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Forest management class notes Compiled By Gopal

Unit – OneIntroduction and backgroung

1.1 Role of Forests in economic Development Foretry sector itself is capital producing sector. It can be used as capital as well as sold as product also. So forest plays an inportant role in economic development and ecological stability. They provide several goods broadly classsified as major and minor forest products which serve as raw material for many industries; railway, housing, furniture, pulp and paper, fibrem packing, particle boards, plywood, carved wooden articles, wooden utensils, safety matches etc.Wood is the main sources of energy for cooking food, especially I rural areas. Non timber forest products like bomboo, cane, medicines, katha, cutch, grasses, essentials oils, waxes, gums, resins, fibres, honey, medicinal herbs, oils seeds, fruits, flowers, fodders assure greater important than major forest products. These contribute rural as well as national economy. Economic growth: sustained increase in per capita output against a static or increasing population.

- Certain rise in average per capita income made possible by containing increade in per capita productivity.

- Not concerned with the distribution of income: it is assumed that income distribution is perfectly equatable.

- Economic Development: It is historical process, which encompasses not only procuction but also the entire economic and social life of a nation (health + education + social outlook + dynamism of its political institution etc.)

i. Greater equity: ii. Employment for everyone higher employment and iii. Self reliance

These above points are essential for economic development of the nation.World Development Report 2002

Income/ economic growth

Country Per Copita Income (US $)

Economic growth

Nepal 220 3.1India 460 3.9USA 34260 4.0China 840 7.3

Switzerland 38120 2.7

Japan 32210 1.7Ethopia 100 2.2

Human Development Index Measured omterms of reaal CaDP/ Capita + life expectancy + educational attainment (knowledge)Nepal – 1997- 134 th 2001 – 129 th in 1970, real capita income in South Korea was 83% of Brazil by 1990, it was 221% of brazil.

Belongs to Bishnu Chandra Poudel. B.Sc. Forestry IIIYr, IInd Semester. 1


1.2 Forest Society and environment Forest provides both major and minor productsFor many Industries local point of economic growth wood provides raw materials for industry.Railway, housing, furniture, pulp and paper, fibre packing causes forest procucts are extensively used. The Scenario of Nepal

- Bomboo, canes, grasses, essential oils, resins, fibre gums, katham medicines, herbs, seeds, fruits and flower etc.

- About 75% of country's energy requirements are met by firewood.- About 42% of fodder for livestock continuous to be extracted from

forst resources.- Rural economy depends on fuel fodder; farmer's ploughs mainly

agricultural equipments- rakes, tools, grasses leaves, pods, fruits, cattle food etc.

- Social and community forestry programs roadside plantation, canalside plantation and plantation on denuded hill slopes, all give employment to rural people.

- Rural Industries such as paper factory, small furniture factory (from canal, bomboos, honey, silk, match industry all generate employment to rural people.

- Forestry is basically a social service. Its contribution (gross) is not truly reflected in GNP.

So the direct benefits of the forest can be listed as;1. Source of energy to household as well as industries.2. Employment generation to the rural people in forestry activities and

forest based industries.3. Development of cottage and small-scale industries.4. Satisfying requirement of individuals.5. Revenue to the government.6. Development of tourism.7. Satisfying requirement of industries.

Social benefits of forests1. Source of human and animal food.2. Source of providing cheap fuel.3. Source of raw material for wood based industries paper, Katha, match,

timber etc.4. Provide employment to the rural population.5. Provide recreation and tourism development.6. Provides scientific and educational research value.7. Provides hunting and fishing facilities.8. Provides revenues from forest products.

Environmental benefits of Forest: Amelioration of climate through Soil conservation. Controlling or minimizing flood/ erosion hazard. Improving air / water quality etc.

Beutification of human environment. Improvement of agro – ecosystem. Control of environmental pollution

Forest Management Objectives:



Definition: Forest management intregely all the biological, social, economic and other factors that effect management decision about the forest (broad sense).

Forest management encompasses all these decision needed to operate a forest on a continuous basis.

Historically: forest management has delt primarily with silvicultural and biological management of the forest.

Forest management refers to the study and application of analysis techniques to art or choosing these management alternatives that contributes most to organization objectives.

Forest managemetn is defined as the practical application of the scientific, technical and economic principle of forestry.

Objectives: Several points should be considered

Objectives implies that there is a desired point that the forest organization desives to reach.

Desired Point: goods and services (fuelwood, fodder, tomber etc). Objectives may or may not be identified; objectives can be changed

with user group (timber / fuelwood / fodder, fodder / fuelwood / timber / fuelwood.)

