# Ecology and Development Series No. 28, 2005

Editor-in-Chief:

Paul L.G.Vlek

Editors: Manfred Denich Christopher Martius Charles Rodgers Nick van de Giesen



## Syahrinudin

The potential of oil palm and forest plantations for carbon sequestration on degraded land in Indonesia

Cuvillier Verlag GöttingenABSTRACT

Terrestrial ecosystems play an important role in regul ating the abundance of atmospheric carbon dioxide (CO 2 ). Plantations of trees and perennial crops on degraded and marginal lands are an effective way of enhancing the bu ild up of the terrestrial carbon (C) pool. The aim of this study is to quantify the potential of C sequestration through the conversion of Imperata cylindrica grasslands into oil palm and Acacia mangium plantations. Research was conducted in Sumatra and Eas t Kalimantan (Indonesia). Total C stored in the systems (both below- and aboveground) was determined with destructive sampling techniques and the rate o f C sequestration estimated with the false-time-series approach. Imperata cylindrica grasslands produce only a relatively small amount of biomass C (5.9-7.6 M g ha -1 ) and have shallow roots (maximum depth 1.8 m) and, therefore, only a low level o f soil carbon storage can be expected in this system. Biomass and biomass C of both oil palm and A. mangium plantations increase with age to a level much higher th an that of I. cylindrica grassland. In the oil palm plantations, rates are 84.4 and 76.8 Mg ha -1 5 m -1 in biomass and soil, respectively, while in A. mangium plantations 78.5 and 157.7 Mg C ha -1 5 m -1

, respectively, can be achieved. Furthermore, the deep penetr ation of the roots (to a depth of 5 m) in these plantations promotes a substantial amou nt of C sequestration in the deeper soils. Soil C storage increases with plantation age to almost twice that of I. cylindrica grassland, suggesting that the establishment of plantation s is beneficial not only in terms of C sequestration but also in terms of land rehabilitation. Although the magnitude of biomass C in the plantations is quite compara ble, due to the longer period for the sequestration (plantation cycle of 9 and 30 years for the A. mangium and oil palm plantations, respectively), the rate of C sequest ration in the biomass of the oil palm plantation is much lower (3.4 and 9.3 Mg ha -1 yr -1 for the oil palm and A. mangium plantations, respectively). However, there is a sig nificant difference in the soil-C sequestration in these plantations (17.5 and 2.6 Mg ha -1 5 m -1 yr -1 for the A. mangium and oil palm plantations, respectively). Of the C stor ed in the systems, 81.2 and 76.9% of the total C of the A. mangium and oil palm plantations, respectively, is assigned to the belowground C pool (soil and belowground bio mass C) to a depth of 5 m. In I. cylindrica grassland, this value is 98.0%. Regardless of the differen ce in magnitude and distribution of the C sink, it is evident that oil pal m and A. mangium plantations can play an important role in sequestering atmospheric CO 2 . The conversion of marginal land (mainly I. cylindrica grasslands) into such plantations should thus be encouraged.

### Das Potential von Ölpalmen- und Waldplantagen zur Kohlens toffspeicherung auf degradierten Böden in Indonesien

KURZFASSUNG

Terrestrische Ökosysteme spielen eine wichtige Rolle be i der Regulierung der Menge von atmosphärischem CO 2 . Baumplantagen und der Anbau von Dauerkulturen auf degradierten Böden oder Marginalland sind wirksame Möglichkeit en, den terrestrischen C-Pool zu erhöhen. Die Studie in Sumatra und Ost-Kalimant an quantifziert das Potential der C-Speicherung durch die Umwandlung von Imperata cylindrica -Grasland in Ölpalmen- und Acacia mangium -Plantagen. Der Gesamtkohlenstoff im System (unter- und oberirdisch) wurde mit destruktiven Beprobungsme thoden und die CSpeicherungsrate in einer ‚falschen Zeitreihe’ bestimmt. Imperata cylindrica -Grasland produziert nur eine geringe Menge Biomasse-C (5.9-7.6 Mg ha -1 ). Aufgrund der relativ flachen Durchwurzelung (maximale Tiefe 1.8 m) ist in dies em System nur eine geringe Boden-C-Speicherung zu erwarten. Biomasse und Biomasse -C von Ölpalmen- bzw. A. mangium -Plantagen nehmen mit deren Alter auf ein Vielfaches der Menge in I.- cylindrica -Grasland zu. In Ölpalmenplantagen erreichen die Werte 84.4 bzw. 76.8 Mg ha -1 5 m -1 in Biomasse bzw. Boden und in A. mangium -Plantagen 78.5 bzw. 157.7 Mg C ha -1 5 m -1 . Außerdem führt das tiefe Wurzelwerk dieser Plantagen zu einer deutlichen Erhöhung der C-Speicherung in den tieferen Bodenschichten. De r Boden-C-Gehalt erreicht mit zunehmendem Alter der Plantage fast das Doppel te der Menge im I.- cylindrica -Grasland, was darauf hindeutet, dass Plantagen nicht nur hinsi chtlich der CSpeicherung sondern auch im Hinblick auf Landrehabilitation vorteilhaft sind. Obwohl der in der Biomasse gespeicherte Kohlenstoff in beiden Plan tagensytemen vergleichbar ist, ergibt die längere Rotationszeit (30 Jahre bei der Ö lpalmenplantage gegenüber 9 Jahre für die A. mangium- Plantage) eine erheblich niedrigere C-Speicherungsrate in der Ölpalmenplantage (3.4 bzw. 9.3 Mg ha -1 Jahr -1 für Ölpalmen- bzw. Acacia mangiumPlantage). Der Unterschied in der C-Speicherung im Boden ist beträchtlich: 17.5 und 2.6 Mg ha -1 5 m -1 Jahr -1 für die A. mangium- bzw. Ölpalmenplantagen). Von dem Gesamtkohlentsoff der Plantagensysteme werden 81.2 ( A. mangium ) bzw. 76.9% (Ölpalmen) im unterirdischen C-Pool (Boden und unterird ische Biomasse) bis zu einer Bodentiefe von 5 m gespeichert. In I. cylindrica -Grasland sind es 98.0%. Unabhängig vom Unterschied in der Menge und Verteilung der C-Speicheru ng wird deutlich, dass Ölpalmen- und. Acacia mangium- Plantagen einen Beitrag zur Festlegung von atmosphärischem CO 2 leisten könnten. Die Umwandlung von Marginalland (hauptsächlich I. cylindrica -Grasland) in derartige Plantagen sollte daher gefördert werden.TABLE OF CONTENTS

1 INTRODUCTION......................................

................................................... ....... 1

2 SITE DESCRIPTION..................................

................................................... ...... 5
2.1 Sumatra .........................................

................................................... ........ 5 2.2 East Kalimantan.................................

................................................... .... 6
3 IMPERATA CYLINDRICA GRASSLANDS: BIOMASS AND CARBON DISTRIBUTION.......................................

................................................... ........ 9 3.1 Introduction ......................................

................................................... ..... 9 3.2 Methodology .......................................

................................................... 11 3.3 Results and discussion ............................ ................................................ 12 3.4 Conclusions .....................................

................................................... .... 17
4 ACACIA MANGIUM PLANTATIONS....................................... ........................ 18
4.1 Introduction ......................................

................................................... ... 18 4.2 Methodology .......................................

................................................... 19 4.3 Results and discussion ............................ ................................................ 21 4.3.1 Biomass distribution............................ ................................................. 21 4.3.2 Root distribution .................................. ................................................ 26 4.3.3 Biomass carbon distribution ..................... ............................................ 32 4.3.4 Soil carbon distribution ........................ ................................................ 40 4.3.5 Carbon distribution in Acacia mangium plantation system.................... 44 4.4 Conclusions .....................................

................................................... .... 46 5 OIL PALM PLANTATIONS .............................. ............................................... 47 5.1 Introduction ......................................

................................................... ... 47 5.2 Methodology .......................................

................................................... 48 5.3 Results and discussions........................... ................................................ 50 5.3.1 Biomass distribution............................ ................................................. 50 5.3.2 Root distribution .................................. ................................................ 55 5.3.3 Biomass carbon distribution ..................... ............................................ 62 5.3.4 Soil carbon distribution ........................ ................................................ 69 5.3.5 Carbon distribution in oil palm plantation syste ms ............................... 75 5.4 Conclusions .....................................

................................................... .... 77 6 SUMMARY AND GENERAL DISCUSSION.................... ............................... 79 6.1 Biomass distribution ............................. .................................................. 79 6.2 Root distribution................................... .................................................. 80 6.3 Carbon distribution ..............................

................................................... 85
7 CONCLUSIONS AND RECOMMENDATIONS ................... ........................... 93 7.1 Conclusions .....................................

................................................... .... 93 7.2 Recommendations.................................. ................................................. 94
8 REFERENCES ........................................

................................................... ....... 96
ACKNOWLEDGEMENTSIntroduction

1 1 INTRODUCTION

Climate change and global warming are among the most ch allenging environmental, economic and social issues worldwide. Global temperatures have increased by 0.3- 0.6 °C over the past 100 years and are expected to increase by a further 1-3.5 °C by 2100, accompanied by changes in precipitation, storm patterns, and drought frequency and intensity (Santer et al . 1996; Kattenberg et al . 1996). Global warming, which has been associated with an unprecedented increase in atmosphe ric greenhouse gas concentrations, is expected to lead to negative impacts on valuable ecosystems, increased intensity and frequency of heat waves, and other climatic-related disasters as well as crop failures and freshwater scarcity. One of the most prominent anthropogenic-induced greenhouse gase s is carbon dioxide (CO 2 ), contributing to more than 51% of the global warming. Th e level of atmospheric CO 2 has increased from 280 ppm in 1800 to a present more than 360 ppm

. The atmosphere now contains about 760 Pg of carbon (C) as CO 2 . The annual global
CO 2 emission in the 1990s was 6.3 ±0.4 Pg C yr -1 (1 Pg = 10 15 g). While most was derived from the burning of fossil fuel (IPCC 2001), land-use change, mainly tropical deforestation, also contributed an estimated 1.6 Pg C yr -1 (Houghton 1999). However, atmospheric C represents less than 30% of the C in terre strial ecosystems. Vegetation contains nearly 500 Pg C, while soils contain another 2000 Pg C in form of organic matter and detritus (Schimel 1995; WBGU 1998; IPCC 2000). Terrestrial ecosystems play an important role in regula ting the abundance of atmospheric CO 2 . Of the 406 Pg of C emitted during the period 1850 to 1998, 270 Pg C were derived from fossil fuel combustion and cement produc tion, and 136 Pg C were emitted through land-use activities (IPCC 2000). Of these emi ssions, roughly 110 Pg C were absorbed back into terrestrial ecosystem sinks and about 120 Pg C were absorbed by oceans. The rest (176 Pg C) accumulated in the atmosphere. Thus, it is evident that there is a need to reduce atmospheric CO 2 , and other greenhouse gases (GHGs) and that policy measures must take into account the role of terre strial ecosystems (IPCC 2000). There are great opportunities in forestry, agriculture, and o ther sectors for mitigating further increases in the atmospheric C pool. The options vary by social and economic conditions. Slowing or halting deforestation, improved natural forestIntroduction

2 management practices, afforestation, and reforestatio n of degraded forests and wastelands are the most attractive opportunities in the fo restry sector (IPCC 2001). All activities leading to the preservation or enhancement of the existing terrestrial C pools, or to the prevention of an increase in atmospheric C pool s such as the use of biomass to
offset fossil fuel use should be the main focus of GHG m itigation projects. Some practical examples of mitigation strategies include fire or insect control, forest conservation, establishing fast-growing stands, changing silvi cultural practices, planting trees in urban areas, ameliorating waste management pra ctices, managing agricultural lands to store more C in soils, improving management of grazing lands, and replanting grasses or trees on cultivated lands (IPCC 2001). In the case of terrestrial C sinks, a forest ecosys tem transforms atmospheric
CO 2 into C stock components (trees, roots, other vegetation, litter, and soil organic matter). Even though C stored in forests may ultimately be released through natural or anthropogenic disturbances, forest-C sequestration has be en identified as one of the most promising options to reduce the build-up of atmospheric C O 2 (Dixon et al. 1993; Sampson and Sedjo 1997; Marland and Schlamadinger 1999). IPCC (1996) estimated that 700 Mha of forestland might be globally available f or C conservation. Of that, 138 Mha might be available for slowed tropical deforestation, 217 Mha for regeneration of tropical forests, and 345 Mha for plantations and agrofor estry. By 2050, a cumulative mitigation impact of 60 to 87 Pg C due to improved forest man agement could be expected, 45 to 72 Pg C of this is likely to occur in the tropi cs. Towards the end of this time interval, the mitigation impact could approach a maxim um rate of 2.2 Pg C/yr (IPCC 2001). Notwithstanding the debate as to whether global fores ts are sources or sinks of greenhouse gases (Pelley 2003; Harmon 2001; Metting et al . 2001; Schimel et al . 2001; Lal and Singh, 2000; Ravindranath et al . 1997), managed fast-growing forests may enhance C sequestration (Lee et al . 2002; Ney et al . 2002; Metting et al . 2001; Papadopol 2000). Silvicultural strategies aiming at accelerat ing the stand growth are likely to increase the rate of C sequestration of the r espective forests (Lee et al . 2002;
Chen et al . 2000; Montagnin and Porras 1998). Plantation of trees and perennial crops on degraded and margi nal lands is likely to be an effective way to enhance the build-up of terrestrial C pools. TheseIntroduction

3 plantations promote C sequestration not only in the biom ass but also in deep soils. However, there is little information on the potential C sink that could be attained by conversion of degraded lands (such as Imperata cylindrica grasslands) into specific tree plantations such as Acacia mangium and oil palm.
About 7.5-8.5 million ha of I. cylindrica grasslands are distributed on various islands in Indonesia (Garrity et al . 1997; Soekardi et al . 1993), an area that has been identified to have low economic and ecological values. I n line with the extensive expansion of oil palm and forestry plantations (mainly in Sumatra and Kalimantan) planned by the government, conversion of these lands into plantations would be a promising option. The oil palm as a perennial crop has become important in Indonesia, firstly, as a major source of oils and fats for human food, second ly, as animal feeds, and thirdly, for the manufacture of many domestic products such as cosme tics, soap and detergents. The establishment of large-scale monoculture oil palm plantations in Indonesia began in 1985 over an area of about 600.000 ha. In 1999, the area had expand ed to about 3 million ha (Glastra et al . 2002; Wakker 2000). Plantations of fast-growing species have been rapidly increasing in Asia in recent years (Cossalter and Pye-Smith, 2003). Acacia mangium is one of the most common fast-growing species in the humid tropics. Acacia mangium used to be planted primarily for site rehabilitation; however, due to its r apid growth and tolerance of very poor soils, this species is playing an increasingly important role in efforts to sustain commercial supplies of tree products while reducing pressure o n natural forest ecosystems. Its quick growth and dense shade make the tree a n effective tool in reforesting Imperata grass swards and reducing fire risk (Nitrogen Fixing Tree Association, 1987). It has been reported that this specie s has a great potential with regard to unproductive and degraded lands such as those infested by I. cylindrica (Otsamo 2002; Hardiyanto et al . 1999; Otsamo et al . 1997). The main goal of this study is to evaluate the potential C sink that could be achieved by conversion of I. cylindrica grasslands into plantations ( Acacia mangium and oil palm). Furthermore, this study aims at quantifying the C pool and distribution of the plantation systems (

Acacia mangium and oil palm) and I. cylindrica grasslands. TheIntroduction

4 rate of biomass and C accumulation of the plantations was estimated from a false time series sampling. Field experiments were conducted on two islands in Indones ia (Sumatra and Kalimantan) between 2002 and 2004. In Sumatra, observation w as conducted in the provinces North Sumatra and Jambi and in the province East K alimantan in Kalimantan. The thesis consists of seven chapters. Following the in troduction in Chapter 1, Chapter 2 provides the site description, and chapters 3, 4 and 5 present the analyses of
biomass and C distribution of I. cylindrica grassland, Acacia mangium and oil palm plantations, respectively. A general discussion on the biomass and C stored in the two plantation systems and I. cylindrica grasslands is presented in Chapter 6, and the overall conclusions and recommendations are given in Chapter 7.Site description

5 2 SITE DESCRIPTION

The study was conducted on the two Indonesian islands of S umatra and Kalimantan.
The sites were selected based on the abundance of the I. cylindrica grasslands and the plan for the establishment of plantations in these r egions.

2.1 Sumatra The study was carried out in two provinces of Sumatra, i.e ., North Sumatra for the 20- and 30-year-old oil palm plantations and Jambi in south Sum atra for the 3- and 10-yearold oil palm plantations. North Sumatra is located bet ween 0° 04’ and 4° 11’ north latitude and 97° 53’ and 100° 13’ east longitude, and Jambi 0° 45’ and 2° 25’ south latitude and 101° 10’ and 104° 55’ east longitude (Anonymous 1997). Altitudes in North Sumatra and Jambi range from 0-250 m asl near the coast to more than 1500 m asl inland. The geomorphology of these r egions is flat to undulating near the coast and rolling to mountainous in the upland o f the Bukit Barisan mountains. The geomorphology of these regions affects the rainfal l pattern, leading to high local
variation in rainfall distribution. Based on the Schmi dt and Ferguson classification, climate types A to E are found, with annual rainfall ran ging from less than 1500 mm to more than 4500 mm. The plots in the study area were all l ocated in climate type A. The climate of the island of Sumatra is humid tropical , being classified as Af according to the Köppen classification (Köppen 1931) or as hu mid forest according to the FAO (2001). In the lowlands, the annual average temperat ures are 26-27° C. Daily maxima range from 30° C to 36° C and daily minima are around 22° C. However, the more specific climate of the study region is classifie d according to Köppen as Aafw – a tropical rainy isothermal climate with hot summers ( hottest month more than 22°C), without a dry season (mean precipitation in driest mont h more than 60 mm) and two rainfall maxima (February-April and October-December). M onthly rainfall and temperature distribution of this site are presented in Figur e 2.1. The soils of Sumatra have developed under year-round high t emperatures and precipitation and are highly weathered and leached. These soils have low cationexchange-capacities, high acidity and shallow top-soils. However, in areas with volcanic ash or alluvial deposits, soils of higher fertil ity are found. Most of the soils inSite description

6 the lowland areas are fine textured and are well drained an d highly weathered (BPN 1993). In some cases, these soils are derived from acid v olcanic tuff sediments and have high Al saturation. Kaolinitic clay minerals dominate t he clay fraction of the soils.

The soils of the study site are Typic Hapludults, char acterized by low fertility, clay loam and silty clay texture for the upper and lower soils, respectively. The drainage of the soils is moderately good (slightly slow) to good, t he effective soil depth of 50- 100 cm and solum depth more than 1 m (PMP-SMART 2001).

2.2 East Kalimantan
East Kalimantan lies between 115 o 26'28" - 117 o 36'43" east longitude and 1 o 28'21" north
latitude - 1 o 08'06" south latitude. Similar to the Sumatra sites, the climate in East Kalimantan is classified as Aafw (Bremen et al., 1990; O hta et al . 1992), i.e., a tropical rainy isothermal climate with hot summers (hottest mo nth more than 22°C), without a dry season (mean precipitation in driest month more than 60 mm) and two rainfall maxima (April-May and December-January). The mean annual r ainfall ranges between approximately 2000 mm in the north and 2500 mm in the south (Voss 1982). Mean monthly temperature is 27°C (RePPProT 1987). Highest daytime temperatures of 35°C

0 20 40 60 80 100 120

J F M A M J J A S O N D
MonthMonthly Rainfall (mm)

0 10 20 30 40 50 60Monthly Temperature (°C) 320 Jambi, Sumatra 1990-2000 50 m a.s.l. 2087 mm

Figure 2.1: Monthly rainfall and temperature curves of study si tes in Jambi, south

Sumatra Temperature RainfallSite description

7 and lowest nighttime temperatures of 19°C have been recorde d (Voss 1979). Mean monthly temperature and rainfall are depicted in Figure 2.2.

The eastern part of the province belongs mainly to the phy siographic region of the Kutai Valley and Ridge Fold Belt. This region is domina ted by systems of high, rugged, strongly folded and faulted mountains, hogbacks and cues tas, piedmont areas, low mountains and rugged hills, and undulating plains (Voss 1982 ; and Ohta 1992). However, the physiography of the western part of this provin ce is rather smooth with altitude ranging between 50 and 1500 m as1. The soils in this region have developed from the middle-la te Miocene and early Miocene rocks dominate the geology of the province. These rocks have a thickness of approximately 2100 m to 8000 m. The middle-late Mioc ene rock consists mainly of muddy sandstone and mudstone. Coal layers are also abundant. Early Miocene rocks are largely calcareous mudstones with inte rbedded limestone, coaly sandstones and occasional tuff beds (Voss 1983; and Ohta et al . 1992). Typic Paleudults and Typic Hapludults are the major soil s in the region (Bremen et al . 1990 and Ohta et al . 1990). However, besides Entisols, Inceptisols and 0 20 40 60 80 100 120

J F M A M J J A S O N D 0 10 20 30 40 50 60 Kenangan, Balikpapan 60 m asl 1960-1980 2281 mm

MonthMonthly rainfall (mm)Monthly temperature (°C) 300

Figure 2.2: Temperature and rainfall curves of Eas t Kalimantan

Temperature RainfallSite description

8 Spodosols, Aquic Paleudults and Aquic Hapludults can also be found (Bremen et al

. 1990 and IHM 1989) The Ultisols have a mixed clay mineralogy consisting of kaolinite,
chlorite/vermiculite and oxides of aluminum and iron. Smal l amounts of mica are reported by Kawana (1976). Sand and silt fractions are dominat ed by quartz Ruhiyat (1989). Soil properties of the Sumatra and East Kalimantan are presented in Table 2.1.

Table 2.1: Soil properties of top- and subsoil in study sites in Sumatra and East

Kalimantan, Indonesia Sumatra East Kalimantan Parameter Topsoil Subsoil Topsoil Subsoil Soil type (USDA) Typic Paleudults Typic Paleudults Soil texture (pipette) SL-SiCL SC-C SL-SiCL CL-C pH (H 2 O) 4.3 4.4 4.3 4.4 Organic C (mg g -1 , dry combustion) 15.4 3.9 16.0 6.0 Total N (mg g -1 , dry combustion) 1.4 0.4 1.6 0.9 Available P (mg kg -1 , Bray II) 5.8 3.4 7.6 2.6 CEC (cmol c kg -1 , NH 4 OAc) - - 26.7 31.8Imperata cylindrica grasslands: biomass and carbon distribution

9 3 IMPERATA CYLINDRICA GRASSLANDS: BIOMASS AND CARBON
DISTRIBUTION

3.1 Introduction
Low income, inappropriate technology, low input and poor unde rstanding regarding land management have led to huge areas of deforested land in t he tropics. In many cases, farmers with land adjacent to forest zones cl eared the forests and converted the land into agricultural land to meet their subsistence nee ds. Due inappropriate land management systems, much of this area has been abandoned and invaded by I. cylindrica, the most common weed in the tropics. Today, I. cylindrica covers an area of more than 8.5 million ha in Indonesia alone (Garrity et al . 1997; Soekardi et al . 1993). Imperata cylindrica is a perennial, rhizomatous grass and reproduces from seed and rhizomes; however, flowering is rare and generally occurs only after human disturbance or stress (Sajise 1972). The plant is stemle ss, growing in loose to compact tufts with slender, flat, linear-lanceolate leaves fro m the rhizomes (Hubbard et al . 1944). It is a serious pest throughout the tropical and subtropica l regions and ranked as the seventh most troublesome weed worldwide (Holm et al . 1977). Imperata cylindrica has been reported to compete for nutrients, light, and water, and cause physical injury to neighboring plants through rhizomes penetrating the roots of these plants (Boonitee and Ritdhit 1984; Eussen and Soerjani 1975; Jagoe 1938). Furthermore, I. cylindrica has low nutritional values due to the high C/N ratio, and high lignin and polyphenol contents (Hartemink and O’Sullivan 2001). The persistent and aggressive rhizomes of I. cylindrica are the main mechanism for survival and local spread, which makes the wee d difficult to control. I. cylindrica is able to invade areas that will not support other veget ation, as it can tolerate a wide range of soil and climatic conditions (Hubbard et al . 1944; Eussen and Wirjahardja 1973). Shade, repeated herbicide application, and mechanical contr ol have all been
used to control I. cylindrica (Macdicken et al . 1997 Terry et al . 1997). Mechanical control is, however, very labor intensive and the use of herbicide (Glyphosate) is costly and open to environmental risks. There is the potential o f using Mucuna in the fallowImperata cylindrica grasslands: biomass and carbon distribution

10 period to control this grass (Carsky 2001; Akobundu 2000). Neverthe less, because of no direct additional product, acceptance by the farmers in so uth east Asia is low. Imperata cylindrica grass is usually found on soils with low pH, fertility, and organic matter content and soils that are highly leached ( Sajise 1980; Wilcut et al

. 1988). However, recent studies report that this grass grows f ast in a wide range of soils and climatic zones (Snelder 2001; Garrity et al . 1997; Santoso et al . 1997) creating a vast area of unproductive grassland. This is unfavorable fro m both ecological and economical points of view: low biomass (Otsamo 2002), C ac cumulation, and biodiversity, enhanced soil degradation and compaction (Ohta 1990); the grass also has a very limited use. Moreover, this grassland is susceptibl e to fire that may extend to the forests in the vicinity of this grassland, resulting in a n increased coverage. Thus, I. cylindrica grasslands emerge as fire-climax vegetation in areas where periodic fires hold back the natural secondary succession of forest (Euss en and Wirjahardja 1973). As a consequence of the unfavorable environmental conditions created by grass competition, allelopathy, fire susceptibility, soil degrada tion and compaction (Ohta 1990; Dela Cruz 1986; Soerianegara 1980), such grasslands are diffic ult to reforest or use for agricultural purposes, unless intensive land preparatio n and management are employed (Otsamo 2002; Otsamo et al . 1997). Land preparation for tree or crop plantations is very labor intensive and may require 200 m an days ha -1 (Van Noordwijk
et al . 1997) or 800-1000 hours ha -1 (Ruthenberg 1976). However, this grass is susceptible to shade (Otsamo 2002; Brook 1989; Eussen 1981) resulting in reduced carbohydrate storage, rhizome and tuber -bulb production, shoot dry weight, increased susceptibility to competition and herbicides, and decreased vigor and regeneration (Macdicken et al . 1997). Plantations of fast growing trees are, therefore, effective in suppressing and elimination of this grass (Otsamo et al . 1997; Turvey 1996). Fast growing tree plantations may ameliorate the strongly fluctuating microclimate conditions and reverse soil degradation by enhancing soil microbiological activities through increased litter production and nitrogen fi xation (Fisher 1995; Ohta 1990; Dela Cruz 1986), thus facilitating the reinvasion of native species (Otsamo 2000; Lugo 1997; Parrotta et al . 1997). The potential use of agroforestry for the reclamation o f I. cylindrica grassland has also been reported (de Foresta and Michon 1997; Santo so et al . 1997).Imperata cylindrica grasslands: biomass and carbon distribution

11 While the distribution of I. cylindrica grassland, its effect on soil properties and its reclamation potential have been intensively st udied, data on the above- and belowground biomass and C distribution of this grassland sy stem are still scarce. Such data are important for determining the base line of C stor age of the system, which can be used in greenhouse-gas mitigation projects such as planti ng trees in marginal lands. The focus of this study is, therefore, to quantify the biom ass and C stock of the system, both above- and belowground, as well as soil-C distribut ion.

