Regulation of production and supply of wood, determination of yield and prescribed means of achieving it.(How much, where and when to cut?)

Objectives:

1. To cut each crop/ tree at maturity
2. To obtain max. yield of desired produce
3. To cut, approximately, same quantity of materials annually/periodically
4. To limit the area to be felled to that which can be regenerated

Yield regulations involved two functions

1. Calculation/ determination of amount of yield and prescribing the means of achieving it.
2. Construction of a cutting (felling) plan

Correct regulation of yield is one of the main functions of sound forest management.

Estimating growing stock

Growing stock can be expressed as right angled triangle.Area under the curve is growing stock volume and can be calculated by area of triangle.

Area of triangle = 1/2 base*ht

Therefore, Gr= 1/2*R*Yr= R*Yr/2

By substituting value of Grin Hundeshagen formula (Ya/Ga= Yr/Gr)

Ya= Ga*Yr / Gr=Ga*Yr/ R*Yr/2=Ga*2/R

Ya= 2*Ga/R = 2Ga/R

Growing stock volume can be estimated by using a yield table:

Summation formula:

Gr=n (Vn+V2n+….Vr-n+Vr/2)

Where r= rotation age, n=no. of years between yield tables, Gr=Total vol. of g. stock on r years, Vn=Yield table volume/ha at age n, 2n,…..

Estimating Yield for Abnormal Stocking

Hundeshagen formula:

Ya/Ga=Yr/Gr

Where Ya= actual yield, Ga=actual growing stock, Yr and Gr at rotation age, Yr=yield in a fully stocked forest ,Gr= Growing stock in a fully stocked forest

Assumptions:

1. Yield to have straight line relationship with growing stock
2. Forest has normally distributed age structure
3. 10% volume produces 10% yield, this assumptions may not be bad for slightly over/ under-stocked stands.

Von Mantel’s formula

Also called ‘triangle formula’. An extension of Hundeshagen formula. Basic assumption is that, in a regulated forest, growing stock increasesin straight line with age.Application of von Mantel’s formula requires measurement of entire G.S. However, there is a limit below which it is practically impossible to measure.

In Howard’s modification, enumeration were down to half exploitable girth, assumptions being made that girth was directly proportional to age.Howard’s formula for yield

Y=V/(3/8r) or 8v/3r

Where V=vol. of G.S. enumerated down to half rotation age

Assumptions

1. Straight line relationship between yield and age
2. All assumptions required for using Hundeshagenformula-Simple, no need of a yield table-Neglects age class distribution and rate of growth-Best applicable to regular, even –aged or nearly even aged normal forest.The estimate using von Mantel’s formula is lower than the yield table estimate. One reason for the difference is that measurement is assumed to start at age zero