AGRICULTURAL AND

FOREST NETEOROLOGY

ELSEVIER Agricultural and Forest Meteorology 84 (1997) 153-167

Forest plantations of the world: their extent, ecological attributes, and carbon storage

Jack K. Winjum a,*, Paul E. Schroeder u

a National Council for Air and Stream Improvement, US EPA National Health and Environmental Effects Research Laboratory / Western Ecology Division - Corvallis, 200 SW 35th Street, Corvallis, OR 97333, USA

b ManTech Environmental Research Services Corporation, US EPA National Health and Environmental Effects Research Laboratory~Western Ecology Division - Corvallis, 200 SW 35th Street, Corvallis, OR 97333, USA

Received 30 September 1995; revised 15 March 1996; accepted 1 April 1996

Abstract

Forest plantations in the world total approximately 130 × 106 ha, and annual rates of establishment are about 10.5 × 106 ha. A total of 124 countries throughout the high, middle, and low latitudes of the world establiSh new plantations each year. In addition to supplying an array of goods and services, plantations contribute to carbon (C~ storage. This analysis integrates information across latitudes to evaluate the potential of forest plantations to achieve these goals. For example, mean carbon storage (MCS) in above- and below-ground phytomass of artificially established plantations generally increases from high to low latitudes ranging from 47 to 81 t C ha - l . Over a 50-year period, harvests from these plantations are credited with storing C at 10, 34, 15, and 37 t C ha -1 in wood products in the high, middle, low-dry, and low-moist latitudes, respectively. Using today's distribution of plantations among the four zones of latitude and C storage values from this analysis, the world's plantations can be credited with storing an area-weighted average of 91 t C ha-1 including MCS and durable-wood products. Based upon these estimates, the world total C storage in forest plantations today is approximately 11.8 Pg C with an annual increase of 0.178 Pg C year- L

Keywords: Forest plantations; Carbon storage; Terrestrial ecology

1. In t roduc t ion Restoration, in turn, serves the other end-uses as well as enhancing the greenness and recreational potential

Forest plantations have historically contributed to of forest landscapes (Palin, 1984). basic human needs. Primary examples are their uses Planting of tree crops for fruit was recorded as far for: domestic products such as poles, fruit, etc.; back as the 6th Century BC (Levingston, 1984). In industrial wood; energy resources; soil a n d water Western Europe as natural forest resources dwindled, conservation; and restoration of degraded land. active tree planting in block patterns was initiated

the mid 1700s to renew wood inventories for build- ing materials (Levingston, 1984). Today, there are an estimated 130 X 106 ha of plantations in the w o r d

* Corresponding author. (Allan and Lanty, 1991).

0168-1923/97/$17.00 ~) 1997 Elsevier Science B.V. All rights reserved. PII S 0 1 6 8 - 1 9 2 3 ( 9 6 ) 0 2 3 8 3 - 0

154 J.K. Winjum, P.E. Schroeder/Agricultural and Forest Meteorology 84 (1997) 153-167

In recent years, scientists and policymakers have ecology from the literature and a recent symposium become mindful of the mitigating role of forests in on planted forests; and (3) a database on world reducing the buildup of CO 2 in the atmosphere, plantations used to estimate their C storage potential. Natural forests have been reduced from occupying ~ 46% of the earth's terrestrial ecosystems in prein- dustrial times to ~ 28% today (Sharma et al., 1992). 2.1. Extent o f world plantations

This reduction, along with other human activities, has contributed to the buildup of atmospheric CO 2 The United Nations Food and Agricultural Orga- (from about 289 ppmv in 1800 to about 356 ppmv in nization (FAO) has completed a global assessment of 1993; Schimel, 1995). Thus plantations, to the extent the forests of the world as of 1990 (FAO, 1995). they replace natural forests or expand the global Forest plantations were part of the assessment. Data forest area, may potentially have another significant are presented on a country basis for 177 countries, contribution to humankind through the uptake and both developed and developing. The assessment is an storage of carbon (C). This paper reviews the extent updated version of a database on world forests as- of plantations in the world today, their ecological sembled by FAO in the early 1980s. Country forest attributes, and their potential contribution toward data are based upon the best-available country-wide global C storage, inventories. Estimates based on these data are sup-

plemented by FAO through the geographic informa- tion systems (GIS), remote sensing imagery, and modeling techniques. Though data quality varies by

2. Methods country, FAO world summaries of forest coverage are considered to be within acceptable statistical

The review is based upon three sources of infor- reliability (FAO, 1995). The World Resources Insti- mation: (1) recent data on the extent of the world's tute (WRI, 1992) presented similar values that aug- forest plantations; (2) current views of plantation ment FAO's 1990 data on plantations particularly for

Table 1 For 32 developed countries, the total natural forest in 1990 (FAO, 1995) and the planting rate per year during the early 1980s (WRI, 1992) a

Country Forest area (ha × 103) Country Forest area (ha × 103)

