cruise design measurement computations. determined by 1.value of product(s) 2.variability within the...
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Cruise Design
Measurement
Computations
Fixed Plot Sampling
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Determined by
1.Value of product(s)
2.Variability within the stand
3.Budget limitations
Sampling Intensity
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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
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If highly variable stand, large plots and/or large numbers of plots may be needed to get accurate estimates.
Potential Problems
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USFS Way
Sampling Intensity
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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
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Number of PlotsValue of t is assumed to be 2Error is set at 10%
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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
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Tree Expansion Factor1 divided by the fixed plot size times the number of plots
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Sample Error - step 1 (Calculate Standard Error)
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Sample Error – Step 2
36.2% is a bit larger than the level we set to begin with (10%) – Implications?
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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
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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
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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:.
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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?
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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
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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
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Offi ce Procedures
Fixed Plot Cruising
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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
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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
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Fixed Plot – 1/10th acre
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Plot Allocation
Can be unbiased yet systematic by randomizing location of start point and bearing of sample lines.
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Example of Systematic Layout
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Fixed Plot Cruising
Field Procedures
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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
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Slope Correction𝑟𝑎𝑑𝑖𝑢𝑠=√ 𝐴𝑟𝑒𝑎/𝑝𝑖❑
cos 𝑠𝑙𝑜𝑝𝑒
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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
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If entire plot doesn’t fall within the survey area, double count the half that does.
Boundary Plots – Half plot
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can be used in corners where all tally trees are counted 4 times.
Boundary Plots – Quarter plots
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Boundary Plots - Mirage Plots (preferred)Imagine folding the plot back on itself
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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.
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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
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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
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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
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Cruise Summary (by species not sizes)