The objectives identification may result from careful through with much planning and public consultation.

Objectives are usually determined by the forestland owner. There is seldom a management objective. Actual management

objectives are a mix of several management objectives. The philosophy of management by objectives is said to be the most widely accepted philosophy of management today.

The essential features are: Set objectives clearly Review them clearly Pursue them clearly etc

Primary objectives of good management are provision of the maimum benefit to the greatest no of people for all time.

1.3 Forest Management alternatives and analysisThe alternatives mentioned in the definitions of the Forest management may be viewed as the many actions that a forest owner may take to achieve his objectives. These are actions that can be taken in the field that will cause production of one or another, or some mix, of forest products; the actions an owner takes can include cutting, reforestation and construction.

Alternatives: Defined by physical production possibilities of the forest.I. Cutting the forest or not cutting- timing and type of cut (clear

cut/ shelterwood etc).II. Reforestation Practice: Artificial and natural regenaration, kind

of site preparation, species to be regenarated etc.the regeneration practices affect the density and species and hence forest production possibilities.

III. Construction can affect the amount of objectives obtained: e.g Road placement affects timber harvestbut also effects on recreation, hunting, asthetic value, soil stability etc. Placement of ponds affects both grazing and wildlife production.



Forest management alternatives may be viewed in another, more general way. The alternatives are defined by the physical production possibilities of the forest, which are determined by the basic biology of the forest being managed. Thus, the alternatives include silviculture, protection, mensuration and electives. This is why; the curricula of forest management include all these discipline

Analytical techniques: Analytical techniques are also part of forest management decisions. These provide guidelines for choosing between the courses of action. The techniques can tell us what will happen if all the assumptions and projections used in the analysis are fullfilled.

Discounting and present net worth are general techniques applied to forestry problems.

These analytical techneques provide guidelines for choosing between the course of action

A decision Making Model:

Model: A model is a simplified representation of something that we wish to describe or explain

or understand

Belongs to Bishnu Chandra Poudel. B.Sc. Forestry IIIYr, IInd Semester.

4

Decision Maker

ObjectivesProblem recognition

Alternatives

Constraints

Problem analysis

Decision

Choose alternatives Do nothing More data

Exit to implementation

Exit to implementation

Problem Solving

If information is not sufficient again proceed to new objectives


Unit – twoConcept and Practice of Sustained Yield

Sustained yield: The material that a forest can yield annually or periodically in perpetuity. As applied to policy, method or plan of management (sustained yield

management) implies continuous production with the aim of achieving at the earliest practical time at the highest practical level. An appropriate balance between net growth and harvest by annual or somewhat longer periods. (BCFT)

The regular continuous supply of desired produce to the full capacity of the forest. (Osmaston).

The yield of timber or other forst produce from a forest which is managed in such a way as to permit the removal of approximately equal volume or quantity of timber or other forest produce annually or periodically in perpetuity.

Sustained yield concept originated in Europe. Germany was the pioneer to develop this concept (early

nineteeenth century). The regular continuous supply of the desired produce to the

fall capacity of the forest.The Concept of Sustained Yield

The yield from the forest includes all the forest products, the tangible and the intangible, including protective, amenity, timber, and non-timber products. The principle of sustained yield ensures stability and continuous supply of raw materials to the industries ans to meet the social and domestic needs of people.

Concept of sustained yield (or substance) has been evolved from the basic consideration that the later generation may derive from the fore at least as much of the benefits as the present generation. It is an accepted norm in forest management and forms and core or organization in forestry.

The concept of sustained yield envisages that a forest should be so exploited that the annual or periodic fellings do not exceed the annual or periodic growth, as the case may be. Sustained yield is therefore, expressed as the allowable cut which may differ little from ne increment (i.e. gross increment minus natural loss due to fire, wind, epedemics etc) depending upon the growing stock and distribution of age- classes.

Sustained yield management as the form is most accurately and commonly employed means continuity of harvest, indefinitely, without inpaired of the productivity of the soil.Thus the sustained yield management is necessary from the following prospectives;

II. It insures stability and continuous supply of raw materials to the industries and to meet social and domestic needs of the people.

III. The basic consideration is that the later generation may derive from the forest at least as much of the benefits as the present generation.

