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Point-Double Sampling

Point-double sampling is the best way to estimate volume. Sampling time can be reduced by at least one-third compared to regular point sampling without losing accuracy. This is really two samples. A large sample of inexpensive basal area points estimates basal area per acre. A small sample of expensive volume points estimates volume-basal area ratios. The two combine to estimate volume per acre.

Point Double Sampling Course Outline

Introduction to Point-Double Sampling

Point Sample Calculations
- Review
- Practice

Volume Basal Area Ratios
- Calculation
- Consistency within products
- Application across cruises

Point-Double Sampling Procedure
- Small sample of volume points
- Large sample of basal area point
- Match volume and basal area categories
- Volume point distribution
- Spacing considerations
- Constant proportion of basal area points to volume points
- Walking time and measurement time

Point-Double Sample Calculations
- Small sample volume
- Large sample basal area
- Combinming small sample volume and large sample basal area

How Good is the Answer
- Do try this at home
- Remove volume points from a cruise
- Compare full cruise and point-double results
- Compare full cruise and point-double times

Sample size
- Replace regular point sample without losing accuracy
- Time to measure volume and basal area
- Calculations for small and larger sample size
- Time comparison for regular point and point-double sample

Stand and Stock Tables
- Regular point sample calculations
- Stand and stock table from volume points
- Adjustment with basal area points

Approved for 6 Class 1 CFE credits by the Society of American Foresters