Review	of	the	literature	on	emissions	from	

tropical	peat	degradation	under	palm	oil

By	CEIC

Author:	Schrier-Uijl,	A.P
2 Review of the literature on emissions from tropical peat degradation under palm oil

Acknowledgements

ICCT	 and the	 author	 would	 like	 to	 thank	John	 Couwenberg	 who	 performed	 the	 external	 peer	 review	 of	 this	

document.
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 3

Chapter	1 Introduction

With	growing	demand	for	both	food	and	fuel,	it	is	likely	that	significant	further	land	use	conversions	to	oil	palm	

will	occur	 (Koh	and	Wilcove	2007;	Levang et	al.,	2008)	and	in	the	case	of	SE	Asia	will	put	 further	pressure	on	

peat	and	peat	swamp	 forests	 (Rijenders	and	Huijbregts,	2008;	Fargione et	al.,	2008).	While	biofuels	based	on	

palm	 oil	 have	 been	 identified	 as	 potential	 low-carbon	 energy	 sources,	 with	 advanced	 understanding	 it	 has	

become	 clear	 that	 when	 oil	 palms	 are	 grown	 on	 peat	 they	 instead	may	 create	 a	‘carbon	 debt’	 and	 increase	

overall	global	carbon	emissions	(Fargione	et	al.,	2008;	Gibbs	et	al.,	2008).	

The	drainage	and	conversion	of	peatlands	for	growing	oil	palms	causes	greenhouse	gas	emissions	and	carbon	

losses because of	 1)	 oxidation	 of	 the	drained	peat,	 2)	 an	 increase	 in	(peat	 and	 forest)	fire	 frequency	 and	 3)	

biomass	 carbon	 loss	 in	 the	 case	 that	 forest	 is	 converted. The	 latter	 is	 a	 one-point	 emission	 in	 time,	 while	

emissions	 resulting	 from	 peatland	 drainage	 continue	 over	 time.	 Emissions	 from	 peatland	 drainage	 are	 not	

restricted	to	land	use	change,	but	are	also	associated	with	the	ongoing	land	use itself.	In	this	respect	peatlands	

differ	from	mineral	soils,	where	the	main	cause	of	soil	carbon	losses	is	from	land	use	change.	

In	addition	to greenhouse	gas emissions	and	carbon	losses	from on-site	drainage, in	many	cases	the	cultivation	

of	 oil	 palm	 on	 peat	 in	 the	 long-term	 may	 also	 cause	soil	 subsidence	 and	 reduced	 water	 retention	 capacity,	

resulting in	significant	on- and	off-site	hydrological	impacts. An	indirect	result	of	drainage	for	agriculture	is	that	

the	 fire	 frequency	 increases,	 and	 thus	 the	 CO2 and	 CH4 emissions	 increase.	 Land	 clearance	 by	 fire	 has	 been	

banned	for	some	years.	However,	despite	this,	using	fire	to	clear	land	is	still	a	widespread	practice,	particularly	

by	 small	 holders	 lacking	 access	 to	 heavy	 machinery	 (Page	 et	 al.,	 2011a).	 Land	 drainage	 also	 results	 in	

hydrological	disturbances	off-site,	which	in	some	cases	make	the	surroundings	extremely	vulnerable to	fire.	

Review	of	the	‘Page	Review’

While	it	is	generally	accepted	that	the	drainage	of	peat	for	palm	cultivation	results	in	peat	decomposition	and	

substantial	 emissions	 of	 carbon	 dioxide,	 there	 is	 not	 yet	 consensus	 about	 the	 magnitude	 of	 those	 carbon	

dioxide	emissions.	A lot	of	research has	been	performed in	the	past,	however,	some	of	the	earlier	studies	on	

greenhouse	gas	fluxes	suffered	from	several	methodological	issues. Examples	of	deficiencies	are	1)	under- and	

over	estimations	of	fluxes	because	of	incorrect	use	of	measurement	equipment,	2)	inappropriate	temporal	and	

spatial	upscaling	of	fluxes,	3)	exclusion	of	significant	sources	and	sinks	and	4)	incorrect	interpretation	of	data.	

