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