Total natural Planting rate year- l Total natural Planting rate year-

Albania 1046 2 Ireland 396 9 Austria 3877 21 Israel 102 2 Australia 39837 62 Italy 6750 l 5 Belgium 620 19 Japan 24158 240 Bulgaria 3386 50 Netherlands 334 2 Canada 247164 720 New Zealand 7472 43 Cyprus 140 0 Norway 8697 79 Denmark 466 6 Poland 8672 106 Finland 20112 158 Portugal 2755 9 Former Czechoslovakia 4491 37 Romania 6190 3 Former Soviet Union 754958 2600 Spain 8388 92 Former Yugoslavia, SFR 8371 53 Sweden 24437 207 France 13110 51 Switzerland 1130 7 Germany 10490 62 Turkey 8856 82 Greece 2512 5 United Kingdom 2207 40 Hungary 1675 19 USA 209573 1094

a Planting rates for seven countires are the means for the decade of the 1980s: Albania, Cyprus, Denmark, Greece, Romania, and Former Soviet Union (UN-ECE/FAO, 1992); USA (USDA FS, 1992).

a'.K. Winjum, P.E. Schroeder /Agricultural and Forest Meteorology 84 (1997) 153-167 155

Table 2 For 92 developing countries, the total existing plantation area in 1990 in ha x 1000, and the average annual increase in plantation area during the period 1980 to 1990 (FAt, 1995) a

Country Plantation area (ha X 103) Country Plantation area (ha x 103) Country Plantation area (ha x 103)

Total Annual increase Total Annual increase Total Annual increase

Algeria 485 18.3 Guyana 8 0.8 Panama 6 0.4 Angola 120 1.0 Haiti 8 0.8 Papua N. Guinea 30 1.5 Argentina 547 4.6 Honduras 3 0.3 Paraguay 9 0.7 Bangladesh 235 12.3 India 13230 1009.0 Peru 184 8.8 Benin 14 0.6 Indonesia 6125 331.8 Puerto Rico 3 0.1 Bhutan 4 0.2 lran 79 4.9 Reunion 7 0.1 Bolivia 28 1.0 Jamaica 15 0.6 Rwanda 88 4.3 Brazil 4900 195.4 Jordan 23 0.8 Samoa 9 0.5 Burkina Fast 20 1.1 Kenya 118 1.6 Senegal 112 10.3 Burundi 92 7.9 Korea, DPR 1470 77.0 Sierra Leone 6 0.2 Cameroon 16 1.2 Kuwait 5 0,5 Solomon Islands 16 0.3 Cape Verde 10 0.7 Laos 4 0,1 South Africa 965 15.5 Chad 4 0.2 Lesotho 7 0,6 Sri Lanka 139 6.0 Chile 1015 54.5 Liberia 6 0.1 Sudan 203 8.8 China 31831 1139.8 Libya 210 11.0 Suriname 8 0.2 Columbia 126 8.9 Madagascar 217 3.1 Swaziland 72 0.1 Congo 37 2.5 Malawi 126 7.0 Syria 127 9.9 Costa Rica 28 2.6 Malaysia 81 6.3 Tanzania 154 8.6 Cote d'Ivoire 63 3.2 Mali 14 1.3 Thailand 529 29.4 Ct. African Rep. 6 0.6 Mauritania 2 0.2 Togo 17 1.2 Cuba 245 13.5 Mauritius 9 0.1 Trinidad/Tobago 13 0.1 Dominican Rep. 7 0.3 Mexico 109 5.3 Tunisia 201 11.2 Ecuador 45 1.5 Morocco 321 9.6 Unit. Arab Emir. 60 5.9 Egypt 34 0.6 Mozambique 28 1.0 Uruguay 156 2.0 E1 Salvador 4 0.3 Myanmar 235 19.6 Vanuatu 7 0.4 Ethiopia 189 12.0 Nepal 56 4.3 Venuzuela 253 16.6 Fiji 78 5.0 N. Caledonia 9 0.4 Vietnam 1470 49.0 Gabon 21 0.8 Nicaragua 14 1.3 Zaire 42 2.6 Ghana 53 1.1 Niger 12 0.8 Zambia 48 2.1 Guatemala 28 1.8 Nigeria 151 3.7 Zimbabwe 84 1.4 Guinea 4 0.1 Pakistan 168 4.2

a Includes only countries with reported average annual increases in plantation area from 1980 to 1990 that were > 100 ha.

deve loped nations. These data were examined statis- forests in the wor ld (Keat ing, 1993). Prior to

t ically for means and trends provid ing insights to U N C E D , the role o f forest plantat ions in the wor ld

wor ld interest in forest plantat ions (Tables 1 and 2). had been the focus o f several rev iews and confer-

ences in past decades (Fenton, 1965; F A t , 1967;

2.2. Current views o f plantation ecology Ford et al., 1979; Wiersum, 1984; W i n j u m et al.,

1991). Since U N C E D , the Planted Fores t Sympo-

Fores t plantat ions have per iodica l ly been the fo- s ium was he ld during June 1995 in Portland, Oregon,

cus, at least in pan:, o f internat ional gatherings so U S A (Boyle et al., 1997). Resul ts f rom all o f these

that v iews on plantat ion eco logy can be t racked ove r events were examined and summar ized for the ma jo r

t ime. Recent ly , the fo remos t example was the Uni t ed eco log ica l posi t ives and negat ives o f plantat ions (Ta-

Nat ions Confe rence on Env i ronmen t and Deve lop - ble 3). These v iews are assumed in this analysis to

ment ( U N C E D ) in 1992 at R io de Janeiro. Key be indicators o f whether plantat ions wil l cont inue to

ou tcomes were the Fores t Pr inciples and A g e n d a 21, be va lued and establ ished around the wor ld through

which general ly endorsed increased use o f planted the next ha l f century.