IV. Forest should be so explained that annual or periodic felling does not exceed the annual or periodic growth.

Sustained yield Management:- Continuity of harvest, indentify, without improvement of the

productivity of the soil.Pre- requisities for the sustained Yield management:



Considering forest from economic point of view, investment in forestry should yield continuous return in terms of definite class of producem and in greatest possible quantity within a reasonable time and to the best financial advantage. This simplest method of achieving this objectives of sustained yield is to maintain a complete succession of equal area of crops of all ages from one year to old upto the age of maturity (say 10 years, for illustration) and remove the 10 year old wood anuually and plant upto the area again.

ii i

i i ii i i i

i i i i ii i i i i i

i i i i i i ii i i i i i i i

i i i i i i i i ii i i i i i i i i i1 2 3 4 5 6 7 8 9 10

This mature wood would represent the increment on the whole forest and the difficulty of removing the annual increment from each unit, say, one hectare, is overcome by removing accumulated production of 10 ha on 1/ 10 th part of the total area as illustrated in above figure. Such series of trees or crops ofall ages, from seedling to maturity, so as to enable the removal of the oldest is known as a complete series of age- gradations.As the forest in the above example has equal area of every age in it, an equal area will be available for felling at maturity. The establishment of such a series of age gradations as illustrated above, in one form of the crop necessary for sustained yield management (or sustainance / sustension) and for maintaining it in perpetuity. Such a forest provides a conceptual picture of a theritical normal forest; the ideal of a Normal forest is a logical corollary to the principle of sustained yield in perpetuity.Hencem for a sustained yield management the forest must be normal, whether regular or irregular, though in the latter case management becomes rather complicated. The sustained yield principle is applicable to production forestry, but where protection and other accessory benefit far out- weight athe other benefits, then must be given precedence over material benefits, and the silvicultural treatment modified accordingly.


500450

400350300250200150100

50

Volu

me

(M3 /

ha

)

Age years (each one ha. areas)

Rotation (R) = 10 years,I= increment at the end of rotation, i = increment per year

I= R

*i =

10

*i


Limitations: Not possible to apply sustained yield pricciple in the 1st rotation (Density and quality

of crop vary due to past management and also the composition of main species in the mixture).

Virgin forest with large proportion of deterioting trees cannot be suitably worked under Sustained yield principle.

Forests under afforestation program provide various yields until after the end of 1st rotation.

In Community forests practice of sustained yield may not be maintained due to demand pattern.

In hilly areas, sustained yield may be difficult to practice (due to geographical location, site variability etc).

Lack of Technical manpower is another problem.

Yield TypesFinal Yield: All the material derived from main fellings.Intermediate Yield: All the materials from thinnings or operation proceeding main felling in a regular forest.Total Yield: Standing Volume of a crop i.e. the total volume removed in thinning (sum of final + intermediate yields)Management Steps for sustained Yield

To bring the forest to clear felling system in which all age gradations from one year to rotation are present.

For natural regeneration 10 or even more age gradations may be grouped (0- 10. 10-20, 20 – 30 etc) to form age class and the oldest age –class felled and regenarated in 10 years. In Selection forest, trees felled for exploitable size diameter. All sizes trees

are present.Unit – 5

Forest Regulation Forest regulation determines the what, where and wnen of timber harvesting on the managed forest, the regulation decisions indicate what species and how much of them should be cut. They also in many cases, indicate where on the ground the cutting should take place. Certain specific stands may be designated for cutting in the plan, alternatively, only the volume and species may be designated and the forest manages must then locate stands in the forest that have indicated characteristics and designate them for harvest. Finally the when of the forest harvesting is shown by cutting schedules the heart of any forest regulation plan is to indicate the time period, most commonly the 5-year period in which the timber should be cut.

The regulated forest is one that yields an annual or periodic crop of about equal volume, size, and quality. This definition implicity refers to timber but is generally enough to cover all forest products if "crop" is defined to include wildlife, recreation, aesthetic values and other forest products. Thus, forest regulation consists of manipulating forestlands and growing stock to best achieve the forest owner's yields objectives.

Regulating forest is one that yields a annual or periodic crop of about equal volume, size, and quality. The regulated forest is desired to obtain a sustained yield of forest crops.however, depending on the current forest condition, sustained yield may not occur for many years. Further, regulating a forest may cause opportunity costs in other management



objectives, such as even currrent wood flow, maximizing PNW or maintaining scenic vistas. Thus as will be seen, a forest may not be regulated as rapidly or as completely as is possible.

