This volume table are compiled from measurements of treesgrowing in restricted locality.

Based on one independent variable i.e. dbh

Local volume tables are used:

• To estimate the volume of standing trees before felling
• To make confidential estimate of the volume of tree.

These tables are either prepared directly from field data or derived from general volume table. This can be prepared either method by graphical or regression equation.

1. Derivation of Local Volume Table from General Volume Table

• General VT gives volume of tree by diameter and height classes
• Figures of general volume table are plotted in a graph showing volumes against the middle of diameter classes for each height class separately
• So, sufficiently large number of trees are measured and recorded by diameter class
• Diameters and height (measured) are then plotted on the same graph
• Volume derived from GVT against average dia and ht
• Table: dia class against volume prepared
• To prepare graph, a smooth curve is drawn through plotted points
• The curve is the desired local volume curve
• It represents the local relationship between diameter and height
• Based on this curve, volume for diameter classes can be calculated and tabulated as Local Volume Table

2. Regression equation from the basic field data

• In this method, dbhand volumes of sufficiently large no. of trees are measured and recorded by diameter classes.
• The average volume for each diameter class is worked out and it is then plotted against the mean diameter of the class and smooth curve is drawn through these points.
• As this method requires calculation of volume of a large number of trees, this method is seldom followed.
• Regression equation or model are first prepared based on the field measured data
• Regression coefficients b and c calculated from the data measured in the field
• Use any of following equations,
  • V = a + b D + c D² (Parabolic equation)
  • V^1/2= a + b D (Linear equation)
• r and d.f. should be mentioned

3. Regression equation from the General Volume Table

Instead of developing regression equation for local volume table, it can be derived from the regression equation of the general volume table for the specific species

If general volume table equation is

V = a+bD²H

And height/diameter relationship is

H = c+dD+eD²

Then, V = a+bD²(c+dD+eD²) = a+bcD²+bdD³+beD⁴

Or, V = a+b₁D²+c₁D³+d₁D⁴

Where, a is regression constant, b1, c1, d1 are regression coefficients

Volume equations used in preparing volume tables

1. Total stem volume: (n(v) = a + b ln(d) + c ln (h) ; v = volume o.b.
2. Stem volume to 10cm top ln(V₁/v)=a+b(d); V₁ = volume o.b of tree (beyond 10 cm dia), V= total stem volume overbark
3. Stem volume to 20cm top ln(V₂/V_t)=a+bln(d) V₂= volume o.b between 10 & 20cm diameter, V_t= volume o.b to 10 cm diameter

To reduce bark volume from stem overbark volume, following equation form has been used:

ln(po) = a + b ln(d)

po= bark porpotion

Total stem volume of Acacia catechu (m³) [vob]

Sources of error in graphical method

• Failure to select proper trees in sufficient number
• Only two variables can be dealt with at a time
• Drawing curves always introduces a personal factor and consequent bias.