3.2 Methodology Observation and sampling for the determination of biomass a nd C storage of I. cylindrica grassland were conducted at both the Sumatra and East Kali mantan sites. Three 3 m x 3 m plots were established on each site. Eac h plot consisted of three 1 m x 1 m sub-plots. All above ground biomass of I. cylindrica inside the sub-plots was harvested and weighed. Sub-samples were dried to a consta nt weight at 60°C and dry weight was determined. Thereafter, the samples were gro und to pass a 0.2 mm sieve and stored for further chemical analyses. Root biomass was sampled and collected at 16 drilling points i n each plot to a depth of 3 m (using an 8-cm-diameter root auger in 15-cm incremen ts) distributed on a systematical sampling basis (Figure 3.1). In some cases a less-weathered parent material layer was found at 3 m depth, presenting a physical barrier and preventing sampling for deeper soil layers. Roots were separated from the soil co re by water saturation and flushing: soil cores were watered in small flasks overnig ht for soil suspension. In the case of heavy clayey soils (common for soil layers de eper than 50 cm), calgon (sodium polyphosphate) was added to the suspension to enhance the dispe rsion capacity of the soils. Hereafter, the suspension was rinsed under a med ium pressure water tap and the
roots were collected with 2-mm and 65- μ m sieves. The samples were processed following the same procedure as for aboveground biomass sam ples. Soil samples for chemical analysis were drawn in line with the procedure of root biomass sampling. A small portion of the soil mass s ample was drawn from each soil core of the root sampling. Samples were then mixed t o six depth classes, 0-15, 15- 30, 30-50, 50-100, 100-200 and 200-300 cm, air dried and ground to pass a 2-mm s ieve. A soil profile was established nearby one of the three p lots on each site for observation of soil morphological characteristics a nd sampling of soil bulk density. SoilImperata cylindrica grasslands: biomass and carbon distribution

12 bulk density was sampled at depths of 0-15, 15-50, 50-100, 100-200 and 200-300 cm. Three to six soil core samples were drawn at each depth depending on the range of the soil depth and its presumed variation (3, 4, 5, 6 and 6 core s amples for the depths 0-15, 15-50, 50-100, 100-200 and 200-300 cm, respectively).

Carbon and nitrogen (N) content of the samples was dete rmined on the basis of dry combustion with a CNS (C, N, Sulfur) analyzer. Total C of the system was calculated based on C content and mass of each compartm ent of the system. The data were analyzed with analysis of variance (ANOVA ) and means were compared with the Least Significant Different (LSD) te st procedure.

3.3 Results and discussion Above- and belowground biomass of I. cylindrica grasslands varied within and among sites (Table 3.1). However, the difference was not sig nificant at α = 0.05. The aboveground biomass ranged from 6.0 to 10.1 Mg ha -1 , which is close to the 11.4 Mg
ha -1 in I. cylindrica grasslands in South Kalimantan reported by Otsamo (2002). Although not significant, both above- and belowground biom ass of the systems in East Kalimantan site were higher than in Sumatra. This diff erence may be the result of genetics, environment or seasonal variations of the sys tems. Nevertheless, since the data Root augering points 1 m

Figure 3.1: Layout of root sampling of Imperata cylindrica grassland at the study sites

in Sumatra and East Kalimantan, IndonesiaImperata cylindrica grasslands: biomass and carbon distribution

13 were consistent with the organic C of the soils, the r esults reflect the difference in soil resources. Belowground biomass was higher than aboveground bio mass by a factor of 1.5 for the systems in East Kalimantan and by a factor of 1.3 for those in Sumatra.

Table 3.1: Above- and belowground biomass of Imperata cylindrica grassland at the

study sites in Sumatra and East Kalimantan, Indonesia

Biomass (Mg ha -1 ) Site Aboveground Belowground 1 Total Below-/ aboveground ratio East Kalimantan 8.8±1.2 13.1±1.2 21.9±2.4 1.5±0.1 Sumatra 7.4±2.3 9.5±1.9 16.9±4.2 1.3±0.1

ns ns ns ns 1 Down to 3 m soil depth; ns not significantly different at α = 0.05; three replications

Root biomass of I. cylindrica grasslands was distributed to a maximum depth of 180 cm. However, most of the roots were confined to the top soil layer (Table 3.2), i.e., 79.5% of the root biomass was found in the top 15 cm and 90% in the upper 41 cm. This implies that the conventional and mechanical elim ination of this grass will never succeed, because of the difficulty of removing of the deep r hizomes. Measures could be combined with a sound and environmentally friendly chemical application before shadebased (Macdicken et al . 1997) and soil fertility improvement measures (Santoso et al

. 1997) could effectively control this grass. The magnitude of root biomass of 12.4 Mg
ha -1 was in the range of that of cool-season grass and swit ch grass of riparian buffers of 10.9-16.8 Mg ha -1 (Tufekcioglu et al . 2003; 1999). Although the biomass of I. cylindrica grassland systems is comparable to that the above sys tems, the distribution in I. cylindrica grassland was more concentrated in the upper soil layers : 88.4% of the roots was found in the top 35 cm, while this was 83.0 and 81.0% for the cool-season grass and switch grass systems, respectively (Tufekcioglu et al . 2003; 1999). Bulk density of soils developed under I. cylindrica grasslands ranged from 1.1 to 1.5 depending on site and soil depth (Table 2). The soil bulk density of the East Kalimantan site was slightly lower than that of the Sumatra site. This difference may relate to past land-use history, parent material and the de velopment of respective soils. Bulk density of the soils in East Kalimantan increased w ith depth, which can be attributed the decreasing biological activities. At the Su matra site, bulk density peaked at the depth of 50-100 cm (maximum illuviation horizon) and dec lined to a depth of 300 cm. However, at both sites, bulk density of the top so ils characterized by the denseImperata cylindrica grasslands: biomass and carbon distribution

14 root biomass (Soepardi 1980; Soerjatna and McIntosh 1980) was s ignificantly lower ( α = 0.05) than that of deeper soils.

Table 3.2: Root biomass and bulk density of soils in Imperata cylindrica grasslands at

the study sites in Sumatra and East Kalimantan, Indonesia, by depth Root biomass (Mg ha -1 ) Bulk density Depth (cm) East Kalimantan Sumatra East Kalimantan Sumatra 0-15 9.9a 7.3a 1.08a 1.11a 15-50 1.5b 1.1b 1.29b 1.36b 50-100 0.9c 0.5c 1.34b 1.50b 100-200 0.2d 0.2d 1.35b 1.43b 200-300 0.0e 0.0e 1.39b 1.37b Values followed with the same letters are not significantly dif ferent at α = 0.05.

Even though the bulk density of soils developed under I. cylindrica grassland was higher than that of primary forests of 1.0 (top soil ) and 1.3 (sub-soil) (Ruhiyat 1989), the bulk density of topsoil of plantations of 1.1 to 1. 2 and subsoil of 1.3 to 1.4 (Bremen et al . 1990; Ruhiyat 1989) is comparable to that of under I. cylindrica grassland. However, compared to the values reported by Bre men et al . (1990) and Ruhiyat (1989), the increase in soil bulk density from the to p- to subsoils of I. cylindrica was much more distinct. Carbon and N content of the aboveground biomass of I. cylindrica (40.7% ± 0.7% and 0.62% ± 0.06%, respectively) was higher than that of be lowground biomass (30.7% ± 2.2% and 0.56% ± 0.05%, respectively) but only the C cont ent was significant ( p of < 0.001 and 0.13, respectively). These values are based on six replications for the aboveground biomass and three replications for the below ground biomass. The C
content of I. cylindrica leaves of 42.6% reported by Hartemink and O’Sullivan (2001) was quite comparable to that of the aboveground biomass of the present study. This concentration did not much differ compared to that of Piper aduncum and Gliricidia sepium (40.4 and 43.8%, respectively) reported by Hartemink and O’Sull ivan (2001). The average C:N ratio of the belowground biomass (55) was lower than that of aboveground biomass (66). However, the values were consider ably lower than the 110 reported by Hartemink and O’Sullivan (2001). Compared to that of Piper aduncum and Gliricidia sepium of 26 and 18, respectively (Hartemink and O’Sullivan 2001), the C:N
ratios of I. cylindrica were much higher. The rate of decomposition of I. cylindricaImperata cylindrica grasslands: biomass and carbon distribution

15 leaves was much slower than that of Piper aduncum and Gliricidia sepium, which could not be explained by the C:N ratio alone; the process is also influenced by the lignin plus polyphenol over N ratio (Hartemink and O’Sullivan 2001). On average, the biomass C of the I. cylindrica grassland systems in the East Kalimantan and Sumatra sites was 3.6 and 3.0 Mg ha -1 (aboveground), 4.0 and 2.9 Mg
ha -1 (belowground) and 7.6 and 5.9 Mg ha -1 (total), respectively (Table 3.3). This magnitude is in the range of the biomass C of cool-season gr ass and switch grass of riparian buffers reported by Tufekcioglu et al. (2003). Compared to aboveground
biomass C of I. cylindrica grassland of 1.7-1.9 Mg ha -1 reported by Ginting (2000) and Lachica-Lustica (1997), the results are somewhat higher, but lower than the 8.5 Mg ha -1 reported by Lasco et al . (1999). Although belowground biomass was significantly higher than aboveground biomass ( p = 0.027), due to the lower C content of the belowground biomass (30.7% and 40.7% for the below- and abovegro und biomass, respectively), the belowground and aboveground biomass C did n ot differ much. The ratio of below- to aboveground biomass C was 1.0 and 1.1 in Sumatra and East Kalimantan, respectively. A similar ratio was reporte d by Tufekcioglu et al . (2003) for the cool-season and switch grasslands of riparian buffers in Iowa.

Table 3.3: Above- and belowground biomass C of Imperata cyli ndrica grassland at the

study sites in Sumatra and East Kalimantan, Indonesia Biomass C (Mg ha -1 ) Site Aboveground Belowground Total East Kalimantan 3.6±0.5 4.0±0.4 7.6±0.9 Sumatra 3.0±0.9 2.9±0.6 5.9±1.5 ns * ns ns = not significantly different at α = 0.05; * significantly different at α = 0.05; three replications

Soil organic C and nitrogen are the main limiting factors i n grassland productivity and are affected by biomass removal (periodic b urning), low input of organic matter and loss of organic matter by surface eros ion (Snelder 2001). Soil C content of soils at both sites decreased persistently w ith depth (Table 3.4). Values were 1.27 and 1.08% in the top 15-cm depth dropping to 0.15 and 0.10% at the 200-300 -cm depth for East Kalimantan and Sumatra, respectively. The re was a sharp decrease in the first 15-cm depth to the second 15 cm, after which the C con tent declined gradually to a depth of 300 cm.Imperata cylindrica grasslands: biomass and carbon distribution

16 Table 3.4: Carbon content and storage of soils in Imperata cylindrica grasslands at the

study sites in Sumatra and East Kalimantan, Indonesia Site East Kalimantan Sumatra Soil Depth (cm) C content (%) C storage (Mg ha -1 ) C content (%) C storage (Mg ha -1 ) 0-15 1.27a 20.6 1.08a 18.1 15-30 0.88a 17.1 0.70b 14.3 30-50 0.75a 19.3 0.57b 15.5 50-100 0.53a 35.7 0.44b 32.7 100-200 0.27a 36.6 0.18b 25.7 200-300 0.15a 21.4 0.10b 14.0 0-300 - 150.6 - 120.3 Values followed by the same letters are not significantly differe nt at α = 0.05.

Imperata cylindrica grassland systems have a dense mat of rhizomes near the surface, which is a positive factor with respect to eros ion control and a source of organic material (Soepardi 1980; Soerjatna and McIntosh 1980). It play s a positive role on sloping lands in reducing soil movement and as a vegetative filter for run-off carrying sediments. The relatively high C content of the top 15 -cm soil could be due to the abundance of root mass. However, compared to the C conte nt of the topsoil of plantation systems of 1.6 to 2.3% (Mackensen 1998; Syahrin udin 1997; Bremen et al

. 1990), the C content of the soils under I. cylindrica grasslands is even lower. This is in agreement with the previous finding that the C content of the soils in regularly burnt I. cylindrica grasslands tends to decline (Van Noordwijk et al . 1997; Ohta 1990). Furthermore, even though without fire a reasonable soil organic matter level might be maintained, litter quality and subsequent N mineralizatio n are low (Hartemink and O’Sullivan 2001; Van Noordwijk et al . 1997). With the exception of the 0-15-cm layer, the C content of the soils at the East Kalimantan site was significantly higher than that of at the Sumatra site (

p < 0.001).
Since there was no evidence of differences in fire even ts at these sites, the difference suggests that there was already a difference in the level of soil C content prior to the
invasion of I. cylindrica

. Distribution of the C storage of soils developed under I. cylindrica grassland is presented in Table 3.4. The results show that the top 50-cm soil depth contributed less than 40% of the total soil C storage to a depth of 3 m, a nd the contribution of the top 100-cm soil was 61.5-67.0%. This suggests that contribution of t he C storage in theImperata cylindrica grasslands: biomass and carbon distribution

17 deep soils is significant and, due to its high variability, must be assessed. The C storage to a depth of 3 m in this study is quite comparable to that in oxisols of secondary and primary Brazilian forests and traditional crops (130.0-145.0 M g ha -1 ), but higher than that of oil palm and passion fruit plantations (108.0 and 125.0 Mg ha -1 , respectively) (Sommer et al ., 2000). Little information exists on the C storage in de ep soils in the study region; however, the 47.9-56.9 Mg ha -1 in the top 50-cm soil are still in the range of values for forest plantations (42.1-67.5 Mg ha -1 ) (Mackensen 1998; Syahrinudin 1997; Bremen et al . 1990; Ruhiyat 1989). Nevertheless, compared to secondary and primary forests (57.7-69.9 Mg ha -1 ) (Ruhiyat 1989), the soil C storage of I. cylindrica grassland systems is lower. Of the total 126.2-158.2 Mg ha -1 C, only 2.3-2.4% were stored in aboveground biomass. Compared to forest ecosystems, contribution of aboveground biomass C to the total C storage of grassland systems is generally much lo wer (Sharrrow and Ismail 2004).

3.4 Conclusions Imperata cylindrica grassland stored only a relatively small amount of biom ass C (5.9- 7.6 Mg ha -1 ) implying that conversion into a more C-rich tree-base d system would be promising tool to enhance C sequestration. Moreover, the roots of I. cylindrica extended to a maximum depth of only 180 cm. With most of these roots being confined to the topsoil, little organic material is deposited in deeper la yers. Despite the dense mat of rhizomes, the extent of C stored in the top soils wa s modest. As sequestration is of global concern, the conversion of this grassland into sy stems with higher biomass accumulation and deeper root penetration is required. Soil C content at both study sites decreased significant ly with depth from the top 15 cm to the 3-m depth and was considerably higher in Eas t Kalimantan than in Sumatra. With similar land-use history, the difference s in soil C are likely to be related to the level prior to the invasion.Acacia mangium plantations

18 4 ACACIA MANGIUM PLANTATIONS

4.1 Introduction Tropical forests play an important role in the global C budget, and some evidence suggests that tropical forests may sequester atmospheric C O 2 (Sataye et al. 2001; Grace
et al . 1995). However, Cox et al . (2000) and White et al . (2000) estimated that a substantial amount of C could be released from tropical fo rests if temperatures increase due to global climate change. Studies on the sequestration and dynamics of C in tropical soils have recently gained importance. These are mainly driven by the fact th at the changes in the magnitude of C held in soil organic matter may significantl y change the levels of atmospheric CO 2 (Schlesinger 1991). Estimates for the quantity of organic C i n the upper meters of soil world-wide range from 1220 Gt to 1550 Gt (E swaran 1995; Post et al . 1982; Schlesinger 1977; Schlesinger 1984), which is nearly twice the aboveground biomass of 560-835 Gt (Sombroek et al . 1993). Soils, in particular those in the tropics, could be large sinks of atmospheric C if well managed (Lugo and Brown 1993). The transformation of forestland into agricultural land lea ds to substantial losses of aboveground biomass, but the effect on soil C stocks rema ins poorly understood. It is commonly assumed that after conversion to agricultural u se the soil becomes impoverished in C, which is reversed during the fallow perio d (Cerri et al . 1991; Greenland and Nye 1959; Lugo and Brown 1993; Raich 1983). The sequestration of C into vegetation and soil sinks is one of the mechanisms for reducing net greenhouse gas emissions. Conservation stra tegies, which sequester C, include converting marginal lands to compatible land-use sys tems, restoring degraded soils, and adopting best management practices. Notwithstand ing the debate as to whether global forests are sources or sinks of greenho use gases (Pelley 2003; Harmon 2001; Metting et al . 2001; Schimel et al . 2001; Lal and Singh, 2000; Ravindranath et al

. 1997), managed fast growing forests may enhance C sequestratio n (Lee et al . 2002; Ney
et al . 2002; Metting et al . 2001; Papadopol 2000). Silvicultural strategies aiming at accelerating stand growth are likely to increase the r ate of C sequestration of the respective forests (Lee et al . 2002; Chen et al . 2000; Montagnin and Porras 1998).Acacia mangium plantations

19 Plantations of fast-growing species have been rapidly increasing in Asia in recent years (Cossalter and Pye-Smith, 2003). Acacia mangium is one of the most common fast growing species planted in the humid tropics. Plantations of A. mangium have been established at many secondary forest and grassla nd sites across the region, covering about 20×10 6 ha (ca. 9.4% of the total forested area) in ASEAN count ries in the year 2000 (FAO 2003). A. mangium used to be planted primarily for site rehabilitation; however, due to its rapid growth and tole rance of very poor soils, this species is playing an increasingly important role in efforts to sustain commercial supplies of tree products while reducing pressure on natural fo rest ecosystems. Its quick growth and dense shade make the tree an effective tool in reforesting Imperata grass swards and reducing fire risk (Nitrogen Fixing Tree Associat ion 1987). It has been reported that this species has a great potential with regard t o unproductive and degraded lands such as those infested by I. cylindrica (Otsamo 2002; Hardiyanto et al . 1999;
Otsamo et al . 1997). The establishment of plantations with this specie s in areas for forestry-based C offset projects is, therefore, promis ing.
There are about 7.5-8.5 million ha of I. cylindrica grasslands distributed in various islands in Indonesia, an area that would be large enough to support the extensive expansion of oil palm and forestry plantations planned by the government. These plantations have high potential to be promoted in the wor ld-C trade and they may, therefore, increase the foreign exchange earnings of th e country. However, the question
as to how much CO 2 equivalent can be sunk by converting I. cylindrica grassland into plantation is still open. To answer this question, studi es on the biomass and C storage of
both I. cylindrica grasslands and man-made forests are of utmost importanc e. In this study, efforts are devoted to quantifying the biomass and C
accumulated in A. mangium plantations of different ages and biomass and C
distribution.

4.2 Methodology Plots for the determination of biomass and C storage of an A. mangium plantation were
established at the East Kalimantan site. Three 0.05-ha ci rcular plots (r = 12.6 m, consisting of 55 trees of a full standing stock plantation with a planting space of 3 m x 3 m) were established in a 1-, 4-, and 9-year-old A. mangium plantation. ExtremeAcacia mangium plantations

20 variation in stand density, undergrowth coverage and land slope was avoided. Thus, 9 plots were established (3 stand ages, 3 replications). To min imize errors induced by the variation of soil type, all observation plots were es tablished in loamy to clayey Ultisols, considering that this is the most common soil in the regi on. The diameters of the trees in each plot were measured a nd the data used to estimate the total biomass of the respective stand. For this, the data was combined with the results of the tree biomass sampling to build an al lometric equation. Twenty trees were harvested and uprooted. Total biomass of the harvested tr ees was weighed, and samples were drawn from the different components (root, stem, branch, twig and leaf) and weighed. Samples were dried to constant weight at 60°C . Thereafter, samples were ground to pass a 0.2-mm sieve for chemical analysis. Three 5 m x 5 m subplots were established to assess the biomass of woody undergrowth occupying the respective plot. All woody undergrow th in these sub-plots was harvested and uprooted. Total biomass was weighed and the samples were sorted into roots (medium and coarse), stems, branches and tw igs, and leaves. Thereafter, the procedure as for the trees was carried out. To estimate the total biomass and C stored in the herbaceous undergrowth, three 1 m x 1 m sub-plots wer e established, and the herbaceous undergrowth in these sub-plots was harvested a nd weighed to calculate the total fresh weight. Samples were drawn representativel y for total dry weight assessment. Thereafter, the same procedure as for the tree samples was followed. Only litter in the L and F layers of the soil was con sidered as litter standing stock in this work, because the H layer was incorporated i nto the soil sample. In each main plot, three 0.5 m x 0.5 m subplots were established t o collect the litter. The litter in these subplots was collected, sorted into woody and no n-woody components and weighed (fresh and air dry). A small sample of each co mponent was drawn and processed following the same procedure as for the tree sam ples. To complete the biomass determination, three subplots 3 m x 3 m in accordance with the planting space of the A. mangium pl antations were established in each main circular plot. Fine root and soil samples w ere drawn at 17 drilling points to a depth of 3 m (using an 8-cm-diameter soil core auger in 15 cm increments) distributed in a systematical sampling system on the basis of the d istance to the closest trunk: 10 cm (A), 50 cm (B), 100 cm (C), 150 cm (D) and 212 cm (E) (Figure 4.1). Roots wereAcacia mangium plantations

21 separated from the soil core by water saturation and flus hing as described in Section
3.2.

A soil profile was established near the center of one o f the three plots of each plantation age for observation of the soil morphologi cal characteristics and sampling of soil bulk density. Soil sampling and analysis were carri ed out following the procedure
described in Section 3.2. Data were analyzed with analysis of variance (ANOVA) and means compared with the Least Significant Different (LSD) test procedur e.

4.3 Results and discussion
4.3.1 Biomass distribution
The biomass of the A. mangium plantations was assessed using an allometric equation based on the results of the destructive sampling of the trees. Six allometric equations were developed; all are at p < 0.001. A 1

D 3 D 1

E C 1 B 1

C 3 D 2 D 4 B 4

C 4

B 2 C 2

A 3 B 3 A 4

A 2 Distance to closest trunk: A = 10 cm B = 50 cm C = 100 cm D = 150 cm E = 212 cm

Figure 4.1: Layout of root and soil sampling in Acacia mangium stand in East

Kalimantan, Indonesia Root auger point

Trunk baseAcacia mangium plantations

22 Y = 0.0065X 2.7601 , r 2 = 0.9452 for root biomass (excluding fine root biomass)
Y = 0.034X 2.7166 , r 2 = 0.9442 for stem biomass
Y = 0.0608X 2.0034 , r 2 = 0.9470 for branch biomass
Y = 0.0399X 1.9189 , r 2 = 0.8711 for leaf biomass
Y = 0.2518X 2.1679 , r 2 = 0.9205 for aboveground biomass
Y = 0.1027X 2.4942 , r 2 = 0.9628 for total biomass Y = expected biomass of the tree compartment X = tree diameter at breast height.

