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Forest Mensuration
35 lecture sessions
Syllabus
Need, objective, accuracy units, habitat variables - basal canopy area, crown stem diameter, cover, density, diversity, etc. Techniques for estimating habitat variables, place of measurement, justification rules of breast height measurement, Measurement instruments - wooden scale, callipers, tape bark gauge andmethods of use, errors, their elimination, comparison. Height measurement – methods, principles - ocular, instrumental, non-instrumental. Christen's, Smythies hypsometer, improvised calipers. Abney’stopographical Abney's level-theory demonstration. Haga altimeter, Spiegal relaskop, error sources correction, height of leaning tree, problem solving, Tree stem form - Metsger's theory, form factors, quotient height, taper table
Contd…
Syllabus
Volume measurement of felled trees stacked logs – empirical formulae and
problem solving, volume measurement of standing trees – methods, concept,
classification, application, volume tables, preparation of volume tables –
graphical method, local volume table from general volume table,
regression equation method, problem solving, measurement of age – methods
of estimation, concept of growth rings, increment – current annual increment
and mean annual increment, increment percent, increment boring,demonstration of Pressler'sborer, Stump analysis - theory & demonstration, Stem analysis – theory, demonstration and problem solving
Assessment
• Examination – written one with 80% weightage, date will be announced in due course of time
• Concurrent Assessment – group or individual efforts, presentation and exercise, 20% weightage, anytime during the sessions allotted with prior notice
Reference books
Elementary Forest Mensuration by M R K Jerram Forest Mensuration by A. N. Chaturvedi and L. S. Khanna Forest Measurements by Chapman and Meyer Forest Mensuration by Donald Bruce & Francis Schumacher Forest Mensuration – Tree Measurement by Pravin Agrawal Silvicultural Research Code Volume III, The Tree and
Crop Measurement Manual by A. L. Griffith and Jagdamba Prasad
http://sres-associated.anu.edu.au/mensuration http://flash.lakeheadu.ca/~fluckai/Field-HP.html
Forest Mensuration
What? Why? Basic concepts, purpose, scope Measurement -unit, errors, accuracy & precision, rounding off
What is Mensuration?
'Mensura' meaning 'measure‘ in Latin
Measurement of length, area, volume, mass and time i.e. determination in relation to some observed standard e.g. metre, kilogram, second, ampere, degree Kelvin etc.
Why measure anything?
To differentiate between quantitative and qualitative assessment
To remove personal bias and error (to a great extent) For responsible use of forests and other natural resources
“When you measure what you are speaking about and express it
in numbers you know something numbers, about it, but when you
cannot (or do not) measure it, when you cannot (or do not) express it in numbers, you knowledge is of a meager and unsatisfactory kind.”
Lord Kelvin
Forest Mensuration
A branch of Forestry that deals with the measurement of volume, growth and development of individual trees and stands, and the various products obtained from them
Since FM deals with the measurement of forest products, the requirement must be studied from the point of view both of producer and user What is there? How is changing ? What can (and should) be done to manage?
Forest Mensuration concerns with linear, area, volume & weight measurements.
“Forest Mensuration deals with the study of the volume of logs,
trees, and stands, and with the study of increment and yield.”
Henry S Graves
Basic concepts of Forest Mensuration
Individual tree measurement forms the basis for all forest inventories
Includes measurements of Felled and standing trees, Sawn wood and round logs and MFPs such as bamboos, bark, fruits, etc.
Measurements are:
Age Diameter- over and under bark Length or height Form or shape Taper or the rate of change of diameter with length Volume over or under bark Crown width Wood density …
• Wood • Bark• Foliage• Resins and gums• Fibers• Medicinal plants• Wildlife
Purpose
Purpose
is to acquire information: To buy or sell timber products To determine condition of the forest:
age species mix ease of harvest
To evaluate damage to forest To manage a forest (basis for economic analysis) To determine the amount, value and/or condition of other forest
resources (wildlife habitat, wetlands, water resources, etc.)
– To estimate quantity of timber/Firewood/NTFP (volume/weight)
– To know the Growing Stock (nursery/thinning/final harvesting)
– To correlate Height/Volume/Age/Increment with Diameter/Girth
– To know the Site Quality/ index of soil fertility/ productive capacity of Soil
Scope
Wide scope as it is required every time wood is sold, converted or used
Linked with the measurement problems of wild life management, watershed management, insect and disease incidence, recreation, tourism etc.