Several	more	recent	studies	have	avoided	such	(methodological) issues,	and	thus	the	scientific	knowledge	has	

been	 increased	 greatly	 in	 the	 last	 couple	 of	 years. Nevertheless,	 issues	 related	 to	 emission	 estimates	 from	

tropical	 peats	 are	 still	 being	 debated.	 In	 2011	 the	 International	 Council	 on	 Clean	 Transportation	 (ICCT)	

published	 a	White	 Paper	 by	 Page	 et	 al.	 (2011a):	 ‘Review	 of	 peat	 surface	 greenhouse	 gas	 emissions	 from	 oil	

palm	 plantations	 in	 Southeast	 Asia’, henceforth	 ‘the	 Page	 Review’,	 focussing	 on	 emission	 factors	 from	 the	

decomposition	of	peat	in	palm	plantations.	Uncertainties	are	identified	and	recommendations	formulated	for	

choosing	the	scientifically	most	appropriate	emission	factor	for	modelling	emissions	from	oil	palm	plantations

on	peat.	This	review	is	a	follow	up	to	the	Page	Review.	It	considers	the	quality	of	the	available	studies	and	the	

numbers	 they	 provide,	 including	 some	 that	 were	 not	 available	 at	 the	 time	 the	 Page	 Review	 was	 being	

developed.	

The	purpose	of	this	new	review,	as	specified by	the	ICCT,	is	as	follows:
4 Review of the literature on emissions from tropical peat degradation under palm oil

To	either

1)	Confirm	the	quality	of	the	work	of	Page	et	al.,	and	endorse	the	conclusions	that	the	peat	emissions	

estimates	provided	by	Hooijer	et	al.	(2012)	are	an	appropriate	source	for	the	EPA	and	other	regulators	

to	use	in	the	estimation	of	iLUC	factors;

or

2)	Identify	clearly	reasons	that	it	would	be	more	appropriate	for	EPA	and	other	regulators	to	assume	a	

value	other	than	that	recommended	by	Page	et	al.,	and	suggest	such	a	value.	

Outline

Chapter	 2	 discusses	 the	 currently	 used	methods	and	 their	 (un)certainties	 for	estimating	 CO2 emissions	while	

Chapter	3	covers	published	studies	on	emissions	from	oil	palm	plantations	on	peat	and	cross-checks	these	with	

the	Page	Review.	In	Chapter	4	 these	published	emission	values	are	discussed	in	 the	light	of	 the	White	Paper	

and	the	suggestions	and	comments	of	MPOC,	Bogor	University,	Nestle	Oil,	IAARD,	and	others	made	to	the	US	

Environmental	Protection	Agency	on	the	EPA’s	Notice	of	Data	Availability	for	the	palm	oil	pathway	under	RFS2.	

Chapter	5	answers	specific	questions	formulated	by	the	ICCT	and	recommends a	default	emissions	factor	for	oil	

palm	plantations	on	peat.	
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 5

Chapter	2	Emissions	and	Carbon	losses

Methods for	determining	emissions	and	C	losses

The	 amount	 of	 greenhouse	 gases	 released	 or	 taken	 up	 in	 an	 ecosystem	 is	 dependent	 on	 a	 variety	 of	

(interrelated)	processes	and	(climatic)	variables	such	as	microbial	activity, temperature,	moisture,	water	table	

depth,	 peat	 type,	 vegetation	 type, drainage,	 compaction,	 logging, etc. Studies	 use	 different	 approaches	 to	

assess	 greenhouse	 gas	 emissions.	 In	 general,	 there	 are	 five	 main	 methods	 to	 assess	 emissions	 and	 carbon	

losses:	

o Chamber	based	methods

o Eddy	covariance	(EC)	based	methods

o Soil	subsidence	based	methods

o Satellite	based	approaches

o Input-output	based	approaches

Methods	discussed	by	Page

Three	 of	 these	 five	 methods	 (chamber,	 eddy	 covariance	 and	 soil	 subsidence)	 are	 addressed	 in	 great	 detail,	

explained	 and	 discussed	 in	 the	 Page	 Review,	 which	 addresses the	 main	 sources	 of	 uncertainty	 and	 the	

assumptions	of	each	method	thoroughly	and	completely.	

As	 well	 as	 considering	 gaseous	 emissions	 from	 decomposing	 peat,	 the	 Page	 Review	 discusses	 the	 losses	 of	

Dissolved	and	Particulate	Organic	Carbon	 (DOC	and	POC)	 from	drained	peat	systems,	which	are	not	captured	

by	methods	like	closed	chambers	or	eddy	covariance.	It	notes	that	“the	ultimate	fate	of	carbon	exported	from	

peatlands	 via	 fluvial	 pathways	 remains	 largely	 unquantified	 and	 it	 is	 not	 known	 how	much	 of	 this	 carbon	 is	

converted	and	emitted	as	CO2 and/or	CH4 during	fluvial	transport.”	A	more	recent	paper	in	Nature	(Moore	et	

al.,	2013)	does	attempt	to	quantify	these	losses	and	is	discussed	below.	

