The Biogenic Fuels by GH Kohlmaier, H Brohl

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The Biogenic Fuels: Fuelwood, Charcoal, CropResidues and Animal Dung as a Net Source

of Atmospheric Carbon Dioxide

Mitt. Geoi.-Paldont. Inst .

Univ. Hamburg

SCOPE/UNEP SonderbandHeft 64

S 29-43 H a m b u r g ,Ju li 1987

,

by

G. H. KOHLMAIER, H. BROHL & R. FRICKE, F ra nk fu rt *)

With 4 Figures and 6 Tables

Contents

Abstract 2 9

1. Introduct ion 3 0

2. Estimate of Net Carbon Dioxide Release from Roundwood, Fuelwood

and Charcoal Statistics for the Developing and Industrialized Countries 3 1

3. Estimate of CO

2 R e l e a s e

f r o m

R o u n

d w o o

d

P r o

d u c

e d

in Land Transformations in the Tropics 3 6

4. Estimate of CO, Release from the Use of Crop Residues,

Animal Dung and other Biogenic Fuels 3 95. Estimate of Net Carbon D iox ide Release Considering E nergy

Demands in Developing Countries 4 06. Conclusions 4 2

References 4 3

Abstract

The present use of biomass as fuel is investigated. Dif fer ent approaches are used toestimate the amount of carbon transferred to the atmosphere by this process. The grossflux of more than 1 GtCia is partial ly balanced by biomass regrowth, which restorescarbon to th e biota. D ue to degradation o f plant cover and soils, whi ch reduces carbon

storage, there remains a net fl ux due to biogenic fuel use estimated to be 0.2 ± 0.1 GtC/a.This net flux is mainly connected with the use of fuelwood, while the contribution of otherbiogenic fuels is relat ively small, unless connected wit h greater land trans formations (e.g.industrial production of bioalcohol). Although the net carbon flux to the atmosphere isrelatively small compared to other anthropogenieally induced carbon fluxes, it may wellinfluence the overall dynamic behavior of the biota within the global carbon cycle andshould therefore not be neglected in related studies and mode lling efforts.

*) Add re ss o f th e au thors : P ro f. D r. G.-H . KOHLMAIER, H . BROHL-KERNER, H. FRICKE,Institut fUr Physikalische und Theoretische Chemie, J.-W.-Goethe Universitat, Nieder-urseler Hang, D-6000 Frankfurt 50, F.R.G.

29



In the developing countries mor e than 2.0 bil li on (10') people (out of about3.4 x 10 i n 1980) depend on fuelw ood as the most im porta nt pr imar y energy

source. F i le lwood is mos t c ommonl y used for cooking and secondar i ly for

heating. Together wi th other biogenic fuels, i t provides up to about 2 7 % of thetotal energy consumption in the developing countries, whil e in the developed

countries it contr ibutes onl y 3 % (Table 1). As the popu lat ion steadily increases,fuelwo od is bec oming more and more scarce. This is because both the annual

consu mptio n increases and because forest land is converted into agricult ure oris overexploited.

Most studies referring to the traditional fuels in the developing nations have

been centered on energy questions, i n p arti cular on energy efficiency, energydevelopment, energy crisis as wel l as on questions concerning indoor poll utio n

by noxious fume gases. In this study our principal interest is directed towardsan est imate o f the n et ra te o f carbon release f r om biomass fuels in to th e

atmosphere. This pro ble m has been neglected i n most carbon cycle studies,because the quantities of carbon involved were referred to as small compared tothe release from fossil fuel burning and cement production which is of the order

POPULATION ( * 1 0 9)

DEVELOPING COUNTRIES

3.4

610 t SKE G t C

DEVELOPED COUNTRIES

1.2

610 t SKE G t C

TOTAL

4. 6

610 t S(E G t C

MODERN FUELS

PETROLEUM 1030 0.584 3200 1.815 4230 2.400

COAL 1025 0.729 2025 1.440 3050 2.169

NATURAL GAS 235 0.096 1735 0.707 1970 0.802

HYDROPOWER 177 0.0 500 0.0 677 0.0

NUCLEAR POWER 8 0.0 315 0.0 323 0.0

SUBTOTAL 2475 1.409 7775 3.962 10250 5.371

( t SKE/ (cep*a) ) (0.720) (6.750) (2.230)

TRADITIONAL FUELS

FUELWOOD 460 0.432 240 0.225 700 0.657

CROP RESIDUES a . o . 340 0.32 10 0.009 350 0.32

ANIMAL DUNG 100 0.09 low low 100 0.09

SUBTOTAL 900 0.842 250 0.234 1150 1.067

( t SKE/ (cap*a) ) (0 .260)* (0 .210) * * ( 0 . 2

.

5 0 )

T a b l e l

6GLOBAL ENERGY CONSUMPTION ( 10 t SKE ) AND CARBON RELEASE ( G t C ) I N 1982

(according to SMITH, 1988)

30

1. Introduction

Consumption o f t r ad i t i o na l f ue ls i s unce r ta in and es t imates f o r f uelwood and an ima ldung a r e l i k e l y t o b e u n de r st a te d . E ne rg y e q u i v al e n t s f o r t r a d i t i o n a l f u e l s a r es i t ua t i on sp ec i f i c and g loba l ave rages a re unce r ta in .

* * : C a l c u l a t e d f r o m U . S. d a t a a ss u mi ng t h a t r e s t o f d e v e lo p ed w o r l d u s e s b i om a ss f u e l si n same ra t io as o f t h e i r re la t i ve commerc ia l energy use t o t he deve loped coun t ry t o t a l(U.S.A. i s 35%).



of 5 GtCia in 1982. Nevertheless, the use of biomass as fuel is one important

anthropogenie impact which influences the dynamics of the biota within theglobal carbon cycle. Even if the direct net i npu t is small, there might be changesin the uptake and release patterns of CO

2 w h i c h i n f l u e n c e

t h e

t o t a l

s o u r c eo r

sink strength of the biota with respect to other anthropogenically inducedperturbat ions o f t he atmospheric CO

2 c o n t e n t .

T h e r e f o r et h i s

s t u d y

i s

a n

attempt to assess the carbon fluxes connected with the use of biogenic fuels,whi ch then can be implemented into carbon cycle models.