Revolutionary changes due to application of statistics and modern computers/instruments
Methods of measurement
Depend on several factors e.g.Purpose of measurement Form of the produce i.e. log, chips etc.Quantity & total value of produce Relative precision & cost of measurement for different
methodFor more valuable produce; greater expenditure is
justifiable e.g. sandal wood
How accurately the measurement should be done?– do we need absolute mathematical accuracy or reasonable accuracy?– reasons to follow relative accuracy
characteristics of trees
biological character of forest
varying methods & conditions of felling/conversion
instruments used
use
Units of measurement
FPS/CGS Length – ft or m
Area – sq.ft. or sq.m.
Volume – cft or cu.m.
Weight – pound or kg
Area = ½ b×hb = baseh = vertical height
Area = a2
a = length of side
Area = b × hb = breadthh = height
Match the area with shape
Area = b × hb = breadthh = height
Area = ½ (a+b) hh = vertical height
Parallelogram Trapezium
Common formulae used in Mensuration
Length and distanceD = S x Cos(Q)
V = D x Tan(Q)
V = S x Sin(Q)
Circumference of a circle
C = π x d d
Area
Common formulae used in Mensuration contd…
A = √ (S x (S-D) x (S-E) x (S-F)) where S = (D + E + F) / 2
Area of a field of irregular shape
Step 1. A rough sketch of the field
Area of a field of irregular shape
Step 2. Division of the field into areas with regular shapes
Surface Area = 4 ×
π × r2
Volume = (4/3) ×
π × r3
Surface Area = 4 × π × r2 Volume = (4/3) × π × r3
Surface Area = ??
Volume = height x width x depth
Surface Area of One End = π × r2
Surface Area of Side = 2 × π × r × h Volume = π × r2 × h
Surface Area of Base = π × r2
Volume = π × r2 × (h/3)
• If you are 180 cm tall and your shadow is 40 cm long, and a nearby building has a shadow of 420 cm the height of the building can be found by …
• 180/40 = x/420
Area = πr2 Circumference = 2πrr = radius
Area = π ab Area = ½ r2 θ r = radiusθ = angle in radians
Angle Degrees Radians
90° /2
60° /3
45° /4
30° /61800 = π radian
Errors
1. Systematic/Biased error – instrument not adjusted or have some wear n tear (Should be removed in the beginning)
2. Accidental error
Significant figures
Rounding offs
Figure whole no. 1 decimal 2 decimal 3 decimal9.3459 9 9.3 9.34 9.3467.6987 8 7.7 7.70 7.699
Accuracy and Precision
Precision Accuracy Accuracy with Precision
Measurement is inexact in nature due to likely error e.g. misreading a scale, wrong/faulty adjustment of an instrument etc.
Felled Logs Stacked Logs Standing Trees
Diameter and girth– Where– What to measure – How to measure
Tree Measurement –wood contd…
Felled Logs Stacked Logs Standing Trees
At thick end & thin end or at middle of log
At thick end & at thin end
Anywhere or at some fixed height
Universal convention at breast height
Difficult to take measurement due to grass/shrub/thorns etc.
Abnormal formation such as buttress or swelling or wound found at base
Stumps are never cut at uniform height
Why measurement at breast height?
• Base generally covered with grasses/shrubs/ thorns etc.• Abnormal formation in majority of trees near the base
(root swell) • Stumps are not cut at a uniform height• Convenient height • Uniform point of measurement which helps in
standardizing diameter/girth measurement
• Conventionally persists, extensive database exist
Diameter at breast height
• DBH at 4’6” or 1.37 m (India, Mynmar, S Africa, Malaya etc.)
• DBH 4’3” or 1.3 m (USA,
Canada, Europe including UK), Standard for international adherence
• DBH at 4’6” or 1.37 m in India, Mynmar, South Africa, Malaya and some other former British Colonies
• DBH at 4’3” or 1.3 m in USA, Canada, Europe including UK and most other countries of Commonwealth (recommended by FAO as a standard for international adherence)
• International symbol for diameter at breast height is d