156 J.K. Winjum, P.E. Schroeder / Agrtcultural and Forest Meteorology 84 (1999) 153-167

2.3. Potential plantation C storage el'ell~eS that gave about 500 useful datapoints. The datapoints included the mean annual increment (MAI)

A planta t ion database was assembled tn 1992 as and rotation ages of plantat ions representing the part of an assessment of C storage by ~vodd forests major forest regions of the world. For MAI and

(Dixon et al., 1993). A detailed description of the rotation length, medians and interquartile values were database and ensu ing analysis have been publ ished determined for each of four zones of latitude or

( W i n j u m et al., 1997). Briefly, a review of the environment , i.e. high, middle, l ow-d ry , and l o w - technical literature produced approximately 200 ref- moist (Table 4). It is assumed that these zones of

Table 3 Commonly cited ecological attributes of forest plantations

Attributes Selected references

Ecological positives A. Contributes to environmental quality through:

1. Restoring or maintaining biog~)ehenileal cycles a. Improving soil nutrition Sedjo (1983) b. Regulating water runoff FAO (1967)

2. Stabilizing soil and reducing erosion Brown and Lugo (1994) 3. Creating habitat favoring biodiversity Sedjo (1983) 4. Taking up and storing carbon Winjum et al. (1997) 5. Improving microclimate Kanowski et al. (1992) 6. Greening landscal~S Wiersum (1984) 7. Reducing deforestation pressures Kanowski et al. (1992) 8. Protecting watersheds Buckman (1997)

B. Enhances forest productivity through: 1. Rapid growth in a. Trees Laarman and Sedjo (1992) b. Biomass accumulation Mlinsek (1979)

2. Accelerating secondary succession 3. Improving yields by a. Matching species with site Matthews et al. (1979) b. Improving genetics Budowski (1984) c. Combining with agriculture Evans (1997)

Ecological negatives A. Risks environmental quality through monocultures which may be prone to:

1. Seedling and juvenile mortality Cleary et al. (1978) 2. Pest attacks Rosoman (1994) 3. Pathogenic losses Rosoman (1994) 4. Natural disturbances Laannan and Sedjo (1992) 5. Reduced biodiversity Sheldon (1989) 6. Invade adjacent ecosystems Bliss (1997)

B. Reduces forest productivity through: 1. Successive crops which may a. Deplete nutriems Adlard (1979) b. Reduce soil moisture Kanowski et al. (1992)

2. Treatments which may include a. Heavy machinery for

• Site preparation Laarman and Sedjo (1992) • Harvests Laarman and Sedjo (1992)

b. Chemical pollution from • Fertilizers Rosoman (1994) • Pesticides Rosoman (1994)

J.K. Win jura, P.E. Schroeder /Agricultural and Forest Meteorology 84 (1997) 153-167 157

Table 4 Mean annual increment (MAI), mean annual biomass C (MABC), and rotation lengths for plantations in high, middle, and low (dry and moist) latitudes of the world

Variables Latitudes

High Middle Low -dry Low-moist

Q1 a Med. Q3 (n) b Q1 Med. Q3 (n) Q1 Med. Q3 (n) Q1 Med. Q3 (n)

MAI(maha - j year - I ) 1.5 2.3 2.7 (13) 4.1 9.9 20.7 (129) 10,1 14.9 20.7 (104) 15.4 20.4 33.4 (274) M A B C ( t C h a -~ year-~) c 0.61 0.96 1.1 (13) 1.7 4.1 8.6 (129) 4.2 6.2 8.6 (104) 6.4 8.5 13.9 (274) Rotation (years) 55 80 80 (13) 20 25 35 (107) 12 19 23 (102) 9 15 20 (264)

a Medians and interquartile values (Q1 and Q3) based upon analyses for non-normally distributed datasets (Devore and Peck, 1986). b Observations (n) are from approximately 200 references cited in the technical forestry literature. ¢ MABC in t C ha- i year- l was computed from m 3 ha- i year- l by Eq. (1) in Methods.

latitudes are analogous to, but not exactly the same The calculation of MCS is made in two steps: as, the boreal, temperate, and tropical regions of the 1. Convert MAI in stemwood volume to mean an- world, nual biomass C (MABC; Table 4) by:

Based upon these data, estimates can be made of the mean carbon storage (MCS) of plantations, both MABC = MAI × WD X 1.6 X 0.5 (1) above and below ground, as well as the C storage in

where: wood products resulting from harvests. For each of MABC is in t C ha-~ year - l ; these plantation characteristics, the median and in- MAI is in m 3 ha- ~ year- 1 ; terquartile values were calculated representing plan- WD is wood density, here an average value is tations within the four zones of latitude described above (Tables 4-7). used of 0.52 t m-3;

1.6 is the conversion factor to compute The concept of MCS assumes that once a planta- whole-stand biomass from stemwood biomass;

tion is established, it will be maintained, harvested • 0.5 is the conversion factor to estimate the C

and replanted continuously, and that there is no yield content of whole-stand biomass in t C t -1 . reduction in later rotations (Winjum et al., 1997).

