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Source: J. Hollenbeck
Fixed Area Sampling
Avery and Burkhart,
Chapter 10
FOR 220 Aerial Photo Interpretation and Forest Measurements
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Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
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Nominal cruise intensity
How much of the land was
sampled?
Examples:
1/10 acre plot on a 2 x 5
chain spacing:
(remember 10sq. ch. = 1 ac.)
100plotbydrepresenteAcres
acresinsizePlot
=I
10%1001
0.1=
=I
Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
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Plot cruise planning:
120 acre tract
10% cruise (sample)
1/10 acre plots
( )percent(cruisearea)TractsampledArea =
acres12.0(0.1)ac)(120sampledArea ==
Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
1. Area to be sampled:
Given
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Plot cruise planning:
120 acre tract
10% cruise (sample)
1/10 acre plotsarea sampled = 12.0 ac.
=
areaplot
sampledAreaplotsofNo.
plots1200.1
12.0plotsofNo. =
=
Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
2. No. of plots needed:.
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=
plots
areaTractareativeRepresenta
ac1plots120
acres120areativeRepresenta =
=
Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
3. Samples represent how much area?
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=
linesbetweenDist
areativeRepresentaplotsbetweenDist
=
plotsbetweenDist
areativeRepresentalinesbetweenDist
( )linesbetween(Distplots)betweenDistAreativeRepresenta =
Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
4. Plot spacing?
Distance between plots
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=
ft200
ftsq43560plotsbetweenDistance
ft)(200plots)between(distance=ftsq43560
Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
5. Plot spacing?
Distance between lines
( )linesbetween(Distplots)betweenDistAreativeRepresenta =
feet215~plotsbetweenDistance =
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Some advantages of plot cruising:
1. Suitable for one-person cruising.
2. Cruisers do not have to tally trees while following a compass
line.
3. Cruisers pause at plot centers, allowing more time to check
measurements.
4. Tree tally is separated by plots: can separate the plots into
sets to calculate volumes for different timber types, etc.
Plot Cruising
Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
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Purposes:
To evaluate regeneration status
To demonstrate compliance with laws
To determine effectiveness of regeneration treatmentsTo identify additional treatments needed
To collect data to predict growth and yield
Regeneration Plots
Fixed Area Plot Sampling - Different plots for different purposes
FOR 220 Aerial Photo Interpretation and Forest Measurements
Plot-count method (number of trees per acre)Stocked-quadrat method (proportion of land utilized) Staked-point method (like permanent plots)
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Nested Circular Plots
Smaller Trees Measured on Smaller Plots
Fixed Area Plot Sampling
Area
(ac)
Area
(ac)
Radius(ft)
1/500 0.002 5.3
1/100 0.01 11.8
1/10 0.1 37.21/10 acre plot
1/100 acre plot
1/500 acre plot
Trees > 5 inch dbh
Trees 2 to 5 inch dbh
Trees < 2 inch dbh
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Plot Sampling with
Fixed Area Plot Sampling
Plots and Product Groups
1/10 acre for sawtimber, poletimber, invasive ( 5 in)
1/100 acre for small trees
1/500 acre for advance reproduction
TwoDog Product Groups
Code Product Group
1 Sawtimber ( 12 inches dbh)
2 Poletimber (5 in dbh < 12 in)
3 Small Trees (2 in dbh < 5 in)
4 Advance Reproduction ( < 2 in dbh)
5 Invasive Species
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Source: J. Hollenbeck
Point Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
Avery and Burkhart (2002)
Chapter 11
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A method of sampling based on a trees size, rather than
its frequency of occurrence.
Tools: prisms, angle gauge, Relaskop
The probability of tallying a tree depends on its cross-
sectional area and the sighting angle used.
The smaller the sighting angle, the more trees included in
the sample.
Point Sampling
Point Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
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Point Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
Point Sampling(Overhead view)
Each tree has a
given plot size in
relation to itssize.
How many of
these plots does
our point fall
into?
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Point Sampling
Point Sampling(Side view)
FOR 220 Aerial Photo Interpretation and Forest Measurements
?
Offset tree bole in prism has no
overlap with actual tree bole
Offset tree bole in prism
does overlap actual tree bole
Borderline tree - must
measure distance from
point center
Using a prism:
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Fixed plot sampling Point sampling
Expansion factor Same for all trees Varies by tree
Sampling is based on.. Frequency of occurrence Tree size
Point Sampling
Comparing Point Sampling and Fixed Area Plot Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
PPF PPS
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Point Sampling
Important Ideas about Point Sampling
1. Basal Area Factor (BAF)
How much BA does each sampled tree represent?
2. Plot Radius FactorHow far away can a tree be and still be sampled?
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Basal area factor (BAF)
Related to the sighting angle size of the prism used in
point sampling.
Chosen to provide a tally of 5 - 12 trees per point (8-10)
Eastern U.S.: 5, 10, 20
Western U.S.: 20, 40, 60
Point Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
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Calculating basal area from a point cruise:
acreft.sq.80.81025
202BA /=
=
Example:
BAF 10 prism 202 trees tallied 25 points
BAFpointsofnumber
talliedtreesTotalBA
=
Point Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
It really is that easy!!
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Plot radius factor (PRF)
The value to use in determining the maximum distance a tree of a
given diameter can be from the point to still be tallied.
For example, when using a BAF 10 prism, the plot radius
factor is 2.75.
Point Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
Which means:
For each inch of dbh, a tree can be 2.75 feet from the point to still
be included in the points tally.
Thus a 12 inch tree can be up to 33 feet (12 x 2.75) from the point and
still be included in the points tally.
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Nested Plots
Point Sampling
FOR 220 Aerial Photo Interpretation and Forest Measurements
10 BAF Prism Sample
1/100 acre plot
1/500 acre plot
Trees > 5 inch dbh
Trees 2 to 5 inch dbh
Trees < 2 inch dbh
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What about TwoDog?
Plots and TwoDog Product Groups
Prism or 1/10 acre plot for sawtimber, poletimber, and invasive
( 5 in)
1/100 acre for small trees
1/500 acre for advance reproduction
TwoDog Product Groups
Code Product Group
1 Sawtimber ( 12 inches dbh)
2 Poletimber (5 in dbh < 12 in)
3 Small Trees (2 in dbh < 5 in)
4 Advance Reproduction ( < 2 in dbh)
5 Invasive Species
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TwoDog Product Groups and Products
TwoDog Product Groups
Code Product Group
1 Sawtimber ( 12 inches dbh)
2 Poletimber (5 in dbh < 12 in)
3 Small Trees (2 in dbh < 5 in)
4 Advance Reproduction ( < 2 in dbh)
5 Invasive Species
Two Dog Products
Code Product
PS Pine Sawtimber ( 12 inches dbh)
01 Grade 1 Sawtimber ( 12 inches dbh)
02 Grade 3 Sawtimber ( 12 inches dbh)
03 Grade 2 Sawtimber ( 12 inches dbh)
TT Tie and Timber Grade ( 12 inches dbh)C Cull ( 12 inches dbh)
PT Pole Timber (5 in dbh < 12 in)
SM Small Trees (2 in dbh < 5 in)
R0 Reproduction < 1 ft tall
R1 Reproduction 1 to 2 ft tall
R2 Reproduction 2 to 3 ft tall
R3 Reproduction 3 to 4 ft tall
R4 Reproduction > 4 ft tall, < 2 in dbhIT Invasive Trees ( 5 inches dbh)
IS Invasive Small Tree (2 in dbh < 5 in)
IR Invasive Reproduction (< 2 in dbh)
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What about snags?
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What about snags?
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