Normal forest: A normal forest is the ideal state of forest condition which serves as standard for conparision of an actual forest on a given site and for a given objectives of management. On a given site, and for a given object of management it is a forest, which has an ideal increment, from sucn a forest, annual or periodic, yields equal to the increment can be realised indefinitely, without endangering future yileds and without detriment to the site. In Forestry, concept of Normal forest, envisages an ideal state of perfection, serving the purpose of good scientific management. It is a forest, which by reason of its normality in these respects, serves as a standard of conparision to sustained yield management. In other words, a normal forest is one in which there is a normal distribution of age gradations, or age-classes, normal increment and a normal growing stock. A normal forest is an ideally constituted forest with such volumes of trees of various ages so distributed and growing in sucn a way that they produce equal annual volumes of produce, which can remove continuously without detriment to future. (Brasnett)Trinity of normsNormal series of age gradations

By normal series of age gradations is meant the presence in the forest of trees of 1,2,3………..r years of age standing on equal areas, where r is the rotation age i.e. the number of years that the tree or crop take to reach exploitable size. In this condition, when trees of r age are felled and the area clearfelled is immediately restocked, then after one year, the series is complete again. When restocking of the whole area is not possible in one year as it takes 20 years to complete regeneration of the area and trees take 80 years to rach maturity, the new crop is divided into 80/ 20 = 4 periodic blocks. Then each of them is regenarated by them. In this way in 80 years the different periodic blocks will contain trees of 1 to 20 years. 21 to 40 years, 41 to 60 years, and 61 to 80 years. In this way, the forest will consist of 4 age– classes and this is said to be a normal distribution of age classes. In a forest, where regeneration is coming up throughout the life of the crop, as happens I selection forest, neither age gradationn nor age classes are distinguishable. But, even such a forest can be normal if trees of various ages occupy equal areas.Normal IncrementNormal increment is the increment attainable by a fully stocked stand or by a series of fully stocked stands arranged in a normal distribution of age classes, under specified management for the locality. In other words, it is the best or maximum increment attainable per unit area on a given site.Normal growing stock

When the above-mentioned conditions are fullfilled by forest, it will ipsofacto have a normal growing stock. In practice, this is taken to be equal to the volume given in the yield table for that age and site quality, eventhough the figures of the yield tables are the averages of the volume of the sample plots which were laid out in forests which were not normal before.

The above discription reveals that normality of a forest mainly on two conditions viz (i). the presence of normal distribution of age classes in the forest and (ii). Normal increment. If these two conditions are fullfilled, it can be taken for granted that the forest has normal growing stock. But, the reverse is not true i.e. if a forest has normal growing stock, it can not be assumed that it has a normal distribution of age-classes or it has normal increment because the volume equal to the volume given in the yield table may be due to prepondarance of mature or overmature trees while the lower classes may be entirely absent. in such a case, even the increment may not be normal.



Normal series of age-gradationsI = RiA = total area.L = MAIAnnual removal area = A / R (each on one ha area).

P.B. IV

0-20

P. B. –I

61-80

P. B. III21-40

P. B. II41-60

Normal forest is the maximum increment concept.


500

400i

i i

300i i

200i i i

100i i i i

1 2 3 4 5

Age classes of 0-20, 21-4041-60 & 61-80 years.

Rotation =80 yearsRegeneration period = 20 years


Regulated forest is one that yields an annual or periodic crop of about equal volume, size and quality

Thus, all the normal forests are regulated but not all regulated forests are normal i.e.in regulated forest, there may not be normal increment, but normal forest is the maximum form of the regulated forest.

Causes of Abnormality in forest Overstocking of mature and overmature trees. Understocking of the crops. Normal growing stock but abnormal distribution of age classes. The increment may be subnormal. Normal increment volume in an abnormal forest.

Normality in regular /evenaged Forest In clear felling system, Age gradation from one to rotation age. In Uniform shelterwood system, trees grouped with age classes on periodic blocks.

Normality in irregular/ unevenaged Forest.In an entirely unevenaged forest worked under selection system, trees of all

ages are found mixed together on every unit of area. Theoritically, in true selection system, the entire Felling Series is gone over for felling every year, but for practical considerations, the fellings are confined to one section each year in turn. i.e.the F.S.is divided into number of sections equal to the number of years in the felling cycle, and each gone over during the felling cycle, which may be 5, 10 or 15 years.Therefore, normality of an unevenaged selection forest can be ascertained by the number of trees en each size class, it must have a normal series of size- gradations istead of age- gradations of the normal evenaged forest. In addition , it must have the normal increment, as well as the amount of irregularity per unit area that is deemed to be most satisfactory.De Liocourt's Law

In a fully stocked selection forest, no of stems falls off from one diameter class to the series – a, aq-1, aq-2, aq-3 ------aq-(n-1)

Where, a= no of stems in the lowest diameter class.q= coefficient of reduction in the number of stems the quotient.


