Source: J. Hollenbeck

Fixed Area Sampling

Avery and Burkhart,Chapter 10

FOR 220 Aerial Photo Interpretation and Forest Measurements

Plot Cruising

Fixed Area Plot Sampling

FOR 220 Aerial Photo Interpretation and Forest Measurements

Nominal cruise intensityHow much of the land was

sampled?

Examples:1/10 acre plot on a 2 x 5chain 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

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

Purposes: To evaluate regeneration statusTo demonstrate compliance with lawsTo determine effectiveness of regeneration treatmentsTo identify additional treatments neededTo 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)

Nested Circular PlotsSmaller Trees Measured on Smaller Plots

Fixed Area Plot Sampling

Area (ac) Area (ac) Radius(ft)1/500 0.002 5.31/100 0.01 11.81/10 0.1 37.2

1/10 acre plot

1/100 acre plot

1/500 acre plot

Trees > 5 inch dbh

Trees 2 to 5 inch dbh

Trees < 2 inch dbh

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

Source: J. Hollenbeck

Point Sampling

FOR 220 Aerial Photo Interpretation and Forest Measurements

Avery and Burkhart (2002)Chapter 11

A method of sampling based on a tree’s 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

Point Sampling

FOR 220 Aerial Photo Interpretation and Forest Measurements

Point Sampling(Overhead view)

Each tree has a given plot size in relation to it’s size.

How many of these plots does our point fall into?

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 - mustmeasure distance frompoint center

Using a prism:

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

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?

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

Calculating basal area from a point cruise:

acreft.sq.80.8 1025

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!!

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 stillbe included in the point’s 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 point’s tally.

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

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

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 ProductPS 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 tallR1 Reproduction 1 to 2 ft tallR2 Reproduction 2 to 3 ft tallR3 Reproduction 3 to 4 ft tallR4 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)

What about snags?

What about snags?