Department of Forestry, Wildlife and Environmental Sciences
Guru Ghasidas Vishwavidyalaya, Bilaspur-495009
Model Answer
B Sc Forestry (III semester)
AS-2930 MM: 60
SECTION-A
Note: Q.No.1 is compulsory which carry20 marks.
Q.1.(a). Multiple choice questions (10)
i. G.O.B can be converted into G.U.B by …………. formula (g = G.O.B, g’ = G.U.B)
a) g = g’-2πt b) g’ = g - 2πt c) g = g’ + 2πt d) g’ = g + 2πt
Ans. a) g = g’-2πt
ii. Which one of the following forest tree species have high specific gravity in wood
a) Shorea robusta b) Acacia catechu
c) Dalbergia latifolia d) Dalbergia sissoo
Ans. b) Acacia catechu
iii. The mean volume of a tree or forest crop at the desired age is called
a) C.A.I b) M.A.I c) P.A.I d) None of the above
Ans. b) M.A.I
iv. The difference between average set of repeated measurements or estimates to its
true value is called
b) Accuracy b) Bias c) Precision d) None of the above
Ans. b) Bias
v. The number of peaks of a wave (Trough or Crest) passing through a fixed point
in space per unit time is called
a) Wavelength b) Velocity c) Frequency d) None of the above
Ans. c) Frequency
(b) Fill in the blanks (10)
i. Small scale photography lies between 1:40000 to1:70000 ratio.
ii. NRSA-National Remote Sensing Agency, Hyderabad
iii. Presslers’s formula on the mean of two diameters is P= 200(D-d)/n(D+d).
iv. Standard stem small wood volume of stem wood round between 20 cm and 5cm
volume being taken inclusive of bark.
v. 10 decimeter= 1 metre
SECTION-B
Q.2. What are the different systems of measurements? Explain in detail the units of
length, area & volume and their related measurements?
Ans. The following are the two systems of measurement which are commonly used
1. British system of F. P. S. system
2. French or metric system or C.G.S system ,
The standards of weights and measures Act, 1956 the British system or FPS system was
used in forestry. Metric or CGS system which was introduced in October 1962, is now a
legal.
Units of length: In the FPS or British system, foot is the unit of length and it is related to
other measurements of this system as follows:
Units of length: FPS Units of area: FPS
12 inches = 1 foot 144 square inches = 1 square foot
3 feet = 1 yard 9 square foot = 1 square yard
66 feet or 22 yards = 1 chain (100 links) 484 square yards = 1 square chain
10 chains or 220 yards = 1 furlong 10 square chains = 1 acre
8 furlongs or 1760 yards = 1 mile 640 acre = 1 square mile
CGS FPS
10 millimeter (mm) =1 centimeter 100 square millimeter =1 square centimeter
10 centimeters = 1 decimeter 100 square centimeters = 1 square decimeter
10 decimeter = 1 meter 100 square decimeter = 1 square meter
10 meters = 1 decameter 100 square meters = 1square decameter
10 decameter = 1 kilometer (km) 100 square decameters = 1 hectare
10 hectometer 1 nautical mile 100 hectares 1 square kilometer
Units of Volume Units of volume
in In
British Metric system
1728 cubic inches = 1 cubic foot 1000 cubic mm = 1cubic centimeter
27 cubic feet = 1 cubic yard 1000 cubic centimeters = 1 cubic decimeter
1000 cubic decimeters = 1 cubic meter
Q.3. What is tree form? What are the different factors effecting tree form? Explain in
detail the methods for studying tree form with suitable diagram?
Ans. Tree form: is defined as the rate of taper of a log or stem. Taper is the decrease in
diameter of a log or stem of a log from base upwards.
Methods of studying form
1. By comparison of standard form ratios
2. By classification of form on the basis of form ratios
3. By compilation of taper table
1. By comparison of standard form ratios : we can study tree form in two way
a. Form factor b. Form quotient
a. Form factor: Form factor is defined as the ratio of the volume of a tree or its part to the
volume of cylinder having the same length and cross section as the tree. These are as follows:
i. Artificial form factor: Also known as Breast height form factor. The basal area is
measured at breast height and the volume refers to the whole tree both above and below the
point of measurement
ii. Absolute form factor: Form factor basal area is measured at any convenient height and
the volume refers only to that part of the tree above the point of measurement.
iii. Normal form factor: In this form factor basal area is measured at a constant proportion
of the total height of the tree, e.g., 1/10 th, 1/20th.
b. Form quotient: FQ is the ratio between the mid-diameter and the dbh.