3000

2500

2000

1000

500

250

0 5 10 15 20 25 30 35 40 45 50 55 60

Inverse J - shaped curve

No

of t

rees

DBH


Meyer (1933) Simplified De- Liocourt's law in the form of an expontential function.

N = Ke –aD ( or Y = Ke –ax)Where, Y= N= No of stems in the diameter intervals.D = x =Diameter at breast height.e = 2.71828, the base of napierian logarithm.k= relative stand density ( dependent on site conditions).a = percentage reduction in number of stems for each dia classes.(i.e.= LogN = Log k – aD loge ) By plotting the log number of stems against their mid- diameter values on an ordinary

graph paper, if the resulting points were in a straight line, it would indicate a balanced crop. The abnormality in number in any diameter class can be readily detected and silvicultural treatment can be given to obtain ideal dustribution in course of time.

It is not known which is the ideal no of trees in a particular DBH class. What the quotient should be.

Yield RegulationYield: Yield is defined as the Volume or no of stands that can be removed annually or periodically as the forest area over which fellings may pass annually or periodically consistent with the object of management. The management of forest for production and supply of wood required continuous (or periodic) cutting of individual trees or crops of trees. The chief object of forest management may, therefore, be stated as the regulation of yield, before it can be regulated. It has to be determined or calculated. Yield regulation is therefore, involves two separate functions, viz. (1) calculation / determination of what the amount of yield should be, i.e. how much, where and when to cut the calculated quantity from the forest. 2) The construction of a cutting (felling) plan, which determines the identity of the stands to be cut.

Correct yield regulation is one of the main functions of sound forest management. Its general function is, however, to control the rate of removal or the progress of fellings of the existing crop, to institue safe guards to ensure yield in perpetuity and, subject to these, to satisfy the main object of management, primary one of which being the production of timber on sustained basis in perpetuity. In a normal forest, the entire annual increment could be removed each year, and the same capital would always be left undisturbed. If the growing stock is old, there will be excess of wood capital and the rate of increment will be low. The capital will have to be reduced by cutting more than the increment to make from for young trees. In a production forest, the object of management is usually to obtain a fairly steady yield, while aiming to bring it to a condition so as to give maximum sustained yield from the wood capital invested in the soil.Yield Regulation: "A term generally applied to the derermination of the yield and the prescribed means of realising it." It means the fixing in advance, usually for a short period- the working plan period- the amount of timber or other produce, which may be removed from the forest, annually or periodically. The object of regulating yield in short is;

I. To cut each crop or tree at maturity.



II. To obtain maximum yield of the desired produce.III. To cut approximately, the same quantity of material annually or

periodically IV. To limit the area to be felled to that which can be regenerated.

In the first rotation, difficulty in yield regulation arises due to the following causes; In virgin forest, crops are generally over mature and decrepit,

ncessitating early removal; regenaration conditions there in are also not favourable.

The crops are usually irregular, both in density and composition. Growth and composition data are available for quite a few decades.

In case of the evenaged systems, the yield is regulated by area, in the first. so as to build up equal age- gradations/ classes for sustained yield in , subsquent rotations, rather than equalising yield in current rotations. The yield is usually regulated for the period of working plan, which is generally 10 years. It is neither possible, nor desirable to fell annually the exat quantity prescribed in the working plan. Unforeseen contingencies silvicultural or economic often necessitate variation, however, it would suffice to restrict the yield within the prescribed yield for the working plan period. i.e. we aim at sustained yield over the period if not over each year, this is quite a practical proposition.

Broadly, the yield is determined on the basis of area, volume of both the parameters; the chief based for which are the growing stock, increment, objects of management and the silvicultural system, proper regulation of yield must take into consideration volume, age and also the area of a crop. Volume alone is insuffficient and regulation purely by area lacks flexibility. Frequent rivision of working plans is essential for check on previous regulations.

The determination of yield does not merely cosist of mathematical calculations, based o crop inventories, the records or the yield table. The result of any such calculations would, at best, give only a priliminary figure. The permissible yield may be more or less than the calculated yield, taking into consideration the growing stock and conposition of the age- classes. These may be in such conditions as may require harvesting less of more than calculated yield.Silvicultural systems in relation to yieldFor the purpose of considering the effect of silvicultural systems o yield regulation, the following three broad types of systems will be recognized.

I. Clear felling: resulting in regular, evenaged forests, in which age gradations are recognozed by area.

II. Regular shelterwood – resulting in regular, evenaged forests in which age classes are recognized by area.

III. Irregular shelterwood and selection: resulting in irregular forests, in which neither age- gradations, nor age classes are recognized.

