Cruise Design

Measurement

Computations

Fixed Plot Sampling

Determined by

1.Value of product(s)

2.Variability within the stand

3.Budget limitations

Sampling Intensity

Trees in the population are selected with equal probability

Normally plot locations are allocated on an unbiased grid pattern

Works best for large areas with relatively uniform density and species distribution

Application

If highly variable stand, large plots and/or large numbers of plots may be needed to get accurate estimates.

Potential Problems

USFS Way

Sampling Intensity

1. Determine the sampling error for the sale as a whole. (set to 10%)

2. Subdivide (or stratify) the sale population into sampling components as needed to reduce the variability within the sampling strata.

3. Calculate the coefficient of variation (CV) by stratum and a weighted CV over all strata. (this will be covered more later in the statistics lectures)

4. Calculate number of plots for the sale as a whole and then distribute by stratum.

Sample Selection – from Precruise data

Number of PlotsValue of t is assumed to be 2Error is set at 10%

For each stratum, the calculation would look like this:

n1 = (17.6 * 185) / 67.9 = 48 plots

n2 = (7.7 * 185) / 67.9 = 21 plots

n3 = (7.2 * 185) / 67.9 = 20 plots

n4 = (35.4 * 185) / 67.9 = 96 plots

Which totals to the 185 plots for the sale.

Distribute Plots by Stratum

Tree Expansion Factor1 divided by the fixed plot size times the number of plots

Sample Error - step 1 (Calculate Standard Error)

Sample Error – Step 2

36.2% is a bit larger than the level we set to begin with (10%) – Implications?

Sampling Intensity

• Without Precruise data (cheaper)

• Assumes fairly uniform distribution of species, sizes and grades

• Can work for even-aged or uneven-aged stands if assumptions are met

Plot cruise planning: 160 acre tract10% cruise (sample)1/5 acre plots

percent(cruise area)TractsampledArea

acres16.0(0.1)ac)(160sampledArea

Plot Cruising

Fixed Area Plot Sampling

1. Area to be sampled:

Given

Plot cruise planning: 160 acre tract10% cruise (sample)1/5 acre plots (0.2 ac.plots)area sampled = 16.0 ac.

areaplot

sampledAreaplotsofNo.

plots800.2

16.0plotsofNo.

Plot Cruising

Fixed Area Plot Sampling

2. No. of plots needed:.

Plot cruise planning: 160 acre tract10% cruise (sample)1/5 acre plotsarea sampled = 16.0 ac.80 plots needed

plotsareaTract

areativeRepresenta

ch.sq.20ac2plots80

acres160areativeRepresenta

Plot Cruising

Fixed Area Plot Sampling

3. Samples represent how much area?

Plot cruise planning: 160 acre tract each represents 2 acres (20 sq. chains)10% cruise (sample)1/5 acre plotsarea sampled = 16.0 ac.80 plots needed

linesbetweenDist

areativeRepresentaplots between Dist

plotsbetweenDist

areativeRepresentalines between Dist

linesbetween(Dist plots)betweenDistAreative Representa

Plot Cruising

Fixed Area Plot Sampling

4. Plot spacing?

Distance between plots

Plot cruise planning: 160 acre tract each represents 2 acres (20 sq. chains)10% cruise (sample) 5 chain spacing between lines1/5 acre plotsarea sampled = 16.0 ac.80 plots needed

chains 5

chains sq. 20plots betweenDistance

chains)(5plots) between (distance chains sq. 20

Plot Cruising

Fixed Area Plot Sampling

5. Plot spacing?Distance between lines

Offi ce Procedures

Fixed Plot Cruising

Tract size times percentage sampling intensity gives you total sample area needed

Example: 23 acre tract X 10 percent sample = 2.3 acres

Area needed times plot area gives plots needed.

Goal: Select plot size that yields around 4 to 8 trees per plot

Example 1: 2.3 acres X 5 (fifth acre plots per acre) = 11.5 plots (make it 12)

each represents 2 acres

Example 2: 2.3 acres X 10 (tenth acre plots per acre) = 23 plots

each represents 1 acre

Number of Plots

Plot center is marked

Circular plot radius measured

Often 10 percent sampled• Unless huge forest with limited budget

• Or highly variable forest

• Or high valued forest

Operational Features

Fixed Plot – 1/10th acre

Plot Allocation

Can be unbiased yet systematic by randomizing location of start point and bearing of sample lines.

Example of Systematic Layout

Fixed Plot Cruising

Field Procedures

Mark plot center

Start checking trees for tally clockwise from the North for consistency

Mark each finished tree to prevent tallying the same tree twice

Procedure

Slope Correction𝑟𝑎𝑑𝑖𝑢𝑠=√ 𝐴𝑟𝑒𝑎/𝑝𝑖❑

cos 𝑠𝑙𝑜𝑝𝑒

If entire plot doesn’t fall within the survey area, don’t simply shift the plot center so it fits into the tract. This results in fewer edge trees sampled.

Boundary Plots

If entire plot doesn’t fall within the survey area, double count the half that does.

Boundary Plots – Half plot

can be used in corners where all tally trees are counted 4 times.

Boundary Plots – Quarter plots

Boundary Plots - Mirage Plots (preferred)Imagine folding the plot back on itself

Boundary Plots - Walkthrough plots

If a line the same distance from the plot center to the tree, when projected through the tree crosses the boundary, count it twice.

Date = 8/19/2013 Size = 1/10th acre Forest Cover Type =

Stand Size and Condition = Stand Age = Stocking or Density Class =

Site Index = Slope = Soil Classification =

Understory Vegetation = Treatments needed =

Plot = 1

Tree SpeciesDBH Form Class Height Grade Crown ClassNotes

1 RO 14 78 1.5 2

2 SP 16 80 2 2

3 YP 18 82 2.5 1

Plot = 2

Etc.

Tally Sheet

Can be preformed by hand, in Excel or in Two Dog

Trees per acre – by species and/or by size

Basal Area per acre – by species and/or by grade

Expansion Factor equals percent area sampled

Computations

No. of trees Cubic-foot volumes------------------------------------ ---------------------------------

DBH Per acrePer acre(in.) Tract total average Tract totalaverage------------------------------------------------------------------------------------------- 5 1195.5 11.2 1730.4 16.1 6 1432.6 13.4 3767.6 35.1 7 1455.1 13.6 5667.8 52.9 8 1150.6 10.7 6294.4 58.7 9 1128.0 10.5 8379.0 78.2 10 1082.9 10.1 10622.4 99.1 11 823.4 7.7 11142.7103.9

-------- ----- ---------- -------Total 8268.1 77.2 47604.3444.0

Combined Stand and Stock Table

Stand table gives estimated number of stems by size (in this case) and per acreStock table gives total volume and per acre volume (could be board foot or cubic foot)

107.2 acre tract of small mixed hardwoods

Cruise Summary (by species not sizes)