 51.5 cm average leader length data indicates that block may be greened-up next year, and will definitely be greened-up in 2 years. A follow-up walk-through is required to confirm achievement of height requirement.