Allometric equations developed to estimate biomass and volu me of the stands in most of the previous studies are based on the diameter and height of trees (Yantasath
et al . 1992; Halenda 1989; Ruhiyat 1989; Bustomi 1988). However, the result s in this study show that estimations of tree biomass based on diam eter alone can provide accurate and reliable results. Since tree height is to a large extent dependent on tree diameter and the relation of tree diameter, and since height is likely species specific,
estimations of tree biomass and volume based on tree di ameter can be quite reliable, especially when the stand consists of mono species. Fur thermore, measurement of the height of the standing trees is difficult in the field and may, therefore, be subject to errors, thus estimation of the stand yield (biomass or volume) based on tree diameter
alone is recommended. Most allometric equations in former studies are developed from a single stand age (Syahrinudin 1997; Halenda 1989; Ruhiyat 1989; Lim 1988, 1986), mainly supported by the assumption that tree form may change wit h stand age. In contrast to this assumption, the results in this study show that the established allometric equations are applicable for a very wide range of stand ages (1- to 9-year-old stands). This implies that the equations can be employed for similar plantat ions elsewhere, regardless of the age of the stand. Soemarna and Bustomi (1986) developed an a llometric equation fitted for 3- to 7-year-old A. mangium stands. Hiratsuka et al . (2003) found that the allometric equations of aboveground biomass of 6-year-old stands of A. mangium in Benakat, Indonesia and Sonbe, Vietnam, 7-year-old stands in Madang, P apua New Guinea (PNG), and 8-year-old stands in Benakat and Bogor, Indonesi a, were not site dependent. The equation developed in this study confirms their finding (r 2 = 0.99, p < 0.001) that the allometric equation for A. mangium plantations is not site specific and that theAcacia mangium plantations

23 equation can be applied for any plantation of this species, regardless of stand age and
site conditions. Biomass distribution of the plantations is presented in Table 4.1. The diameter distribution of the 4- and 9-year-old stands is comparabl e to that of the so-called site index 18.0 m of 15.3 and 20.5 cm, respectively, reported by Newaz an d Millat-EMustafa (2004). Nevertheless, the results on the diamete r distribution of the 1-year-old stands of 5.6 cm in this study are higher than their findin g of 3.2 cm. The average diameter of 1-year-old A. mangium stands ranged widely from 1.8 to 8.8 cm (Yanthasath et al . 1986; Paudyal and Nik Muhamad 1990), depending on site conditions, planting space and material, and plantation management.

Table 4.1: Stand density, diameter and biomass distribution in Acacia mangium plantation system in East Kalimantan, Indonesia
Stand age Stand

density Diameter

of trees (DBH) BGB AGB Litter Total biomass RBGB RWUG RHU
(year) (trees ha -1 ) (cm) (Mg ha -1 ) (%) Mean 1580 5.6 11.3 16.8 1.6 29.7 38.1 5.0 14.3 SD 121.7 1.2 2.7 1.9 0.3 4.6 2.7 4.4 7.9 1 n 3 237 3 3 3 3 3 3 3 Mean 626.7 15.0 18.7 64.8 9.3 92.8 20.1 13.4 1.0 SD 30.6 3.4 4.4 1.5 1.8 7.05 3.2 1.2 0.2 4 n 3 94 3 3 3 3 3 3 3 Mean 713.3 20.7 36.3 139.2 5.9 181.4 20.0 0.4 0.1 SD 83.3 5.7 4.9 18.5 0.8 23.3 1 0.1 0.03 9 n 3 107 3 3 3 3 3 3 3 SD = standard deviation, DBH = diameter at breast height, BGB = b elowground biomass, AGB = aboveground biomass, RBGB = relative belowground biomass to total biomass, RWUG = relative woody undergrowth biomass to total biomass, RHU = relative herbaceous under growth to total biomass.

There was an increase in stand diameter variation in line with age of the plantation. Since it is assumed that the stand is gene tically homogeneous, this may
reflect the increase in the effect of the environmental factors such as differences in micro relief, access to soil nutrients and water, as well as symbiosis with certain Rhyzobium strains (Martin-Laurent et al . 1999; Galiana et al . 1995; 1998). Total biomass accumulation increased from only 25.4 Mg ha -1 in the first year of the plantation to 181.2 Mg ha -1 in the ninth year. It is obvious that the biomass of t he A. mangium

stands already surpassed that of I. cylindrica of 21.9 Mg ha -1 in the very early stage of the plantation. This implies that esta blishment of A. mangium plantationsAcacia mangium plantations

24 is a promising tool if the biomass is the concern, especi ally in marginal and degraded lands (Otsamo, 2002, Otsamo et al . 1997). Aboveground biomass of the 4-year-old stands (52.6 Mg ha -1 ) (Table 4.2) in this study was in the range of that of 5- to 7-year-old Eucalyptus deglupta stands (45.7- 81.2 Mg ha -1 ) (Syahrinudin 1997; Ruhiyat 1989). Compared to the biomass of 4 -yearold Gmelina arborea stands (3.7 – 10.9 Mg ha -1 ) studied by Swamy et al . (2003), this value is higher. However, the contribution of belowground bi omass of 17.5-40.2% (Swamy et al . 2003) is in agreement with the results of the present st udy of 20.0-38.1%. It is important to notice that the accumulation rate of belowground biomass was quite high in the first years (almost similar to that of ab oveground biomass) and declined with plantation age.

Table 4.2: Biomass distribution of Acacia mangium plantation system in East

Kalimantan, Indonesia
Stand age Fine

root Coarse root Stem Branch Leaf AGB BGB Total biomass (year) (Mg ha -1 ) Mean 9.5 1.3 6.5 3.2 1.8 11.5 10.8 22.3 1 SD 2.7 0.3 1.4 0.6 0.3 2.3 3.0 5.3 Mean 9.5 8.0 37.2 10.7 4.7 52.6 17.5 70.1 4 SD 4.3 0.3 1.5 0.4 0.2 1.9 4.2 4.2 Mean 12.3 23.9 108.7 19.6 10.2 138.4 36.2 174.7 9 SD 2.2 3.5 15.5 1.9 1.2 18.5 4.9 23.1 SD = standard deviation, GB = belowground biomass, AGB = aboveground biomass; three replications of each stand age; fine roots were defined to depth of 3 m.

Information on the biomass of young plantations (less th an 3 years old) is scarce. Compared to the aboveground biomass of 1-year-old Eucalyptus deglupta plantations of 3.1 Mg ha -1 (Syahrinudin 1997), the results in this study are much highe r. Aboveground biomass of A. mangium plantations ranges widely depending on factors such as planting space (tree density), site quality, sil vicultural practices and plant material characteristics. However, in general, the m agnitude of aboveground biomass in this study is still in range of that reported in previous studies (Table 4.3). Biomass of all compartments of the stands increased wit h stand age. There is, however, no significant difference in fine root biomass a cross plantation age. Belowground biomass of the 4- and 9-year-old stands is in th e range of that ofAcacia mangium plantations

25 Amazonian primary forest and secondary vegetation (22.0 – 34.0 ton ha -1 6 m -1 ) (Sommer et al . 2000).

Table 4.3: Stand density and aboveground biomass of Acacia ma ngium plantations of

different ages and sites Stand age (year) Stand

density (trees ha -1 ) Aboveground

biomass (Mg ha -1 ) Site Reference

1 1580 11.5 East Kalimantan, Indonesia This work 3.5 1089 54.4 Sarawak, Malaysia Lim and Hamzah 1985 3.5 625 64.1 Malaysia Lim 1985 4 626.7 52.6 East Kalimantan, Indonesia This work 4 2500 48.0 Thailand Yantasath 1992 4 10000 128.0 Thailand Yantasath 1992 4 1566 90.4 Malaysia Lim 1988 4.5 1089 86.9 Sarawak, Malaysia Lim 1986 5 600 58.9 East Kalimantan, Indonesia Ruhiyat 1989 6 696 67.5 East Kalimantan, Indonesia Ruhiyat 1989 6 1289 122.4 Sonbe, Vietnam Hiratsuka et al . 2003 6 822 132.6 Benakat, Indonesia Hiratsuka et al . 2003 6 1369 157.5 Benakat, Indonesia Hiratsuka et al . 2003 6 787 133.2 Benakat, Indonesia Hiratsuka et al . 2003 6 877 172.8 Benakat, Indonesia Hiratsuka et al . 2003 6 903 143.5 Benakat, Indonesia Hiratsuka et al . 2003 6.8 730 123.2 Malaysia Halenda 1989 7 708 96.6 East Kalimantan, Indonesia Ruhiyat 1989 7 506 99.7 Madang, PNG Hiratsuka, et al . 2003 9 713.3 138.4 East Kalimantan, Indonesia This work 9 1382 189.5 South Sumatra, Indonesia Hardiyanto, et al . 1999

Information on the undergrowth biomass of forest plantat ions is very scarce, and reports on the importance and contribution of undergro wth in tropical forest plantations are even rarer. Biomass distribution of litter standing stock and undergrowth is presented in Table 4.4. Total biomass of woody undergrowth of the 4-year-old stands was notably higher than that of the 1- and 9-year-old sta nds. In the first year of the plantation, there was intensive undergrowth management c ontrolling the development of the undergrowth. This management was less intensive in the second year and only occasional during the consecutive years, since the canopy closure became well developed (Syahrinudin 1997). Nevertheless, tree mortality i n the 4-year-old stand was rather high (this is a common case for plantations est ablished in degraded lands, e.g., I. cylindrica grassland, if there is no intensive management) (Soeria negara 1980; Otsamo
et al . 1997). A stand density of 626 trees ha -1 allowed vigorous development of woody undergrowth.Acacia mangium plantations

26 Table 4.4: Biomass of undergrowth (above- and belowground) an d litter standing stock

in Acacia mangium stands of different ages in East Kalimantan, Indonesi a Aboveground biomass Stand age Belowground

biomass WU HU Total Litter standing stock (year) (Mg ha -1 ) Mean 0.45 1.04 4.25 5.29 1.64 SD 0.39 0.58 1.51 1.73 0.63 1 n 6 6 9 6 9 Mean 1.15 11.31 0.91 12.22 9.27 SD 0.40 3.62 0.38 1.24 3.71 4 n 6 6 9 6 9 Mean 0.11 0.60 0.17 0.78 5.96 SD 0.04 0.19 0.13 0.17 1.58 9 n 3 3 9 3 8 SD = standard deviation, WU= woody undergrowth, HU = herbaceous undergrowth.

In line with the undergrowth biomass, the litter standi ng stock of the 4-yearold stands was highest. This may relate not only to the dense undergrowth, but also to the growth physiology of the stand, i.e., litter producti on is normally highest in the early fast growing period of the stand and then declines as the stand gets close to maturity (Lugo et al., 2004). A 9-year-old stand is possibly very close to the mature state for the A. mangium stands. The litter standing stock in this study is, how ever, in agreement with that of former studies (7.0-19.6 Mg ha -1 ) (Syahrinudin 1997; Ruhiyat 1989).

4.3.2 Root distribution Roots are important for anchorage, water and nutrient uptake , storage of carbohydrates and synthesis of growth regulators. Fine roots represent a small portion of the total biomass of the ecosystem (De Agelis et al . 1981), typically less than 5 % (Jackson et al

. 1997; Vogt et al . 1996), but play a significant role in determining the funct ioning of the system. A significant part of the net primary production of both native and managed ecosystems is in some cases allocated to the fine root pr oduction (Harris et al . 1977; Buyanovsky et al . 1987). A magnitude of 30% to 50% of the C cycled annually in for est ecosystems is probably allocated to fine root production ( Grier et al . 1981; Vogt et al

. 1996). Of the global primary production, roots consume about 30% (Jackson et al

. 1997).
Fine root biomass of the A. mangium plantation system ranged from 9.5 Mg
ha -1 3 m -1 (in the first and fourth year) to 12.3 Mg ha -1 3 m -1 (in the ninth year). This isAcacia mangium plantations

27 quite comparable to the root biomass of I. cylindrica of 12.4 Mg ha -1 3 m -1 . However,
the vertical distribution of the root biomass of I. cylindrica grassland was restricted to the topsoil (Figure 4.2). The results of this study are in agreement with those of previous works (Curt and Prévosto 2003; Makkonen and Helmisaari 1999; Hendri cks and Bianchi 1995; Vogt et al . 1996). Curt et al . (2001) reported estimates of fine root biomass of Douglas fir in the upper 30 cm soil of 17.3-28.4 Mg ha -1 . These values are clearly higher than those in this study, which are, howev er, quite comparable to those reported by Santantonio et al . (1977) studying fine root biomass ( < 5 mm) in the upper soil in Douglas-fir forests of Oregon ranging from 8.5 to 10.1 Mg ha -1 . The values in this study are also in agreement with those for plantati ons in Michigan and Oregon reported by Fogel (1983) (about 8.0 to 24.1 Mg ha -1 ). Generally, fine root biomass contributes only a small por tion of the total biomass of the system, typically less than 5% (Jackson et al . 1997; Vogt et al . 1996). The results in this study are, nevertheless considerably higher, especially for the younger stands (1- and 4-year-old stands) with averages of 37. 35, 10.33 and 6.81% for the 1-, 4- and 9-year old stands, respectively. It seems t hat the fine root system of the plantation developed early from the beginning of the plant ation to a required level, thereafter being maintained in a narrow dynamic range. In line with the results of previous works (Swamy et al . 2003; Tufekcioglu et al . 2003; Curt et al . 2001; Dhyani and Tripathi 2000; Sommer et al . 2000), the fine
roots of the A. mangium plantation systems were concentrated in the top centi meters of the soil profile. In the 3 m-deep soil profile, more tha n 50% of the fine root biomass was found in the top 30 cm. However, compared to I. cylindrica grassland, the fine roots of A. mangium penetrated much deeper to a depth of 3 m. This is much deepe r than the 1.8
m in I. cylindrica grassland. Moreover, 90% of the root biomass of I. cylindrica grassland confined to a depth of 41 cm was clearly much shall ower than for A. mangium plantation systems, where values were of 157 cm, 167 cm an d 170 cm for the 1-, 4- and 9-year-old stands, respectively. Fine root biomass showed a continuous decrease with soil dept h, thus being in accordance with many previous studies (Curt and Prévosto 200 3; Curt et al . 2001; Tufekcioglu et al . 1999; Nie et al . 1997), which indicate that this root profile usually corresponds to a vertical decrease in nutrients, porosi ty, and water storage capacity inAcacia mangium plantations

28 the soil profiles (Sainju and Good 1993). Fine roots prolifera te in the A-horizon of most soils due to the accumulation of organic matter, higher CE C and organic C, N, P and K concentration (Bowen 1984; Kalisz et al . 1987; Pritchett and Fisher 1987; Sainju and Good 1993). A rapid vertical decrease in fine root density was observed in a highly acidic soil under spruce stands (Jentschke et al . 2001).

The vertical distribution of fine roots indicates the r ooting strategy of trees and is species specific and genetically inherited (Curt and Pré vosto 2003; Polomski and 0

50

100

150

200

250

300 0.0 0.1 1.0 10.0



### Fine root biomass (Mg ha -1 

### 15 cm -1 

### )Soil depth (cm)

IC AM1 AM4 AM9

Figure 4.2: Vertical distribution of fine root biomass of the Acacia mangium

plantation system (AM) and Imperata cylindrica grassland (IC) in East Kalimantan, Indonesia (1, 4 and 9 = 1-, 4- and 9-ye ar-old stand)Acacia mangium plantations

29 Kuhn 1998; Brown 1992). There are very few reports on the ro ot distribution in A. mangium plantation systems. However, the results of this stud y show that the distribution of the fine root biomass of the plantation s was similar regardless of age. This high fine root biomass accumulation in the top few ce ntimeters of the soil is typical for many pioneer trees (Polomski and Kuhn 1998; Perala an d Alm 1990; Grime 1979). This shallow concentrated rooting strategy may allow an e fficient use of the topsoil resources (Crabtree and Berntson 1994).

The lateral extent of woody roots may exhibit a high degree of plasticity and depend on environmental conditions (Millikin and Bledsoe 1999; Belsky 1994). In line with previous findings (Purbopuspito and Van Rees 2002; Jose et al . 2001; Peter and Lehmann 2000; Jones et al . 1998), although not significant, there was a slight decrea se in the horizontal distribution of the fine root biomass with distance to the tree base in 1- and 9-year-old stands (Figure 4.3). Such a decrease could no t be observed in the 4-yearold stand. This may relate to the dense undergrowth occupyi ng the sites of this stand. However, Millikin and Bledsoe (1999) reported that distance f rom tree did not significantly affect fine root biomass of blue oak. Root distribution is highly variable and is constrained by t he microsite spatial variability created by the soil environment or by the diffe rent plant species existing on each site (Roy and Singh 1995; Vogt et al . 1995). The present results show that the Figure 4.3: Horizontal distribution of fine root bi omass of Acacia mangium

plantation system in East Kalimantan, Indonesia; re ctangles are means and stake bars are standard deviations

4-year-old stand

0 2 4 6 8 10 12 14 16

0 50 100 150 200 250 Distance to closest trunk (cm)Biomass (Mg ha-11 m-1) 1-year-old stand

0 2 4 6 8 10 12 14 16

0 50 100 150 200 250 Distance to closest trunk (cm)Biomass (Mg ha-11 m-1) 9-year-old stand

0 2 4 6 8 10 12 14 16

0 50 100 150 200 250 Distance to closest trunk (cm)Biomass (Mg ha-11 m-1)Acacia mangium plantations

30 distribution of the fine root biomass in the A. mangium plantations was highly heterogeneous, with coefficients of variation ranging from 41.3-216.2% and 5.6-153.7% for within and among sites, respectively. The variabilit y within sites was much higher than that among sites, on average by a factor of 2 (coe fficient of variation of 108.0 ± 21.0% and 57.1 ± 22.3% for within and among sites, respectively ). A considerable variability of Douglas-fir root biomass within microsite ha s also been observed (Curt et al

. 2001). This high variability of fine root biomass within sites m ay reflect a high micro-spatial variability of the soil resources of the system. It could, therefore, be of
interest to determine to what extent soil and microsit e patches can modify fine root biomass, architecture, and seasonal turnover, thus condit ioning the exploitation of soil resources (Drexhage and Gruber 1998; Fitter 1994; Pritchett an d Fisher 1987).

Details on the variability of the vertical fine root bi omass distribution of the system are depicted in Figure 4.4. In general, the variabilit y was considerably low in the first 15 cm of the soils, followed by an increase to a de pth of 120-165 cm. Thereafter, variability decreased to the depth of 3 m. However, there were some exceptions to this general trend. The 1-year-old stands exhibited a persistent increase in the variability of vertical fine root biomass distribution to a depth of 3 m. It is the question whether this 4-year-old stand 0

50

100

150

200

250

300 0 50 100 150 200 250 Coefficient of variation (%)Soil depth (cm)

1-year-old stand 0

50

100

150

200

250

300 0 50 100 150 200 250 Coefficient of variation (%)Soil depth (cm)

9-year-old stand 0

50

100

150

200

250

300 0 50 100 150 200 250 Coefficient of variation (%)Soil depth (cm)

Within Site Among Site

Figure 4.4: Variability of vertical fine root biomass distribut ion within an d among

sites of Acacia mangium plantation systems in East Kalimantan, IndonesiaSoil depth (cm)Soil depth (cm)Acacia mangium plantations

31 increase is the result of the insufficient sample siz e or whether it illustrates the real variability of the distribution. In the first 1 m depth of the soil, the same sample s ize was applied in determining the fine root biomass distribution in all stand ages (153 root auger points). However, for the second and third 1-m depth, a more intensi ve sampling was undertaken for the 4-year-old stand, i.e., a sample size of 65 and 45 root auger points, respectively. The sample size for the respective depth of the 1- and 9-year-old stands was only 20 and 15. Based on the variability of the fine root biomass of the defined soil profile (to depth of 3 m) and the sample size, it was o bserved that the variability of the fine root biomass was not significantly affected by the sa mple size. Compared to the deeper part of the soil profile (second and third 1-m depth) where a 15-65 sample size was used, employing a 153 sample size in the first 1-m depth di d not significantly reduce the variability. It is also evident that increasing the sample size from 15 to 45 auger points and from 20 to 65 auger points for the third and s econd 1-m depth, respectively, did not result in a significant reduction i n the variability. This implies that employing the core sampling method does not give a precise re sult in the assessment of the fine root parameters of a system, especially if a sm all sample size is applied. The variability of the fine root biomass was, to some e xtent, defined by the soil bulk density of the sites (Figure 4.5). Generally, there was a positive non-linear correlation between soil bulk density and coefficient of variation of fine root biomass. It
was observed that the correlation between soil bulk density and coefficient of variation of fine root biomass followed the Modified Exponential mode l (y = ae b/x , r = 0.75, p < 0.001, a = 1086.26, b = -3.45). This is in line with the finding o f Curt et al . (2001) reporting that the soil physical characteristics may al ter the root system of Douglas fir. Nevertheless, it is interesting that the coefficient s of variation of fine root biomass of the 9-year-old A. mangium stand were distributed below the expectation line of the equation. This may reflect that the older plantations h ave a somewhat better ability to manipulate the detrimental environment, thus allowing an op timal exploitation of the
soil resources. Compared to that of I. cylindrica grassland (coefficient of variation ranged from 34.65 to 94.85%) in the vicinity of the plantation syst ems, the variability of the
fine root biomass of A. mangium was higher. However, the vertical trend of theAcacia mangium plantations

32 variability of the root biomass distribution in the I. cylindrica grassland system was rather similar to that of 1-year-old A. mangium plantations. On the one hand, this high variability may be beneficial, if it reflects the abi lity of the system to adapt to the unfavorable environment so that the optimal utilization o f resources may still be maintained. On the other hand, it may be disadvantageous, if this variability has resulted from the disability of the system to manipulate its envir onment.

4.3.3 Biomass carbon distribution
Carbon content of the stand biomass varied from 27.9% to 45.6% (Table 4.5) depending on the tree compartment. These figures are slightly l ower than the assumption of 50% proposed by Brown and Lugo (1984) and Hamburg (2000). Compared to the root biomass of secondary and primary forests (43.9-46.6%) (Somme r et al . 2000), C content of the root biomass in this study (excluding thos e of fine root biomass) was quite comparable. Among those compartments, C content va riability of fine root and Figure 4.5: Relationship between soil bulk de nsity and variability of fine root biomass

of Acacia mangium plantation system (A) and Imperata cylindrica grassland (IC) in East Kalimantan, Indonesia; 1, 4 and 9 = 1-, 4- and 9- year old stands; E(CV) = expected coefficient of variat ion of the systems 0 20 40 60 80 100 120 140 160

1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 Soil bulk densityCoefficient of variation of fine root biomass(%)

E(CV) IC A1 A4 A9Coefficient of variationof root biomass (%)Acacia mangium plantations

33 leaf biomass was the highest, ranging from 27.9-34.2% and 39.1-43 .9% (coefficient variation of 10.9 and 7.7%) for the fine root and leaf biomas s, respectively. The variability of the C content in other compartments was considerably low (coefficient variation ranging from 0.7 to 2.8%). Excluding the C content of the fine root biomass, the C c ontent among tree compartments was not significantly different. This imp lies that sampling of tree compartments is only important in determining the dry matter of each compartment of the stand, and sampling in different compartments to deter mine their C content is not

necessary. Contrary to expectation, there was no significant diff erence in C content of the tree compartments across plantation age. This also im plies that sampling for different stand ages to determine their C content is unnecessary.

Table 4.5: Carbon content of tree compartments of diffe rent ages of Acacia

mangium stands in East Kalimantan, Indonesia

Root Stand age Fine Coarse Stem Branch Leaf (year) (%) 1 29.7 43.8 44.6 45.6 39.1 4 34.2 43.6 45.1 44.3 43.9 9 27.9 44.9 45.1 43.8 42.9 Mean 30.6a 44.0b 44.9b 44.5b 42.4b SD 3.3 0.9 0.3 1.3 3.3 n 9 7 6 7 8 SD = standard deviation, mean values followed by the same letters are no t significantly different at α = 0.05.
The C content of undergrowth biomass in the studied stands ranged from 37.3 to 41.6% (Table 4.6). Average C content of the woody undergrow th biomass was 40.9, 40.7, 39.3, and 38.9 for the root, stem, branch, leaves compar tment of the woody undergrowth, respectively and 38.8% for the herbaceous undergro wth. Nevertheless, there were no significant differences in C content amo ng the compartments. The variability of C content within compartments was consider ably low (coefficient of variation of 2.1, 2.9, 5.4, 3.3, and 4.6% for the root, stem, branch, leaves compartment of the woody undergrowth and herbaceous undergrowth, respective ly).Acacia mangium plantations

34 Table 4.6: Carbon content of undergrowth and litter stan ding stock under different

ages of Acacia mangium stands in East Kalimantan, Indonesia

Woody undergrowth Stand age Roots Stems Branches Leaves Herbaceous undergrowth Litter

standing stock (year) (%) 1 38.0 41.6 nd 38.8 40.8 35.4 4 41.5 41.2 39.3 38.4 37.3 34.4 9 40.5 39.5 nd 39.5 38.3 37.8 Mean 40.9a 40.7a 39.3a 38.9a 38.8a 35.8b SD 0.9 1.2 - 1.3 1.8 4.9 n 6 6 2 6 6 6 SD = standard deviation, nd = not determined; mean values followed by the s ame letters are not significantly different at α = 0.05.
Compared to that of trees and undergrowth, the C content of litter standing stock biomass was, however, slightly lower (average of 35.8%), but the variability was higher (coefficient variation of 13.6%). This implies tha t a larger number of samples is required for a better assessment of the C content of the litter standing stock.

