Forest Management and Forest Mensuration
Forest Management and Forest Mensuration tests inventory design, measurement, growth and yield, and management planning. In Nepal, questions often use community forest operational plans and national forest inventory data.
Core rules and formulas
- DBH is measured at 1.37 m above ground; basal area of a tree = pi/4 x d squared. With d in cm, BA in square metres = 0.00007854 x d squared.
- Tree volume = basal area x height x form factor. Stand volume sums tree volumes; expansion factor = 1 divided by plot fraction.
- MAI = total volume divided by age; CAI is current annual increment; PAI is periodic annual increment. Rotation is the planned harvest age; felling cycle is the interval between harvests in uneven-aged forest.
- Sampling may be random, systematic or stratified; a 0.1 ha circular plot has radius 17.84 m; a 0.05 ha plot has radius 12.62 m.
- Yield can be regulated by area, volume or increment; the plan must match growing stock and prescribed silviculture.
Worked example
A 0.1 ha plot contains 30 trees of DBH 30 cm and height 20 m, with form factor 0.5. BA per tree = 0.00007854 x 30 squared = 0.0707 square metres. Plot BA = 30 x 0.0707 = 2.12 square metres. Per hectare = 2.12 x 10 = 21.2 square metres/ha. Volume per tree = 0.0707 x 20 x 0.5 = 0.707 cubic metres. Plot volume = 21.2 cubic metres; per hectare = 212 cubic metres/ha. The reasoning: use the cm formula or convert DBH to metres, then multiply by height and form factor; the expansion factor 10 converts 0.1 ha to 1 ha.
Traps
Using DBH in cm directly in pi/4 d squared without conversion gives absurd values. Do not confuse form factor with taper or bark allowance. Do not treat MAI as CAI. Do not expand a 0.1 ha plot by 100; the factor is 10.