The conversion factors in Eq. (1) are adapted Specifically, MCS is the same as the average amount

from Brown and Lugo (1982) and Sedjo and of C on site over one full rotation. Also, since any Solomon (1989). number of biological, climatic, or social events could

2. Calculate MCS (Table 5) by: contribute to some level of yield reduction that can- not be predicted (Wenger, 1984; Smith, 1986), the r MABC approach presented here may represent an upper MCS = ~ R (2) bound, year= 1

Table 5 Calculated values for me~m carbon storage (MCS) for plantations of Table 4

Variables MCS (t C ha- 1 )

Latitudes

High Middle Low-dry Low -moist

Q1 ~ Median Q3 Q1 Median Q3 Q1 Median Q3 Q1 Median Q3

Above-ground b 17 39 45 18 53 155 27 62 103 32 68 146 Below-ground c 3 8 9 4 11 31 6 12 21 6 13 29 Total 20 47 54 22 64 186 33 74 124 38 81 175

a Medians and interquartile values (Q1 and Q3) based upon analyses for non-normally distributed datasets (Devore and Peck, 1986). b Above-ground values are calculated from MABCs and rotation lengths in Table 1 and Eq. (2) in Methods. c Below-ground values are estimates based upon 0.20 times the above-ground biomass (references in Methods).

158 J.K. Winjum, P.E. Schroeder / Agricultural and Forest Meteorology 84 (1997) 153-167

where : the a b o v e - g r o u n d s torage for the h igh and midd le

• M C S is the m e a n C s torage in t C h a - l ; la t i tudes (Kurz et al., 1992; U n i t e d Na t ions Eco-

• R is the ro ta t ion l eng th in years ; and n o m i c C o m m i s s i o n for E u r o p e / F o o d and Agr icu l -

• M A B C is in t C h a -1 yea r -1 f rom Eq. (1) ture O r g a n i z a t i o n o f the U n i t e d Nat ions , U N -

( S c h r o e d e r and Ladd, 1991). E C E / F A O , 1992) as wel l as for the l o w - d r y and

Es t ima te s of b e l o w - g r o u n d C in roots were ca lcu- l o w - m o i s t la t i tudes ( F e a m s i d e , 1992; B r o w n et al.,

l a ted us ing p ropor t iona l add i t ions to a b o v e - g r o u n d C 1992) (Tab le 5).

in b iomass . Da ta are ve ry l imi ted on the root b i o m a s s Fo r each hec ta re tha t is p lanted , the C tha t is

o f fores ts re la t ive to the a b o v e - g r o u n d b iomass . For s tored in p roduc t s m a d e o f ha rves t ed w o o d f rom the

the pu rpose o f this analys is , it was a s s u m e d tha t the p l an ta t ion mer i t s an accoun t ing . Es t ima te s were m a d e

b e l o w - g r o u n d C s torage was an add i t iona l 2 0 % of of this a m o u n t o f s tored C in severa l steps. First , the

Table 6 Calculations leading to long-term storage of C in harvested wood at the end of each rotation

Variables Latitudes

High Middle Low-dry Low-moist

Q1 a Median Q3 Q1 Median Q3 Q1 Median Q3 Q1 Median Q3

Sternwood at harvest Volume (m 3 ha- 1) b 82 184 216 82 247 724 121 283 476 138 306 668 Weight

Total (t C ha -j ) ¢ 21 48 56 21 64 188 31 74 124 36 80 174 Removed (t C ha- J ) d 19 43 50 19 58 169 28 66 111 32 72 157

Percent (%) of harvested wood used for: e Fuel/charcoal 20 15 65 35 Paper products 40 45 25 40 Solidwood products 40 40 10 25

Allocation of harvested wood (t C ha - 1) Fuel/charcoal 4 9 10 3 9 25 18 43 72 11 25 55 Paper products

Total 8 17 20 9 26 76 7 17 28 13 29 63 Yield (50%) f 4 8 10 4 13 38 4 8 14 6 14 31

Solidwood products Total 8 17 20 8 23 68 3 7 11 8 18 39 Converted (1.75:1) g 5 10 12 4 13 39 2 4 6 5 10 22

