SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Forest Measurements
Tree Diameter
Diameter at breast height (DBH) is measured at 4.5 feet above the ground on the uphill side of
the tree with a caliper or diameter tape. Leaning trees are measured 4.5 feet from the ground up
the length of the bole. Trees that fork below breast height are measured as if they are separate
trees. Trees forking above breast height are treated as one tree. When an irregularity (scar,
branching, canker, butt swell, etc.) occurs at breast height, measure diameter above or below the
irregularity and record the distance from breast height.
Leaning tree
Forked tree

Irregularity at breast height
Trees growing on objects
1
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014


In this class, calipers are used to measure diameter
o Open the caliper and place the “jaws” on each side of the tree at DBH. Push the jaws
together until you have a snug fit.
o Read the measurement
o Rotate the calipers 90°and make a second measurement.
o Take the average of the two measures and record the value on the data sheet.
 The caliper scale is metric. 1 inch = 2.54 cm
 Record the DBH to the closest tenth of a centimeter.
Basal area
o Basal area (BA) is commonly calculated from DBH
o BA is the cross-sectional area of the stem which is the area of a circle
o
Area=Pi X radius2
o The value is expressed in square feet. Therefore, DBH must be converted to feet
(DBH/12) before calculating the area: BA = ((DBH/12)/2)2 X 3.1415
o BA is expressed as the total basal area occupied by trees for 1 acre or BA = squ ft
/acre.
o This value will indicate how much of the land area is occupied by tree stems. High
basal area values (generally >120 squ ft / acre) indicate dense forest stands.
2
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Height Measurement