2. Estimate of Net Carbon Dioxide Release from Roundwood,

F u e

l w o

o d

a

n

d

Ch

a

r

c

o

a

l

S

ta

t

i

s

t

i

c

s

f

o

r

t

h

e

D

e

v

e

lo

p

i

n

g

a

n

Industrialized Countries

The foll owing analysis is based on the FAO forests products statistics (FAO,1984) on total r ound woo d p rod ucti on ( Table 2), and on fuelw ood and charcoalproduction (Table 3), which is part of the roundwood production. Four groups of

industrialized nations: No rt h America, Europe, USSR, a nd Pacific developedcountries, and three groups o f developing nations: La ti n (Central and South)

America, Africa and South East Asia including China are distinguished. It isseen that while the product i on rate o f roundwood is nearly constant for thedeveloped countries, i t has been increasing by about 2.5-3 %/a for the develop-

ing na tions. Accord ing to the s ta tis tics the roundwood product ion o f thedeveloping countries is o f equal magnitude as tha t of the developed nationsleading to a total worl dwide product ion of about 3 x 10 m ' corresponding toabout 0.65 m'icap./a. Th e average carbon content of 1 m ' woo d i s ta ken to

correspond to 0.33 t carbon, derived f rom mult ipli cati on of the average woo ddensit y (0.73 & i n ' ) and the average carbon contents per g of dry mat ter (0.45 gC/

gDM) (Table 4). ROTTY (1986), assuming a specific weight for dry hardwood of0.52 and of dry s oftwood of 0.40 and a carbon to tota l dry weig ht ratio of 0.51,calculates a corresponding conversion factor of 0.25. Wit hi n the lim its of uncer

tai nty for pro ducti on data and for density and carbon contents it therefore maybe estimated that about 1 Gt of carbon is involved annually.

Looking at the fuelwood data (Table 3) a total annual increase of 2.4% isregistered, which is dominated by the production of fuelwood by the developing

nations (Figs. 1 and 2). It is seen from Figure 1 that Asia has the highest share offuelwood, followed by Af rica and Lati n America. The per capita consumption,

however, is highest in Afr ica wit h about 0.85 m'ica pla and lowest in Asia wi thabout 0.25 m'icapla, a result w hi ch reflects availabili ty o f fuelwood and sup-plementa ry energy sources as well as geographic and cult ura l differences.

I t s hould be noted, however, that due t o dif fer ent statist ical evaluat ionmethods the produ ctio n data show several discontinuities fo r differ ent coun-

tries or groups of countries, especially in the early 60'.

Comparing Tables 2 and 3, i t is seen that on l y a smal l f ract ion o f theroundwood produc tion of developed countries is used as fuelwood, whi le the

greater part goes into the pulp, paper and furniture production and into build-

ing, rai lroad construct ion and mining. Forest management i n the developedcountries is more or less based on the pr inc ipl e of sustained yield. i.e. annual

yield should be equal to annual increments. Although the use of roundwoodspans a wide spe ctrum of residence times o f wood f rom a few months to a few

hundred years, we can assume in first order, that the carbon is nearly balanced

in such a way, that no essential net flu x in or out of the atmosphere is occurring.

31



In the developing countries a wid e spectr um of forest management prac-tices can be found, reaching f rom resource-preserving silvi cultur e to excessiveoverexploit ation. For a first estimate of the influence on carbon balance, we mayclassify wood production according to three categories: Category I contains

forest areas managed for sustained yield, Le. no net f lux of carbon should result

Mio cbm Gt C Mio cbm Gt C Mio cbm (It C Mio cbm Gt C

NORTH AMERICA 296 0.0975 409 0.135 448.7 0.148 510 0.168

EUROPE 209 0.069 308.8 0.102 331.8 0.109 333.7 0.11

USSR 104 0.0343 369 0.122 385.1 0,127 356.6 0.12

PACIFIC DEVELOPED 79 0.026 72 0.024 66.5 0.022

DEVELOPED ALL 609 0.201 1166 0.384 1238 0.408 1267 0.417

CENTRAIASOUTH AMERICA 139 0.046 212.7 0.07 244.3 0.081 334 0.11

AFRICA 96 0.032 225.1 0.074 293.8 0.097 430.4 0.142

ASIA 93 0.031 491.3 0.162 764.4 0.252 955.8 0,315

DEVELOPING ALL 328 0.108 929.1 0.306 1302.1 0.429 1720.2 0.567

TOTAL 937 0.308 2095.1 0.69 2540.1 0.837 2987.2 0.984

Mio cbm Gt C Nio cbm Gt C Silo cbm Gt C Mio cbm Gt C

NORTH AMERICA 31 0.0102 46.5 0.0153 25 0.0082 51.5 0.0169

EUROPE 88 0.0289 88 0.0289 57:8 0.0187 37.5 0.0123

USSR (56) (0.0184) 93 0.0306 86.5 0.0283 78_9 0.0259

PACIFIC DEVELOPED 47 0.0154 52 0.017 61 0,02

DEVELOPED A l *

175 0.0576 274.5 0.0902 221.3 0.0727 228.9 0.0752

CENTRAUSOUTH AMERICA 130 0.0428 155 0.0512 198 0.0652 285 0.0930

AFRICA 90 0.0296 135 0.0445 293 0.0965 370 0.122

ASIA 57 0.0185 362 0.1189 625,5 0.2055 716 0.235

DEVELOPING AL L 277 0.091 652 0.214 1116.5 0.367 1371 0.45

TOTAL 452 0.148 ,926.5 0.304 1337.8 0.439 1599.9 0.326

Consumption ca lcu l a ted as i n Tab le 2 .