Long-term C storage from harvests at end of rotation (t C ha - I) Paper products h 2 4 5 2 6 19 2 4 7 3 7 16 Solidwood products i 4 9 10 4 12 35 1 4 6 4 9 20 Total 6 13 15 6 18 54 3 8 13 7 16 36

a Medians and interquartile values (Q1 and Q3) based upon analyses for non-normally distributed datasets (Devore and Peck, 1986). b Computed by rotation length (year) × MAI (m 3 ha- 1 year - 1) = m 3 ha- 1. ¢ Weight of C at rotation age (t C ha- 1 ) is volume (m 3 ha- l) × 0.52 t m- 3 wood (density) × 0.5 t C t - J wood. d Weight of C removed at harvest is t C ha- 1 × 0.9 (i.e. harvest efficiency). e Percentages developed from references discussed in Methods. f Paper yields average about 50% in weight per weight of roundwood harvested. g Conversion efficiency for sawn or peeled roundwood logs from plantation average 1.75 units of harvested logs to 1 unit of solidwood products. h Assumes 50% of the carbon in paper products remains in long-term products (e.g. books, discarded paper retained in landfills, etc.) for several decades. i Assumes 90% of the carbon in solidwood products remains in wood structures for several decades.

Tab

le 7

E

xten

t of

wor

ld p

lant

atio

ns,

esti

mat

ed C

sto

rage

per

ha,

and

tot

als

for

all

plan

tati

ons

by l

atit

udes

.~

Var

iabl

es

Lat

itud

es

Hig

h M

iddl

e L

ow

-dry

L

ow

-mo

ist

Tot

al

~"

Pla

ntat

ion

esti

mat

es in

the

wor

ld f

or 1

990

.~

Tot

al a

rea

(ha×

106

) a

18

82

18

12

130

Ann

ual n

et i

ncre

ase

betw

een

1965

and

199

0 0.

27

1.24

0.

27

0.18

1.

96 c

(h

a× 1

06 y

ear-

i)

b ~

Q1

d M

ed.

Q3

Q1

Med

. Q

3 Q

1 M

ed.

Q3

Q1

Med

. Q

3 A

rea-

wei

ghte

d va

lues

e

.~

Q1

Med

. Q

3 ~

.

C s

tora

ge c

redi

t (t

C h

a- 1

) ~"

P

lant

atio

n M

CS

f

20

47

54

22

64

186

33

74

124

38

81

175

26

64

157

Pro

duct

s at

50

year

s g

6 10

12

14

34

79

11

15

19

25

37

63

13

27

60

T

otal

at

50 y

ears

26

57

66

36

98

26

5 44

89

14

3 63

11

8 23

8 39

91

21

7 ~-

Tot

als,

wor

ld p

lant

atio

ns

C s

tora

ge in

199

0 (P

g C

) h

0.5

1.0

1.2

2.9

8.0

22.0

0.

8 1.

6 2.

6 0.

7 1.

4 2.

9 5.

0 11

.8

28.2

A

nnua

l net

incr

ease

inC

isto

rag

e 0.

007

0.00

15

0.01

8 0.

043

0.12

2 0.

329

0.01

2 0.

024

0.03

9 0.

006

0.02

1 0.

043

0.07

6 0.

178

0.42

5

(Pg

C y

ear-

i )

a R

efer

ence

s: A

llan

and

Lan

ly (

1991

), F

AO

(19

93),

UN

-EC

E/F

AO

(19

92).

b

Ass

umes

net

inc

reas

es i

n pl

anta

tion

are

a by

lat

itud

es i

s in

the

sam

e pr

opor

tion

s as

tot

al a

rea

by l

atit

udes

.

Ref

eren

ce:

All

an a

nd L

anly

(19

91).

d

Med

ians

and

int

erqu

arti

le v

alue

s (Q

1 an

d Q

3) b

ased

upo

n an

alys

es f

or n

on-n

orm

ally

dis

trib

uted

dat

aset

s (D

evor

e an

d P

eck,

198

6).

e A

rea-

wei

ghte

d va

lues

bas

ed u

pon

plan

tati

on a

reas

by

lati

tude

s an

d C

sto

rage

cre

dits

by

lati

tude

s.

~'~

f V

alue

s fr

om T

able

5.

g V

alue

s fr

om s

imul

atio

ns w

hose

res

ults

for

med

ians

are

dep

icte

d in

Fig

. 1.

h

Val

ues

are

tota

l ar

ea (

ha×

106

)×to

tal

C s

tora

ge a

t 50

yea

rs (

t C

ha

-1 )

. --4

i

Val

ues

are

annu

al n

et i

ncre

ase

(ha

× 10

6 ye

ar-

i ) ×

tot

al C

sto

rage

at

50 y

ears

(t

C h

a- l

).

160 J.K. Winjum, P.E. Schroeder/Agricultural and Forest Meteorology 84 (1997) 153-167

22 a . 7O b .

2O

18 6 0

16 50.