FQ= Mid-diameter/d.b.h.
2.By classification of form on the basis of form ratios : two way
a. Form class b. Form point ratio
a. Form class: is defined as one of the intervals in which the range of form quotients of
trees is divided for classification and use.
b. Form point ratio: is the relationship, usually expressed as a percentage of the height
of the form point above ground level to the total height of the tree.
3. By compilation of taper table:
i. Ordinary taper tables or diameter taper tables
ii. Form class table
Paraboloid Conoid Neiloid
If we knew more about the factors determining stem form we might be in a better position to
control it. Following are some of the important factors which affect the tree form;
a) Type of forest tree species
b) Genetics of the forest tree species
c) Age of the forest tree species
d) Competition among the forest tree species
e) Site conditions
f) Wind exposure
g) Silvicultural treatment given to the tree species
h) Size and structure of the crown
These factors the one which plays a decisive role in determining stem form is crown,
particularly crown length. As such all factors that influence the crown also influences the tree
form.
Q.4. (a) Write the different methods for calculating Volume of logs?
Ans. There may be different formula for different shape of the log, i.e. Cylinder, Paraboloid –
Smalian’s formula & Huber’s formula Cone Neiloid – Newton’s formula or Prismoidal
formula
where, s is the sectional area at the base in square units, s1 is the sectional area at the thick
end in square units m is the sectional area at the middle in square units, s2 is the sectional
area at the thin end in square units l is the length of the log or height of the solid in linear
units. Measurement of Logs: Different shapes of solid wood Log size:
Log size:
3m for research purpose
< 4.5 m for transport
Section area
The area under each section Area = (π d2)/4 and Area = g2/(4π)
Newton’s Formula: Most accurate formula. It gives volume not only frustum of neiloid
correctly, but also cylinder, paraboloid and cone. All other formulae can be derived from it
Cumbersome to use as it necessitates the measurement of diameter and calculation of areas of
three cross-sections. Difficult to apply when logs are stacked and mid-diameter can not be
measured. Hence, Newton's formula is not used in practice. It is only used to calculate the
error in volume calculated by other formulae
Quarter Girth Formula: The volume of the log will be calculated using quarter girth
formula V = (g/4)2 * l π of value 3.14 is approximated to 4. Thus this formula underestimates
the volume almost 21.5% as compare to full circular volume. It is known as Hoppus’
Formula in Britain. Even if the log had no taper, the volume of the square timber would be 2r
2l.
Smalian’s Formula: Requires the areas of end cross-sections. Overcomes the difficulty of
measuring mid-diameter of logs when they stacked. Gives volumes of frustums of cylinders
and paraboloid with absolute accuracy. Overestimates the volume and has positive error.
Easier to apply than Huber’s and Newton’s formula. Easier to measure by wooden scale than
tape or calliper as log may be lying on the ground.
Huber’s Formula: Requires the areas of mid cross-sections. Impossible to use it when logs
are stacked. Gives volumes of frustums of cylinders and paraboloid with absolute accuracy
Underestimates the volume and negative error. Nearer true value than the Smalian’s formula
Better than the Smalian’s formula because the effect of root swell does not vitiate the result in
lower-most log.
(b) Explain the xylometric method for calculating volume of firewood?
Ans. Xylometer is used to calculate the volume of billets by the principle of water
displacement consisting of graduated vessel and volume of wood. Water is poured in the
vessel and reading of water level is taken. Then the piece of wood is submerged and the
reading is again taken.The difference between two readings gives the volume of the piece of
wood submerged. To obiviate the necessity of submerging large quantities of wood the whole
stack is first weighted and only a portion is submerged.Let W be the weight of whole stack of
wood and w be the weight of submerged pieces, V be the volume of the former and v be the
volume of latter the ,
W:w:: V:v
W/w=V/v
Or V/v = W/w
Or V= v x W/w
Q.5. A tree is standing on a flat ground. If an observer standing at a distance of 28 m
from the base of tree. Measures with the help of an Abney’s level, angles’ of 450 and 200
respectively to the top and base of the tree. Calculate the height of the tree with suitable
diagram?