32

T a b l e 2

PRODUCTION OF ROUNDWOOD OVER THE LAST THREE DECADESBASED ON THE FAO STATISTICS

1950 (1951) 1 9 6 0 1970 1980

T a b l e 3

CONSUMPTION OF FUELWOOD AND CHARCOAL OVER THE LAST THREE DECADESBASED ON THE FAO STATISTICS (FAO 1984)

1950 (1951) 1 9 6 0 1 9 7 0 1980

Consumption i s ca lc u la te d as Product ion p lus Impor ts minus Expor ts



fro m wood prod ucti on in these areas. Category II includes wood p roduc tion inareas which are transformed from forests to other types of land use, mainlypermanent agricult ure and pasture. I f this wood is burned, it should result in anet in put of carbon into the atmosphere, because regrowth on the respective

areas is ve ry muc h l imited. Category I I I contains wood w hic h is most ly col-

1. 0

0 .9

0 , 8

0 . 7

0 .6

0 . 5

0 .4

0 . 3

0 . 2

0 .1

I a b l e 4CHARACTERISTIC ENERGY VALUES AND CONVERSION FACTORS

1kW = 1000 Wa t t sec / sec = 1000 Jou le s / se c = 31 .56 GJ /a

1 t E K E ( Ge rm an c o a l e q u i v a l e n t ) = 2 9 . 3 GJ

1 t SKE/a = 29 .3 G J / a

.

= 9 3 01 t f u e lw o od = 1 4 - 1 8 G J ( p r e f e r r e d v a l u e 1 4 G J) = 0 . 4 8 0 , 6 1 L SKE

1 t f ue lwood /a = 440 - 570 W3

1 m f u e l w o o d = 1 0 - 1 3 G J3

1 m f u e l w o o d / a = 3 2 0 - 4 20 W

d a i l y f o o d co ns um pt io n : 2 0 0 0 - 3 00 0 k c a l / d

.= 1 0 0 - 1 5 0

W a t t

a pp ro x im a te p r i m a r y e n e rg y u s e i n d e v e l o p i n g n a t i o n s : l k W r e s u l t i n g

i n a n e n d e n er g y u s e o f c a . 2 0 0 F ( e f f i c i e n c y c a . 20 % )

a pp ro xi ma te p ri m a r y e ne r gy u s e i n i n d u s t r i a l i z e d n a t i o n s : 6 . 5 kW

r e s u l t i n g i n a n en d e ne rg y u se o f 2 - 3 kW ( e f f i c i e n c y 3 0 - 5 0 T )3

1 m r o u n dw o o d /f u e l w o od = 0 . 7 3 2 t d r y m a t t e r

1 t w o od ( d r y m a t t e r ) = 0 . 4 5 t c a r b o n

1 t S KE ( f u e l wo o d ) = 0 . 9 3 9 t C

1 t S KE ( c r o p r e s i d u e s ) = 0 . 8 7 - 0 . 9 7 t C ( e s t i m . )

1 t S KE ( a n i m a l d u ng ) = 0 . 8 - 1 . 0 t C ( e s t i m . )

1045 5 0

Auto

1

55 6 0 6 5 7 0 7 5 8 0 1 9 8 5

- 3 0 0

_ 2 5 0

_ 2 0 0

_ 1 5 0

1 2 - -

- 5 -

P 4 -4 11

- 4 2

A f r i c a - 1 0 0

L a t i n A m e r i c o _ 5 0

Fig. 1: Co ns um pt io n of fuelwood in 10 m

3 ( l e f t ) a n d i n

1 0 ' t o f

c a r b o n —

r i g h t )

i n

d e v e l o p

i n g

countries in Afri ca, Asia and La tin A meri ca for t he time period 1945-1982.Discontinui t ies i n th e ear ly s ixt ies are mai nly due to changing assessment

methods (data from FAO, 1984).

33



1. 0

0 . 9

O. 8

O. 7

0. 6

O. 5

O. 4

O. 3

O. 2

O.

1945

Fig. 2:

34

I • " I • 1 1 1 1

50 5 5 6 0 6 5 7 0 7 5

A f r i c a

s 0 e e -e e o 0eL c t i n A m e r i c o

A s i a

1

80

300

250

, 200

_ 150

_ 100

_ 5 0

1985

Per-capita consumption of fuelwood in m' (left) and in kg of carbon (right) indeveloping countries in Africa, Asia and Lat in Amer ica as well as for the develop-ing countries as a wh ole for the t ime period 1945-1982. Fur the r explanation see

Figure 1 and text.

lected fr om open forests, forest fringes, bushlands and s hrublands o r singletrees in the neighbourhood of settlements without clearing the entire area. Inthis case the impact on carbon balance may reach fro m zero, when annual y ieldis ba lanced b y regrowth , to h ig h ne t inpu ts to the a tmosphere when the

respective areas are degraded due to ove rexploitat ion.

It is impossible to classify the produ ction data directly since no info rmatio nabout the origin of the produced wood is given wi th regard to the introduced

categories. To estimate the amount of wood produced in category I. one maycalculate the possible yield out of these forest areas, where sufficient manage-

ment practices are executed. According to the FAO classif ication of tropicalforest resources (LANLY, 1982) 42 x 10

6 h a o f t r o p i c a l

f o r e s t s

c a n

b e

r e g a r d e

d

a s

intensively managed, annual allowable cut ranging from 0.5-1.7 1W/ha/a on theaverage, with values up to 8 m'lhaia possible at most favourable sites. Total yield

may l ie between 40 and 50 x 10' m

3

/ a .

Anot her contr ibut ion to this category comes from forest plantations, a term

wh ic h in the FAO termi nology comprises artific ially established stands of woodfor industrial as well as non-industrial purposes, the latter is to a major part

designed to fuel wood product ion. The tota l area of plantat ions amounts to11.5 x 10

6

h a ,

o ut

o

f

w

h i

c h

7

.

1

x

10

'

h

a

a

r

e

f

non-indus trial purposes. Ou t of the total plantat ion area 4.6 X 10

6 h a h a v e b e e nstablished w it hi n the time period of 1976 - 1980 and should not have given any

yield at all, such that at most 6.9 x 106 h a ( 4 . 6 x

1 0 ' h a

i n d u s t r i a l ,

2 . 3

x

1 0 '

h a

n o n

-

industri al) have to be taken into account. The average annual yield for indust rialplantat ions i n the time span from 1978 to 1982 is estimated by L A = (1982) to be31.4 x 10

6 m

3

.

A s s

u m i

n g

t

h

e

s

a

m

e

y

i

e

tions, this adds ano ther 15.6 x 10' m

8

.Since the FAO study does not include China, the appropriate figures from

this country have to be added to the above estimate. According to SM1L (1983)

wood product ion from forests managed for sustained yield in the People's

Republic of China should no t exceed 50 x 10' in', though the total roundw oodpro duc tio n amounts to 212 x 10' m' in 1980.