Table 4.7: Total C distribution of different ages of Acac ia mangium plantation

system in East Kalimantan, Indonesia Stand age BGB AGB Litter Total RBGB RWUG RHU (year) (Mg ha -1 ) (%) Mean 3.6 7.2 0.6 11.4 31.5 5.3 15.2 1 SD 0.8 0.9 0.1 1.7 7.3 2.9 4.7 Mean 7.2 28.5 3.2 38.9 18.6 13.1 0.9 4 SD 1.5 0.7 0.6 2.5 3.8 1.3 0.2 Mean 14.2 62.1 2.2 78.6 18.1 0.4 0.1 9 SD 1.9 8.3 0.3 10.3 0.7 0.1 0.02 SD = standard deviation, BGB = belowground biomass C, AGB = aboveground biom ass C, RBGB = relative belowground biomass C to total, RWUG = relative woody undergrowt h biomass C to total C of the system, RHU = relative herbaceous undergrowth to total biomas s C to total C of the system.

Total biomass C distribution of the A. mangium plantation system is presented in Table 4.7. Both below- and aboveground biomass C increased persistently in line with age of the plantation. It was 3.6 and 5.5 Mg ha -1 in the 1-year-old plantation and 14.2 and 62.1 Mg ha -1 in the 9-year-old plantation, respectively. Total C stored in the plantation system increased from 9.6 Mg ha -1 in the 1- year-old plantation to 78.6 Mg ha -1 in the 9-year-old plantation. Compared to I. cylindrica grassland, where values were 7.5, 4.0, 3.6 Mg ha -1 for the total, below- and aboveground biomass C, respectively, it is clear that the total biomass C accumulated inAcacia mangium plantations

35 the plantation system has surpassed that of I. cylindrica grassland early in the beginning of the plantation. However, the curve of the annual ra te of C sequestered by the system is quite flat across plantation age (Figure 4.6). This im plies that when C sequestration is the concern, plantation management for more than 9 yea rs (harvesting expectation for pulp production) seems to be beneficial. Furthermore, if t he C of the stems as the harvested component is the concern, harvesting of a 9-ye ar-old A. mangium stand is considered too early, because it would not have reached the pe ak of its economic cycle. The average annual C sequestration in the biomass of th e system of 9.3 Mg ha -1

yr -1 was remarkably higher than that of riparian planted poplars of 2.9 Mg ha -1 yr -1 (Tufekcioglu et al . 2003).

With regard to the practical implication of the measurem ent of biomass C of A. mangium in forestry-based C offset projects, a simple and rel iable method should be established. The results in this study show that estimati on of the biomass of A. mangium stands from tree diameters is sufficiently accurate a nd reliable. Both aboveground and belowground biomass C of the stand could be well estimated with this method (Table 4.8). However, there is no parameter for simplifying the measurement of the biomass C Figure 4.6: Annual carbon storage in bio mass of Acacia mangium plantation system

in East Kalimantan, Indonesia ; TC = total biomass carbon, SC = stem biomass carbon 0 2 4 6 8 10 12

0 2 4 6 8 10 Plantation age (year)Annual carbon stored (Mg ha-1)

TC SCAnnual carbon stored (Mg ha-1)Acacia mangium plantations

36 of undergrowth, litter standing stock and fine roots of the plantation. There is a wide range of biomass values of undergrowth and litter standin g stock in A. mangium plantations, and they should, therefore, be measured di rectly in each specific stand. Among of the biomass compartments, measurement of fine r oot biomass is the most time consuming and labor intensive. The results show that there was a small variation of fine root biomass and biomass C among plantation ages, b ut the variation within sites was considerably high (see Figure 4.5). This implies that e stimation of fine root biomass and biomass C with a small sampling size is subject to hi gh errors. Applying a sample size of 153 auger points resulted in coefficients of varia tion of 108.0 ± 21.0% and 57.1 ± 22.3% for within and among sites, respectively. However, fine root biomass C ranged from 2.8 to 3.4 Mg ha -1 , producing less than 5% of the total biomass C of the matur e plantation system. Therefore, estimations of fine r oot biomass C of A. mangium plantation systems with a factor of 4% of the total bio mass C of the system for the mature plantations or adopting a magnitude of 3.0 Mg ha -1 for the young plantations
would be sufficient and is recommended.

Table 4.8: Allometric equations for biomass C (Mg ha -1 ) estimation of Acacia

mangium plantations in East Kalimantan, Indonesia, based on tree diameter (DBH, cm) Dependent Variable a b r 2 p Coarse and medium roots C 0.0051 2.6198 0.9669 < 0.001 Stem C 0.0599 2.2971 0.9111 < 0.001 Branch C 0.0752 1.6512 0.9428 < 0.001 Leaf C 0.0265 1.8208 0.8941 < 0.001 Aboveground biomass C 0.1188 2.1546 0.9258 < 0.001 Total biomass C 0.1143 2.2219 0.9441 < 0.001 Regression model: Y = a * DBH b

There is little information on the total biomass and C s torage of plantations in the tropics. Most publications deal with aboveground biomas s of stands (excluding biomass of undergrowth and litter standing stock, an exce ption to studies of Syahrinudin 1997 and Ruhiyat 1989) and information on belowground biomass and C stock is very scarce. Based on available data on aboveground biomass of A. mangium plantations presented in Table 4.3 and the assumption of a C content o f 43.3% (overall average of CAcacia mangium plantations

37 content of A. mangium plantations in this study), a general rate of C accumu lated in this plantation system was constructed (Figure 4.7).

Figure 4.7 shows that general accumulation of C in above ground biomass of A. mangium stands follows the Gompertz Relation (Y = a*exp(-exp(b- cx)), a = 75.18, b = 1.38, c = 0.39, r 2 = 0.58 and p < 0.001). Calculation of the general rate of C sink in t he aboveground biomass of the stands gave an average of 8.0 Mg ha -1 yr -1 , which is slightly higher than the calculation based on the data i n the present study of 6.5 Mg ha -1

yr -1 . These figures are, however, lower than the estimatio n by ISME (1999) of 12.5 Mg
ha -1 yr -1 . Compared to the total biomass C sink in this study of 9. 3 Mg ha -1 yr -1

, aboveground biomass C of the stand produced 70% of the total C accumulated in the system. Applying this value, the general rate of total C s ink of A. mangium plantation system of 11.4 Mg ha -1 yr -1 was calculated. With regard to timber production, if there is no requirement for a minimum tree dimension and the price for the timber is flat across tree dimension and age, the best cutting cycle would be at the age of 6 years (Figure 4.8), because at this point of time, the CAI (Current Annual Increment) crosses the MAI

0 10 20 30 40 50 60 70 80 90

0 2 4 6 8 10

Plantation age (year) 0 2 4 6 8 10 12CAI and MAI (Mg ha-1yr-1)Aboveground biomass C (Mg ha-1)

Figure 4.7: General r ate of carbon sink in Acacia mangium plantation system;

references see Table 4.3Acacia mangium plantations

38 (Mean Annual Increment) indicating the highest stand grow th rate and revenue for the plantation. In contrast to the persistent increase of the belowgro und biomass, the relative contribution of belowground biomass C to total biomass C dec reased in the older stages of the plantation. However, the contribution of below ground biomass C of the 4-yearold stands was quite comparable to that of the 9-year-old stands. This suggests that the contribution of the belowground biomass C in the older st ands is fairly stabile (average 18.4% ± 2.7%). As sampling of the belowground biomass C is ti me and labor consuming, this figure could be adopted for estimation of th e belowground biomass C of similar plantation systems elsewhere. The ratio of belowground to aboveground biomass (root/shoot ra tio) of forest systems is strongly influenced by stand age and site char acteristics (Cairns et al . 1997). However, the results show that the range of this rati o is relatively narrow for the older plantations (4- and 9-year-old stands) (0.23-0.27). These va lues are in the range of those of temperate forests of 0.15-0.40 reported by (Cairns et al . 1997). In general, relative contribution of both woody and herba ceous undergrowth biomass C decreased with plantation age. The contributi on of woody and herbaceous undergrowth biomass C dropped from 6.7 and 18.9% in the first ye ar to 0.36 and 0.08% in the ninth year, respectively. This drop relates to the canopy development of the stand,
since well established A. mangium stands have a dense canopy, and there is little available light for the development of undergrowth. Nev ertheless, due to the high mortality rate of the stands, contribution of woody under growth in the 4-year-old stands was remarkably high (13.2%).
The distribution of total biomass C in A. mangium stands is presented in Table 4.9. Excluding that of the fine root compartment, total biomas s C of all compartments of the stand increased in line with the plantation age. Of t hose compartments, the stem compartment stored the largest amount of biomass C, follo wed by the branch, coarse root and leaf compartments. However, the biomass C in the coarse root compartment in the 9-year-old stand was higher than that in the branch compartment. It is interesting to
note that the ratio between the biomass C of the coar se root and stem compartment seemed to be maintained in the specific narrow range. It was 20.5%, 20.9% and 21.9%Acacia mangium plantations

39 for the 1-, 4-, and 9-year-old stands, respectively. This s trongly implies that estimates of coarse root biomass C from that of the stem compartment are quite credible.

Table 4.9: Total C distribution in Acacia mangium stands of different ages in East

Kalimantan, Indonesia Stand age Fine

root Coarse root Stem Branch Leaf AGB BGB Total (year) (Mg ha -1 ) Mean 2.8 0.6 2.9 1.5 0.7 5.0 3.4 8.5 1 SD 0.8 0.1 0.6 0.3 0.1 1.0 0.9 1.9 Mean 3.2 3.5 16.8 4.7 2.1 23.6 6.7 30.3 4 SD 1.5 0.1 0.7 0.2 0.1 0.9 1.4 1.5 Mean 3.4 10.7 49.0 8.6 4.4 61.9 14.2 76.1 9 SD 0.6 1.6 7.0 0.8 0.5 8.3 1.9 10.1 SD = standard deviation, BGB = belowground biomass C, AGB = aboveground biomass C; three replications of each stand age; fine roots were defined to depth of 3 m.

Total fine root biomass C of the A. mangium plantation system ranged from 2.8 Mg ha -1 in the first year to 3.4 Mg ha -1 in the ninth year. However, there was no significant difference in fine root biomass C among the pl antation ages. The overall average of total fine root biomass C was 3.2±0.9 Mg ha -1

.

Table 4.10: Total C distribution of litter standing stock a nd undergrowth in Acacia

mangium stands in East Kalimantan, Indonesia Aboveground biomass C Stand age Belowground

biomass C WU HU Total Litter standing stock C (year) (Mg ha -1 ) Mean 0.17 0.43 1.73 2.16 0.58 SD 0.13 0.20 0.53 0.73 0.12 1 n 6 6 9 3 9 Mean 0.47 4.61 0.34 4.95 3.19 SD 0.10 0.57 0.05 0.61 0.62 4 n 6 6 9 3 9 Mean 0.04 0.24 0.07 0.30 2.21 SD 0.01 0.08 0.03 0.10 0.30 9 n 6 6 9 3 9 WU= woody undergrowth, HU = herbaceous undergrowth

Although undergrowth biomass C played only a minor contrib ution to the total biomass C of the system, it may have an important rol e in litter production of the system, which in turn may benefit the enrichment of th e soil C of the system. Since undergrowth grows fast and has a short life cycle, a cons iderable amount of litter mayAcacia mangium plantations

40 have been contributed. This hypothesis is supported by the dat a (Table 4.10) showing that a large amount of litter standing stock C was foun d in the 4-year-old stand, which had a considerably high amount of undergrowth biomass C. H owever, litter production of a plantation system does not solely rely on the pr esence of undergrowth but to some extent also depends on the physiological characteristics of the stands.

4.3.4 Soil carbon distribution The patterns of soil C distribution vary highly with soi l age, soil texture, rainfall and temperature patterns, and vegetation type. The vertical d istribution in both I. cylindrica grassland and A. mangium plantation systems was quite similar to that in previ ous studies reported by Syahrinudin (1997) and Ruhiyat (1989) in soils in t he same region. Soil C content decreased in line with the soil depth (F igure 4.9) and was highly depth dependent (r 2 ranged from 0.97 to 0.99). The slope of the decrease in the s oil C content is steep in the upper 50 cm of the soils and more gentle in the deeper soils. Nevertheless, a distinct difference in the vertical s oil C distribution can be observed
between I. cylindrica grassland and A. mangium plantation systems. Compared to that
of the A. mangium plantation system, the slope of the decrease in I. cylindrica grassland was less steep in the upper 50 cm but m steeper for the lo wer part of the soil profile (see Figure 4.8). This demonstrates the strong influence of fine root biomass on soil C content. Although the vertical distribution of soil C i s determined by soil depth, spatial variation seems to be dictated by the fine root biomass d istribution (r 2 of 0.83-0.99). Soil C content is the result of litter (above- and b elowground) production defined by vegetation type and development stage, and soil re spiration controlled by root respiration and by decomposition of litter and soil organic matter. Soil physical properties such as texture and structure may control the respiration of the soils (De Jong and Schappert 1972). Soil temperature and moisture are the mo st important factors regulating soil respiration (Kicklighter et al . 1994; Lloyd and Taylor 1994; Howard and Howard 1993). However, the results in this study do not show a significant difference in soil C content in the upper part of the soil (top 50 cm), w hich is the layer affected most strongly in terms of soil temperature by the conversion of I. cylindrica grassland into A. mangium plantation. It seems that the influence of the plant ation on soil temperature and moisture was offset by the effect of belowground litter production. In the upper 50Acacia mangium plantations

41 cm soil, the fine root biomass of I. cylindrica grassland (2.5 kg dm -3 ) was much higher
than that of A. mangium (1.4-1.6 Mg dm -3 ). However, the roots of I. cylindrica grassland, which were confined to a shallow top layer of t he soil (1.8 m) may explain the lower soil C content in the deeper soils in contras t to the fine roots of A. mangium , which extend to a depth of 3 m.

Soil C storage in this study is in the range of that report ed in previous studies (Mackensen 1998; Syahrinudin 1997; Bremen et al . 1990; Ruhiyat 1989). Total C
stored in the soils in A. mangium plantation systems ranged from 158.6 – 246.2 Mg ha -1

3 m -1 (Figure 4.9). These values are somewhat higher than the values of primary and secondary forests of 130.0 – 145.0 Mg ha -1 3 m -1 reported by Sommer et al . (2000). The
C values in the soils in the I. cylindrica grassland ranged widely (from 120.3 Mg ha -1 3 Figure 4.8: Vertical distribution of soil C content (%) in diff erent ages of Acacia mangium stands in East Kalimantan, Indonesia 0

50

100

150

200

250

300 0.00 0.20 0.40 0.60 0.80 1.00 1.20 1.40 1.60



### Carbon content (%)Soil depth (cm)

Imperata cylindrica

Acacia mangium 1-year-old stand Acacia mangium 4-year-old stand Acacia mangium 9-year-old stand Imperata cylindrica

Acacia mangium

Acacia mangium

Acacia mangiumAcacia mangium plantations

42 m -1 in Sumatra to 150.6 Mg ha -1 3 m -1 in East Kalimantan). However, since the A. mangium plantations are located in East Kalimantan, the bas e line for all calculations of the soil C sink of the plantations is the soil C stora ge of I. cylindrica in East
Kalimantan.

Soil C storage is largely dependent on environmental, biogeoc hemical and land management factors. Different land use and manageme nt practices influence soil properties such as soil temperature, moisture, microbial bi omass, organic matter and fine root biomass, which in turn affect the magnitude of soi l respiration (Lee and Jose 2003; Raich and Tufekcioglu 2000; Kelting et al . 1998) and soil C dynamics. Trees can substantially increase the organic matter input into the s ystem through the turnover of leaves and roots (Jose et al . 2000). The results in this study show that the conversion of I. cylindrica grassland into A. mangium plantation considerably increased the soil C storage. The rate of soil C accumulation was 1.7 – 3.0, 3. 4 – 4.6 and 3.5 – 4.9 Mg ha -1

yr -1 for the first, second and third 1-m-depth, respectively. There was a slight decrease Figure 4.9: Soil C storage in Imperata cylindrica grassland and Acacia mangium

plantation systems in East Kalimantan, Indonesia 0 50 100 150 200 250 300 350

0-50 50-100 100-200 200-300 0-300 

### Soil Depth (cm)Total carbon (Mg ha-1) Imperata cylindrica Acacia mangium, 1-year-old stand Acacia mangium, 4-year-old stand Acacia mangium, 9-year-old stand Acacia mangium , Acacia mangium , Acacia mangium ,Total carbon (Mg ha-1)



### Soil depth (cm)Acacia mangium 

### plantations

43 at a depth of 0-50 and 50-100 cm during the early s tages of plantation establishment, which may be related to the lower litter production . However, the deeper soils experienced an increase in C storage from the begin ning of the plantations (Figure 4.9). An increase in soil C accumulation (0-100 cm) from 0.66 to 1.17 Mg ha -1 

### yr -1 

### by incorporating legume trees in a grass pasture was r eported by Tarré et al 

### . (2001). Sataye
et al. 

### (2001) estimated an increase in soil C of 0.5 to 3 .0 Mg ha -1 

### yr -1 

### in forest plantations in the tropics. A magnitude of soil org anic matter sink of 1.1 Mg ha -1 

### yr -1 

### was reported by Lugo et al 

### . (2004) in restored neotropical forest systems in Puerto Rico. The most important finding of this study is that th e conversion of I. cylindrica 

### grassland into A. mangium 

### plantation led to a much higher C sequestration in deep soils than in the upper soil layers. This finding is in c ontrast to the proposed soil C change measurement in forestry offset projects to a depth of only 1 m (Hamburg 2000). While most previous soil C studies concentrate on the upp er soil layers down to a maximum depth of 2 m (Tufekcioglu et al 

### . 2003; Tarré et al 

### . 2001; Brown and Lugo 1990; Fisher
et al 

### . 1994; Moraes et al 

### . 1995), the results of this study confirm the find ing of Sommer
et al 

### . (2000), Trumbore et al 

### . (1995) and Nepstad et al 

### . (1994) showing the importance of root penetration in deep soil layers for C seque stration. Moreover, the C sequestered in deep soils could be more beneficial than that se questered in shallow soils, because soil organic matter of deep soils is more resistant to decomposition and thus has a longer resident time (Gaudinski et al 

### . 2000; Van Dam et al 

### . 1997). The overall rate of soil C sequestration by this conversion was 8.6 – 1 2.7 Mg ha -1 

### yr -1 

### . These figures are indeed much higher than those reported in former st udies. With a rate of biomass C accumulation of 9.3 Mg ha -1 

### yr -1 

### , an aboveground litter production of 3.2 Mg ha -1 

### yr -1



### , and a fine root biomass production ranging from 66 –70% of net primary production (Fogel 1985; Grier et al 

### . 1981), a magnitude of 41.7 Mg C ha -1 

### yr -1 

### could be allocated for fine root production. This suggests that the ab ove values of soil C sequestration are still reasonable. Furthermore, it should be taken i nto account that most of the sequestration (more than 75%) is assigned to the de eper part of the soils (1-3 m depth). If the plantations are harvested after 9 years (exp ected harvesting age for pulp production), a soil C sink of 77.4 – 113.9 Mg ha -1 

### could be expected. These values are higher than for C sequestered in the biomass of the plantation system amounting to only 78.6 Mg ha -1



### .Acacia mangium 

### plantations

44 4.3.5 Carbon distribution in Acacia mangium plantation system


### Carbon content of the stand biomass of the A. mangium 

### plantation varied from 27.9% to 45.6% depending on the tree compartment. Variabilit y was highest in fine root and leaf biomass, ranging from 27.9-34.2% and 39.1-43.8% (co efficient variation of 10.9 and 7.7%), respectively. Variability in other compartme nts was considerably low, with coefficient variations ranging from 0.7 to 2.8%. Th e C content of undergrowth biomass of 37.3 to 41.6% was quite comparable to that of st and biomass. Compared to that of trees and undergrowth, the C content of litter stan ding stock biomass was, however, slightly lower (average of 35.8%), but variability was higher (coefficient variation of 13.6%).

Below- (to depth of 3 m) and aboveground C stocks i ncreased substantially from 162.2 and 7.8 Mg ha -1 

### for the 1-year-old plantation to 260.4 and 64.4 Mg ha -1 

### for the 9-year-old plantation, respectively (Figure 4.1 0). Compared to I. cylindrica 

### grassland with 154.6 and 3.6 for the below- and abo veground C stocks, respectively, it
is clear that the level of C stocks of the A. mangium 

### plantation was higher than that of
the I. cylindrica 

### grassland since the early stages of the plantation . Of the C stored in the -100 -80 -60 -40 -20 0 20 40 60 80 Carbon stock (Mg ha -1 ) Belowground biomass Soil Litter Undergrowth Crop

Figure 4.10 : Carbon distribution of Imperata cylindrica grassland and Acacia

mangium plantation systems in East Kalimantan, Indonesia; belowground C stock was defined to depth of 3 m; va lues for the above

and belowground C of the Imperata cylindrica grassland were considered as the baseline for the plantations Belowground baseline Aboveground baseline

60 120 180 240 300 Belowground Aboveground A. mangium , 9-yr-old

A. mangium , 4-yr-old

A. mangium , 1-yr-old

Imperata cylindricaAcacia mangium 

### plantations

45 biomass of the plantation systems, 18% (4- and 9-ye ar-old stands) to 32% (1-year-old stand) was allocated to the belowground biomass. Th e rate of C accumulation in the
biomass of the A. mangium 

### plantation systems averaged 9.3 Mg ha -1 

### yr -1



### . Soil C content of the systems decreased in line wit h soil depth and was highly depth dependent (r 2 

### ranged from 0.97 to 0.99 and p 

### of < 0.001). However, spatial variation seems to be dictated by the fine root bio mass distribution in the system (r 2 

### = 0.83-0.99 and p 

### < 0.001).
Conversion of I. cylindrica 

### grassland into A. mangium 

### plantation led to a much higher C sequestration in the deep soils. The rate was 1.7-3.0, 3.4-4.6 and 3.5-4.9 Mg
ha -1 

### yr -1 

### for the depths 0-1, 1-2 and 2-3 m, respectively. A potential soil C sink of 77.4- 113.9 Mg ha -1 

### could be expected by this conversion. More than 75 % of this amount was allocated to the deep soils (100-300 cm soil depth) . Together with the C sequestered in the biomass of the plantations, C sequestration of 156.0-192.5 Mg ha -1 

### could be
achieved. It is interesting that most of the C stored in the plantation system was allocated to the belowground stock (soil and belowground biom ass C), a fact that has been ignored in most previous works, due probably to the difficulty in the assessment of this component. The results show that belowground C cont ributed to more than 95% in the early stages of the plantation (1-year-old) and the n declined with age to only 80% in the 9-year-old plantation (Table 4.11). However, the re lative contribution of the belowground C stock of the A. mangium 

### plantations was lower than that of the I. cylindrica 

### grassland system (98%).

Table 4.11: Below- and aboveground C stock distribu tion of Imperata cylindrica



### grassland and Acacia mangium 

### plantation systems in East Kalimantan, Indonesia Belowground

Soil Biomass Aboveground biomass Belowground / total System (Mg ha -1 ) (%) Imperata cylindrica 150.6 4.0 3.6 97.7

1-year-old 158.6 3.6 7.8 95.4 4-year-old 196.9 7.2 31.7 86.6 Acacia mangium 9-year-old 246.2 14.2 64.4 80.2 Belowground C stock was defined to depth of 3 mAcacia mangium 

### plantations

46 4.4 Conclusions


### Biomass and biomass C of the A. mangium 

### plantation system increased with age to a level much higher than that of I. cylindrica 

### grassland, implying that the conversion of marginal lands into plantations should be encourage d. In term of greenhouse gas mitigation, these plantations may lower the magnitu de of atmospheric CO 2 

### not only through sequestration, but also by preventing an in crease in atmospheric CO 2 

### through the use of the biomass produced in this plantation for bio-fuel replacing the use of fossil
fuel. The deep penetration of the roots in A. mangium 

### plantations likely has important implications for C sequestration in the d eeper soils. Soil C storage increased with plantation age to almost twice that of I. cylindrica 

### grassland, suggesting that the establishment of plantations is beneficial not only in terms of C sequestration but also in terms of land rehabilitation, as a considerable amo unt of nutrients may associate with C stored in the system. Furthermore, an increase in s oil C storage may improve soil physical properties such as stability of soil struc ture and water holding capacity, and soil chemical properties such as nutrient availabil ity. It could also increase CEC and thus decrease the risk of toxicity through certain elements, e.g., Al, which in turn would increase the fertility status of the respective soi ls.
Conversion of I. cylindrica 

### grassland into A. mangium 

### plantations could sequester 78.4 Mg C ha -1 

### in the plantation biomass during a period of 9 yea rs. The average rate of C accumulation in the biomass of th e plantation was 9.3 Mg ha -1 

### yr -1



### . Compared to total C stored in the biomass of I. cylindrica 

### grassland of 7.6 Mg ha -1 

### , an additional 70.8 Mg C ha -1 

### could be expected in the biomass alone. Together w ith that sequestered in the soil (to a depth of 3 m) of 95.7 Mg ha -1 

### , a magnitude of C sequestration of 166.5 Mg ha -1 

### could be achieved.

### Oil palm plantations

47 5 OIL PALM PLANTATIONS

5.1 Introduction 

### There is an increasing interest in the importance o f the role of terrestrial ecosystems in the global C budget. Tropical forests store a large amount of C (428 Pg in soil and vegetation, Watson et al 

### . 2000) and serve as both a sink for and source of atmospheric C. Land-use change and forestry activities, primari ly deforestation of the tropical forests, are a significant source of CO 2 

### emissions, representing 1.6 Pg yr -1 

### of the total anthropogenic emission of 6.3 Pg yr -1 

### (Watson et al 

### . 2000; Houghton et al 

### . 1995). Plantations, either forests or woody perennial crop s, have led to a decrease in the C pool to a magnitude of 50% lower than the ori ginal forest stock (Lasco 2002). Oil palm plantations are becoming the center of environ mental controversies with regard to deforestation in the tropics. They have been made r esponsible for most of the deforestation in South East Asia. Nevertheless, thi s would not be the case if the plantations were established in degraded lands or i n unproductive forests. It is obvious that whether such plantations facilitate the sink o r emission of CO 2 

### depends on the initial condition of the land on which the plantati ons are established. The oil palm as a perennial crop has become importa nt, firstly, as a major source of oils and fats for human food, secondly, a s animal feeds, and, thirdly, for manufacture of many domestic products such as cosme tics, soaps and detergents (Khalid et al 

### . 1999). The establishment of large-scale monocultu re oil palm plantations in Indonesia began in 1985, when they covered about 600.000 ha. In 1999, the area had expanded to about 3 million ha (Glastra et al 

### . 2002; Wakker 2000). Production and trade in oil palm commodities has ex panded rapidly in response to an increasing world population and impr oved living standards. The global production of palm oil has increased very rapidly, more than doubling between 1970 and 1980. In 1980, palm oil became the world’s seco nd most important vegetable oil after soybean. Oil palm is currently one of the major sources of v egetable oil in the world. The crop ranks second among the world oil productio n crops and first in the international market of vegetable oils and fats. Th is crop is grown in lowlands of the humid tropics (15° N - 15° S) with an evenly distri buted rainfall of 1,800-5,000

### Oil palm plantations

48 mm/year and is well adaptable to a wide range of so ils and to low pH, but sensitive to high pH (above 7.5) and to stagnant water (Wichmann 2001). These plantations show a very high productivity (La made and Setyo 2002) and there is evidence of the success of plantations in degraded land such as I. cylindrica 

### grasslands in Sumatra and Kalimantan. There are abo ut 7.5-8.5 million ha of I. cylindrica 

### grassland distributed over many islands in Indonesi a, an area which would be sufficient for the extensive expansion of oil palm and forestry plantations planned by the government. These plantations have a high poten tial to be promoted in the world C trade and may, therefore, increase the foreign exch ange earnings of the country. However, the question as to how much CO 2 

### can be sunk by converting I. cylindrica 

### grassland into plantations is still open. To answer this question, studies on the biomass and C storage of oil palm plantations compared to t hose of I. cylindrica 

### grassland are of utmost importance. In this study, efforts are focused on quantifying t he biomass and C accumulated in the oil palm plantations at differen t ages, as well as biomass and C distribution in the plantations.