Solution:
Figure
Let AB be the Total height of tree
Where AB= AD+DB
EB= DC= 28m………(Given)
CE= Observer height
Angle ACD= 450…….. (Angle of elevation given)
Angle DCB= 200…….. (Angle of depression given)
In ∆ ADC
AD/DC = Tan450
As we know that Tan450= 1
And DC= 28m………..given
Therefore AD/28m = 1
Or AD= 28m x 1
Or AD = 28 m………………………………… (i)
Now in ∆BDC
BD/DC = Tan200
Since Tan200 = .36
DC = EB = 28m……….given
Therefore BD/28m = .36
Or BD = .36 x 28m
Or BD = 10.08m……………………………….(ii)
From (i) & (ii) we get
AB = AD +DB
Or AB = 28m + 10.08m
Or AB = 38.08m
Therefore the total height of tree AB = 38.08m…Ans
Q.6. Write Short notes of the following
Ans. (i) Growing stock of a forest
The growing stock of a forest is defined as the sum (by number or volume) of all trees
growing in the forest or a specified part of it. In other words, it’s the forest capital or
capital in the form of growing trees even otherwise, the term is very suggestive. Stock
is a commercial term which means a store or a godown containing articles. In this
stock, the trees growing in the forest are the articles. Thus, growing stock refers to the
inventory of trees growing in a particular forest. Therefore growing stock is very
important aspect from the point of view of forest management. All calculations of
yield are based on it and, therefore, at each revision of working plan, inventory of the
growing stock is prepared before yield can be calculated.
(ii) Nutritional and Hormonal theories of tree form
Nutritional theory of tree form relates tree bole shape to the need of the tree to
transport nutrients and water within the tree. These theories are based on the ideas that
deal with the movement of liquids through pipes ie vascular bundles which decreases
with the increase in the height of the tree, thus it explains that the diameter of a tree
decreases from the base to the top of the tree.
The Hormonal theory of stem from envisages growth substances originating in the
crown regulating the distribution of radial growth on the stem by controlling the
activity of the cambium. It provides physiological explanation of how a tree grows
and why trees differ in the way they do, but it does not specify the particular shapes
trees may have under varying circumstances .the hormonal theory offers the most
promising approach to the stem form problem. It provides a physiological basis for
the nutritional as well as the functional theories of stem form.
Q.7. Explain in detail the following
Ans. (i) Principles of remote sensing: Remote sensing is defined as the technique of
obtaining information about objects through the analysis of data collected by special
instruments that are not in physical contact with the objects of investigation. As such, remote
sensing can be regarded as "reconnaissance from a distance," "teledetection," or a form of the
common adage "look but don't touch."
All recording devives require energy to produce images. The most common and important
source of energy used to produce image is the sun. the solar energy is received in the form of
electromagnetic waves travelling at the speed of light (299000 km/second). The wave motion
is described by wavelength, frequency and velocity. The wavelength (w) of the
electromagnetic waves is the distance from one wave crest or peak to the next. The frequency
(f) is the number of peak passing through a fixed point in space per unit of time. As the
velocity (c) is constant at the speed of light, the three are related as follows:
C= fw
The usual unit of measurement of wave length is micrometer one thousand th part of a
millimeter. Thus it is numerically equal to 10-6 m. The electromagnetic radiation occurs as a
continuum of wave length and frequencies from short wave length and high frequency
cosmic waves to long wave lengths and low frequency radio waves and is known as
electromagnetic spectrum.
The science of remote sensing deals with the technique of detecting these changes in
photographically or electronically.
(ii) Classification of remote sensing: Remote sensing classified into two broad categories:
(1) Aerial remote sensing (2) space remote sensing
(1) Aerial remote sensing: Arial remote sensing is that method of remote sensing in which
cameras or other devices, fixed in an aircraft flying at fixed altitude are used to take
photographs of any resource on earth. Films are processed after landing. The interpretation of
the photographs gives information about
(iii) Advantages of remote sensing:
Remote sensing has enabled mapping, studying, monitoring and management of various
resources like agriculture, forestry, geology, water, ocean etc. It has further enabled
monitoring of environment and thereby helping in conservation. In the last four decades it has
grown as a major tool for collecting information on almost every aspect on the earth. With
the availability of very high spatial resolution satellites in the recent years, the applications
have multiplied. In India remote sensing has been used for various applications during the
last four decades and has contributed significantly towards development. Since remote
sensing has reduced the labour, cost and energy for the land resource assessments. Following
are the main advantages of remote sensing;
a) Relatively cheap and rapid method of acquiring up-to-date information over
a large geographical area.
b) It is the only practical way to obtain data from inaccessible regions
c) At small scales, regional phenomena which are invisible from the ground are clearly
visible. Examples: faults and other geological structures. A classic example of seeing
the forest instead of the trees.
d) Cheap and rapid method of constructing base maps in the absence of detailed land
surveys.
e) Easy to manipulate with the computer, and combine with other geographic coverages
in the GIS.