Summi ng up the above figures, we fin d that about 140 X 10' m ' of round-

wood or about 8 % o f the to ta l y ie ld m ay be harvested i n the developingcountries according to the princ iple of sustained yield, i.e. not contr ibut ing to anet carbon inpu t i nto the atmosphere.

To estimate the share of categories I I and II I to total w ood pr oduct ion onemay try to evaluate the possible contribution of open tree and shrub formationsto wood production. Fr om data given 133

•7 L A M A ( ( 1 9 8 2 )o n e

m a y

c a l c u l a t e

t h e

total annual wood incremen t on the 734 x 10 ha of open forest format ions to bebetween 350 and 700 x 10' m

3

i a , o u t o f

w h i c h

a t

m o s t

2 0

x

1 0 '

m

3/ a

a r

e

o b t a i

n a b l e

as sawlogs and veneer logs. Th e s hru b format ions m ay contr ibute about125 x 10' nf ia on an area of 624.1 x 10' ha. It is well kn ow n that in many regions

open tree formati ons are overexploi ted, i.e. annual yields exceed annual incre-ments, mainl y due to fuel wood collection. Therefore total wood harvest fro m

these formati ons can be assumed at least to equal annual wood increment, but isprobably much higher.

Fig. 3:

IME18111*

II: 3 8 0 ± 180

1720

II I. 1200 t 160

b)

I I 7 15 -1

- / 7 5

0,24 t 0 05 Gt C

net carbonreLeas

I . 2 5± 10

I I 2 0 0 ± 100

1370

Roundwood f 1 0

5

m3

1 a )

F u e t

w o o d

I D 1145 ± 100

Scenario 1

0.24 ± 0,06 Gt C

net carbonre[ease

Scenario 2

a) Roundwood and b) f uelwood pro ductio n in developing countries according todiffer ent categories:I . Wood f rom forests managed according to the pr incip le of sustained yie ld(intensively managed forests, forest plantations); carbon budget is balanced.

Wood from conversion of forests (selective loggings, clearings for permanentagriculture/pasture, shift ing cultivation); carbon release not balanced by re-growth.

Wood fr om open forests, woodlands an d shrublands, small woodlots a ndforest fringes. Carbon release partiall y or t otally balanced by regrowth, accordingto d iffer ent scenarios.

Assump tions for secenarios 1 and 2 are explained i n the text. A ll values are givenin 10' ms/a and GtC/a, resp.. Numbers given are best estimates; where ranges aregiven, they are meant as ranges of estimates rather than real error bounds.

35



In F igure 3a two l imit ing scenar ios for the d ist r ibut ion of roundwood

harvest onto categories II and I II are considered. I n scenario 1 it is assumed thatwood product i on i n category I I I equals annual wo od increments, i.e . 650

± 175 x 10 m

3

/ a .

B y

d i f f e

r e n c

e

w o

o d

p r

o d

u c t

i o n

i

n

c

a t

e

g

o r

y

I

I

,

w

hi

c

h

a

c

c

o

u

n

t

s

for wood harvested in selective loggings and clearings for permanent agricul-ture or pasture as wel l as in s hif ting c ulti vation, is obtained to be 930 + 175 x 10'

m'ia. As wi ll be discussed in the n ext chapter, this nu mbe r appears muc h too

high.

A lo wer and probably more realistic estimate assumes that the c ontri butio nof category I I is restr icted to woo d harvested in select ive loggings and thefuel wood used by about 200 x 10

6 f o r e s t

f a r m e r s ,

a d d i n g

u p

t o

3 8 0

±

1 8 0x

1 0

'

i n

3

/

a. This t ime by d ifference category II I is obta ined, where 1200 ± 180 x 10

6 m ' i a a r ehen harvested. Tha t w oul d mean that harvest exceeds annual increment by 550

± 180 x 10' ma/a, i.e. severe over exp lo ita tio n and land degradation is indica ted.

Figure 3b is constructed b y apply ing a s imi l ar procedure to fue l wood

production. C ont ri but ion of category I is assumed here to be small, essentiallyrestricted to the yield of non-industrial plantations mostly established for fuel-

wood supply. P roduc tion of industrial wood in category I II was estimated above

to be 20 x 10' m3

/ a ,

t h e r e f o

r e

a l l

t h

e

r e

s t

i

sa s

s u

m e

d

t

o

b

e

f u

e l

w oo d

.

Fuelwood produced in category II is accounted for as net release of carbon

to the atmosphere, whil e i n category II I o nly t hat part exceeding annual incre-ments is taken into account.

As can be seen fr om Figure 3b, the net release of carbon due to fue lwood useamounts to 0.24 ± 0.06 GtCia, cor res pondin g to 715 ± 175 x 10' m

a / a , i n d e p e n d e n tf the scenar io used. I t is essent ia lly the a mount o f wood harvestable i n

sustained yield from category III, which determines the net release.

When the open forest and shrub fo rmations are overexploi ted, an additional

in put from land degradation, soil erosion etc. is to be expected. This is t rue f orscenario 2, wher e severe overexploitati on is considered, b ut it is also true on a

smaller scale for scenario 1, due to oth er usages o f the respective areas, li kegrazing.

3. Estimate of CO

2 R e l e a s e

f r o m

R o u n

d w o o

d

P r o

d u c

e d

i

n

L

an

d

Transformations in the Tropics

Based on the FAO study on tropical forest resources (LANLY, 1982), presentchanges i n land use in 76 countr ies o f the tropics have been analyzed wi threspect to their impact onto the carbon balance (KOHLMAIER et al., 1985). The

major impacts causing transformati ons of forest land to other vegetation types

are: shifting cultivation, selective logging and clearings for permanent agricul-ture and pasture (Fig. 4).

To obtain the amount of roundwood produced by these impacts, one mayfirst calculate the total amount of woody biomass involved. Our calculations arebased on areal transformations given by LANLY (1982) and on biomass densities

deri ved fr om a s tudy of BROWN & LUGO (1982) based on ecological estimates. It

36



undisturbed

forests

Area

10

6

h

a

Woody Biomass

A 4.0 770 - 1020

B1 3.0 670

B2 3.2 830

Cl 34.9 2270

C2 4,1 1130

C3 1.0 260

AB1

agricult. land

( permanent)

2

logged-overforests

i

dagricult. land

(shifting cult.)

forestfallow

Timber F u e l w o o d E xc es s Wood

1 0

6

M

3

90 - 260 n . a . 5 1 0 - 930

120 n . a , 5 5 0

130 - 260 n . a . 5 7 0 - 700

n.a.

n.a,

n

,

a

.