5.2 Methodology 

### Sampling for the biomass and C storage inventory of oil palm plantations was carried
out on sites in Sumatra and East Kalimantan. Howeve r, due to the time and labor constraints, sampling for aboveground biomass and C stock was conducted for plantations in Sumatra alone. Three 0.05 ha circula r plots (r = 12.6 m, consisting of 7 oil palm trees; Figure 5.1) were established in 3-, 10- , 20- and 30-year-old oil palm plantations in Sumatra and 3- and 10-year-old plant ations in East Kalimantan. Extreme variation in stand density, undergrowth coverage an d land slope was avoided. Thus, 12 plots were established in Sumatra (4 stand ages, 3 replications) and 6 plots in East Kalimantan (2 stand ages, 3 replications). To minim ize errors induced by the variation of soil type, all observation plots were establishe d in loamy to clayey Ultisols, as this soil type is the most common in these regions. For the biomass estimation, a palm tree from each c rop age, with diameter and height approximately equivalent to the mean of the population, was harvested and uprooted. Total biomass of the harvested trees was weighed and samples were drawn

### Oil palm plantations

49 from the different components (trunk base, trunk, f rond base, petiole, rachis, leaflet, spear, cabbage and inflorescence) and weighed. Samp les were dried to a constant weight at 60°C to obtain the total dry weight of ea ch component. Thereafter, samples were ground to pass a 0.2-mm sieve for chemical ana lysis. The trunk base was defined as the part of trunk developed belowground includin g roots developed underneath the trunk base to a depth of 1 m.

Nine 0.5 m x 0.5 m sub-plots were randomly establis hed to assess the biomass of the herbaceous undergrowth occupying the respect ive plot. All undergrowth in these sub-plots was harvested and weighed to calculate th e total fresh weight. Samples were 50 cm

Sub-plot for undergrowth inventory and litter standing collection Soil profile observation point Observation plot Root sampling zone Oil palm t ree

C Oil palm tree

C

B Oil palm tree

B Debris piling zone

Root sampling A 1 B 1 C 1

D 1 E 1

F

A 2 C 2

B 2 D 2 E 2 A 3 B 3 C 3 D 3 E 3 A 1 B 1 C 1

D 1 E 1

F

A 2 C 2

B 2 D 2 E 2 A 3 B 3 C 3 D 3 E 3

A 1 B 1 C 1

D 1 E 1

F

A 2 C 2

B 2 D 2 E 2 A 3 B 3 C 3 D 3 E 3 Root sampling

Figure 5.1: Layout for the biomass and carbon storage sampling on oil palm

plantation in Sumatra and East Kalimantan, Indonesi a Root sampling

### Oil palm plantations

50 drawn representatively for the total dry weight ass essment. Thereafter, the same procedure as for the tree samples was followed. Litter standing stock was defined as the litter in the L and F layers of the soils, because the H layer was incorporated into the soil sample. Sampling for litter standing stock was carried out as for undergrowth sampling. All litter in the sub-plots was collected, sorted into woody and non-woody componen ts and weighed (fresh and air dry). A small sample from each component was drawn and processed following the same procedure as for tree samples. To estimate the total biomass of the system, root b iomass was sampled and collected at 16 drilling points in each subplot (th ree subplots/plot) to a depth of 5 m (using an 8-cm-diameter root auger in 15 cm increme nts) distributed in a systematical sampling on the basis of the distance to the closes t trunk – 10 cm (A), 100 cm (B), 200 cm (C), 300 cm (D), 450 (E) and 520 cm (F). Roots w ere separated from the soil core by means of water saturation and flushing. A soil profile was established nearby the center of one of the three plots of each plantation age for observation of soil morphol ogical characteristics and sampling of soil bulk density. Soil sampling and analyses we re carried out following the procedure described in Section 3.2. Data were analyzed with analysis of variance (ANOVA ) and means were compared with the LSD-test procedure.

5.3 Results and discussions
5.3.1 Biomass distribution 

### Both below- and aboveground biomass of the system i ncreased persistently with plantation age. Total biomass of the system was 40. 9, 117.9, 157.9 and 204.3 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations (T able 5.1), respectively. Compared to
the total biomass of I. cylindrica 

### grassland near the plantations of 16.9 Mg ha -1 

### , the total biomass of the oil palm plantations already surpassed that of I. cylindrica 

### in the very early stage of the plantation. This suggests that c onversion of I. cylindrica 

### grassland into oil palm plantation is beneficial if biomass a nd land rehabilitation is the concern. Of the compartments of the system (crop, undergrowth a nd litter standing stock), the crop contributed the highest amount of biomass, accounti ng for 85.6-94.3%. Undergrowth

### Oil palm plantations

51 contributed 1.4-2.9% of the total biomass and litte r standing stock 4.3-11.5%. Despite the minor contribution of these compartments to the total biomass, they could play an important role in the functioning of the system suc h as controlling soil erosion and surface run-off, and promoting soil C and nutrient cycles as well as soil biological activities. The undergrowth dry matter of a 5-year- old oil palm plantation can range from 2-3 Mg ha -1 

### to 7-8 Mg ha -1 

### depending on the extent of weeding (Chen et al 

### . 1991) and this could decline to between 0.5 and 1 Mg ha -1 

### in the consecutive years. The values in this study ranging from 1.2 to 3.6 Mg ha -1 

### are still in this range.

Table 5.1: Above- and belowground biomass distribut ion of different ages of oil

palm plantation systems in Sumatra, Indonesia

Aboveground biomass Age Belowground

biomass Litter Undergrowth Crop Total biomass Relative

belowground to total (year) (Mg ha -1 ) (%) 3 13.3 4.7 1.2 21.7 40.9 32.5 10 25.0 5.1 1.6 86.3 117.9 21.2 20 40.1 15.7 3.6 98.4 157.9 25.4 30 52.4 17.9 3.2 130.7 204.3 25.6 Belowground biomass was defined to depth of 5 m.



### Aboveground crop biomass increased from 21.7 Mg ha -1 

### in third year of the plantation to 130.7 Mg ha -1 

### for the 30-year-old plantation. Aboveground biomas s in previous studies varies widely from 68.9 to 86.0 Mg ha -1 

### for a 25-year-old oil palm (Nordin 2002) and a 23-year-old plantation (Khalid et al 

### . 1999) to about 192.0 to 202.0 Mg ha -1 

### for the 14- and 19-year-old oil palm (Sitompul and Hairiah 2000), respectively. Rees and Tinker (1963) reported a magnitude of abov eground biomass in 7- to 22-yearold oil palm plantations of 26.2-84.4 Mg ha -1 

### . It is obvious that the aboveground biomass of the plantation systems is variable and m ay be influenced by the inherent characteristics, pedoagroclimatic conditions and ma nagement. Of the crop aboveground biomass, the trunk contribu ted 56.7 to 75.3%. These figures are considerably higher than those reported by (Khalid et al 

### . 1999a) of 48% but are in agreement with those reported by Rees and Ti nker (1963) of 7- to 22-year-old oil palm plantations of 42.8-73.0%. Trunk biomass in th is study ranged between 13.1 and 94.3 Mg ha -1 

### for the 3- and 30-year-old plantations, respective ly (Table 5.2). Compared to the trunk biomass reported in previous studies o f 36.7-46.8 Mg ha -1 

### for 22- to 27.5-

### Oil palm plantations

52 year-old plantations (Khalid et al 

### . 1999a; Corley et al 

### . 1971; Tinker and Smilde 1963), the results are considerably higher. However, they are in agreement with the 88.5 Mg
ha -1 

### of a 15-year-old plantation reported by Ng et al 

### . (1968).

Table 5.2: Biomass distribution of the oil palm tre es of different ages in Sumatra,

Indonesia Belowground Aboveground Age Root Trunk base Trunk Frond base Rachis Leaflet Others (year) (Mg ha -1 

### ) 3 12.0 1.3 13.1 1.2 4.6 1.4 1.40
10 16.1 8.9 49.0 20.5 9.9 4.8 2.16
20 27.6 12.5 74.1 2.3 15.8 4.3 5.71
30 35.7 16.7 94.3 3.3 24.2 6.4 6.54 Trunk base, defined as part of trunk developed belowground including roots de veloped underneath the trunk base to depth of 1 m; rachis, including petiole; others, includi ng spear, cabbage and inflorescences; root biomass was defined to depth of 5 m.



### The biomass of the frond base increased substantial ly from 1.2 Mg ha -1 

### in the 3-year-old plantation to 20.5 Mg ha -1 

### in the 10-year-old plantation, then declined to on ly 2.3 and 3.4 Mg ha -1 

### in the 20- and 30-year-old plantation, respectivel y. There was an increase in frond base biomass from 3- to 10-year-o ld plantations in line with the increase in the trunk dimension of the crops. Howev er, due to the abscission of the frond base of the older plantations (in most cases, frond bases begin to be detached from the trunk at the plantation age of 13 to 18 years), the biomass of the frond base of the older plantations (20- and 30-year-old) was pronoun cedly lower. Khalid et al 

### . (1999a) reported a magnitude of frond base of a 23-year-old oil palm plantation of 129.1 kg palm -1 

### equivalent to 17.6 Mg ha -1 

### . This is quite comparable to the results in this s tudy for the 10-year-old plantation (23.7%), which is in agreement with the 18-22% reported in the previous studies (Khalid et al 

### . 1999a; Henson 1993). Rachis biomass, including petioles, increased from 4.6 to 9.9, 15.8 and 24.2 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations, respectively. Compared to the values reported by Khalid et al 

### . (1999a) for a 23-year-old oil palm plantation of 110.5 to 127.9 kg palm

-1 

### equivalent to 15.0-17.4 Mg ha -1 

### and Rees and Tinker (1963) for 7- to 22-year-old oil palm plantations of 42.7-101.8 kg p alm -1 

### equivalent to 5.8-13.8 Mg ha -1



### ,

### Oil palm plantations

53 the results in this study are still comparable. The relative contribution of the rachis was considerably high in the young plantation. It was 2 1.1% in the 3-year old plantation and dropped to only 11.4% in the 10-year-old plantation as the other compartments of the crop developed, especially trunk and frond base. Ne vertheless, there was an increase in the contribution of rachis to the crop aboveground biomass of the older plantations. It was 16.1 and 18.5% for the 20- and 30-year-old plan tations, respectively. Similar values (17.6-20.4%) in a 23-year-old oil palm plantation i n Malaysia were reported by Khalid et al 

### . (1999a) and (12.9-22.2%) in a 7- to 22-year-old p lantation (Rees and Tinker 1963). Leaflet biomass of the plantation system increased from only 1.42 Mg ha -1 

### (3- year-old plantation) to 4.82 Mg ha -1 

### (10-year-old plantation), then fluctuating between 4.34 Mg ha -1 

### (20-year-old plantation) and 6.44 Mg ha -1 

### (30-year-old plantation). These figures are still comparable to those of 7- to 22-y ear-old oil palm plantations (24.7-48.5 kg palm

-1 

### equivalent to 3.4-6.6 Mg ha -1 

### ) (Rees and Tinker 1963) and of a 23-year-old plantation (7.9 Mg ha -1 

### ) (Khalid et al 

### . 1999a). However, the relative contribution of leaflet biomass was somewhat low, ranging from 4.4- 6.5%. Compared to the values reported by Khalid et al 

### . (1999a) of 9.3% of the crop aboveground biomass a nd by Rees and Tinker (1963) of 8.0-12.8%, these are somewhat lower. Biomass of other components (spear, cabbage and inf lorescences) increased from only 1.4 to 2.2, 5.7 and 6.5 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantation systems, respectively. The relative contribution of these components was rather high in the early stage of the plantations. It was 6.4% for the 3-year-old plantation, decreased to 2.5% for the 10-year-old plantation and to only 1.9 % for the 20- and 30-year-old plantations. Khalid et al 

### . (1999a) reported a slightly higher contribution o f 3.2% in a 23- year-old oil palm plantation in Malaysia. Root biomass of the system was 12.0, 16.1, 27.6 and 35.7 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations, respectively. Compared to the root biomass of a 23-year-old plantation of 16.00 Mg ha -1 

### reported by Khalid et al 

### . (1999b) and that of a 27.5-year-old of 17.8 Mg ha -1 

### reported by Corley et al 

### . (1971), the root biomass of mature oil palm in this study was considerably high . However, Khalid et al 

### . (1999b) defined the root biomass to a depth of 60 cm and Co rley et al 

### . (1971) to a depth of 90 cm, while in this study the total depth was 5 m. Biomass to a depth of 90 cm was 7.7, 10.1, 18.2 and 24.2 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations,

### Oil palm plantations

54 respectively. These figures are quite comparable to the findings of Khalid et al 

### . (1999b) and Corley et al 

### . (1971). Sommer et al 

### . (2000) reported a similar root biomass in a 9- year-old oil palm plantation in Eastern Amazon (14. 0 Mg ha -1 

### 6m -1 

### ). Roots contributed 14.4-34.2%, and together with the trunk base produc ed 22.4-38.0% of the total crop biomass. These results are in agreement with those reported in previous studies (Khalid
et al 

### . 1999b; Corley et al 

### . 1971). There was a persistent increase in both below- and aboveground biomass of the oil palm plantation with age. However, the abov eground biomass was logarithmically correlated with age, while belowgro und biomass was linearly correlated (Figure 5.2). A similar trend in relation of oil pa lm biomass with plantation age in Malaysia was found by Nordin (2002).

Figure 5.2: Trend of relation of bio mass of oil palm compartments with age of

plantation in Sumatra, Indonesia y = 68.2Ln(x) - 36.7
R 2 = 0.99**

y = 44.6Ln(x) - 25.0
R 2 = 0.97* y = 34.5Ln(x) - 27.0
R 2 = 0.99*
y = 1.45x + 9.88
R 2 = 0.99** y = 0.56x + 2.04
R 2 = 0.90

ns

0 50 100 150 200 250

0 5 10 15 20 25 30 Plantation age (year)Biomass (Mg ha-1) Total Crop Trunk Root & trunk base Litter standing stock

### Oil palm plantations

55 The rate of biomass accumulation in the system was 13.6, 11.8, 7.9 and 6.8 Mg ha -1 

### yr -1 

### for the 3-, 10-, 20- and 30-year-old plantations a nd the overall weighed average was 8.3 Mg ha -1 

### yr -1 

### . Compared to the 10.0 Mg ha -1 

### yr -1 

### reported by ISME (2000), the annual rate of biomass accumulation in this study is somewhat lower. However, depending on how this rate is calculated, without weighing, the annual rate of the biomass of the oil palm in this study reaches 1 0.0 Mg ha -1 

### yr -1



### .

5.3.2 Root distribution 

### There was a large difference in root biomass betwee n the oil palm plantation in Sumatra and that in East Kalimantan (Table 5.3). The reason s will be elaborated in the following discussion. Root biomass in Sumatra ranged from 12. 0 to 16.1, 27.6 and 35.7 Mg ha -1 

### 5

m -1 

### for the 3-, 10, 20 and 30-year-old plantations, re spectively. Compared to the values in East Kalimantan of 21.2 and 31.7 Mg ha -1 

### 5 m -1 

### for the 3- and 10-year-old plantations, respectively, the root biomass in Suma tra was much lower. However, the root biomass in both sites was higher than that of I. cylindrica 

### in the neighborhood of the respective sites, which was 8.7 Mg ha -1 

### 5 m -1 

### in Sumatra and 12.4 Mg ha -1 

### 5 m -1 

### in East Kalimantan. Moreover, the vertical distributio n of the root biomass of I. cylindrica 

### grassland was restricted to the top soil layer (Fig ure 5.3).

Table 5.3: Vertical root biomass distribution in oi l palm plantation systems in East

Kalimantan and Sumatra, Indonesia East Kalimantan Sumatra Depth 3-year-old 10-year-old 3-year-old 10-year-old 20-year-old 30-year-old 

### (m) (Mg ha -1 

### ) 0-1 16.5 21.6 8.1 10.8 19.7 26.4 1-2 2.5 5.9 2.2 2.7 4.8 5.9 2-3 1.1 2.7 1.0 1.7 1.8 1.9 3-4 0.9 1.1 0.5 0.6 0.9 1.1 4-5 0.3 0.3 0.1 0.2 0.4 0.3 0-5 21.2 31.7 12.0 16.1 27.6 35.7

In the 5-m deep soil profile, more than 50% of the root biomass was found in the top 60 cm. However, compared to I. cylindrica 

### grassland, the roots of the oil palm penetrated much deeper, i.e., to a depth of 5 m. Th is is much deeper than the I.

### Oil palm plantations

56 cylindrica 

### grassland with a depth of only 1.8 m. Penetration of oil palm roots to a depth of 6 m was reported by Sommer et al 

### . (2000).

Distribution of the roots of the oil palm plantatio n seems to be site and age dependent. It is interesting that although distribu tion of 50% of the root biomass of the oil palm plantation in East Kalimantan (31 and 41 c m depth for the 3- and 10-year-old plantations, respectively) was shallower than in Su matra (46, 58, 58, and 59 cm depth for the 3-, 10-, 20- and 30-year-old, respectively) , distribution of 90% of the root biomass in both sites was not significantly differe nt: 90% of the root biomass in East Kalimantan was found to a depth of 244 and 223 cm i n the 3- and 10-year-old plantations, respectively, and in Sumatra to depths of 228, 239, 207 and 219 cm in the

0

100

200

300

400

500 0.0 0.1 1.0 10.0 100.0 Root biomass (Mg ha -1 30cm -1 )Soil depth (cm)

I. cylindrica Oil palm Average A B C D E F

Figure 5.3: Vertical distribution of root biomass of a 10

- year

- old oil palm plantation

and Imperata cylindrica grassland (IC) systems in East Kalimantan
, Indonesia ; A, B, C, D, E and F = 10, 100, 200, 300, 450 and 520 cm from the trunk baseSoil depth (cm)

### Oil palm plantations

57 3-, 10-, 20- and 30-year-old plantations, respectiv ely. The first 1-m depth produced 67- 78% of the total root biomass (to depth of 5 m). The root biomass consisted mainly of primary roots, which contributed 47, 70, 84 and 80% to total root biomass of the 3-, 10-, 20 - and 30-year-old plantations, respectively. Secondary and tertiary (including qua ternary) root biomass contributed 11- 16% and 5-37%, respectively. Compared to the root b iomass reported by Khalid et al



### . (1999b) of 50, 20 and 30% for the primary, secondar y and tertiary roots, respectively, these results are still comparable. While the bioma ss of both primary and secondary roots increased continuously with age, the biomass of tertiary roots (including quaternary roots) fluctuated, which is probably the result of the physiological demands of the plant and environmental conditions (Figure 5 .4).

However, the contribution of tertiary and quaternar y roots to the total root biomass was considerably high in the top 15 cm of s oil, declining sharply in the deeper soils (77 to 22%, 41 to 11%, 27 to 4% and 44 to 8% for the 3-, 10-, 20- and 30-year-old plantations, respectively). A similar trend in a 23 -year-old oil palm plantation in Malaysia was reported by Khalid et al 

### . (1999b), who found that tertiary roots Figure 5.4: Biomass of primary, secondary and tertiary (includi ng quaternary) roots

of oil palm plantation systems in Sumatra, Indonesi a y = 0.08x + 0.56
R 2 = 0.96

y = 0.07x + 0.20
R 2 = 0.95
y = 0.008x + 0.10
R 2 = 0.96

0.1 1.0 10.0

0 5 10 15 20 25 30 Plantation age (year)Biomass (kg m-3) All roots Primary roots Secondary roots Tertiary & quaternary roots

### Oil palm plantations

58 contributed 53% in the top 15 cm and declined to on ly 25% of the total root biomass at the 15-30 cm soil depth. Wright (1951) reported tha t most of the tertiary roots of oil palm on deep acid sandy soils in West Africa were c onfined to a depth of 10 cm.
Vertical distribution of fine roots indicates the r ooting strategy of trees and is species specific and genetically inherited (Curt and Prévos to 2003; Polomski and Kuhn 1998; Brown 1992); this shallow concentrated rooting stra tegy may allow an efficient use of the topsoil resources (Crabtree and Berntson 1994). Fine-roots proliferated in the Ahorizon of most soils, due to accumulation of organ ic matter, higher CEC and higher nutrient concentration in organic C, N, and K (Bowe n 1984; Kalisz et al 

### . 1987; Pritchett and Fisher 1987; Sainju and Good 1993).

Although roots of oil palm can penetrate deeper tha n 4 m, the majority have been found in the top 45 cm (Lambourne 1935). The l argest magnitude of root biomass is to be found between a soil depth of 20 and 60 cm (Tailez 1971), but the exact depth Sumatra 0

10

20

30

40

50

60

70

80

90

100 0 2 4 6 8 Root biomass (Mg ha -1 15cm

-1 )Soil depth (cm)p

3-year-old 10-year-old 20-year-old 30-year-old

East Kalimantan 0

10

20

30

40

50

60

70

80

90

100 0 2 4 6 8 Root biomass (Mg ha -1 15cm -1 )Soil depth (cm)pSoil depth (cm)Soil depth (cm)



### Figure 5.5: Vertical distribution of root biomass o f oil palm pla ntations in Sumatra

and East Kalimantan, Indonesia

### Oil palm plantations

59 of the root concentration depends to large extent o n the soil type (Chan 1977). Root biomass of the oil palm plantations at both sites s howed a parallel trend of vertical root distribution. Most of the roots of the young planta tions (3-year-old) were concentrated in the uppermost 15 cm and decreased with soil dept h. However, the concentration of roots in the uppermost soils was more pronounced fo r the plantations at the East Kalimantan site (Figure 5.5).