14

10 ~ 30-

20-

,01

01 50 100 150 200 250 300 50 100 150 200 250 300

Yrs Y r s

30 70 j

• ] d . C

25 60-

5O 2O

40

i 30 I

2O

'i 60 100 160 200 250 300 1 50 100 160 200 250 300

Yrs Yrs

Fig. 1. For plantations in the high (a), middle (b), low-dry (c), and low-moist (d) latitudes, simulated trends of C storage in durable-wood products for repeated rotations of 80, 25, 19, and 15 years, respectively. The saw-tooth peaks occur at the end of each rotation and the downward-connecting-curved lines represent a 1% decay rate in diagrams (a) and (b) and 2% for diagrams (c) and (d). The dotted line from 50 years on the horizontal axes projected through the curved wood-product storage line to vertical axes gives an estimate of C storage credit in wood products for plantations in each latitudinal zone (Winjum et al., 1997).

above-ground biomass values of Table 4 were con- defect in the forest (adapted from Briggs, 1994). verted to harvested stemwood C (Table 5) by the The flow of stemwood C into forest products, i.e. equation: fuel/charcoal, solidwood, and paper, was calculated

by multiplying the proportion of products produced SWC = MAI × R × WD × 0.5 × 0.9 (3) in latitudinal zones as developed from the literature

(Herendeen and Brown, 1987; Kuusela, 1992; WRI, where: 1992; Powell et al., 1993) times the harvested stem-

SWC is stemwood C in t C ha- l ; wood C per hectare. The proportions (%) of C flow MAI is stemwood growth in m 3 ha-~ year-1 into various products by latitudes were (Table 6): (Table 1); R is rotation length in years (Table 1); Latitude Fuel/charcoal Paper Solidwood WD is wood density in t m -3 as for Eq. (1); High 20 40 40 0.5 converts total tons of stemwood to tons of C, Middle 15 45 40 i.e. t C t-1 stemwood; and Low-dry 65 25 10 0.9 is the harvest efficiency assumed for planta- Low-moist 35 40 25 tions that allows for wood lost to breakage and

JK. Winjum, P.E. Schroeder / Agricultural and Forest Meteorology 84 (1997) 153-167 161

It is recognized that these wood-utilization cate- wood products are utilized (Kiirsten and Burschel, gories (fuel/charcoal, solidwood, and paper) and 1993). These decay rates and the values noted above their proportions among latitudes are only approxi- from Tables 4 and 6 were entered into a simulation mations that represent a mix of wood removals from routine that determines the declining amount of C both natural forests and plantations. However, they storage in wood products over a rotation. The simu- are intended to repre:~ent the primary pathways and lation is run through enough successive rotations so pools of forest C following harvest of plantations at that the upward trend approaches a horizontal line a global scale. (about 250 years in each of the four latitudinal

For the harvested wood that is manufactured into zones; Fig. 1). The midpoint of the vertical lines paper and solidwood products, conversion efficien- from the saw-tooth peaks at the end of each harvest cies must be considered. Here, it is assumed that the represents the C stored, on average, throughout each average yield from the harvested wood allocated for rotation. The curve connecting these midpoints takes paper products is 50% (Briggs, 1994). Also used is the form of an ascending curve that approaches an an average conversion efficiency for sawn or peeled upper limit asymptotically (Fig. 1). Differences roundwood logs frora plantations of 1.75 units of among the curves represent differences in: (1) C harvested logs to one unit of solidwood products accumulation in wood products at the end of each (Centre for Agricultural Strategy, CAS, 1980; Direc- rotation (Table 3); (2) decay rates; and (3) rotation torate General of Forest Utilization, DGFU, 1989; length. To determine the product C credit for a Sedjo and Lyon, 1991); Harmon et al., 1990; Briggs, 50-year period (i.e. closer to the period of concern 1994). for mitigating increasing atmospheric CO2), a point

Other assumptions were that 90% of the solid- on the vertical axis was also projected from the wood products made from harvested plantations 50-year point on the horizontal axis (Fig. 1). would remain in some structural use for several The estimate of total long-term C storage per decades, e.g. wood-flame houses and other durable- hectare for the plantations was determined simply by wood products (Row and Phelps, 1992). Also half of summing the C above-ground, below-ground, and in the harvested wood used for paper products is as- durable-wood products (Table 7). The estimate as- sumed to contribute to long-term storage of C through sumes that: (1) when new plantations are established, retention in books, recycling, landfills, or other each hectare will be continuously managed for suc- long-term paper forms (Row and Phelps, 1992). cessive forest crops; and (2) at maturity each crop

To credit the C sequestered in durable-wood prod- will be harvested with the wood utilized in the ucts to plantations maintained through an indefinite approximate proportions noted above for: (1) number of rotations, estimates for product C are fuel/charcoal without C storage and (2) paper and needed that can be added to the MCS in biomass, solidwood products with portions in long-term C The amount of C in wood products credited to such storage (Table 7). plantations was calculated in the computer simula- tion described below. Simulations were conducted for plantations in each of the four latitudinal zones (Fig. 1). Input value:~ were rotation ages (Table 4),

3. Results the 'total' values (medians, Q1, and Q3 values) for C in durable-wood products at harvest (Table 6), and a decay rate for durable-wood products. The method is Results from the assembled information and cal- described in detail in previous papers (Kiirsten and culations above are additive in support of a contin- Burschel, 1993; Winjum et al., 1997). ued and expanded role for plantations in the world.

