# Variable plot cruising I by ert554898

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```									Forest Biometry Lecture Number 11                      Outline
n Basics of variable plot cruising
n How variable plot cruising
works
Variable plot cruising I                           n Instruments for variable plot
cruising
n Borderline trees

Forest Biometry Lecture No. 11   2

Basics of variable plot cruising                       Basics of variable plot cruising
“The Bitterlich method”
n   In un-evenaged forests, there are always
many small trees and much fewer large trees        n In variable plot sampling – or point
n   In fixed area plots, most of the time is             sampling – trees are tallied according to
invested measuring the small trees                   their size
n   However, large trees determine the basal           n The probability of tallying a given tree
area and the timber volume of the stand              depends on its basal area
n   Sampling for timber volume would be most           n The bigger a tree the more likely it is to
efficient, if we could focus on the large trees,     be selected
without ignoring smaller ones completely

Forest Biometry Lecture No. 11   3                     Forest Biometry Lecture No. 11   4

Basics of variable plot cruising                       How variable plot cruising works
“The Bitterlich method”
n   The decision if a tree is ‘in’ a plot depends on
n The system is extremely efficient and                    both, its basal area and its distance from the
accurate, because larger trees are more                  plot center
important when it comes to estimating                n   Small trees are only included when they are
basal area and timber volume                             close to the plot center
n The system was developed in 1948 by                  n   Large trees are also included at further
Walter Bitterlich, a forester and                        distances
biometrician from Salzburg, Austria

Forest Biometry Lecture No. 11   5                     Forest Biometry Lecture No. 11   6

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How variable plot cruising works                                     How variable plot cruising works
n   More precisely, the decision which tree to                       n   Example
include is based the ratio between diameter                      Ratio                       Tree 1                Tree 2   Tree 3
and distance to plot center                                                   Diameter 6                           6        6
n   A tree is ‘in’ a plot when this ratio is equal to,
or larger than, a predefined ratio                                            Distance 12                          16.5     33
n   One commonly used ratio is 1/33                                               in feet
Distance 144                         198      396
in inches
1/33    Diameter/ 0.0417                     0.0303   0.0151
0.0303   distance

Forest Biometry Lecture No. 11                 7                    Forest Biometry Lecture No. 11                   8

How variable plot cruising works                                     How variable plot cruising works
n    Example                                                         n   The BIG advantage of variable plot cruising is
Ratio                     Tree 1              Tree 2   Tree 3            that counting trees is all that is necessary to
measure basal area per acre
Diameter 12                       12       12
n   A ratio of 1/33 is equal to a basal area factor
(BAF) of 10
Distance 12                        16.5     33
in feet                                                   n   This means that each tree ‘in’ a plot
Distance 144                       198      396               represents a basal area of 10 square feet per
in inches                                                     acre
1/33 Diameter 0.0833                     0.0606   0.0303
0.0303 /distance
Forest Biometry Lecture No. 11                 9                    Forest Biometry Lecture No. 11                  10

How variable plot cruising works                                     Instruments for variable plot cruising
n   In the field, all that is necessary is                           n   Angle gauge
u Tree  are counted “in” when they are wider than
u tostand at the center of the plot
the intercept at the end of the gauge
u examine each tree in the surrounding
u User’s eye must be placed over the plot center
u decide if the tree is ‘in’ or ‘out’
u Good for dense stands
u multiply the number of tree by 10
u Usually designed for a BAF of 10
n   Result is an accurate estimate of total basal
u Slopes > 15% require slope correction, which is
area per acre                                                          cumbersome with the angle gauge

Forest Biometry Lecture No. 11                11                    Forest Biometry Lecture No. 11                  12

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Instruments for variable plot cruising                       Instruments for variable plot cruising
n   Penny                                                    n   Cruz-All
u Same   idea as the angle gauge                             u Also based on the angle gauge principle as the
u The penny must be 24” away from the eye, eye               u Difference  is that that you look at an opening and
must be over the plot center                                 decide if a trunk fills the opening completely
u At this distance, the BAF is 10                            u The distance to the eye is measured via a little
u Slopes also problematic                                      chain that you hold with your teeth
u Less precise than the angle gauge,                         u Eye must be over the plot center
but easier to carry around                                 u Slopes also problematic
u Has four BAFs built in (5, 10, 20, and 40)

Forest Biometry Lecture No. 11        13                       Forest Biometry Lecture No. 11       14

Instruments for variable plot cruising                       Instruments for variable plot cruising
n   Wedge prism                                              n   Wedge prism
u Trees are “in” when their shifted image in the
u Slope    correction in three steps
prism still overlaps with the rest of the trunk
F Point  the long side of the prism at eye
u Low cost and light weight
level towards the tree
u The prism must be placed over the plot
F Maintain the slope angle while rotating the
NOT THE EYE!
prism 90 degrees
u Allows slope correction
F Make the decision if tree is “in”

Forest Biometry Lecture No. 11        15                       Forest Biometry Lecture No. 11       16

Instruments for variable plot cruising                       Instruments for variable plot cruising
n   Spiegel relascope                                        n   Contra spiegel relascope
u Trees  are counted “in”, when they are wider than          u Problematic      on dark, rainy days
the predetermined number of stripes inside the             u Takes    a little bit more training
viewing field                                              u Costly
u The relascope must be positioned over the plot
center
n   Pro spiegel relascope
u Built in topographic correction, great for steep
terrain
u Contains several BAF thus flexible

Forest Biometry Lecture No. 11        17                       Forest Biometry Lecture No. 11       18

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Borderline trees                                   Borderline trees
n Trees that are neither clearly “in” nor          n   More accurate is to actually measure
“out”                                                borderline trees
u Multiplying the dbh (in inches) with the plot radius
n The simple way of dealing with is to                   factor gives the maximum distance (in feet) from
count every second borderline tree “in”                the sampling point for a given tree to be “in”
u For a ratio of 1/33, the plot radius factor is 2.75
n The first borderline tree is “out”
u The plot radius factor depends on the BAF,
n When you cruise multiple plots,                        for a BAF of 5, the plot radius factor is 3.89,
continue the in-out list from one plot to              and for BAF 20 1.94
the next                                         n   In the field, a table is used to check the
critical distance for a given dbh
Forest Biometry Lecture No. 11   19                       Forest Biometry Lecture No. 11     20

Outline
n Basics of variable plot cruising
n How variable plot cruising
works
n Why variable plot cruising
works
n What size Basal Area Factor?

Forest Biometry Lecture No. 11   21

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Walter Bitterlich

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