Regulating of plantation forest

Working circle (W.C): A forest area (forming the whole /part of the working plan area) organized with a particular object and subject to one and same silvicultural system and same Set of working plan preparation. Felling series: A forest area forming the whole/part of the working circle to…

Distribute felling and reeneration and suit local conditions.



To maintain/ create normal distribution of age classes (when W.C to undivided, it in F.S.)

Coupe: In clear felling system a forest site is divided into a number of annual coupes (annual felling areas) equal to number of years I the rotations. Size of each coupe – A/ R hac.A = Area of forestR = Rotation.Cutting Sections: A sub division of F.S. for regulating cutting I same special manner; a planned seperation of felling in succession year (4/ 5 years) to avoid felling for danger of fire/ insect attack in ccessive coupes.Felling Cycle (FC): Felling series in selectio forest. Time that elapses between successive main felling on the same area.

I1, 11---91

II2, 12----92

III3, 13--93

IV4,14…. 94

V5, 15…95

VI6, 16…96 VII

7, 17…97VIII8, 18…98

IX9, 19…99

X10, 20…100

R= Rotations.Felling series in a selection forest worked on a 10-year felling cycle.

P-B III P- B II30-60 yrs 60-90 yrs

P- B IV P- B I0-30 yrs 90-120 yrs

30 years – regeneration periodR = 120 yearsP. B = Periodic blocks

1 2 3 4 5 6 7 8 9 10

Plan of an undivided W.C. with ten coupes.

Yield regulation in clear felling systemA) Area control: Method of determination of the annual cut or harvest by

specifying number of hectares to be cut each year. Can be used for both even and uneven aged forest.

Area to be cut = Total ha in forest (A)/ Rotation age (R) Site may be varied from coupe to coupe; this equiproductive area should be

taken widely used in clear felling and coppice system. Also applies to regular shelterwood system with periodic blocks (regenation

periods).

Area of each P.B. of the felling series = A / R * P Belongs to Bishnu Chandra Poudel. B.Sc. Forestry IIIYr, IInd Semester.

13

Felling

R= 10 yrs rotations


Where, R = rotation period.P = regeration period. (B) Volume Control: Method of determining annual cut or harvest by specifying volume of wood to be cut each year. Hundeshagen and Von- Mantel's formulas can be used.

Better suited in unevenaged management.

Yield regultion in regular shelterwood system(A) Permanent allotment method: consist in permanent

allocation of areas in all P.B.s possible in forest where there is no difficulty in regenerations.

(B) Revocable allotment Method: Only the regenaration block (P.B. I) i.e. block for felling is alloted , the other P.B. 's may be re alloted at each revision.

(C) Floating periodic blocks (F.P.Bs) – consist in the allotment of areas ripe for regenaration limits to the site of P.B. or to the length of the period.

- F.P.B. was evolved in France under the name quarter blue method (because FPB was colored blue on the maps). Not suitable for irregular forest.

Estimating Growing StockGrowing stock volume can be estimated by using a yield table.Yield Table: Necessary forest Management tool used for predicting yield, as a standard for stocking and as a measure of site quality.(Many yield table's represent a normal forest)

Yield table for Sal. SQT, evenaged fully stocked stand

Age H.dam (m) Stems/ haBA / Ha

(m2)

Stem Volume(m3/Ha) standing

5 4.9 8581 19.4 49

10 11.2 3553 23.4 119

15 16.8 2127 27.4 191

20 21.2 1481 31.0 259

25 24.6 1120 34.1 320

30 27.2 892 36.9 374



Summation Formula

Gr = n (Vn + V2n + ………………+Vr-n + Vr/2)Where, r = rotation age.n = no of years between yield tables.Gr = total volume of growing stock on r years.Vn = yield table volume/ ha at age n, 2n ……r.Estimation Yield for abnormal StockingAlllowable cut methodThe allowabel cut method of timber considered available for cutting during a specified time period, usually 1 year. It is the amount of timber the forest manager wpi;d ;ole tp have cut and thus is a target or guideline that the manages attempts to reach. However, there are many external reasons why the allowable cut is not reached in a particular year, or even in a particular decade.

Why allowable cut is not achieved?1) Fluctuations in the forest products market.

- Decrease I economic activity and hence, decrease in demand of timber.- Decrease housing starts can cause decreased sawn timber demand.- Local shifts in demand e.g opening or closing of a small mill.- Rise in stumpage prices may cause more allowable cut, which may be due

to increased demand of forest products.

2) Cyclic weather conditions: It may affect annual cuts for several consequative years.3) Woods labours availability4) Other foreces external to the forest:

- Can cause an under or overcut of the previously determined allowable cut.- Addition to and sustractions from the managed land base.- Newland acquisitions and land sales and trades.