1

(( 100 - 3003360-3560

Fig. 4: E st im at ed areas, biomass and wood pr oduction in different land transformationsin developing countries.A: Selective loggings for timber harvestB L Clearings o f pr imary and old secondary forests for permanent agriculture orpastureB2: Clearings of already logged-over forests for p ermanent agricultur e or pastureCl: Clearings of forest fallow for shifting cultivat ionC2: Clearings of primary and old secondary forests for shifting cultivationC3: Clearings of already logged-over forests for shif ting c ultiv atio nn. a.: no data available, but the corresponding numbers are assumed to be small

37



should be noted that the same authors more recently publis hed another esti-

mate, based on t imber volume stat ist ics, with considerably lower biomassdensities for all types of tropical forests (BROWN & LUGO, 1984). If we had used

this latter estimate, yields w oul d be reduced by at least a factor of two.

If a forest is logged over for harvest of selected tree species (Flux A in Fig.

4), usu all y o nly 5 t o 15% o f the biomass o f the affected area is used. Wi th anannually logged area of about 4 x 10' ha in tropic al forests, yiel d of timber mayamount to 90-260 x 1 0

6

m " , w h i l e

t h e

t o t a l

a f f e c t

e d

w o o

d y

b i o

m a ss

m

a

y

a m

o u

n t

to 770-1020 x 10' m

3

,

a c c o r d i n g

t o

d i f f e r

e n t

i m p

a c t

s c e

n a r

i o s

( K O

H L M

A T E

R

e

t

a

l

.,

1985). Thi s means that about 510-930 x 1 0

6

m

3 o f w o o d

a r e c u t

d o w n

o r

d y i n g

o f f

but are not used as timber. Usu all y this w ood is not commercialized, bu t some

part may be collected by people living in the neighbouring areas.

The amount o f wood obtained fro m land clearings for permanent agricul-

ture and/or pasture (B1 + B2) was previous ly estimated to be about 315 ± 65 x 10'an estimate wh ic h i s pr obabl y stil l on the hig h side (KOHLMAIER et al.,

1985). No data seem to be available concerning the future use made of this wood.

Much larger amounts o f wood are cut down and burnt in clearings for shift ing

cult ivat ion. Again, based on data about land transformations and biomass

densities, one may calculate that up to 1100 x 10' M3 o f w o o d a r e

c u t i n

t h e

a r e a s

of undi stur bed forests (C2), wher e 4.1 x 10

6 h a a r e a n n u a l l y

c l e a r e d

f o r

s h i f t i n g

cultivation, wh il e L 0 x 10' ha of already logged-over forests cleared each yearcontribu te 260 x 10' m'ia (C3). The fal low areas already invol ved in the shift ing

cul tiv ation cycle (34.9 x 10' ha) ma y cont ribute up to 2300 x 10" M

3 ( C l ) . T h o u g hhese f igures even exceed the f igures fo r total ro undwood pr oduct ion, i t isunli kely that shift ing cultivation contributes very much to the fuelwood budgetoutside the forest farmer commun ity. On the one hand forest farmers are usuallyunable to commercialize th eir wood because of lack o f infrastructure. O n the

other hand wood extraction is in principle limited by the fact that crops grown

on these plots usually need the nutr ients stored i n w ood w hic h are released by

bur nin g on the site. I f one assumes that t he 200 x 10' people liv ing in shi fti ng

cultivation satisfy their own fuelwood demand from this wood, then between100 and 300 x 10' m' may be used as fuel .

In consequence, 690 ± 250 x 10

6 m '

r o u n d w o o d

m a y

b e

h a r v e s

t e d

i n

l a n

d

transfo rmat ions , 490 ± 150 x 10

6 m ' a s

t i m b e r

a n d

2 0 0

±

1 0 0

x

1 0

m a

a s

f u e l w

o o d .

The excess wood, which is cut but probably not harvested as roundwood mayamount to 5350 ± 400 x 10

6 m ' , a

f i g u r e

m o r e

t h a n

t h r e

et i m

e s

h i g

h e r

t h

a n

t

h

e

total roundwood production in these countries. Though the largest part of thiswood is n ot wasted b ut used as a nutr ient source for agricultural soils, there

remain remarkable amounts of wood, which either may be prevented from

being cut by more careful harvesting techniques or may be used as fuelwood.Today such usage is mostl y prevented by c onfl ict ing economical interests andlack of means of transportation.

From Tables 2 and 3 it is seen that the amo unt of roundwoo d no t used as

fuelwood is ab out 350 x 10' m" i.e. par t of the ti mbe r harvest estimated here is

probably also converted to fuelwood or charcoal. The est imated range forfue lwood product ion f r om lan d t ransfo rmat ions is therefo re extended t o

100-600 x 10

6 m

3

/ a ,

c o r r e

s p o n

d i n g

t

o

a

c a

r b

o n

f

l

The total net carbon fl ux to the atmosphere caused by these land transfor-

mations was prev ious ly estimated to be about 1 GtC/a, wh ile a simil ar po rtion o fnon-volat i le carbon compounds remains on site or is eroded into the r iver

systems (KOHLMAIER et al., 1985).

38



4. Estimate of CO

2 R e l e a s e

f r o m

t h e

U s

eo

f

C r

o p

R e s

i d u

e s ,

Ani mal Dung and other Biogenic Fuels

The use o f crop residues and animal dung has a long tr adit ion in someregions o f the world, b ut is recently increasing very rapi dly due to the wide-

spread shortage of fuelwood. Very little data are available about the amounts

used on a global scale. Est imates for use o f animal du ng var y f ro m 200 to400 x 10' t ta i n the mid-70t ies t o beginning 8 0 t i e s ,

6

' W h i l e t h e s p a n

f o r c r o p

residues reaches from 60-80 x 10' t/a for the m id 70ties to 500-700 x 10' tia for the

beginn ing 80ties (GLOBAL 2000, 1980; SMITH, 1985). As many as 800 x 10' peoplemay re ly on c rop residues and animal dung as the ir pr incipal cooking fue l(BARNARD, 1985).