The vertical distribution of root biomass in the ol der plantations is in agreement with that reported by Khalid et al 

### . (1999b) and Chan (1977). There was an Figure 5.6: Lateral distribution of root biomass of different a ges of oil palm

plantations in Sumatra (below) and East Kalimantan (above), Indonesia East Kalimantan

0 10 20 30 40

0 100 200 300 400 500 Distance to closest trunk Base (cm)Root biomass (Mg ha-11m-1)rr 3-year-old 10-year-old

Sumatra

0 10 20 30 40

0 100 200 300 400 500 Distance to closest trunk Base (cm)Root biomass (Mg ha-11m-1)rr 3-year-old 10-year-old 20-year-old 30-year-old 130

130

Distance to closest trunk base (cm)Root biomass (Mg ha-11m-1)Root biomass (Mg ha-11m-1)

### Oil palm plantations

60 increase in root biomass at a depth of 15-30 cm for the 10- and 20-year-old plantations, and at a depth of 15-45 cm for the 30-year-old plan tation. Thereafter, biomass declined with depth, but again at a depth of 0-45 cm, the ma gnitude of root biomass of the plantations in East Kalimantan was much higher. The lateral extent of woody roots may exhibit a hig h degree of plasticity and depend on environmental conditions (Millikin and Bl edsoe 1999; Belsky 1994). Roots of oil palm may grow laterally to a distance of mor e than 12 m (Wright 1951). However, Zaharah et al 

### . (1989) reported that roots of mature oil palms ca n absorb nutrients as far as 36 m away from the base trunk. Feeding roots up to more than 6 m away from the trunk base and lateral roots of more than 20 m have also been observed (Lambourne 1935). Nevertheless, root density decrea ses with distance to the trunk base, and the majority of the absorbing roots of mature o il palms may extend to a radius of at least 3.5-4.5 m from the trunk base (Ruer 1967). A high root biomass was concentrated near the trunk base (10 cm from the trunk base), de creasing sharply at a distance of 1 m, then declining gradually to a distance of 3 m from the trunk base. Hereafter, it was more or less stabile or fluctuated slightly to a distance o f 5.2 m from the trunk base (Figure 5.6).
Khalid et al 

### . (1999b) reported that the lateral distribution of the roots of a 23- year-old oil palm plantation in Malaysia was the sa me as in this study, which is also in agreement with that of a 14-year-old oil palm plant ation in West Africa (Purvis 1956). A similar distribution in other systems has also be en reported (Purbopuspito and Van Rees 2002; Jose et al 

### . 2001; Peter and Lehmann 2000; Jones et al 

### . 1998). The lateral and vertical trend of root biomass density in the 1 0-year-old oil palm plantation in East Kalimantan is depicted in Figure 5.7. There was a h igh concentration of root biomass close to the trunk base to a depth of less than 50 cm. In general, root biomass density can be classified into 6 zones. The first zone constituted the highest concentration of root bioma ss, which reached more than 10 kg

m -3 

### in the 10-year-old oil palm plantation. This zone developed near the trunk base to a distance of less than 1 m and within a soil depth o f 15 cm and 50 cm. However, this zone sometimes extended to a depth of more than 75 cm in the old plantation (30-yearold) without an increase in the lateral distance to the trunk base. The second zone developed directly in the outer of the first zone t o a distance of rarely more than 2 m from the trunk base and to a depth of 50 cm, where the root biomass showed a density

### Oil palm plantations

61 of 5-10 kg m

-3 

### . The third zone emerged in the outer area of the s econd zone, extending
to a distance of 4 m from the trunk base close to t he soil surface but confined to a shallow soil depth below the second root zone of le ss than 60 cm. The root biomass density of this zone ranged from 3-5 kg m -3 

### . The fourth root zone showed a biomass density of 1-3 kg m -3 

### and developed in the outer area of and below the t hird root zone to a distance of 5.2 m from the trunk base (planting s pace was a triangular 9 m x 9 m x 9m) to a depth of 40 cm at a distance of 5 m from t he trunk base and of 160 cm near the trunk base. Below this zone, a root zone with a roo t biomass density of 0.5-1 kg m -3 

### was sometimes observed. This zone developed at depths o f 40-150 cm to a distance of 5 m
from the trunk base and of 160-280 cm near the trun k base with some discontinuousness. The final root zone developed be low the fifth root zone, with a biomass density of less than 0.5 kg m -3 

### ; due to the high spatial variation, further zonation of this root biomass is not possible.

It is important to bear in mind that this is not a static zonation. The zones may shrink and swell depending on numerous genetically inherited factors and the environmental conditions of the plantation. In some cases, it was observed that the second and third zones had developed in a very narr ow lateral range of between 50 and Trunk

> 10 kg m - 3
5

- 10 kg m - 3
3

- 5 kg m

- 3
1

- 3 kg m

- 3
0.5

- 1 kg m

- 3 < 0.5 kg m - 3

Figure 5.7: Vertical and lateral root biomass density of a 10

- year

- oil oil palm plantation in East Kalimantan, Indonesia

Distance to trunk base (cm)Soil depth (cm)

### Oil palm plantations

62 100 cm from the trunk base. An intensive sampling o f roots near to the trunk base (0- 100 cm) is, therefore, of utmost importance, if an accurate estimate is required.

5.3.3 Biomass carbon distribution 

### The C content of the compartments of the oil palm p lantation systems ranged widely from 32.3 to 44.2% (Table 5.4). However, only leaf litter and tertiary roots (including quaternary roots) compartments had low C contents o f 32.3 and 36.6%, respectively, while for the other compartments these values range d from 39.4 to 44.2%. The average C content of 41.7, 38.4 and 40.3% for the crop abov eground biomass, non-crop aboveground biomass, and root and trunk base biomas s, respectively, resulting in an overall average of 40.4%, was much lower than the a ssumed values of 50% applied for most of the previous studies. However, the average values have to be corrected with the relative biomass of each compartment. The calculati ons resulted in a weighed average of 41.3%, and the use of this value in converting b iomass to C stock instead of the
above-mentioned 50% is recommended.

Table 5.4: Carbon content of compartments of oil pa lm plantation systems in

Sumatra and East Kalimantan, Indonesia Mean SD Compartment (%) n Spear 39.5 bcd 3.3 6 Leaf 43.7 de 2.5 6 Rachis 41.4 cd 1.1 10 Frond base 41.4 cde 0.9 6 Trunk 42.6 de 1.6 6 Crop aboveground compartments Average 41.7 1.0 -

Undergrowth 39.3 c 2.9 8 Non-leaf litter 43.7 de 1.1 4 Leaf litter 32.3 a 6.6 8 Non crop compartments Average 38.4 2.8 -

Trunk base 44.2 e 1.8 12 Primary root 41.1 cd 2.9 20 Secondary root 39.4 c 3.9 20 Tertiary root 36.6 b 4.4 20 Trunk base and roots Average 40.3 1.2 - Average 40.4 1.7 - SD = standard deviation; mean values followed by the same letter are not significantly different at

α = 0.05

### Oil palm plantations

63 The C content of the both the aboveground compartme nts and the trunk base of the oil palm plantations was not affected by pla ntation age. Although intensive root and soil sampling was performed in East Kalimantan, there was no sampling for aboveground biomass, so that it is not possible to compare C content and accumulation of the aboveground biomass. However, there is no di fference in the C content of the non-crop biomass (litter and undergrowth). Contrary to the aboveground biomass C content, site and plantation age had a significant effect on the C content of root biomass . In general, the values in East Kalimantan averaged 35.7%, which is significantly l ower ( α 

### = 0.05) than the 40.7% in Sumatra. Plantation age may also have a significant effect on the C content of the root biomass (Table 2); younger plantations (3- and 10-y ear-old) showed a significantly lower C content than the older plantations (20- and 30-year-old). Root type was also a source of variation. Coarser roots (primary and sec ondary roots) show a higher C content than smaller roots (tertiary and quaternary roots). Nevertheless, in contrast to the younger plantations, the effect of root type on C content of the root biomass was less pronounced in the older plantations (Table 5.5).

Table 5.5: Carbon content of different root types o f different ages of oil palm

plantations in Sumatra and East Kalimantan, Indones ia

Root type Plantation age Primary Secondary Tertiary Mean 

### SD (year) (%) n

3 39.4 39.2 34.1 37.6a 

### 3.4 18 10 40.9 36.7 34.5 37.4a 

### 5.0 18 20 43.7 42.9 42.1 42.9b 

### 1.0 9 30 42.0 41.4 40.0 41.1b 

### 2.7 15 Mean 41.1b 39.4b 36.6a 39.8 a - - 

### SD 2.9 3.9 4.4 - 

### 4.1 - n 20 20 20 - 

### - 60 SD = standard deviation; mean values followed by the same letter ar e not significantly different at α = 0.05; tertiary roots including quaternary roots



### Biomass C of the system increased decisively with p lantation age and was 16.6, 49.4, 65.3 and 84.6 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations, respectively (Table 5.6). These values are slightly lower than those reported by Noordwijk et al 

### . (2000) and Hairiah and Sitompul (2000), which ran ged from 62.4-91.0

### Oil palm plantations

64 Mg ha -1 

### , given that they defined the belowground biomass C to depth of 30 cm only. Compared to the biomass C of the neighboring I. cylindrica 

### grasslands of 3.0, 2.9 and 5.9 Mg ha -1 

### for the aboveground, belowground and total biomass C, respectively, it is obvious that total biomass C of oil palm plantations has already surpassed that of I. cylindrica 

### in a very early stage of the plantation. This sugge sts that conversion of I. cylindrica 

### grasslands into oil palm plantations is beneficial if C sequestration and land
rehabilitation are of interest. Of all compartments (crop, undergrowth and litter s tanding stock), the crop provided the major biomass C to th e system, accounting for 87.8- 94.5%. Undergrowth contributed 1.3-2.8% and litter standing stock 3.9-9.4%. Despite the minor contribution of these compartments, they could play an important role in the functioning of the system, such as in controlling s oil erosion and surface run-off, and promoting soil C and nutrient cycles as well as soi l biological activities.

Table 5.6: Above- and belowground biomass C distrib ution of four different ages of

oil palm plantation systems in Sumatra, Indonesia

Aboveground biomass C Plantation age Belowground

biomass C Litter Undergrowth Crop Total Relative belowground to total (year) (Mg ha -1 

### ) (%) 3 5.41 1.56 0.47 9.15 16.59 32.63 10 10.40 1.94 0.63 36.37 49.35 21.08 20 16.63 5.51 1.43 41.69 65.26 25.48 30 21.75 6.25 1.26 55.33 84.60 25.71 Belowground biomass C was defined to depth of 5 m



### Carbon stored in the aboveground crop biomass incre ased from 9.2 Mg ha -1 

### in the 3-year-old plantation to 36.4, 41.7 and 55.3 Mg ha -1 

### for the 10-, 20- and 30-year-old plantations. Aboveground biomass C of previous stud ies varied considerably from 31.0- 62.0 Mg ha -1 

### for a 10-year-old oil palm to as high as 96.0-101. 0 Mg ha -1 

### for 14- and 19- year-old oil palm plantations (Sitompul and Hairiah 2000). It is clear that the aboveground biomass of the plantation systems is hi ghly variable; this may be the result of inherited characteristics, pedoagroclimatic cond itions and management. However, to some extent, it also depends on the method of bioma ss quantification and conversion to the C pool.

### Oil palm plantations

65 There is only little information on the fractionati on of biomass C of oil palm plantations in the literature. The following discus sion is based on biomass fractionation data and an assumption of a biomass C content of 41 .3%. Of the crop aboveground biomass C, the trunk contributed 57.3 to 75.7%. The se figures are relatively higher than the 48% reported by Khalid et al 

### . (1999a), but are in agreement with those reported by Rees and Tinker (1963) of 7- to 22-year-old oil pal m plantations of 42.8-73.0%. Biomass C of the trunk in this study increased from 5.6 Mg ha -1 

### for the 3-year-old plantation to 20.9, 31.5 and 40.2 Mg ha -1 

### for the 10-, 20- and 30-year-old plantations, respectively (Table 5.7). Compared to the trunk bio mass C of previous studies of 15.2- 19.3 Mg ha -1 

### (36.7-46.8 Mg ha -1 

### biomass) for 22- to 27.5-year-old plantations (Kha lid et al 

### . 1999a; Corley et al 

### . 1971; Tinker and Smilde 1963), these results are considerably higher. However, they are in agreement with the val ue for a 15-year-old plantation of 36.6 Mg ha -1 

### (88.5 Mg ha -1 

### biomass) reported by Ng et al 

### . (1968).

Table 5.7: Above- and belowground biomass C distrib ution of four different ages of

oil palm trees in Sumatra, Indonesia Belowground Aboveground Stand age Root Trunk base Trunk Frond base Rachis Leaflet Others (year) (Mg ha -1 

### ) 3 4.8 0.6 5.6 0.5 1.9 0.6 0.6 10 6.5 3.9 20.9 8.5 4.1 2.1 0.9 20 11.1 5.5 31.5 1.0 6.5 1.9 0.7 30 14.4 7.4 40.2 1.4 10.0 2.8 1.0 Trunk base, defined as part of trunk developed belowground including roots de veloped underneath the trunk base to depth of 1 m; rachis, including petiole; others, includi ng spear, cabbage and inflorescences; root biomass was defined to depth of 5 m



### The C stored in the biomass of the frond base incre ased substantially from 0.5 Mg ha -1 

### in the 3-year old plantation to 8.5 Mg ha -1 

### in the 10-year-old plantation, then declined to only 1.0 and 1.4 Mg ha -1 

### in the 20- and 30-year-old plantations, respectively. In line with the increase in the trun k dimension, there was an increase in
the biomass C accumulated in the frond base in the early stage of the plantations (from 3- to 10-year-old). However, due to the abscission of the frond base in the older plantations (generally plantation age of 13 to 18 y ears), the biomass C accumulated in the frond base of the older plantations (20- and 30 -year-old) was pronouncedly lower.
Khalid et al 

### . (1999a) reported a magnitude of frond base biomas s of a 23-year-old oil

### Oil palm plantations

66 palm plantation of 129.1 kg palm -1 

### equivalent to 7.3 Mg C ha -1 

### . This is quite comparable to the 23.3% for the 10-year-old plantat ion in this study, which is in agreement with the 18-22% in previous studies (Khal id et al 

### . 1999a; Henson 1993). Carbon stored in rachis biomass, including petioles , increased from 1.9 to 4.1, 6.5 and 10.0 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations, respectively. These values are comparable to those reported by Kh alid et al 

### . (1999a) for a 23-year-old oil palm plantation (110.5-127.9 kg palm -1 

### equivalent to 6.2-7.2 Mg C ha -1 

### ) and those reported by Rees and Tinker (1963) for 7- to 22-yea r-old oil palm plantations (42.7- 101.8 kg palm

-1 

### equivalent to 2.4-5.7 Mg C ha -1 

### ). The relative contribution of the rachis biomass C to the crop aboveground C stock was consi derably high in the early stage of the plantation. It was 20.7% in the 3-year-old plan tation and dropped to only 11.2% in the 10-year-old plantation as the other compartment s of the crop developed, especially trunk and frond base. Nevertheless, there was an in crease in the contribution of rachis biomass C of the older plantations (15.7 and 18.1% for the 20- and 30-year-old plantations, respectively. A similar contribution t hrough rachises (17.6-20.4%) of a 23- year-old oil palm plantation in Malaysia was report ed by Khalid et al 

### . (1999a) and 12.9- 22.2% of 7- to 22-year-old plantations by Rees and Tinker (1963). Leaflet biomass C increased from only 0.6 Mg ha -1 

### (3-year-old plantation) to 2.1 Mg ha -1 

### (10-year-old plantation), then fluctuating between 1.9 Mg ha -1 

### (20-year-old plantation) and 2.8 Mg ha -1 

### (30-year-old plantation). These figures are compar able to those of 7- to 22-year-old oil palm plantations of 24.7-48.5 kg palm -1 

### equivalent to 1.4- 2.7 Mg C ha -1 

### (Rees and Tinker 1963) and of a 23-year-old planta tion of 7.9 Mg ha -1 

### equivalent to 3.3 Mg C ha -1 

### (Khalid et al 

### . 1999a). However, the relative contribution of leaflet biomass C was somewhat low, ranging from 4. 6-6.8%. Compared to the 9.3% reported by Khalid et al 

### . (1999a) and the 8.0-12.8% reported by Rees and Ti nker (1963), these values are somewhat lower. Biomass C of the other components (spear, cabbage a nd inflorescences) increased from only 0.6 to 0.9, 0.7 and 1.0 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantation systems, respectively. The relative cont ribution of these components was rather high in the early stage of the plantations. It was 6.0% for the 3-year-old plantation, decreasing to 2.4% for the 10-year-old plantation and only 1.8% for the 20-

### Oil palm plantations

67 and 30-year-old plantations. Khalid et al 

### . (1999a) reported a slightly higher value for a 23-year-old oil palm plantation in Malaysia (3.2%). Root biomass C was 4.8, 6.5, 11.1 and 14.4 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations, respectively. Compared to the root biomass of a 23-year-old oil palm of 16.0 Mg ha -1 

### equivalent to 6.6 Mg C ha -1 

### reported by Khalid et al 

### . (1999b) and that of a 27.5-year-old oil palm of 17.8 Mg ha -1 

### equivalent to 7.4 Mg C ha -1 

### reported by Corley et al 

### . (1971), the values for the mature oil palm were c onsiderably high. However, instead of to a depth of 5 m as in this st udy, Khalid et al 

### . (1999b) defined the root biomass to a depth of 60 cm and Corley et al 

### . (1971) to a depth of 90 cm. The biomass C of the oil palm roots to a depth of 90 cm in this study was 3.2, 4.2, 7.5 and 10.0 Mg ha -1 

### for the 3-, 10-, 20- and 30-year-old plantations, respectively. These figures are quite comparable to the findings of Khalid et al 

### . (1999b) and Corley et al 

### . (1971).
Sommer et al 

### . (2000) reported quite similar values for a 9-year -old oil palm plantation in Eastern Amazon (6.0 Mg ha -1 

### 6m -1 

### ). Biomass C of roots contributed 13.8-33.1% and, together with that of the trunk base, produced 22.2 -37.2% of the total crop biomass C. Individual values were 29.1, 13.1, 17.0 and 17.0% f or the 3-, 10-, 20- and 30-year-old plantations, respectively, which, together with tru nk base, gave 32.6, 21.1, 25.5 and 25.7% of the biomass C for the 3-, 10-, 20- and 30- year-old plantations, respectively. The low contribution of the belowground biomass C o f the 10-year-old plantation was due to the accumulation of the frond base biomass; there was no abscission of the frond bases in the 10-year-old plantation in this study. Since belowground biomass C may contribute significantly to the total biomass C – i n this study it was more than 20% of
the total biomass C without abscission of the frond bases and more than 25% with regular abscission – incorporation of belowground b iomass C in studies of C stock and budget is of utmost importance. There was a persistent increase with age in the C a ccumulated in both belowand aboveground biomass of the oil palm plantations . However, aboveground biomass C was logarithmically correlated with age, while be lowground biomass C was linearly correlated (Figure 5.8). A similar trend was observ ed in Malaysia by Nordin (2002). As elaborated above, there was a strong dependency of C sequestration in the biomass of the oil palm plantations with plantation age. This suggests that, if biomass data are lacking, estimation of biomass C based on plantation age is quite credible.

### Oil palm plantations

68 Estimation of belowground biomass C with an allomet ric equation is strongly recommended, since data on belowground biomass are very limited, due mainly to the difficulty in its quantification, as quantifying be lowground biomass is not only labor intensive and time consuming but also costly. If su fficient information on aboveground biomass C is available, estimating belowground biom ass C with a factor of 0.2 of the total biomass C if there is no pronounced abscissio n of the frond bases or 0.25 if the frond bases are intensively detached is recommended

.

The rate of biomass C accumulation of the system wa s 5.5, 4.9, 3.3 and 2.8 Mg ha -1 

### yr -1 

### for the 3-, 10-, 20- and 30-year-old plantations a nd the overall weighed average 3.4 Mg ha -1 

### yr -1 

### . In comparison with the value reported by ISME (20 00) of 5.0 Mg ha -1 

### yr -1 

### , the annual rate of biomass C accumulation in this study was somewhat lower. However, depending on how this rate is calcu lated, i.e., without weighing, the
annual rate of biomass accumulation would come to 4 .1 Mg ha -1 

### yr -1 

### and, employing the Figure 5.8: Trend of relation of biomass of oil pal m compartments with the age of the

plantations in Sumatra, Indonesia y = 28.3Ln(x) - 15.5
R 2 = 0.99**

y = 18.9Ln(x) - 10.7

R 2 = 0.97* y = 14.7Ln(x) - 11.5
R 2 = 0.99**

y = 0.60x + 4.03
R 2 = 0.99** y = 0.20x + 0.73
R 2 = 0.91*

0 10 20 30 40 50 60 70 80 90

0 5 10 15 20 25 30 Plantation age (year)Biomass carbon (Mg ha-1) Total Crop Trunk Root & trunk base Litter standing stock

### Oil palm plantations

69 assumption of a C content of 50%, increase the esti mation of the biomass C accumulation to 5.0 Mg ha -1 

### yr -1



### .

5.3.4 Soil carbon distribution


### Soil C content of the systems varied highly dependi ng on site, vegetation type, plantation age, spatial position and depth; all fac tors had a highly significant effect on soil C content (

p 

### < 0.001). Although the values for the plantations in Sumatra and East Kalimantan differed, the vertical trend was similar (Figure 5.9). The effect of vegetation type, plantation age and spatial position (distance to closest trunk) on soil C content was primarily associated with the effect of the fine ro ot biomass of the system. This is demonstrated by the high correlation between fine r oot (tertiary and quaternary roots) biomass of the system and soil C content (r 2 

### = 0.69-0.87 and p 

### < 0.001). However, the correlation between fine root (tertiary and quatern ary roots) biomass and soil C content of the younger plantations (3-year-old) was rather weak for the plantations in East Kalimantan (r 2 

### = 0.52 and p 

### < 0.001), and there was no correlation for the 3-y ear-old plantation in Sumatra (r 2 

### = 0.04 and p 

### = 0.32). This suggests that the effect of roots in the young er plantations on soil C content was significantly held back by other factor s, such as changes in soil temperature, moisture and disturbances in soil stru cture during the establishment of the plantation. A slight increase in root biomass from 8.9-12.2 Mg ha -1 

### 1 m -1 

### for the grassland system to 8.1-16.5 Mg ha -1 

### 1m -1 

### for the young oil palm plantation was not enough to maintain the level of the soil C content of the plantations. One of the most important findings in this study is that the vertical distribution of soil C in the oil palm plantations was not the s ame as that in the I. cylindrica 

### grassland system. The oil palm plantation system wa s apparently able to achieve higher soil C accumulation in the deep soils, either by en hancement of organic C deposition or by inhibition of decomposition of the soil organic matter in the respective soil depth. However, the former seems to be more important. As a consequence of the deep penetration of the roots of oil palm plantations (t o a depth of 5 m) compared to the I. cylindrica 

### grassland systems (to a depth of only 1.8 m) a sub stantial amount of organic

### Oil palm plantations

70 C could be deposited in the deep soils, thus increa sing the soil organic C of the respective soil depth.

Although the C content in the soils in older oil pa lm plantations was higher
than that in I. cylindrica 

### grassland, it should, nevertheless, be noticed tha t there was a significant decrease in the upper soil layers in th e younger plantations (3-year-old). This
decrease indicates that there were losses in soil o rganic matter and thus nutrients, either by the more intensive decomposition of the soil org anic matter due to changes in soil Figure 5.9: Vertical distribution of carbon content of soils in Imperata cylindrica

grass land and oil palm plantation systems in East Kalima ntan (above) and Sumatra (below), Indonesia Sumatra 0
50
100
150
200
250
300
350
400
450
500 0.0 0.1 1.0 10.0 Soil C content (%)Soil depth (cm)

Imperata cylindrica

Oil palm, 3-year-old Oil palm, 10-year-old Oil palm, 20-year-old Oil palm, 30-year-old East K alimantan 0
50
100
150
200
250
300
350
400
450
500 0.0 0.1 1.0 10.0 S oil C content (% )Soil depth (cm)Soil depth (cm)Soil depth (cm)

### Oil palm plantations

71 moisture and temperature or through surface soil er osion; elimination of the I. cylindrica 

### grassland with its dense root mat increases the so il erosion risk, especially on slopes.
The vertical distribution of soil C in both I. cylindrica 

### grassland and oil palm plantation systems was quite similar to that report ed by Syahrinudin (1997) and Ruhiyat (1989) in previous studies in the same region. Soil C content of the systems decreased in line with soil depth and was highly depth depend ent (r 2 

### = 0.99 and p 

### < 0.001). There was a very marked decrease in soil C content with d epth in the upper 50 cm of the soil, which slowed down below this depth. Nevertheless, t here was a distinct difference in
the vertical soil C distribution between the I. cylindrica 

### grassland and oil palm plantation systems. Compared to that in soils in th e oil palm plantation system, the
decrease in the I. cylindrica 

### grassland was less abrupt in the upper 50 cm of th e soil, whereas it was more distinct deeper down (see Figur e 5.9). This demonstrates the strong
influence of fine root biomass on soil C content. O n the one hand, the high root biomass and dense root mat in the uppermost soils in the I. cylindrica 

### grassland led to a higher C content in the upper soils (on average, root biomas s density of the top 15 cm soil in the oil palm plantations of 2.6 g cm -3 

### was much lower than that of the I. cylindrica 

### grassland of 6.6 g cm -3 

### ); on the other hand, the deeper root penetration o f the oil palm plantations led to a higher C content in the deeper soils. Soil C content is the result of litter (above- and belowground) production defined by the vegetation type and development stag e of the system, and of the soil respiration, which is controlled by root respiratio n and decomposition of litter and soil organic matter. Soil physical properties such as te xture and structure may also control respiration (De Jong and Schappert 1972). Soil temp erature and moisture are, however, the most important factors regulating soil respirat ion (Kicklighter et al 

### . 1994; Lloyd and Taylor 1994; Howard and Howard 1993). Conversion of I. cylindrica 

### grasslands into oil palm plantations could affect soil C content severa l ways, such as through changes in the rate of litter production, increase in temperature of the uppermost soils, increase in surface run-off facilitating surface erosion, altered soil horizonization, and modified soil structure and bulk density. Carbon content of the upper soils in the younger plantations (3-year-old at both sites and 10-year-old in East Kalimantan) w as significantly lower than that in the I. cylindrica 

### grasslands (

p 

### < 0.001). Biomass production of oil palm plantatio ns is, indeed,

### Oil palm plantations

72 much higher than that of

I. cylindrica 

### grasslands; however, little of the produced biomas s is returned to the soils, especially in the early s tages of the establishment of the plantations. The impact of the plantations on the t emperature of the uppermost soils could be significant for the younger plantations, as the canopy closure is not yet established and the development of undergrowth is suppressed. Elimi nation of I. cylindrica 

### may reduce the rate of infiltration, causing an increase in su rface run-off and surface erosion, which in turn may alter soil horizonisation, structurization and bulk density. The impacts on soil horizonisation and bulk density are summarized in t ables 5.8 and 5.9. It is clear that the establishment of oil palm plan tations on I. cylindrica 

### grasslands was, in most cases, detrimental to the p edogenesis processes, especially in the early stages of the plantations. This adverse i mpact was, nevertheless, reversed in later stages. In contrast to the impacts on soil ho rizonisation, the unfavorable impacts on the soil bulk density of the uppermost soils was re tained till the end of the plantation cycle. Since soil fertility plays an important role in determining plant growth and productivity, proper attention should be focused on this subject, otherwise sustainability of the plantation will never be achieved.

