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1. FOREST MENSURATION

2. Tree Stem Form
 Form is the rate of taper of a log or
stem
 Taper is defined as the rate of
decrease in the diameter of the
stem/bole of a tree per unit increase
in height above the base of the tree.
OR
 It is the decrease in diameter of a
stem of a tree or of a log from base to
upward.
 expressed in centimeter per meter
stem length
 The taper varies with species, age,
site and crop density and in the
different parts of the same tree.

3.  Trees often are combinations
of form.
 The basal portion of tree –
corresponds to frustum of a
neiloid,
 middle portion - frustum of a
paraboloid,
 top portion - cone

4. Importance of estimating form
1. To estimate bole volume
2. Improved estimation of presence and amount
of wood products
3. Better understanding of competition and
growth conditions of the tree
4. To study laws of growth

5. Methods of studying form
• By comparisons of standard form ratios (form
factor and form quotient)
• By classification of form ratios (form point
ratio and form class)
• By compilation of taper table

6. Form factor
 Form factor is the ratio of the volume of a tree
or its part to the volume of a cylinder having
the same length and cross section as the tree.
OR
 It is the ratio between the volume of a tree to
the product of basal area and height.
 Varies between 0 to 1.

7. Formula
units
linear
in
tree
the
of
height
h
units
area
in
height
-
breast
at
area
basal
S
units
cubic
in
volume
tree
V
factor
form
,





F
Where
Sh
V
F

8. Form Quotient
• It is the ratio between the mid-diameter of a
tree and the dbh
• Taper/ Form factor depends upon form quotient
(A. Schiffel)
dbh
diameter
-
mid
. 
Q
F

9. Volume Measurement
• Essential for estimation of quantity of wood
contained in trees or crops for sale, research,
predicting future yields, growth/ increment
etc
• Volume measurement is different for felled
and standing trees.

10. Measurement of volume of felled
trees
Volume of felled trees consists of
• Stemwood volume
• Branch wood/firewood/fuelwood volume
• Pulpwood volume
• Charcoal volume
• Bark volume

11. Volume measurement of stemwood
• For commercial utilization of stem timber, the
stem is converted into logs of suitable length.
• When calculating volumes of logs and trees we
normally assume that the sections are
circular, or the tree stem is cylindrical.
• But the shape of logs and sections of trees as
similar to certain solids as example the
cylinder, paraboloid, cone, or neiloid.

12. • Tree is cut into logs for more accurate estimation
• Length of log depends on rate of taperness and
market demand
• When the logs are made for calculating volume of
felled trees for research work, all logs are of
uniformly 3m in length except the top end log
which may be up to 4.5 m.
• But if the end section is more than 1.5m in length,
it is left separate rate log.
• The cross sectional area or basal area (S) is found
from the diameter as follows:
4
2
d
BasalArea



15. • Quarter Girth formula (Hoppus’s rule)
l
g
V *
4
2







log
the
of
length
the
l
middle
at the
log
the
of
girth
the
Logs
of
Volume
V
Where,



g

16.  This is the system of measurement used for
sale purpose when round timber is sold by
volume
 This formula gives only 78.5% of the cubic
volume of cylinders, thus allowing a loss of
21.5%

17. Volume of sawn timber It is the simple product
of three dimensions; length, breadth and height
 Volume of sawn timber varies according to its
cross sectional size and length.

18. Volume of stacked timber
• Products such as firewood and pulp logs are
frequently commercialized according to their
volume in piles or stacks. A steer metre is the
volume of a stack of 1×1×1 metres (a cubic metre
stacked), and it is used for firewood
 This volume contains air space and wood in
variable proportions according to the form of logs
Stacked timber

19. Solid volume of fire wood
 The stacked volume is not the actual volume of
firewood, it is only for the convenience of
paying the labour in the forest where there is
no arrangement for weightage.
Two methods-
 Xylometric method
 Specific gravity method

20. (i)Xylometric method
 Volume of billets calculated with the help of
xylometer which consists of a graduated vessel
 Volume of wood calculated by the principle of
water displacement
 Water poured in vessel, reading taken, wood are
submerged in water and reading taken again.
 Difference between two reading gives the volume
of submerged wood

21. • For large quantities of wood
• This method is cumbersome and seldom used in
practice
w
v
*
W
V
v
:
V
w
:
W
pieces
submerged
of
Volume
v
wood
of
stack
whole
the
of
Volume
V
pieces
submerged
of
Weight
w
wood
of
stack
whole
of
Weight
,






W
If

22. Specific gravity method
 Specific gravity is a unitless measure of mass.
 If specific gravity of wood is known than volume can be
calculated.
 As density for pure water is 1 gm per cc, the density of
wood in gm per cc is the same as its specific gravity minus
the units.
• Specific gravity typically varies from 0.35 to 0.81 for most
commercial tree species
cc
Volume
gravity
Specific
(gms)
Weight
water
of
Density
wood
of
Density
wood
of
piece
a
of
gravity
Specific
water
of
volume
same
of
Weight
wood
of
Weight
wood
of
piece
a
of
gravity
Specific




23. • Pulpwood volume
• Charcoal volume
• Bark volume

24. Volume measurement of standing
trees
Direct measurement
• Measurement of diameter at different heights by
climbing with the help of ladder and then estimating
the volume.
• This process is tiring and time consuming.
Indirect measurement
• Measurement of upper stem diameter at different
heights by different instruments and then estimating
the volume of each section like felled trees.

25. Standard sectional method
• This is a old method and can be applied to all
types of trees for total volume or volume to any
particular limit.
• In this method, the main stem is theoretically
divided into number of standard length sections
normally 3m.
• The exception is the odd log less than the standard
length that fits between the last standard section.
• These sections are assumed to be the second
degree paraboloid in shape.

26. • The diameter at midpoint of each section is measured,
and then the volume is calculated by Huber’s formula-
Volume = Length x Sectional area at midpoint of log
V = l x πr2
V = l x π (d/2)2
V = π(d2/4) x l
• The volume of tip is considered as conoid is calculate
by the fomula of volume of cone-
Volume of tip = 1/3 x Length x Sectional area at base of
cone
V = 1/3 x l x π (d/2)2
V = π (d2/12) x l