Overview
This lecture explains the concept of tree form factor, its calculation methods, key formulas, and its significance in estimating tree volume and understanding tree growth.
Tree Form Factor: Concept & Importance
- Tree form factor describes the degree of taper (change in thickness) of a tree stem from base to top.
- It is defined as the ratio of the volume of a tree to the volume of a cylinder with the same height and basal area.
- Form factor values range from 0 (highly tapered) to 1 (cylindrical).
Types of Form Factors
- Artificial (Breast Height) Form Factor: Calculated using diameter at breast height (1.37m above the ground); most commonly used in India for its convenience.
- Absolute Form Factor: Basal area measured at any convenient height, with reference volume from that point to the top.
- Normal/True Form Factor: Basal area measured at a constant proportion of total tree height (e.g., 1/10 or 1/20), requiring more complex and often destructive sampling.
Calculating Form Factor
- Artificial form factor formula: ( f = \frac{V}{S \times H} )
- ( V ): volume of the tree (m³)
- ( S ): cross-sectional/basal area at measurement point (m²)
- ( H ): total height of the tree (m)
- Example: Given volume = 3.26 m³, diameter = 0.48 m, height = 30 m; calculate S using ( S = \frac{\pi d^2}{4} ), then use the formula above.
Form Class & Tree Shape
- Form class refers to intervals of form quotient, which relate to tree shapes (neiloid, conic, paraboloid, cubic).
- Lower form factor indicates more tapered trees; higher values approach cylindrical shape.
Form Height and Its Use
- Form height is the product of form factor and total tree height.
- It is used to assess when tree volume can be considered proportional to basal area.
- Form height remains constant as diameter increases if volume is proportional to basal area.
Form Quotient
- Ratio of mid-diameter to reference diameter, used to classify tree form.
- Normal Form Quotient (Schiffel): Mid-diameter at half-tree height divided by diameter at base.
- Absolute Form Quotient (Tor Johnson): Mid-diameter between DBH and top divided by DBH.
Taper Equations
- Used to predict changing diameters along a tree stem.
- Hosse's formula: ( d/DBH = c \log[(c+l)/c] )
- ( d ): diameter at any point, ( l ): distance from top, ( c ): constant.
- Vares' formula: ( d/DBH = l/(a \times b) ), where a and b are constants.
- These formulas are used for creating taper tables.
Applications of Form Factor
- Crucial for accurately estimating standing tree volume.
- Helps in analyzing tree growth dynamics, especially in managed forests.
Key Terms & Definitions
- Basal Area — cross-sectional area of a tree stem at a specific height.
- DBH (Diameter at Breast Height) — tree diameter measured at 1.37 meters above ground.
- Form Factor — ratio of actual tree volume to volume of equivalent cylinder.
- Form Height — product of form factor and total tree height.
- Form Quotient — ratio between mid-diameter and reference diameter.
- Taper Equation — mathematical formula predicting stem diameter at different heights.
- Form Class — interval-based classification of trees based on form quotient.
Action Items / Next Steps
- Review the formulas for calculating form factor and basal area.
- Practice example calculations using provided data.
- Prepare for the next lecture on volume tables (local and general volume tables).