Table 5.8: Horizonisation of soils developed under Imperata cylindrica 

### grasslands

and oil palm plantations in East Kalimantan and Sum atra, Indonesia East Kalimantan Sumatra Oil palm Oil palm Soil depth Imperata cylindrica 3-yr-old 10-yr-old Imperata cylindrica 3-yr-old 10-yr-old 20-yr-old 30-yr-old 1 AE E EB AE E E AE AE 2 E BE BE E Bt EB E E 3 EB Bt1 Bt1 EB Bt2 Bt Bt1 Bt1 4 Bt1 Bt2 Bt2 Bt1 BC Bg/BC Bt2 Bt2 5 Bt2 CB BC Bt2 BC BC 6 BC BC



### Table 5.9: Bulk density of soils developed under Imperata cylindrica 

### grasslands and

oil palm plantation systems in East Kalimantan and Sumatra, Indonesia East Kalimantan Sumatra Oil palm Oil palm Soil depth Imperata

cylindrica 3-yr-old 10-yr-old Imperata cylindrica 3-yr-old 10-yr-old 20-yr-old 30-yr-old (cm) (g cm -3 ) 0-15 1.1 1.3 1.3 1.1 1.2 1.2 1.3 1.2 15-50 1.3 1.4 1.4 1.4 1.3 1.3 1.3 1.3 50-100 1.3 1.5 1.4 1.5 1.4 1.3 1.3 1.4 100-200 1.4 1.4 1.4 1.4 1.3 1.3 1.4 1.4 200-500 1.4 1.4 1.4 1.4 1.2 1.4 1.4 1.5

### Oil palm plantations

73 Soil C storage in this study is in the range of tha t reported in previous studies (Mackensen 1998; Syahrinudin 1997; Bremen et al 

### . 1990; Ruhiyat 1989). Total C stored in the soils in oil palm plantation systems ranged from 139.2-260.6 Mg ha -1 

### 5 m1 

### . These values are somewhat higher than those of pr imary and secondary forests of 156.0-176.0 Mg ha -1 

### 5 m -1 

### and the value for a 9-year-old oil palm plantation of 131.0 Mg ha -1 

### 5 m

-1 

### reported by Sommer et al 

### . (2000). However, there was an extremely high magnitude of soil C in the 10-year-old plantation i n Sumatra (482.4 Mg ha -1 

### 5 m -1 

### ). This reflects the high variation of C sequestration in t ropical soils. Nevertheless, this figure does not represent the common magnitude of C stock in most Ultisols in the tropics; the soil C stock to a depth of 1 m of 250.2 Mg ha -1 

### in this plantation was very much higher than that reported in previous studies (83.3-95.2 M g ha -1 

### ) (Mackensen 1998; Syahrinudin 1997; Bremen et al 

### . 1990) and is, therefore, excluded in the estimate of the C sequestration rate of the oil palm plantation. Th e values for the C stored in the soils in I. cylindrica 

### grassland varied strongly (from 137.6 Mg ha -1 

### 5 m -1 

### in Sumatra to 188.1 Mg ha -1 

### 5 m

-1 

### in East Kalimantan). Soil C storage is largely dependent on environmenta l, biogeochemical and land management factors. Different land use and man agement practices influence soil properties such as soil temperature, moisture, micr obial biomass, organic matter and fine root biomass, which in turn affect the magnitu de of soil respiration (Lee and Jose 2003; Raich and Tufekcioglu 2000; Kelting et al 

### . 1998) and soil C dynamics. Trees could substantially increase the organic matter inp ut into the system through the turnover of leaves and roots (Jose et al. 2000). Th e results in this study show that the
conversion of I. cylindrica 

### grassland into oil palm plantation considerably in creased the amount of soil C stored in the system. However, the C stock in soils in the younger plantation (3-year-old) in East Kalimantan was cons iderably lower than that of the I. cylindrica 

### grassland. However, the C stock to a depth of 3 m in the 3-year-old oil palm plantation in East Kalimantan was lower than that o f the I. cylindrica 

### grasslands; only at a depth of 0-1 m, it was significantly different (F igure 5.10). The C stock at a depth of 0-1 m in the 10-year-old plantation in East Kaliman tan was also lower than that in the I. cylindrica 

### grasslands but not significantly different. In con trast to the uppermost soils, the C stock in the deeper soils (1-5 m) in the 10-y ear-old oil palm plantation in East Kalimantan was significantly higher than that in bo th I. cylindrica 

### grassland and 3-year-

### Oil palm plantations

74 old plantation. The overall C stock to a depth of 5 m of the soils in the oil palm plantations was higher than that of I. cylindrica 

### grassland, and the rate of soil C sequestration to a depth of 5 m was 1.8 Mg ha -1 

### yr -1



### .

In Sumatra, the C stock only in 0-1 m depth in the 3-year-old plantation was
lower than that in the I. cylindrica 

### grasslands (Figure 5.10). The C stock to the depth 5 m in oil palm plantations of all ages was significa ntly higher ( p 

### < 0.001) than that in the Figure 5.10: Carbon stock of soils in Imperata cylindrica grassland and oil palm

plantation systems in East Kalimantan (a bove) and Sumatra (below), Indonesia East Kalimantan

0 50 100 150 200 250 300 350

0-100 100-200 200-300 300-400 400-500 0-500 Soil depth (cm)Soil carbon stock (Mg ha-1)

Sumatra

0 50 100 150 200 250 300 350

0-100 100-200 200-300 300-400 400-500 0-500 Soil depth (cm)Soil carbon stock (Mg ha-1) Imperata cylindrica Oil palm, 3-year-old Oil palm, 10-year-old Oil palm, 20-year-old Oil palm, 30-year-old 500

### Oil palm plantations

75 I. cylindrica 

### grasslands. On average, conversion of I. cylindrica 

### grassland into oil palm plantations led to a soil-C sink of 2.6 Mg ha -1 

### 5 m -1 

### . Compared to East Kalimantan (1.8 Mg ha -1 

### 5 m

-1 

### ), the value in Sumatra was much higher; this is pr imarily due to the
difference in the soil-C stock at the establishment of the plantation. Oil palm plantations showed a higher C stock in the deeper soils (1-5 m), which was detected in the early stage of the planta tions (3-year-old). In contrast to deeper soils, there was a decrease in the C stock i n the upper 1-m soil in the oil palm plantations, especially in the early stage (3-year- old). However, the soil-C stock increased with age to a level that was higher than that of the I. cylindrica 

### grasslands.

5.3.5 Carbon distribution in oil palm plantation systems 

### Biomass C of the system increased persistently with plantation age, and there was a strong correlation between biomass C and age of the plantations. Total and aboveground biomass C are highly logarithmically correlated wit h plantation age (r 2 

### = 0.99 and 0.97,

p 

### = 0.006 and 0.015, respectively), whereas belowgro und biomass C is highly linearly correlated (r

2 

### = 0.99 and p 

### = 0.002). These high correlation and probability l evels suggest that the models might be applicable to othe r oil palm plantations elsewhere having similar pedoagroclimatic conditions. However , in cases where there is sufficient information on aboveground biomass C of the system, estimates of belowground
biomass C with a factor of 0.2 of the total biomass C (equivalent to 0.25 of the aboveground biomass C) if there is no pronounced ab scission of the frond bases or 0.25 of the total biomass C (equivalent to 0.33 of the a boveground biomass C) if the frond bases are regularly detached from the trunk of the crops are recommended. The rate of biomass C accumulation in the system wa s 5.5, 4.9, 3.3 and 2.8 Mg
ha -1 

### yr -1 

### for the 3-, 10-, 20- and 30-year-old plantations, respectively, and the overall weighed average was 3.4 Mg ha -1 

### yr -1 

### . Total biomass C of the system was 16.6, 49.4, 65.3 and 84.6 Mg ha -1 

### for the 3-, 10, 30-, 20- and 30-year-old plantatio ns, respectively (Figure 5.11). Compared to the biomass C of the I. cylindrica 

### grasslands in the neighborhood of the plantations of 3.0, 2.9 and 5.9 Mg ha -1 

### for the aboveground, belowground and total biomass C, respectively, it i s clear that total biomass C of oil palm plantations already surpasses that of I. cylindrica 

### grasslands at a very early stage of the plantation. This suggests that conversion of I. cylindrica 

### grassland into oil palm

### Oil palm plantations

76 plantations is beneficial if biomass C accumulation and land rehabilitation are the

concerns.

Of total biomass C, roots and trunk base produced 2 2.2-37.2%. The crop contributed the highest magnitude of aboveground bi omass C (81.9-93.4%) followed by litter standing stock (5.0-13.9%) and undergrowth ( 1.6-4.2%). Of the crop aboveground biomass C, trunk contributed the highest portion (5 7.3 to 75.7%) followed by frond base (2.3-23.3%), rachis including petiole (11.2-20.7%) and leaflet (4.6-6.8%). Other compartments, including spear, cabbage and inflores cence, contributed 1.8-6.0% to the total crop aboveground biomass. The soil-C content was strongly affected by vegetat ion type, plantation age, spatial position (distance to closest trunk) and de pth ( p 

### < 0.001). However, the effect of vegetation type, plantation age and spatial positio n on soil-C content was primarily
associated with the effect of the fine root biomass ; this is demonstrated by the high -100 -80 -60 -40 -20 0 20 40 60 80 Carbon stock (Mg ha -1 ) Belowground biomass Soil Litter Undergrowth Crop



### Figure 5.11: Carbon distribution of Imperata cylindrica 

### grassland and oil palm

plantation systems in Sumatra; belowground carbon s tock was defined to depth of 5 m; values for above- and belowground car bon of Imperata cylindrica 

### grassland were considered as baseline for the plan tations 540 Belowground 180

240 120 6 0 Aboveground Belowground baseline Aboveground baseline Oil palm, 30

- yr

- old

Oil palm, 20

- yr

- old

Oil palm, 10

- yr

- old

Oil palm, 3

- yr

- old

Imperata cylindrica

### Oil palm plantations

77 correlation between fine root (tertiary and quatern ary roots) biomass and soil-C content (r 2 

### = 0.69-0.87 and p 

### < 0.001). A sizeable amount of soil C could be gained by conv ersion of I. cylindrica 

### grassland into oil palm plantations. The average ra te of soil C sequestration was 0.7, 0.4, 0.5, 0.5 and 0.5 Mg ha -1 

### yr -1 

### for the depths 0-1, 1-2, 2-3, 3-4 and 4-5 m, respectively. A potential soil C sink to depth 5 m of 76.8 Mg ha -1 

### could be expected by
this conversion. More than 70% of this amount was a llocated to the deep soils (1-5 m depth). Together with that sequestered in the bioma ss of the plantations, a C sink of 178.8 Mg ha -1 

### could be achieved. The average rate of soil-C sequ estration to a depth of 5 m (2.6 Mg ha -1 

### yr -1 

### )was lower than the rate in the biomass (3.4 Mg ha -1 

### yr -1 

### ). This may reflect that oil palm assigns little biomass to the belowground compartment of the plantation system. It is interesting that most of the C stored in the oil palm plantation was allocated to the belowground stock (soil and belowg round biomass C); this has been ignored in most previous works due probably to the difficulty in the assessment of this component. The results show that belowground C cont ributed to more than 93% at the beginning of the plantation (3-year-old) and then d eclined with age to only 75% in the 30-year-old plantation (Table 5.10). However, the r elative contribution of belowground
C stock was lower than that of the I. cylindrica 

### grassland system (98%).

Table 5.10: Below- and aboveground C-stock distribu tion in Imperata cylindrica



### grassland and oil palm plantations in Sumatra, Indo nesia

Belowground Soil Biomass Aboveground

biomass Belowground /

total System (Mg ha -1 

### ) (%) Imperata cylindrica 

### 137.6 2.9 3.0 97.9

3-year-old 161.2 5.4 11.2 93.3 10-year-old 482.2 10.4 38.9 92.1 20-year-old 155.0 16.6 48.6 71.7 Oil palm 30-year-old 232.4 21.7 62.8 75.3 Belowground C stock was defined to depth of 5 m

5.4 Conclusions 

### The persistent increase in biomass and biomass C of the oil palm plantation with age suggests that establishment of this plantation in d egraded lands such as those infested by I. cylindrica 

### weed is an effective tool to promote higher terres trial C storage.

### Oil palm plantations

78 Although the rooting system of the oil palm plantat ion was deep, it could only moderately improve the soil C storage compared to I. cylindrica 

### grassland. This implies that the plantation allocates only a small portion of the biomass to the belowground production, and thus oil palm plantations are less effective in soil C enrichment. With a rate of C sequestration in biomass of 3.4 Mg ha -1 

### yr -1 

### and in soil of 2.6 Mg ha -1 

### yr -1 

### , conversion of I. cylindrica 

### grassland into oil palm plantations could increase the terrestrial C storage of 96.1 Mg ha -1 

### in biomass alone; together with that sequestered in the soil (to depth of 5 m), a C sink of 172.9 Mg ha -1 

### in 30 years could be expected.

### Summary and general discussion

79 6 SUMMARY AND GENERAL DISCUSSION

6.1 Biomass distribution 

### Biomass production of both A. mangium 

### and oil palm plantations increased with plantation age. Although the rate of biomass produc tion of A. mangium 

### plantations (21.3 Mg ha -1 

### yr -1 

### ) was much higher than that of the oil palm plantat ions (8.3 Mg ha -1



### yr -1 

### ), due to the short rotation of A. mangium 

### plantations (9 years for pulp production but 25-30 years for oil palm), the amount of biomas s accumulated at the end of the rotation was quite similar (Figure 6.1).

In contrast to I. cylindrica 

### grassland, the main part of the biomass of these plantations is allocated to the aboveground compart ments. Furthermore, at the end of the rotation, the total biomass of the A. mangium 

### and oil palm plantations (181.2 and 204.3 Mg ha -1 

### , respectively) was much higher than that of the I. cylindrica 

### grassland systems near these plantations (21.9 and 16.9 Mg ha -1 

### ). This shows clearly that the Figure 6.1: Biomass distribution of Imperata cylindrica grassland, Acacia mangium

and oil palm plantations; belowground biomass defin ed to depth of 5 m for oil palm plantation, 3 m for Imperata cylindrica grassland and Acacia mangium plantation -60 -30 0 30 60 90 120 150 Biomass (Mg ha -1 ) Litter Undergrowth Crop

Belowground 60 30 Aboveground 30

- year

- old

9

- year

- old Oil palm

I. cylindrica

A. mangium

I. cylindrica

### Summary and general discussion

80 conversion of I. cylindrica 

### grassland into A. mangium 

### and oil palm plantations is highly
beneficial if biomass enhancement is to be addresse d. The biomass of the undergrowth in the 9-year-old A. mangium 

### plantation (0.8 Mg ha -1 

### ) was considerably lower than that of the oil palm plantation (3.2 Mg ha -1 

### ). This is probably related to the dense canopy closure of the A. mangium 

### plantation. Although an allelophatic effect of leaf exudates of A. mangium 

### has been reported, this low biomass accumulation was more likely the effect of light deficiency, as the undergrowth biomass was higher under the more open canopy of th e 4-year-old plantation (12.2 Mg
ha -1 

### ). A wide range of values of undergrowth biomass of fast growing tree plantations has been reported in previous studies with values r anging from 2.9 to 4.6 Mg ha -1 

### for A. mangium 

### plantations, 2.8 to 5.9 Mg ha -1 

### for Paraserienthes falcataria 

### plantations, and 2.6 to 18.5 Mg ha -1 

### for Eucalyptus deglupta 

### plantations (Syahrinudin 1997; Ruhiyat 1989). The litter standing stock accumulated under the A. mangium 

### plantations (6.0 Mg ha -1 

### ) was significantly lower than that under the oil p alm plantations (17.9 Mg ha -1 

### ). The values for fast growing tree plantations report ed in previous studies ranged from 10.1 to 13.8 Mg ha -1 

### for A. mangium 

### plantations, 14.9 to 17.0 Mg ha -1 

### for Paraserienthes falcataria 

### plantations and 7.0 to 19.5 Mg ha -1 

### for Eucalyptus deglupta 

### plantations (Syahrinudin 1997; Ruhiyat 1989). The belowground biomass of the A. mangium 

### plantations (36.3 Mg ha -1 

### ) was significantly lower than that of the oil palm plant ations (52.4 Mg ha -1 

### ) However, the relative contribution of belowground biomass to tot al biomass for the A. mangium 

### (20.1%) and oil palm plantations (25.6%) was not si gnificantly different.

6.2 Root distribution 

### Tree root systems are involved in soil-C and nutrie nt enrichment through root turnover, acting as a safety net by interception of leached n utrients or the physical improvement of compact soil layers (Alongi et al 

### . 2004; Suamy et al 

### . 2003; Tufekcioglu et al 

### . 1999).
Root distribution in I. cylindrica 

### grassland, A. mangium 

### (fine root) and oil palm plantation systems is depicted in Figure 6.2. The f ine root biomass of the A. mangium 

### plantations ranged from 9.5 Mg ha -1 

### 3 m -1 

### (in the1- and 4-year-old plantations) to 12.3 Mg ha -1 

### 3 m

-1 

### (in the 9-year-old plantation). This is quite comp arable to the root

### Summary and general discussion

81 biomass of I. cylindrica 

### of 12.4 Mg ha -1 

### 3 m -1 

### . However, the vertical distribution of the
root biomass of I. cylindrica 

### grassland was restricted to the top shallow soil l ayer, i.e., the roots were distributed to a depth of 1.8 m in t he I. cylindrica 

### grassland and up to 3 m
in the A. mangium 

### plantations. The root biomass of the oil palm plan tations in East Kalimantan of 20.0 and 30.3 Mg ha -1 

### 3 m -1 

### for the 3- and 10-year-old plantations, respectively, and that in Sumatra of 11.4, 15.3, 26 .3 and 34.3 Mg ha -1 

### 3 m -1 

### for the 3-, 10-, 20 and 30-year-old plantations, respectively, was considerably higher than that of
the A. mangium 

### plantations.

The fine root biomass showed a continuous decrease with soil depth. In the 5- m deep soil profile, more than 50% of the fine root biomass of the A. mangium 

### plantations was concentrated in the top 30 cm of th e profile, which was considerably shallower than that of oil palm plantations of 50 c m. However, 50% of the root biomass 0

100

200

300

400

500 0.0 0.1 1.0 10.0 100.0 Root biomass (Mg ha -1 30cm -1 )Soil depth (cm), Oil palm

Average A B C D E F A. Mangium 1-yr-old 4-yr-old 9-yr-old I. cylindrica

Figure 6.2: Vertical distribution of root biomass in 10

- year

- old oil palm plantation

(to depth of 5 m; A, B, C, D, E and F = 10, 100, 20 0, 300, 450 and 520 cm from the trunk base), Acacia mangium plantation (fine root biomass; to depth of 3 m) and Imperata cylindrica grassland (to depth of 3 m)Estimated root biomassbelow 3mSoil depth (cm)

### Summary and general discussion

82 of both A. mangium 

### and oil palm plantations was still deeper than tha t of I. cylindrica 

### grassland, which was concentrated in the top 10 cm of the soil profile. Furthermore,
90% of the root biomass of I. cylindrica 

### was confined to a depth of 41 cm; this was clearly much shallower than that in the A. mangium 

### plantations with a depth of 237 cm and that in the oil palm plantations of 227 cm.

Figure 6.3 shows the distribution of the root bioma ss with depth. Both absolute (in Mg ha -1 

### ) and relative (in % of 0-5 m depth) root biomass c umulatively increased with cumulative soil depth. However, the variation of the relative root biomass decreased with the increase of the cumulative sampl ing depth, while the variation of the
absolute root biomass increased or was maintained a t a certain level.
The root biomass of I. cylindrica 

### was distributed within a depth of less than 2 m (9 4, 98 and 100% for depths 0-0.6, 0-1 and 0-2 m, respectiv ely). Root biomass of A. mangium 

### was sampled to a depth of 3 m, but the established root distribution curve (Figure 6.2) Figure 6.3: Vertical distribution of root biomass o f Imperata cylindrica grassland,

Acacia mangium (fine root biomass) and oil pa lm plantations; columns are means, stake bars are standard deviations 0 5 10 15 20 25 30 35

0-60 cm 0-1 m 0-2 m 0-3 mRoot biomass (Mg ha-1), Imperata cylindrica

Acacia mangium Oil palm

40 50 60 70 80 90 100

0-60 cm 0-1 m 0-2 m 0-3 m Soil depthRoot biomass (% of 0-5 m),

### Summary and general discussion

83 does not indicate that there are no roots immediate ly below this depth. The distribution of the roots below 3 m is, therefore, estimated bas ed on the distribution curve of A. mangium 

### at a depth of 0-3 m combined with the distribution curve of oil palm at a depth
of 0-5 m. Root biomass of the A. mangium 

### plantation was 67, 76, 87 and 94% for the depths 0-0.6, 0-1, 0-2, and 0-3 m, respectively. Ro ot biomass of the 30-year-old oil palm plantation was 55, 71, 88 and 95% for the dept hs 0-0.6, 0-1, 0-2, and 0-3 m, respectively. The established curve for the oil pal m plantations indicates that very little root biomass is to be found at a depth of more than 5 m. Root sampling in the deep soils is time and labor c onsuming. It was found that when using a manual root sampler, sampling roots to a depth of 1 m took three times as long as sampling to a depth of 60 cm; sampling to a depth of 3 m required 16-20 times more time and labor than for the depth 1m. Sampling to a depth of 5 m took three times longer than for the depth 3 m. A flexible and relia ble method for root studies should, therefore, be established. The results of this study show that there is no gre at constraint in the estimation of roots of grassland systems, because these roots are mainly (> 98%) concentrated in the topsoil to a depth of less than 1m. However, th is is not the case for the oil palm and A. mangium



### plantation systems, where 90% of the root biomass is distributed to a depth
of more than 2 m. Given the constraints in root sam pling and the coefficient variation of the relative root biomass to a depth of 1 m of less than 10%, root sampling to a depth of 1 m employing a factor of 1.3 and 1.4 to estimate t he total root biomass of A. mangium 

### and oil palm plantations, respectively, is recommen ded. Although the lateral extent of woody roots may exhi bit a high degree of plasticity and depend on environmental conditions ( Millikin and Bledsoe 1999; Belsky 1994), the results show that the lateral distributi on of the root biomass in the plantations ( A. mangium 

### and oil palm) was species specific and is probably genetically inherited. In contrast to that of the oil palm plantations, later al distribution of root biomass in the A. mangium 

### plantations was not significantly affected by the distance to the closest trunk base. However, in line with previous findings (Purb opuspito and Van Rees 2002; Jose et al 

### . 2001; Peter and Lehmann 2000; Jones et al 

### . 1998), there was a slight decrease in the
horizontal distribution of the fine root biomass in the A. mangium 

### plantations with distance to tree base (Figure 6.4), i.e., 9.3 and 7 .4 Mg ha -1 

### 1m -1 

### at a distance of 10 cm

### Summary and general discussion

84 and 212 cm, respectively. Root biomass of the oil p alm plantations, which was mostly
concentrated at a distance of less than 1 m from th e trunk base, is in agreement with former findings (Khalid et al 

### . 1999b; Purvis 1956). Values were 30.2, 15.3, 10.0 , 7.7, 7.7 and 8.1 Mg ha -1 

### 1m -1 

### at a distance of 10, 100, 200, 300, 450 and 500 cm from the trunk base, respectively.

Acacia mangium

0 5 10 15

0 50 100 150 200



### Oil palm

0 10 20 30 40

0 100 200 300 400 500



### Distance to closest trunk base (cm)

Figure 6.4: Lateral distribution of root biomass of Acacia mangium (fine root

biomass) and oil palm plantations; rectangles are m eans, stake bars are standard deviations.Root biomass (Mg ha-11m-1)

### Summary and general discussion

85 6.3 Carbon distribution


### The C content of the biomass in the oil palm planta tion systems ranged widely from 32.3 to 44.2% (Figure 6.5). However, while the C co ntent of the leaf litter (32.3 %) and tertiary roots, including quaternary roots, (36.6%) was low, that of the other compartments ranged from 39.4 to 44.2%. The weighed average was 41.3%; this figure was used for converting biomass to C stock instead of the value of 50% (Hamburg 2000).