Though i t turns out that agr icu l tural residues are an important energysource, their contribution to an additional anthropogenic CO

2 i n p u t i n t o t h etmosphere is neglig ib le : they wo ul d rapi d ly decompose on the f ie ld and

therefore a lso be oxid ized i f not used as fue ls. Oxidat ion mi gh t be morecomplete in burning, b ut under tropical conditions there is usually no extensivebuild-up of organic matter in soils, such that even under natural condit ions

inp ut of organic wastes and decomposi tion wi ll nearly be balanced.

On th e other hand, a small indir ect i npu t can be expected i f extensive

removal of organic material by harvesting all crop residues leads to a depletion

of soil organic mat ter and degradation of soils, but the amounts invo lved aredif fi cu lt to estimate.

In some o f the developing countr ies biogas product i on f rom animal andplant residues has become an impor tan t additi onal energy source whi ch helpsto save fuelwood. Extensive programs for biogas plants for individual familiesor rural communiti es have in partic ular been installed i n China and to a lesserextent in India and other developing countries. I t is reported (MouLIK, 1985) that

over 7 mil li on biogas plants in China could serve, if all were operational, morethan 5 % of China's rural population. It is clear that bi ogasification also is neit hera direct source or sink for atmospheric carbon, bu t it helps to save other fuelsand to recycle nutrients of wastes efficiently, if the residues of biogasificationare taken back into the fields.

Even more recent ly biomass is also used on a larger scale fo r energy i nThir d Worl d countries. The Brazilian Biomass Energ y Program, as one of thelargest installed up to n ow, is p art of the Brazilian eff ort to face the need tosubstitute biomass energy fo r non-renewable energy sources GOLDEMBERG et

al., 1985. Of the about 5.2 x 10' m

3 e t h a n o l

p r o d u c e d

i n

B r a z i l

i n

1 9 8 2

,

0 . 8

x

1 0

'

m

3

are used in the chemical industry, 2 x 10' m

3 a r e u s e d a s

f u e l f o r

a b o u t

5 5 0

0 0 0

a l l -

ethanol cars, and 1.9 x 10' m

3 s e r v e a sa

g a s o l i n e

a d d i t i v

e

f o r

m o r

e

t h

a n

8

m i l

l i o

n

vehicles. The alcohol produc tion goal is to produce about 10.7 x 10' m3 f o r 1 9 8 7 ,iming at th e subst i tut ion o f 170. 000 barrels o f petroleum p er day, wh ic h

represents about 10 % of the forecasted oil consumption in that year. Today wecan recognize this goal no t to be reached, due to pl ann ing mistakes as wel l as thechanging economic and social conditions. Nevertheless the Brazilian Energ yProgram is the most impo rtant experiment to use bioalcohol for energy. Again,no direct net input of CO

2 i n t o t h e

a t m o s p h e

r e

i s

t o

b e

e x p e

c t e d

f r

o m

t

h

e

this biomass, bu t depending on the ki nd of implementat ion o f energy crops

there migh t be indi rect inputs, e.g. whe n forests are cleared fo r gro wing sugarcane.

39



5. Estimate of Net Carbon Dioxide Release ConsideringEnergy Demands in Developing Countries

The per capita use of fuelwood i n deve loping countries is characterized by

varying amounts of consumption. depending on climatic and nutritional condi-t ions as w el l as o n the avai lab i l i ty o f fue lwood and ot her energy sources.

According to a FA O sur vey (FAO, 1981), annual needs of fuelwood ma y v ary

fro m 0.5 to 2 m'icap, wh i c t corresponds to app rox ima tely 160 to 840 Watt. Due tothe lo w efficiency of tradit ional fuelwood stoves (12-18 %), this wi ll result in anaverage end-use energy of about 50 Watt, i f only c ook ing is cons idered as end-

use. Im pr ovi ng stove efficiencies mig ht be an impor tant measure in energy andfuelwood saving; i t should be mentioned, however, that even cooking fires often

serve other purposes such as heating or lighting or have social functions.

I f fuelwood cannot be gathered nearby, w hi ch is usually the case in urb anhomes, people often shif t to charcoal as pr imary energy source, si mp ly because

transportation becomes easier. Transformation of wood to charcoal also causeslosses o f energy. Ac co rd in g to REVELLE (1980), 30')/o o f energy i n wo od isconverted into energy in charcoal on average, wh il e h ighl y efficient charcoalki lns convert 50 to 60%. That means that 1/2 to 2/3 of the wood energy is lost, bu t

this loss is part ly compensated by the two times higher efficiency o f charcoalbraziers compared to wood stoves.Furthermore, since less energy is necessaryto transport one energy equivalent in form of charcoal than in form of wood, it

mig ht be more economic to use charcoal instead o f wood despite conversionlosses, when transport distances of more than about 100 km are involved. This

will also reduce air pollution, since charcoal produces less smoke and fumes.

The „Map of the Fuelwood Situat ion in the Developing Countries" com-

piled by FAO in 1981 uses an approach by region to account for the differentneeds and types of use of f uelwood in rural areas of the developing countries aswell as for the availability o f fuelwood to meet this demand. (The term „fuel-woo d" here also includes ligneous material f rom agricul tural residues).

In Table 5a we have summarized the FAO data on people living in different

categories of fuelwood supply. We have further estimated the possible sustain-ing fuelwood consumption wi th in the different regions and categories. This is

done by mult iply ing the num ber of people wi th the lower of the two f iguresgiven for need and avail abili ty of fuelwood per capita, assuming that fuelwo odis consumed according to the given basic needs, but does not exceed theavailability, i.e. the fuelwood resources are not degraded. This analysis reveals

that in the given regions (excludi ng China and the Near East and Nort h Africa,where the data given are not b roken dow n i nto diff erent categories) the rural

population, w hic h amounts to 86 % of the total population, may consume about880 x 10 m

3

/ a o f

f u e l

w o o

d

o

n

a

s u

s t

a i

n i

n gb

a

s

i

s

.