Be sure to be at least 1 tree height or more from the tree.
o This is the most common source of error in forest inventories (particularly hardwood
dominated stands) and is critical for getting accurate estimates of volume. The most
common error is being too close to the tree or in other words, having too steep of a
measurement angle.
 Measure at right angles to the lean of a tree.
Typically, we will use a clinometer to measure tree heights. The basic steps are:
 Measure the horizontal distance from the tree to the height measurement point.
o With a hypsometer, measure a distance that matches a scale on the instrument
o With a clinometer, use a distance that allows you to clearly see the top of the tree; try
and be at least the distance from the tree as the approximate height of the tree.
 Record the angle from to the base of the tree (depression angle).
o With a hypsometer, you can read a linear measure in “ft” or “m” from the scale
associated with the distance from the trees
o With a clinometer, measure the angle in percent, i.e., 10% = 10 ft rise in every 100
horizontal feet.
o Determine if the measure is “negative” (below your eye height) or “positive” (above
your eye height).
 Record the angle to the top of the tree (elevation angle).
 Add the two measurements if the signs are opposite. If the signs are the same subtract
the depression angle from the elevation angle
 If using a clinometer, multiply the sum value by the distance from the tree to the
measurement point
Using a clinometer. Look through the viewing window
with one eye and look at the tree with the other. This
will create the illusion that the scale and cross hairs are
on the tree you are measuring. Once you have set the
cross hairs on the target, wait for the scale to stop
moving and take your measure. The percent scale is
usually on the right side; angle in degrees is on the left.
3
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Tree height measurement, nonleaning tree
Live Crown Ratio
Use the clinometer to measure the height of the crown’s base. Use the uncompacted method for
determining the height to live crown. Record the height to the lowest live foliage of the main
crown, ignoring any small amount of foliage below. LCR is a key measure of tree health.
4
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Practice Measurements
Complete DBH measurements on as many of the seven tagged trees as time permits.
Tree DBH Dist
Measure Measure
(cm) to tree to base
to top
(ft)
(+ or -)
Measure
to base
of live
crown
Total ht =
(top –
base)*dist.
/100
Crown ht
= (top-live
crown
base)*dist
/100
Live crown
ratio =
Crown
ht/Total ht
1
2
3
4
5
6
7
5
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Inventory Plots
Inventory plots are used to calculate an estimate on what and how much exists in a forest stand.
The best estimate is a 100% sample – you measure every tree in a forest stand. That isn’t
practical in most cases. Therefore, “Inventory Plots” are used to collect data that represent the
forest stand. By measuring trees only on the inventory plots, a useful estimate can be made on
the species composition and size of trees that are in the forest stand. There are 2 primary ways of
establishing and measuring inventory plots, “Fixed-radiaus Plots” and “Point Sampling with a
Prism” plots.
Fixed-radius plot
Fixed area plots are widely used in forestry as they provide the most accurate estimates of
ingrowth, mortality, and growth. Fixed area plots give all individuals an equal probability of
selection. However, they are very time-consuming to install and measure. Fixed-area plots can
take many different shapes, but the most commonly used in forestry are circular, square, and
rectangular. In particular, circular plots are the most widely used because fewer decisions for
trees near the plot boundary must be made and it has no predetermined orientation. The main
disadvantage of a circular plot is that significant error can arise if the plot boundary is not
observed carefully. The most common sizes are 1/50th and 1/20th acre, which have radii of 16.67
and 26.33 ft.
At a sample point:
 Establish plot cents with a ground stake or a staff.
 Measure the plot radius going due North.
 Going clockwise, measure all trees > 4.5 in (11.4 cm).
o Height and diameter
o Borderline trees: If the center of a tree at DBH lies within the boundary of a plot, it
gets measured.
This plot type will be used for the Wednesday Ecological Inventory.
6
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Point Sampling with a Variable Radius Plot:
This plot type will be demonstrated today (Monday).
Variable radius plot sampling is the preferred method for timber cruising because it is efficient,
weights the larger individuals more, and is easy to implement in the field. The method requires
sighting trees using an angle gauge, prism, or Relascope. These measurement tools vary in their
basal area factor (BAF), which controls the number of trees sampled and generally ranges from
10-40. A tree is considered “in” if a tree’s width exceeds the edge of the cutout on the angle
gauge (Figure 2). The basal area per acre is simply the number of “in” trees multiplied by the
basal area factor used. The middle cutout in Figure 2 is BAF 10. For example, if you had 10
“in” trees for the plot, the basal area per acre is 100 ft sq per acre.
Borderline trees must be check by measuring the tree’s DBH, measuring its distance from plot
center and comparing it to the product of DBH and the computed plot limiting radius factor
(Table 1). Generally, DBH is recorded for each “in” tree and a subsample of “in” trees are
measured for total height. The plot limiting factors for common BAFs are given below.
BASAL AREA FACTOR (BAF; ft2 ac-1)
PLOT LIMITING RADIUS FACTOR (ft in-1)
10
2.750
15
2.245
20
1.944
30
1.588
40
1.375
Table 1. Plot limiting radius factor.
7
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
To sample a variable radius plot with an angle gauge:
At a sample point:
 The angle gauge (Figure 1) is made of a sighting piece and a small chain. Hold the end of the
chain in one hand at an eye and extend the sighting piece with the other hand until the chain
is taught.
 Place yourself so that the gauge is above the sample point, not your body. Be sure to keep
the prism above the sample point as you turn 360°.
 The gauge must be held as seen in figure 2.
 Start by looking due north and then go clockwise.
 While looking through the gauge, any tree that that exceeds the edges of the middle cutout
(see Figures 2) is counted; all others are not counted. The middle cutout calibrated for a
Basal Area Factor (BAF) of 10.
 Borderline trees must be check by measuring the tree’s DBH, measuring its distance from
plot center and comparing it to the product of DBH and the computed plot limiting radius
factor (Table 1).
 Record the species and DBH on the tally sheet. Measure tree height and record that value.
Figure 1: Angle guage
Figure 2: Using the gauge
8
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Procedure
Plot Measurements
1. Establish a Variable Radius plot in the assigned forest stand..
2. Start by looking north and then rotate clockwise around the plot center. Begin recording
trees that are “in”. Remember “in” is based on the 10 BAF gauge. For each “in” tree,
record the following information on the data sheet.
a. Species
b. Diameter
3. Measure the total height of the three tallest trees on your plot by using the clinometer.
Record this on the same line as the species and diameter for that tree.
4. Rotate rolls for each crew member after each tree is measured.
9
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
Record the trees that the BAF 10 gauge indicates should be sampled.
Measure height of the 3 tallest trees.
Tree DBH (cm) Dist to
Measure Measure to
Measure
Total ht = (top –
Num X.X cm
tree (ft)
to base
top
to base of
base)*dist.
(+ or -)
live crown
Total Number of Trees = __________
X 10 = ________Basal Area (sq. ft) Per Acre
10
SFR 101
Forest Measurements
Prepared by W.H. Livingston,
Aaron Weiskittel
August 2014
DBH
(cm)
Tree
Measur
Measur
e to
Dist to e to
Measur
base of
tree (ft) base (+ e to top
live
or -)
crown
Total ht
= (top
–base)*
dist.
/100
1
2
3
4
5
6
7
43.434
34.036
42.164
48.514
46.228
38.1
44.45
70
75
80
75
75
75
65
-12
-13
-11
-8
-7
-6
-3
100
102
88
100
102
92
98
16
31
8
15
30
26
78.4
86.25
79.2
81
81.75
73.5
65.65
Crown
Live
ht = (topcrown
live
ratio =
crown
Crown
base)*di
ht/Total
st
ht
/100
58.8
0.75
53.25 0.61739
0
69 0.85185
65.25 0.79817
46.5 0.63265
46.8 0.71287
11