Adjustment of the allowable cuts The under and over cuts caused by the external forces can be compensated by adjusting the allowable cut in subsequent time periods.

- By changing the merchantability, standards.- By changing the logging technology.- By increasing the cash flow in increased investment opportunity- so

increasing the cut generates cash by not only the revenues it brings but also by reducing income tax liability through the depletion accounts.

Allowable cuts are usually developed for large geographical areas and for long time periods. Forests may be divided into districts and districts subdivided into working circles. Allowable cuts are sometime calculated for working circles and often calculated for districts. These are then aggregated for the forest or total ownership. Allowable cut, then, is a large area concept and infrequently applied to individual stands.Allowable cuts are often calculated for long time periods. This depends on the organization's planning horizon and can cover variable length time periods. Orientation towards large areas and long time periods is purposeful because it facilitates averaging the cut over time and space.



Calculation of allowable cut with Area Control (Equiproductive area calculation)

Recall that area cotrol requires cutting equal areas or areas of equal productivity annually or periodically. This requires cutting the same number of acres each year in the simplest case of the normal forst with equal productivity on each acre. For example- 60000 acres forest on a 60-year rotation would have a 100-acre annual cut, as follows Annual allowable acre cut = 6000/ 60 = 100 acres per year.Looking up the yield in the appropriate table and multiplying by the number of acres estimate the volume of the annual allowable cut. Suppose, for example, the yield at 60 years was 45 cords, then, the volume of the annual allowable cut is estimated by; Annual allowable volume cut = 100 acres * 45 cords / acres = 4500 cords. 'The 5 or 10-year estimate is then simply the annual estimate multiplied by the appropriate number of years. e.g. 5-year estimate

- Allowable acre cut (5) = 100 acres * 5 year = 500 acres.- Allowable volume cut (5) = 4500 cords * 5 year = 22,500 cords.

Allowable cut estimation becomes more complex when the acres in the forest have different productivity levels. This requires cutting areas of equal productivity rather than equal area. Suppose, for example, the forest was pure, natural unthinned sissoo stand with 110 ft of basal area and on a 30-year rotation. Assume further that the site indices (SI) were unequal and distributed as shown below.

Example of equivalent area calculationSIa

Acres Cordsb

Total yield Equivalent Acres

50 100 19.9 1990 1.389

60 250 23.4 5850 1.18270 375 27.4 10275 1.00980 225 32.3 7267 0.85690 75 39.5 2963 0.700 Total- 1025 Total 28345

Ϋ = 28385 /1025 = 27.65 cords/ acre.

EA SI 50 = 27.65 / 19.90 = 1.389

Base age = 50

Unmodified are control requires cutting 34.17 (1025/30) acres each year. However, this woild result in unequal volumes each year. eg. Cutting in SI50 results in about 680 cord annual cut (34.17*19.9) where as m cutting in SI90 result in about a 1350 cord annual cord (34.17*39.5). There is almost a 10o percent fluctuations between the cuts, These great fluctuations would be



very difficult to accommodate if one were attempting to maintain an even wood flow for a manufacturing plant or an even cash flow as a management objective. The allowable cut can be modified for equal productivity by using the mean yield as the numerator and calculating equivalent acres such that cutting an equivalent acre in any site class results in the a yield equal to the mean yield per acre. The mean yield per acre is simply the mean weighted by the number of acres in each site class, or

Ϋ = Σ (YI *AI) / ΣAI

Where,

Ϋ = the mean yield per acre for the forest.

i = the ith site class.

Yi = the yield per acre in the ith site class.

Ai = the number of acres in the ith site class.

Advantages

- It is uncomplicated

- The area on the ground to be harvested is readily identified when area control is

used with a harvesting rule.

- Area control will readily produce a regulated forest.

- Area control seems particularly well suited to even -aged management.

Disadvantages- From commercial viewpoint, unmodified area control can cause large fluctuations

in the volumes harvested.- Area control must be combined with some type of volume control when applied

with unevenaged stands.Calculating the Allowable cut with Volume Control

Volume control requires cutting equal volumes annually or periodically. The allowable cut is determined y one of the several formulas, and this volume is then cut each year. However, many of these formulas are quite different, so it is important to be familiar with each before using it. As in any other model, the user should be certain that it reasonably fits the actual facts of the particular situation on the ground.

1. Hundeshagen's Formula Ya / Ga = Yr / GrWhere, Ya = Actual yield.Ga = Actual growing stock.Yr = yield in a fully stocked forest at rotation age.Gr = growing stock in a fully stocked forest at rotation age.