T

h

tion, however, amounts t o about 1260 x 10' m'ia, acc ording to the same data set(Table 5b). If one assumes that the basic needs must be met, then the difference

between these t wo figures, abo ut 380 x 106 m ' o f w o o d ,

i s

h a r v e s t e d

a n d

n o t

compensated for by regrowth, i.e. must be accounted for as a net source ofatmospheric CO

2

. I n

f a c t ,

i n

s e v e r

a l

r e g i

o n s

p eo p

l e

a

r

e

n

o

t

basic needs, but this m ig ht be partial ly compensated by cuttings b eyond basicneeds in areas where fuelvvood is abundant.

The data in Tables 5a/b do no t acc ount f or about 70 x 10

6 p e o p l e l i v i n g i nural areas of North A fri ca and the Near East, where a fuelwood de fic it s ituation

is assumed to prevail. I f we appl y the mean values o f sustained and needed

fue lwood consump t ion o f 0 .40 a n d 0 .69 m

3

/ c a p l a , r e s p e c t i v e l y ,

t ot h i s

popula tion, we obtai n addi tion al 28.0 and 48.5 x 10' me/a, leading to t otal figures

40



of about 915 x 10' m

3

/ a o f

f u e l w o o

d

o b t a i n

a b l e

i

n

s u s t

a i n e

d

y i

e l

d

a

n

d

o

f

a

b

o

u

t

1310 x 10 m

3 o f

f u e l

w o o d

n e

e d

e d

e

a

c

h

y

e

a

r

.

T

h

e

d i

f f

e r

e n

c e

a

m

o

un

t

s

t

o

n

e

a

r

l

y

400 x 10' m

3

/ a o r

0 . 1 3

G t C

/ a ,

w h

i c

h

s h

o u

l d

e

n

t

e

r

t

h

e

a t

m

o s

p h

e r

e

a

s

n

e

t

i

n

p

u

t

.

Though the annua l demand of 1310 x 10' m

3 f u e l v v o o d

o b t a i n e d

h e r e

n e a r l y

equals the FAO figure for total fu elwood cut in developing countries o f 1370 x10' m

3

/ a ,t h

e r

e

a

r

e

s

o

m

e

o

t

h

e

r

f

u

e

l

w

o

o

d

d

e

m

a

n

d

s

n

o

t

a

c

c

o

u

n

t

e

d

fo

r

i

n

t

h

e

a

analysis. First of al l , the People's Republic of China is not included, were

fuelwood is used on a large scale, leading to over exploitati on of large forestareas. Furthermore, consumption in urban areas of developing countries and

consumpt ion for large-scale indus tri al purposes, as e.g. the steel industries i nBrazi l, are a lso n ot included. Therefore one m ay guess that the net inp utobtained above w i l l be a lo wer l i mit , t he factors not accounted fo r in th is

analysis may add up to the same amount, such that the net inp ut may reach 0.26GtC/a.

AFRICA (w it ho ut N-AFRICA) EAST ASIA (w it ho utP.R.CHINA/ LATIN

AMERICA

TOTAL

TOTAL

3

pop

6.

m

Ac

a

p

*

a

)

Pop.6

3a Acap .a)

3m/ a

6pop.

6

3m / ( t a P * 0

3a / a

6 pop

e

3a /(cap*a)

3

m / g pop

e

3m/(cap*a)

3

mq i

,

0.50

*10

29

*10 *10

2

*10 *ID *10 *10 0

1

0a 13.1 0.08 0.98 29 0.25 7.25 2 0.3 0.6

1.31 125,01lb 35.7 1,65 58.91 16 0.75 12.0

95.8 0 . 3 5 33.4514 35.7 0.6 21.42

164.25 297 0.45

16 0.2 3.2

135.85

Eta 131.4 0,85 111.69 297 0.2 59.4 143 0.8 114.4

983.4 0.69 680.95I I4 412 0.6 247.2

983.4 0 . 4 0 388.49l i b 412 0.25 103.0

81,25 148 0.7 103.6 30

I I I a 65 1.25 81,25 148 0.7 103.6 30 0.85 25.5

279.5 0.94 263.28M b 36.5 1.45 52.93

279.5 0 . 9 4 263.28M b 36.5 1.45 52.93

IVa 6.2 1.35 8.37 21

IVa 6.2 1.35 8.37 21 0.6 12.6 38 0.85 32.3

194.2 1.01 195.171V4

194.2 1 . 0 1 195.17

i n

129 1.1 141.9

129 1.1 141.9

SUM 288.9

SUM 288.9 0.96 276.64 1036 0.41 427.75 229 0.77 176.0 1552.9 0 . 5 7 880.3

AFRICA (withola. N-AFRICA)EAST ASIA (w it ho ut P.R.CH INA)/ LAT IN

AMERICA TOTAL

3

pop

6.

m

Ac

a

p

*

a

)

3a / a

6*10

pop.-

6lo

3m/(cap*a)

3m/ a

6*10

po .P

610

3m f ( t u e a )

3m/ a

6*10

P

9

1

,

*to

3a /(caP*a)

3

a /g*10

la 13.1 0.50 6.55 29 1.55 44.95 2 1.3 2.6

95.8 1.31 125,01lb 35.7 1,65 58.91 16 0.75 12.0

IIa 131.4 1.25 164.25 297 0.45 133.65 143 0.95 135.85983.4 0.69 680.95

I I4 412 0.6 247.2

I I I a 65 1.25 81,25 148 0.7 103.6 30 0.85 25.5279.5 0.94 263.28

M b 36.5 1.45 52.93

IVa 6.2 1.35 8.37 21 0.6 12,6 38 0.85 32.3194.2 1.01 195.17

1V4 129 1.1 141.9

SUM 288.9 1,29 372.26 1036 0.66 683.90 229 0.91 208.25 1552.9 0 . 8 1 1264.41

T a b l e 5 a

ESTIMATED SUSTAINING FUFLWOOD CONSUMPTION I N RURAL AREAS OF THE DEVELOPING COUNTRIES

ESTIMATED REQUIRED FUELWOOD CONSUMPTION I N RURAL AREAS OF THE DEVELOPING COUNTRIES

41



42

Explanation to Tab. I s / 5b

I :

.