The C content of the stand biomass of the A. mangium 

### plantations varied from 27.9% to 45.6%, depending on the tree compartment. The C content of the fine root biomass was the lowest (mean of 30.6%) followed by litter standing stock (35.8%) and undergrowth (35.8%). The average C content of the o ther compartments (coarse root, stem, branch and leaf) ranged from 42.4 to 44.9%. T he overall average of the C content
of A. mangium 

### (43.3%) was slightly higher than that of I. cylindrica 

### (35.7%) and oil palm plantation (41.3%). These figures are slightly lower than the 50% proposed by Hamburg (2000). Compared to that of the root biomas s of secondary and primary 20 25 30 35 40 45 50

Fine root Li

tt e r

U nd e rgrowth

C

oarse root Stem Bra nc h L

e afCarbon content (%) I. cylindrica A. mangium Oil palmCarbon content



### Figure 6.5: Carbon content of compartments of Imperata cylindrica 

### grassland,

Acacia mangium 

### and oil palm plantations; branch = including twig for Acacia mangium 

### , includ ing frond base, petiole and rachis for oil palm plantationsCarbon content (%)

### Summary and general discussion

86 forests (43.9-46.6%) (Sommer et al 

### ., 2000), the C content of root biomass in this stu dy (excluding that of fine root biomass) is quite comp arable. In the plantation systems, C content of fine roots, litter standing stock and leaf biomass of the oil palm plantations was higher than that of A. mangium 

### plantations, while that of the remaining compartments (undergrow th, coarse roots, stem and branch) was lower. Excluding the C content of the leaf biom ass, the order of magnitude of the A. mangium 

### and oil palm plantations was identical, i.e., stem > branch and coarse root > leaf > undergrowth > litter > fine root. The variability of the C content of litter standing stock and fine root biomass
of both A. mangium 

### and oil palm plantation systems was considerably h igher than that of the other compartments; coefficient of variation was 13.6 and 10.9% for A. mangium 

### plantations and 20.4 and 12.0% for the oil palm pla ntation systems, respectively, while the coefficients of the other compartments (undergr owth, coarse root, stem, branch and leaf) were less than 10%. Below- and aboveground biomass C of both A. mangium 

### and oil palm plantation systems increased persistently in line w ith age of the plantations. Carbon stored in below- and aboveground biomass of A. mangium 

### plantations increased from 3.6 and 6.1 Mg ha -1 

### in the early stage of the plantation (1-year-old) to 14.2 and 64.3 Mg
ha -1 

### at the end of the plantation cycle (9-year-old); t his does not differ much from the values for the oil palm plantations, which increase d from 5.4 and 11.2 Mg ha -1 

### in the early stage of the plantation (3-year-old) to 21.8 and 62.8 Mg ha -1 

### at end of the plantation cycle (30-year-old), respectively. At th e end of the plantation cycle, the total
C stored in the biomass of the A. mangium 

### and oil palm plantation systems amounted to 78.5 and 84.6 Mg ha -1 

### , respectively. Compared to that stored in the biom ass of the I. cylindrica 

### grasslands of 7.5, 4.0, 3.6 Mg ha -1 

### for total, below- and aboveground biomass C, respectively, it is clear that the biomass C acc umulated in both A. mangium 

### and oil palm plantation systems already surpassed that of I. cylindrica 

### grassland in the early stage of the plantation. The rate of C sequestration in the biomass of the A. mangium 

### plantations (9.3 Mg ha -1 

### yr -1 

### ) was remarkably higher than that of the oil palm p lantation (3.4 Mg ha -1 

### yr -1 

### ). However, due to the length of the plantation cycle, i.e., 9 years for A. mangium 

### plantations for pulp production and 25-30 years for commercial oil palm plantations, at

### Summary and general discussion

87 the end of the plantation cycle, the magnitude of b iomass C was similar (Figure 6.6). These rates are also higher than those of riparian poplars (2.9 Mg ha -1 

### yr -1 

### ) (Tufekcioglu
et al 

### . 2003).

Of the total biomass C, belowground biomass C was 3 8.1, 20.1 and 20.0% for the 1-, 4-, and 9-year-old A. 

### mangium plantations, respectively, equivalent to a rootshoot ratio (below-aboveground ratio) of 61.4, 25.2 and 25.0%, respectively. This high contribution of belowground biomass C in the early stage of the plantations was mainly due to the fast development of the fine roots in th e beginning of the plantation cycle. It was maintained in a narrow dynamic range of magnitu de until the end of the plantation cycle. Belowground biomass C of the oil palm plantations g ave 32.6, 21.1, 25.5 and 25.7% of the total biomass C equivalent to a root-s hoot ratio (below-aboveground ratio) of 48.4, 26.7, 34.2 and 34.6% for the 3-, 10-, 20- and 30-year-old plantations, respectively. The low contribution of belowground b iomass C of the 10-year-old plantation was due to the accumulation of frond bas e biomass; there was no abscission of the frond bases in the 10-year-old plantation in this study. -120 -100 -80 -60 -40 -20 0 20 40 60 80 Carbon stock (Mg ha -1 ) Belowground biomass

Soil Litter Undergrowth Crop

Figure 6.6: Carbon stock distribution of Imperata cylindrica grassland, Acacia

mangium plantation and oil palm plantation systems 300 240 180 120 Aboveground Belowground 360 60 Oil palm, 30-yr-old

I. cylindrica

A. mangium , 9-yr-old

I. cylindrica

### Summary and general discussion

88 Since belowground biomass C may contribute signific antly to the total biomass C of the plantation systems (in this study it was more than 20% in both systems), incorporation of belowground biomass C in studies of C stock and budget is of utmost importance. However, due to the difficult y in determining belowground biomass, it is proposed to estimate the magnitude o f belowground biomass C from that of aboveground of the system. Estimation of belowgr ound biomass C with a factor of 0.25 of the aboveground biomass for A. mangium 

### plantations, of 0.25 for oil palm plantations if there is no pronounced abscission of the frond bases, or of 0.33 if the frond bases are regularly detached, is recommended.

Table 6.1: Aboveground biomass, C storage and C seq uestration rate of plantation

systems in different regions in the tropics Plantation Age Biomass Carbon C sink rate

(year) (Mg ha -1 ) (Mg ha -1 yr -1 ) Site Reference

4 69.5 31.3 7.8 Philippines Kawara et al . 1981 5 87.4 37.8 * 7.6 East Kalimantan Ruhiyat, 1989 5 75.6 34.0 6.8 Philippines Kawara et al . 1981 7 96.4 43.4 6.2 Philippines Kawara et al . 1981 9 108.2 48.7 5.4 Philippines Kawara et al . 1981 10 111.5 48.3 * 4.8 East Kalimantan Ruhiyat, 1989 Paraserienthes falcataria

9 90.1 39.0 * 4.3 East Kalimantan Ruhiyat, 1989

9 120.7 54.3 6.0 Philippines Kawara et al . 1981 7 85.7 38.6 5.5 Philippines Kawara et al . 1981 Gmelina arborea 9 87.4 39.3 4.4 Philippines Kawara et al . 1981 Tectona grandis 5 49.6 21.5 * 4.3 De Angelis et al . 1981 Eucalyptus grandis 4 63.7 15.9 North Sumatra, Indonesia Retnowati 1998
9 114.9 49.8 * 5.5 East Kalimantan Ruhiyat, 1989 7 89.0 38.6 * 5.5 East Kalimantan Ruhiyat, 1989 4 49.3 21.4 * 5.3 East Kalimantan Syahrinudin, 1997 6 65.3 28.3 * 4.7 East Kalimantan Syahrinudin, 1997 9 94.1 40.7 * 4.5 East Kalimantan Ruhiyat, 1989 E. deglupta

5 47.4 20.5 * 4.1 East Kalimantan Ruhiyat, 1989 E. nitens 5 72.6 31.4 * 6.3 New Zealand Oliver et al ., 1984 E. saligna 4 38.5 16.7 * 4.2 New Zealand Krapfenbauer and Andrea, 1989 E. urograndis 4.5 40.4 17.5 * 3.9 North Amazon, Brazil Spangenberg, 1994
4 64.8 28.5 7.1 East Kalimantan This study Acacia mangium 9 139.2 62.1 6.9 East Kalimantan This study

3 22.9 9.6 3.2 Sumatra This study 10 87.9 37.0 3.7 Sumatra This study 20 102.0 43.1 2.2 Sumatra This study Oil palm
30 133.9 56.6 1.9 Sumatra This study

* Values were computed from aboveground biomass with a factor of 0.43.

### Summary and general discussion

89 Aboveground biomass C of plantations in the tropics ranges widely depending primarily on the plantation species (Table 6.1). Acacia mangium 

### and Paraserienthes falcataria 

### plantations are among the most productive plantati ons with regard to aboveground biomass and C accumulation. However, th e rate of biomass and C
accumulation of Paraserienthes falcataria 

### declines sharply in the older plantations. There was a very high rate of aboveground biomass C sequestration of a 4-year-old Eucalyptus grandis 

### plantation in North Sumatra, Indonesia, of 15.9 Mg ha -1 

### yr -1 

### (Retnowati 1998). This is twice as much as the valu es for A. mangium 

### of 6.9 – 7.1 Mg
ha -1 

### yr -1 

### . In contrast to the high annual net primary produc tion of oil palm plantations, ranging from 11.9 Mg ha -1 

### yr -1 

### in Sumatra (Setyo et al 

### . 1999; Lamade and Setyo 2002) to 20.1 Mg ha -1 

### yr -1 

### in Malaysia (Henson and Chai 1997; Henson 1998), t he rate of the accumulation of the aboveground biomass C of oil pa lm, ranging from 1.9 to 3.7 Mg ha 1 

### yr -1 

### was the lowest among the plantations. This is prim arily due to the removal of the harvested biomass, which can amount to 20-42% (Sety o et al 

### . 1999; Lamade and Setyo 2002; Henson and Chai 1997; Henson 1998). Compared to that of natural forests (Table 6.2), th e aboveground biomass C density of plantations is much lower. This implies that if C sequestration is the concern, plantations should be established in non-forested a reas or those with a low viability of
natural succession.

Table 6.2: Aboveground biomass and C density of nat ural forests in different

regions in the tropics Biomass C Density No (Mg ha -1 ) Site Reference 1 406 175.8 Brazil Klinge 1976 2 357 154.6 Caparo, Venezuela Hase 1981 3 460 199.2 East Kalimantan, Indonesia Ruhiyat 1989 4 390 168.9 Indonesia Hairiah and Sitompul 2000 5 325 140.7 Indonesia Sitompul and Hairiah 2000 6 254 110.0 Indonesia Noordwijk et al . 2000 7 264 114.3 Khade, Ghana Greenland and Kowal 1960 8 316 136.8 Panama Golley et al . 1975 9 378 163.7 Rio Lara, Panama Golley et al . 1975 10 276 119.5 Rio Sabana, Panama Golley et al . 1975 11 265 114.9 Philippines Kawara et al . 1981 Values for C density were computed from aboveground biomass with a factor of 0.43.

### Summary and general discussion

90 The patterns of soil C distribution vary highly wit h soil age, soil texture, rainfall, temperature patterns, and vegetation type . The vertical distribution of the soil C
of both I. cylindrica 

### grassland and A. mangium 

### and oil palm plantation systems in this study was quite similar to that of previous studies by Syahrinudin (1997) and Ruhiyat (1989) for the soils in the same region. The soil C content decreased in line with soil depth and was highly depth dependent (r 2 

### = 0.97 to 0.99 and p 

### < 0.001). However, spatial variation was driven by the distribution of the fine root biomass of the system: r 2


### = 0.83-0.99 and p 

### < 0.001 for the A. mangium 

### plantations and r 2 

### = 0.69-0.87 and p 

### < 0.001 for the oil palm plantations. Soil C content decreased sharply in the upper 50 cm of the soils and more gradually deeper down. Nevert heless, a distinct difference in
vertical soil C distribution between I. cylindrica 

### grassland and A. mangium 

### and oil palm plantations was observed. Compared to A. mangium 

### and oil palm plantations, the
decrease in the soil C content under I. cylindrica 

### grassland was less abrupt in the upper 50 cm of the soils and more distinct in the lower p art of the soil profile. This difference seemed to be governed by the difference in fine roo t distribution. On one hand, a high root biomass and dense root mat in the top layer of the soils under I. cylindrica 

### grassland led to a higher C content (6.6 g dm -3 

### ) in the first 15-cm depth compared to the A. mangium 

### plantations (2.6 dm -3 

### ) and the oil palm plantations (3.4 dm -3 

### ); on the other hand, deeper root penetration in the A. mangium 

### and oil palm plantations led to a higher C content in the deeper soils. Soil C storage in this study is in the range of tha t reported in previous studies (Mackensen 1998; Syahrinudin 1997; Bremen et al 

### . 1990; Ruhiyat 1989). Total C
stored in the soils in the A. mangium 

### plantations (210.4 – 325.5 Mg ha -1 

### 5 m -1 

### ) was considerably higher than that in the oil palm plant ations (139.2 – 260.6 Mg ha -1 

### 5 m -1 

### ). These values are somewhat higher than those of prim ary and secondary forests (156.0 – 176.0 Mg ha -1 

### 5 m -1 

### ) and a 9-year-old oil palm plantation (131.0 Mg ha -1 

### 5 m -1 

### ) reported by Sommer et al 

### . (2000). However, there was an incredibly high mag nitude of soil C in the 10-year-old plantation in Sumatra (482.4 Mg ha -1 

### 5 m -1 

### ). This reflects the high variation of C stock in tropical soils. This figure , however, does not represent the common magnitude of C stock in most Ultisols in the tropics; the soil C stock to a depth of 1 m in the 10-year-old oil palm plantation (250. 2 Mg ha -1 

### ) was very much higher than that reported in previous studies (83.3-95.2 M g ha -1 

### ) (Mackensen 1998;

### Summary and general discussion

91 Syahrinudin 1997; Bremen et al 

### . 1990) and is, therefore, excluded in the estimate of the C sequestration rate of the oil palm plantations. T here was a wide range of C stored in
the soils under the I. cylindrica 

### grasslands (ranging from 137.6 Mg ha -1 

### 5 m -1 

### in Sumatra to 188.1 Mg ha -1 

### 5 m -1 

### in East Kalimantan). Soil C storage is largely dependent on environmenta l, biogeochemical and land management factors. Different land use and man agement practices influence soil properties such as soil temperature, moisture, micr obial biomass, organic matter and fine root biomass, which in turn affect the magnitu de of soil respiration (Lee and Jose 2003; Raich and Tufekcioglu 2000; Kelting et al 

### . 1998) and soil C dynamics. Trees can substantially increase the organic matter input int o the system through the turnover of leaves and roots (Jose et al 

### . 2000). The results in this study show that the co nversion of I. cylindrica 

### grassland into A. mangium 

### and oil palm plantations considerably increased the amount of soil C. On average, the rate of soil C accumulation in the A. mangium 

### plantations (2.3, 4.0, 4.2 and 6.9 Mg ha -1 

### yr -1 

### ) was much higher than that of the oil palm plantation (0.7, 0.4, 0.5 and 1.0 Mg ha -1 

### yr -1 

### ) for depths 0-100, 100-200, 200-300 and 300-500 cm, respectively. As oil palm plantations d o not allocate a large part of the biomass production to the belowground compartment ( Lamade and Setyo 2002), a lower soil C sequestration could be expected. An in crease in soil-C accumulation (0-100 cm) from 0.7 to 1.2 Mg ha -1 

### yr -1 

### by incorporating legume trees into a grass pasture was reported by Tarré et al 

### . (2001). Sataye et al. 

### (2001) estimated an increase in soil C of 0.5 to 3.0 Mg ha -1 

### yr -1 

### in forest plantations in the tropics. A rate of so il organic matter sink of 1.1 Mg ha -1 

### yr -1 

### was reported by Lugo et al 

### . (2004) for restored neotropical forest systems in Puerto Rico. The C sink in the fi rst 1-m depth in this study is still in the range of the above-mentioned studies. To depth of 5 m, the rate of soil C sequestration in the A. mangium 

### and oil palm plantations systems reached 17.5 and 2.6 Mg ha -1 

### yr-1 contributing to 157.7 and 76.8 Mg ha -1 

### soil C for the entire plantation cycle, respectively (Figure 6.6). It was, however, observed that there was a slight d ecrease in soil C storage at a depth of 0-100 cm during the early stages of both A. mangium 

### and oil palm plantations. This may relate to the lower litter production in t his stage. Nevertheless, the deeper soils experienced enrichment of C storage from the very b eginning of the plantations.

### Summary and general discussion

92 It is interesting that the conversion of I. cylindrica 

### grassland into A. mangium 

### plantation led to a much higher amount of C sequest ered in the deep soils than in the upper layers. In contrast, conversion of I. cylindrica 

### grassland into oil palm plantation led to a higher amount of C sequestered in the uppe r soils (0-1 m). The results show that the soil C stock at a depth of 0-1 m represents onl y 36.1% and 46.7% of the total soil-C stock (0-5 m depth) of A. mangium 

### and oil palm plantation systems, respectively. Compared to that of the I. cylindrica 

### grassland system of 56.1%, there is no doubt that
the conversion of I. cylindrica 

### grassland into plantations improves the C sink in deep soils (1-5 m). This finding is in contrast to the p roposed soil-C change measurement in forestry offset projects to a depth of only 1 m (Ha mburg 2000). While most previous soil-C studies concentrate on the upper soil layers down to a maximum depth of 2 m (Tufekcioglu et al 

### . 2003; Tarré et al 

### . 2001; Brown and Lugo, 1990; Fisher et al., 1994; Moraes et al., 1995), the results confirm the findi ngs of Sommer et al 

### . (2000), Trumbore
et al 

### . (1995) and Nepstad et al 

### . (1994), which show the importance of root penetra tion in deep soil layers for C sequestration. Moreover, the C sequestered in deep soils could be more beneficial than that sequestered in shallow soils, because soil organic matter in deep soils is more resistant to decomposition and t hus has a longer resident time (Gaudinski et al 

### . 2000; Van Dam et al 

### . 1997). Together with the C sequestered in the biomass of t he plantations, a magnitude of soil-C sequestration during the whole plantation cycle of A. mangium 

### (9 years) and oil palm (30 years) of 236.3 and 161.4 Mg ha -1 

### , or an average rate of 26.8 and 6.0 Mg
ha -1 

### yr -1 

### , respectively, could be achieved. Of these amounts , 72.7 and 61.1% were assigned to the belowground C pool (soil and belowg round biomass C). Thus, 81.2 and
76.9% of the total C of the A. mangium 

### and oil palm plantations, respectively, were stored to depth 5 m. However, compared to the I. cylindrica 

### grassland system (98.0%), the relative contribution of belowground C of A. mangium 

### and oil palm plantations was
much lower.

### Conclusions and recommendations

93 7 CONCLUSIONS AND RECOMMENDATIONS

7.1 Conclusions Imperata cylindrica 

### grassland stored only a small amount of biomass C (5.9 – 7.6 Mg
ha -1 

### ) implying that conversion of this grassland into a biomass- and C-rich system is a promising tool for the building of the terrestrial C. Moreover, due to the root distribution pattern of this grassland, i.e., most of the roots were concentrated in the upper centimeters of the soil, only a small amount of C could be stored in the deep soils. Furthermore, although there was a dense mat of rhiz omes in the top centimeters of the
soil under the I. cylindrica 

### grasslands, the magnitude of C stored in the upper most soils was only moderate. Hence, if C sequestration is the concern, conversion of this grassland into a system promoting higher biomass ac cumulation and deep root penetration is of great interest. Both oil palm and A. mangium 

### plantations could sequester much more C than I. cylindrica 

### grassland. However, although the magnitude of biom ass C in these plantations was quite comparable (at the end of the plantation cycle it was 78.5 Mg ha -1



### in the A. mangium 

### and 84.4 Mg ha -1 

### in the oil palm plantations), due to the longer sequestration period (plantation cycle of 9 years f or the A. mangium 

### and 30 years for the oil palm plantations), the rate of C sequestration in the biomass of the oil palm plantation was much lower (9.3 Mg ha -1 

### yr -1 

### for the A. mangium 

### and 3.4 Mg ha -1 

### yr -1 

### for the oil palm plantations). The roots of both plantations penetrate to deep soi ls; however, due to the different nature of the roots and also probably the different allocation strategy of the produced organic constituents combined with the dif ferent management practices, significant differences in the soil-C sink of these plantations were determined. The C
sink of the A. mangium 

### plantation was much larger than that of the oil pa lm plantation: 157.7 Mg ha -1 

### 5 m -1 

### or 17.5 Mg ha -1 

### 5 m -1 

### yr -1 

### for the A. mangium 

### plantation and 76.8 Mg ha -1 

### 5 m -1 

### or 2.6 Mg ha -1 

### 5 m -1 

### yr -1 

### for the oil palm plantations. These differences seemed to affect not only soil-C sink of the systems but also C accumulation pattern. Although the magnitude of b iomass C stored in both systems was quite similar, the C accumulated in the biomass of the A. mangium 

### plantations,

### Conclusions and recommendations

94 representing only 29% of the total C sequestered in the system, was much lower than that of the oil palm plantations of 45%. On average, the total C sink (soil and biomass C) d uring the whole plantation cycle of A. mangium 

### (9 years) and oil palm (30 years) reached a magnit ude of 236.3 and 161.4 Mg ha -1 

### , equivalent to the average rate of C sequestration of 26.8 and 6.0 Mg ha -1



### yr -1 

### , respectively. Of these amounts, 72.7 and 61.1% we re assigned to the belowground C pool (soil and belowground biomass C) and, thus 8 1.2 and 76.9% of the C of the A. mangium 

### and oil palm plantations, respectively, were store d to depth of 5 m. However, compared to the I. cylindrica 

### grassland system (98.0%), the relative contributio n of the belowground C stock of A. mangium 

### and oil palm plantations was much lower. These figures demonstrate the importance of the abovegrou nd biomass C in the plantations.

7.2 Recommendations 

### Neither the biomass of the plantations nor that of I. cylindrica 

### grassland could reach the 50% C content suggested by former authors (Brown an d Lugo 1984; Hamburg 2000). The calculations in this study on the C content of the biomass of A. mangium 

### and oil palm plantations came to averages of 43 and 41%, re spectively. However, there was a large difference in C content between above- and be lowground biomass of I. cylindrica 

### grassland (41 and 31%, respectively). Therefore, it is proposed to use these figures for the computation of the biomass C of these systems. Measurements of the biomass of plantations with des tructive sampling methods are lengthy and costly. Therefore, there is a need to develop methods for estimating the biomass of plantations with non-dest ructive methods. There was a high dependency of the biomass and biomass C of the oil palm plantations on age (r 2 

### > 0.9, p 

### < 0.05) (figures 5.2 and 5.8). Biomass and biomass C of the A. mangium 

### plantations were highly dependent on the tree diameter of the s tand (r 2 

### > 0.9, p 

### < 0.001) (Table 4.8). Allometric equations established in this study coul d be used to estimate both above- and belowground biomass and biomass C of the respective plantations, while belowground
biomass could be estimated either with the allometr ic equation or with the belowground-aboveground ratio described in chapters 4 and 5. Among the compartments of the biomass of the planta tion systems,
measurement of the fine root biomass is the most ti me consuming and labor intensive.

### Conclusions and recommendations

95 In the oil palm plantations, total belowground biom ass and biomass C could be estimated with allometric equations, but this was n ot the case for the A. mangium 

### plantations. Only those of coarse roots of A. mangium 

### plantation can be estimated with allometric equations, but not for those of fine roo ts. The results show that there was a
small variation of fine root biomass and biomass C among plantation ages, but the variation within sites was considerably high (see F igure 4.4). This implies that
estimation of fine root biomass and biomass C with a small sampling size is subject to high errors. Applying a sample size of 153 auger po ints resulted in coefficients of
variation of 108.0 ± 21.0% for within and 57.1 ± 22 .3% among sites. However, fine root
biomass C of A. mangium 

### plantations ranging from 2.8 to 3.4 Mg ha -1 

### produced less than 5% of the total biomass C of the mature planta tion system. Therefore, estimation of
fine root biomass C of A. mangium 

### plantations with a factor of 0.04 of the total bio mass C of the system for the mature plantations or adopt ing a magnitude of 3.0 Mg ha -1 

### for the young plantations is recommended. The biomass of undergrowth and litter standing stoc k of A. mangium 

### plantations varied widely and there is no simple pa rameter which could be employed to estimate the magnitude of these compartments. They should, therefore, be measured directly in each specific stand. This also applies to soil C.

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### : 384-388.ACKNOWLEDGMENTS



### I am very grateful to Prof. Dr. Paul Vlek, my first supervisor, for his guidance, support and encouragement at all stages of my work. I also thank Prof. Dr. Mathias Becker, my second supervisor, for his advice and sh aring his idea on the manuscript. I could not have completed this dissertation without the generous help of Dr. Manfred Denich, who provided support, suggestion, and const ructive comments on the manuscript. His technical and editorial advices gre atly improved the content of this dissertation. For this, I am very grateful. I would like to express my gratitude to DAAD and GT Z for giving me the support during my study in Germany and my field res earch in Indonesia. I also deeply appreciate Barito Pacific Co. Ltd, Surya Hutani Jay a Co. Ltd, Rea Kaltim Plantation Co. Ltd and SMART Co. Ltd for allowing me doing my fiel d work in their concessions. A special thank goes to Dr. Guenther Manske for hel ping with many adminstrative matters and visiting my field site in East Kalimantan, Indonesia. I also wish to thank Ms. Hanna Peters, Mrs. Sabine Aengenendt-Baer and Mrs. Andrea Berg of ZEF for their office assistant and kind help, Ms. Deborah Rupprecht for analyzing my samples in Bonn and Mrs. Margaret Jend for editing my dissertation draft and translating my abstract and summary into German. To all who have assisted me in this venture, I am d eeply indebted. Without their assistance, this work would never have been c ompleted. Finally, I sincerely thank my beloved wife and chil dren for the patience and encouragement during all stages of my study.