Adopted for this analysis, the decay rate for the There is wide-spread plantation establishment among high and middle latitudes, a relatively cooler climate, countries in all latitudinal regions; ecologically, there is 1% annually and fi~r the warmer low latitudes, 2% are strong positives as well as cautions to be heeded annually. The rates are assumptions that reflect the from the negatives; and estimates show that the latitudinal zone where a predominant amount of the potential for plantation C storage is significant.

162 J.K. Winjum, P.E. Schroeder /Agricultural and Forest Meteorology 84 (1997) 153-167

3.1. Plantation extent A total of 124 countries out of about 200 coun- tries and territories in the world are reported to have

Across all latitudinal regions in 1990, about 130 an annual projects of plantation establishment equal × 106 ha of plantations exist in the world (Allan and to or greater than 100 ha (WRI, 1992; FAO, 1995) Lanly, 1991). The distribution by latitudinal region is (Tables 1 and 2). Useful trends are seen in these approximately: high, 14%; middle, 63%; low-dry, data. For developed countries, a log-log diagram 14%; and low-moist, 9% (UN-ECE/FAO, 1992; shows that the greater the area of natural forest FAO, 1993). within a country (x axis), the higher the annual

Annual rates of plantation establishment in the plantation rate (y axis; Fig. 2). The proportions of world during the early 1980s were estimated to be new plantations established for reforestation, af- 10.5 X 10 6 ha year- 1 (WRI, 1992). Exact figures are forestation, or agroforestry are unknown. not available, but this rate in the late 1980s may have For developing countries, annual rates of planta- slowed to about 8.5 × 106 ha year- ~ (Sharma, 1992; tion establishment are not given in the 1990 assess- UN-ECE/FAO, 1992; FAO, 1993). Estimates by ment by FAO (1995). Instead, the average annual latitudinal region are: high, 27%; middle, 63%; and increase in plantation area is presented and tends to low-dry plus moist, 10% (WRI, 1992; FAO, 1993). be higher within countries with larger areas of exist- It is unknown what portions of the new plantations ing plantations (Fig. 3). That is, for 88 developing are replacing harvested forests (natural or older plan- countries with an average annual plantation increase tations) or are the result of afforestation or agro- equal to or greater than 100 ha, a log-log diagram forestry projects. However, in 1965, existing planta- shows that the more plantations that countries have tions in the world were estimated to cover 81 × 106 in place (x axis), the more the net increase in ha compared with the 130 × l 0 6 ha in 1990 (Allan plantation area each year (y axis). For this diagram- and Lanly, 1991). The average annual net gain in matic analysis, the four super-size countries of Brazil, plantations for that 25 years, therefore, is assumed to China, India, and Indonesia were omitted because be 1.96 × 106 ha year- 1 the size of their forests and average annual plantation

10000

1000.

>,

o i00 0 •

0

• -~ ° ° 0

~ 10

< 1 10"'5 10**6 10**7 10**8 10**9

Exist ing n a t u r a l fo re s t s (ha; log scale)

Fig. 2. For 32 developed countries (Table 1), a log-log scatter digram showing the trend for increased level of annual plantation establishment during the 1980s (WRI, 1992) when plotted against the area of existing natural forests in each country during 1990 (FAO, 1995).

J.K. Winjum, P.E. Schroeder / Agricultural and Forest Meteorology 84 (1997) 153-167 163

increases relative to the other 88 countries inordi- period, harvests from these plantations are credited nately dominated the analysis (Table 2). with storing C at median values of 10, 34, 15, and 37

t C ha -1 in wood products in the high, middle, 3.2. Ecological poshives and negatives of planta- low-dry, and low-moist latitudes, respectively (Fig. tions 1). (Interquartile values (Q1 and Q3) for all medians

are given in Table 7.) Summary documents coveting the wide-spread The sum of the respective medians give the total

use of forest plantations in the world point to many C credit in t C ha -1 for plantations in the four ecological attribute,,;, both positive and negative, latitudinal regions, i.e. high, 57; middle, 98; low-dry, Some attributes apply to specific locations, but a 89; and low-moist, l l8 (Table 7). The area-weighted number are applicable to most forest regions of the median for C storage credited to all plantations is 91 world (Table 3). Attributes suggested since UNCED t C ha -1 (Q1 = 39 and Q3 = 217 t C ha-l) . are generally consistent with those published prior to Multiplying the total C credits per ha times the 1992 (Boyle et al., 1997). One additional positive 1990 areas of existing plantations provides estimates attribute noted was the role of plantations to protect of the amount of C stored in each region. Median watersheds (Buckman, 1997), and negatively, the values are 1.0, 8.0, 1.6, and 1.4 Pg C for the high, risk of exotic planted trees to invade adjacent ecosys- middle, low-dry, and low-wet latitudes, respec- tems (Bliss, 1997). tively (Table 7). The total C storage that can be

credited to global forest plantations today, therefore, 3.3. Potential C storage per ha is an estimated 11.8 Pg C (Q1 = 5.0 and Q3 = 28.2

Pg C). Mean carbon storage (MCS) in above- and Similarly, the product of the annual increase in

below-ground phytomass of plantations generally in- plantation area for the period leading up to 1990 and creases from high to low latitudes ranging in medi- the C credits gives an estimate of the annual uptake ans from 47 to 81 t C ha-1 (Table 5). Over a 50-year in C for world plantations. Median values are 0.015,

100.0

2 I

i0.0 ": " : • . .