R

e

g i

o

n

s

o

f

A

c

u

t

e

S

c

a

r

c

i

ty

a

:

i

n

a

r

i

d

/

s

u

b

a

r

i

d

a

r

e

a

s

b: i n mountaneous areas

11 : Regions o f Fuelwood D e fi c i t a : i n savanna areas

b : in r i ve r p la ins

I I I : Regions o f Prospective D ef i ci t a : i n s ub tr opi ca l areasb: i n a reas w i th fast

growing population

IV : Regions of Sat isfact ory Fuelwood Supply a : i n h i gh fore st areas

b: other areas

"Sustaining fuelwood consumption" means th e amount o f fuelwood harves table

without degradat ion of the respect ive ecosystems ( i . e . "av ai l abl e fuelwood"

in FAO terms), while "required fuelwood consumption" means that amount

necessary t o meet basi c needs o f th e res pective popula tion.

Source : FAO 1981

6. Conclusions

The use of biomass as fuel leads to a carbon f l ux fro m the bi ota to the

atmosphere in an order comparable to other anthropogenic perturbations of theglobal carbon cycle. Carbon from fuelwood consumpt ion may amount to almosthalf a gigaton per year, while the other biomass energy sources may contribute

up to the same amount, such that about 1 gigaton o f carbon from biomass isannually oxidized and transferred to the atmosphere.

When the biomass is harvested i n such a w ay that ecosystems are not

degraded, then a reverse carbon f lu x f ro m the atmosphere to the biota wi ll beinduced b regrowth, such that no net input into the atmosphere will occur. On

the other hand, when biomass harvest causes a degradation of the plant cover,or soil erosions, or transforms the plant communi ties toward s ignific antly lowerbiomass density, less carbon wi ll be restored to the biomass and a net fl ux to the

atmosphere occurs.

Due to the lack of knowledge about the ti me development of the ecosys-tems supply ing b iomass fo r energy purposes o n a g lobal scale, i t is t verydiff icult to evaluate the compensating flux induced by biomass regrowth. Inthis s tudy diffe rent approaches were used to estimate the ranges of the source

strength of the biota due to human energy demands, the results are summarizedin Table 6. Biomass energy seems to be a small net source for atmospheric CO2of 0.2 ± 0.1 GtC/a. or 2 -6 % of the annual in pu t of fossil fuel carbon.

It is even more diff icu lt to estimate a probable furth er net in put connected

wi th the use of biomass for energy, st emmin g f rom soil organic carbon whi ch isoxidized when biomass harvest leads to ecosystem degradation and soil erosion,Because decline of soil carbon is relatively slo w compared to t he immedi ateoxid atio n when biomass is removed for fuel, it would be diffic ult to estimate the

annual inp ut even i f the amounts o f carbon stored i n the affected soils wereknown. Nevertheless, one may come to the conclusion that the contribution of

biomass used for energy to the source strength of the biota for addit ionalatmospheric C O

2 s h o u l d

n o t

b e

n e g l

e c t e

d .

I

t

s h

o u

l d

e s p

e c i

when one analyses scenar ios for fu ture energy use dr iven by increasingdemands of a steadily increasing population.



Approach

E v a l u a ti o n o f P r o d u c t i o n D a ta 0 .45 0 .1 8 - 0 . 3 0

Eva l ua t io n o f Energy Demand0 .5 0 - 0 . 6 0 0 .1 3 - 0 . 2 6

C o n t r i b u t i o n f r o m L a n d Tr a n s f o r m a t i on s a l o n e 0 .04 - 0 . 20

Other B ioger l ic Energy Sources: 0 .27 - 0 . 5 0 smal l

Fuelwood:

T a b l e 6

To ta l Ca rbon F lu x

Gt C/a

Es t ima ted Ne t F lu x

Gt C/a

References

BARNARD, G. W., 1985: The use of agricultural residues as fuel. - Ambio 14: 259-266.

BROWN, S. & A . E. LUGO, 1982: The storage and p roduct ion o f organic ma tter i n t ropic

forests and their role in the global carbon cycle. - Biotropica 14/3: 161-187.BROWN, S. & A. E. LUGO, 1984: Biomass of tropica l forests: a new est imate based on forest

volumes. - Science 223: 1290-1293.

FAO, 1981: Map of fuelwood situat ion in the developing countries. - Unasylva Supple-ment, Food and Agriculture Organization, Rome.

FAO, 1984: Year books of Forest Products. - Ith-34th issue, Rome, 1948-84.

GLOBAL 2000, 1980: Der Bericht an den Prasidenten. Frankfurt, Zweitausendeins: 1438

GOLDEMBERG, J., J. R. MOREIRA, P. U. M. Dos SANTOS & G. E. SERRA, 1985: Ethanol fuel: ause of biomass energy in Brazil. A m b i o 14: 193-297.

KOHLMAIER G. H., H. BROHL, P. STOCK, M. PLOCHL, U. FISCHBACH, A. JANECEK & R. FRICKE,1985: Biogen ic CO

2 r e l e a s e

a n ds o i l

c a r b

o n

e r o

s i o

n

c o n

n e c

t e d

w

i

th

c h

a n

g e

s

i

n

l

a

n

d

use in the tropical forests of Africa. America and Asia. I n „Transport of Carbonand Minerals i n Ma jor World R ivers, Pt . 3 " (eds. E. T. DEGENS, S. KEMPE & R.

HERRERA), Mitt. Geol.-Paldont. Inst. Univ. Hamburg, SCOPE/UNEP Sonderbd. 58:123-136.

LANLY, J.-P., 1982: Tro pi cal F orest Resources. - Foo d a nd Agr icu lt ure Organization,Rome: 106 pp.

MOULIK, T. K., 1985: The biogas progra m in Ind ia and China. A m b i o 14 (4-5): 288-292.

REVELLE, R., 1980: Energy dilemmas in Asia: The needs for research and development. -Science 209: 164-174.

ROTTY, R. M ., 1986: Estima tes o f CO

2 f r o m w o o d

f u e l

b a s e d

o n

f o r e s t

h a r v e s

t

d a t a

.

-

Cli mat ic Change 9: 311-325.

SKIL, V., 1983: Deforestation in China. A m b i o 12 (5): 226-231.

SMITH, K., 1988: Biofuels, Ai r Pollut ion and Health: A Global Review. - N e w York, Plenu mPubl. Co.: ( in preparation).

43

The Biogenic Fuels by GH Kohlmaier, H Brohl

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Transcript of The Biogenic Fuels by GH Kohlmaier, H Brohl