Assumptions Yield has a straight-line relationship with growing stocks. Forest has normally distributed age structure.


Age (R)

Vol


10% volume produces 10 % yield, this assumption may not be bad for slightly over/ under stocked stands.

Conditions necessary to apply this formula1. The yield table or function from which YI and Gr obtained is applicable to the

stand or forest for which allowable cut is being estimated.2. A straight must be a good representation of the relationship between fully and

under or over stocked stands.3. Finally, the forest must be regulated or have a normal age distribution.

2. Von Mantel's Formula Also called triangle formula. An extension of Hundeschange's formula

eliminates the need for yield table. Basic assumption is that in a regulated forest, growing stock increases in a

straight line with age. Growing stock can be expressed as a right-angled triangle calculated by area of

triangle.

Area = 1/2 base * heightGr = 1/2 R * Yr = R * Yr /2By substituting value of Gr in Hundeshagen's formula Ya / Ga = Yr / GrYa = Yr / Gr * Ga = (Ga * Yr)/ R *Yr/2 = 2 Ga /RWhere, Ya = actual yield or allowable cut.Ga = actual growing stock.R = Rotation age.

Von Mantel's formula as with Hundeshagen's formula requires a forest that is regulated or has a normal age distribution and that yield has a straight-line relationship with groeing stock. The existence of rotation age as a variable imply that the formula be used on evenaged stands. The above both formulas do not specially consider growth. Hundeshagen's formula depends on an existing yield table and Von Mantel's formula on the triangle relationship those substitutes into Hundeshagen's formula. There are other formulas that consider growth. Some of these are discussed below.

Assumptions Straightline relationship between yields and age. All assumptions required for using Hundeshagen's formula.

Advantages; Simple. No need of yield table.

Disadvantages: Neglets age class distribution and rate of growth.Best applicable to regualar, even-aged or nearly evenaged forest only.



Meyer's Amortization FormulaThis formula specially includes stand growth and is;

Vn = Vo (1 + it) n – {a (1 + im) n – 1} / im

Where, Vn = growing stock volume at future time n.Vo = growig stock volume today (time zero).it = compound growth percent on entire tand , including ingrowth.im = compound growth percent on the cut portion of the stand. a = annual cutn = number of years in the estimate period.

Allowable annual cut (a) = {Vo (1 + it) n – Vn} * im / {(1 + im)

n – 1}

Assumptions1. All parts of forest have the same growth percent if the formula is applied forest

wide.2. Growth percent remains the same before and after cutting regardless of stocking

distribution is unchanged by the cut.3. The cut is equal each year.

Meyer's formula is particularly well suited to unevenaged management because it directly considers growing stock levels and growth percent.

Austrain Formula This is a simplified version of Meyer's formula and is

Annual cut = I + (Ga – Gr) / a

Where,

I = annual increment.

Ga = present growing stock (Vo in Meyer's)

Gr = Desired growing stock (Vn in Meyer's)

a = adjustment period chosen.

Hanzlink FormulaThe hanzlik formula was developed for old growth in the Douglas – fir region as a glance at it

will indicate. The formula is

Annual cut = (Vm / R) + I

Where,

Vm = volume of overmature timber.



R = rotation age.

I = annual growth ageraged over the rotation.

Assumption The growing stock needs no adjustment and only the overmature timber need to be

changed.Advantages of Volume control

Very little data are suffcent for the estimates. These allowable cut estimation techniques can be applied as rough first estimates or

when better data simply are unavailable, as in developing nations. These formulas are particularly well suited for uneven-aged management.

Disdvantages of Volume control Though the formula requires little data, these estimates may be inprecise and

inaccurate. Several of the formulas require growth or increment estimates. These can be expensive and difficult to make if they are not already available. The volume to cut is known but its location is unknown.

Unevenaged regualtions

5000

0 5 10 15

The cutting cycle for a single stand Annual ha. Harvest = Total area (ha) Yrs in cutting cycle

Point 'a' is the volume before forest. Point 'b' is the volume just after harvest.Distance 'c' is the amount of harvest." " " 'd' is the amount of Reserve growing stock." " " 'e' is the cutting cycle (planned interval between major felling operations in the same stand)

Example:- Growth rate = 5% a year Reserve growing stock = 500m3

Cutting cycle = 5 yearsIn 5 years, the stock would increase to = 5000*1.055 {Vn = v0 (1+in)}

= 6381m3

At harvest, it would be cut back to original level of 500m3 and the harvest would be (6381-5000) = 1381m3.


C

D

6381

vol m3 /ha

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