¢~ , *°

O * O • O o •

1 0 o • • e

, ~ I l l

0 1 . . . . . •

= i0 I00 I000 i0000 Exist ing p lantaLions (i000 ha; log scale)

Fig. 3. For 88 developing countries (Table 2), a log-log scatter diagram showing the trend for greater average annual increase in plantation area in each country with larger amounts of existing plantations during the period 1980-1990 (FAO, 1995). Data for the coutnries of Brazil, China, India and Indonesia are omitted because values are inordinately large compared with these 88 countries (Table 2).

164 J.K. Winjum, P.E. Schroeder / Agricultural and Forest Meteorology 84 (1997) 153-167

0.122, 0.024, and 0.021 Pg C year-1 for the four 1993). These human constraints and adverse impacts, latitudinal regions from high to low-moist, respec- however, can be and have been overcome as evi- tively (Table 7). The global total estimate is 0.178 denced by the above statistics. This indicates that Pg C year - l (Q1 = 0.076 and Q3 = 0.425 Pg C plantation programs will likely continue as long as year-l) , ecological constraints do not exist that make the

practice unreasonable or forbidding. Furthermore, the positive attributes indicate

4. Diseussion strongly that plantation programs can contribute to environmental quality and forest productivity (Table

Support for forest plantations establishment ap- 3). Recent advances in forest technology have greatly pears ongoing in the world today. This is strongly contributed to such projects. Examples are improved evident by the 124 countries (over half of the world' s knowledge of forest ecology relative to more species, 200 countries and territories) engaged in some form particularly in the their regeneration phases; and a of plantation establishment totaling between 8.5 and half century of research and operations in forest 10.5 × 106 ha year-~. The net gain in area is about genetics have greatly increased the capability of 2 × 10 6 ha year -1 plantations to grow more vigorously with increased

There appears to be momentum toward plantation resistance to pests and pathogens (Talbert et al., establishment within countries having existing forests 1985; Gadgil and Bain, 1997). and plantations. That is in the developed countries, At the same time, the negative attributes are the more natural forest area they have, the greater the seemingly forbidding (Table 3). In careful reading of annual rate of plantation establishment (Fig. 2). In the technical literature on these attributes, however, the developing countries, the data show that the more authors consistently describe these negative at- area they have in existing plantations, the higher tributes more as warnings to be heeded before imple- their net annual increase in planting area (Fig. 3). At menting plantation programs (Sedjo, 1983; Mather, first glance these results seem self-evident, but it also 1993). In that context, people who favor plantation indicates that the more forests countries have or the establishment generally feel that with careful plan- more experienced they are with plantations, the ning, implementation, and follow-up measures, the greater is the propensity to establish new plantations, threat of the ecological negatives can be held to an

Thus globally, plantations continue to be used. acceptable minimum (Savill and Evans, 1986; Indeed, continuing and perhaps expanding forest Kanowski et al., 1992). plantations was urged in 1992 within UNCED's Assuming then that forest plantations will be an Agenda 21 and the Forest Principles (Keating, 1993). ongoing activity in the world for the foreseeable

Yet the purpose in considering the ecological future, it is of interest to estimate their contribution attributes of plantations was to determine if any to an increasingly important attribute, C storage. critical new ecological evidence has arisen for not Estimates here show that the world plantations in continuing this forest practice. Human constraints to 1990 can be credited with storing approximately 11.8 plantation establishment are widely known. Included Pg C with Q1 = 5.0 Pg C and Q3 = 28.2 Pg C are many combinations of factors such as limitation (Table 7). The median value is less than one percent of land tenure systems, insufficient capital, lack of of the 1500 to 2000 Pg C estimated to be stored by knowledge about some species, poorly understood all the world's forests (Smith et al., 1993). site conditions, unavailability of trained labor and The annual increase, however, in stored C cred- supervisors, and inconsistent commitments by forest ited to plantations is a median of 0.178 Pg C year- management organizations, both public and private (Q1 = 0.076 and Q3 = 0.425 Pg C year-l) . This (Wiersum, 1984). Adverse effects of plantations on median is about 11% of 1.6 Pg C year -! that was humans are sometimes cited. Examples are: high risk the estimated net annual gain of C in the atmosphere of scarce capital; an excuse to clear mature forests ( _ 1.0 Pg C year -~) in the 1980s (Houghton et al., thereby reducing biodiversity; and displacement of 1993). Such a contribution is important considering indigenous people (Kanowski et al., 1992; Mather, that studies of global mitigating options to the prob-

J.K. Winjum, P.E. Schroeder / Agricultural and Forest Meteorology 84 (1997) 153-167 165

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