Discussion	on	methods	that	were	not	considered

Satellite	based	approaches have	not	been	addressed	in	the	Page	Review. These	approaches	have	been	used	to	

assess large	and	small	scale	carbon	loss	of	above	ground	biomass due	to	land	use	changes	(e.g.	Franke	et	al.,	

2012)	and	are	also	used	to	estimate	carbon	losses	from	peat	fires	by	monitoring	the	area	impacted	by	fire	and	

coupling	 this	 to	 fire	 scar	 depth	 and	 volumetric	 carbon	 content	 of	 the	 peat	 (Ballhorn	 et	 al.,	 2009).	 Remote	

sensing can	also	be	used	to	separate	natural	trends	in	atmospheric	concentrations	from	the	effects	of	human	

induced	fires	(Mikaloff	Fletcher	et	al.,	2004a,b;	van	der	Werf	et	al.,	2006;	Denman	et	al., 2007).	Remote	sensing	

is	not	used	to	determine	emissions	that	are	related	to	drainage	of	peat	and	increased	soil	respiration,	although	

van	der	Werf	et	al	 (2008)	use	gas	concentration	measurements	in	atmospheric	columns	to	derive	total	fluxes	

and	 refer	 to	 bottom-up	 conversion	 numbers	 to	 allocate	 these	 changes	 to	 single	 sources.	 Satellite	 based	

approaches	 do	 not	 (yet)	give	 detailed	emission	 factors	 per	land	 use	 type	 (e.g.	oil	 palm)	and	 therefore	it	was	

reasonable	 that	 the	 Page	 Review did	 not	 consider	 this method,	 and	 this	 omission	 does	 not	 affect	 the	

conclusions	 reached.	 Table	 1	 describes	 remote	 sensing	 methods	 that	 are	 able	 to	 estimate	 the	 events	
6 Review of the literature on emissions from tropical peat degradation under palm oil

responsible	 for	emissions	 caused	 by	 land	 use	 change	 (e.g.,	 deforestation)	and	 for	greenhouse	gas	 uptake	 by	

sinks.

Table	1.	Current Land Remote Sensing	Instruments	in	the	Public	Domain.

Instrument Measurement Resolution and 

Coverage

Data Availability

Land Remote Sensing Satellite 

(Landsat)

Provides the longest continuous 

record of the Earth’s continental 

surfaces

30-60 m, global Landsat 7: 1999-present

Landsat 5: 1984-present

Advanced Spaceborne Thermal 

Emission and Reflection 

Radiometer (ASTER)

Provides high-resolution images of 

the land surface, water, ice, and 

clouds

15-90 m, global 1999-present

Moderate Resolution Imaging 

Spectrometer (MODIS)

Measures biological and physical 

processes occurring on the surface 

of the Earth, in the oceans, and in 

the lower atmosphere

250 m-1 km, 

global

1999-present

Airborne Visible/Infrared Imaging 

Spectrometer (AVIRIS)

Measures constituents of the Earth’s 

surface and atmosphere

5-20 m, aircraft is 

tasked

1998-present

The	input-output	based	approach has not	been	addressed	in	the	Page	Review.	This approach	estimates	carbon	

gains	and	losses	to	the soil	including	e.g.	litter	fall,	root	mortality,	soil	respiration,	solubles and fires.	Basically,	it	

tries	to	correct	(dark	chamber)	total	soil	respiration	measurements	for	litter	input	and	autotrophic	respiration.	

This method	is	not	often	used for	peat	soils	 (almost	no	peer	reviewed	publications	exist) since	below	ground	

carbon	 related	 processes	 are	 difficult	 to	 measure	 and	 because	 there	 is	 a	 current	 lack	 of	 data.	 Strong	

assumptions	 have	 to	 be	 made for	 peat	 soils	 and	 therefore	 the	 method	 should	 be	 applied	 with	 the	 utmost	

caution.	 The	 latest	 input-output	 based	research	 for	 tropical	 peat	 is	 that	 of	Hergoualc’h	 and	 Verchot	 (2011)	

which	used	the	following	assumptions:

• Vegetation	grows	the	same	on	mineral	and	peat	soil	(above	and	below	ground);	the	sources	that	were	

used	to	determine	C	stock	values	were	almost	all	from	mineral	soils.

• Litter	and	dead	wood	are	considered	to	be	one	pool	and	decay	of	both	is	covered	by	the	chamber	

method;	Total	C	input	is	considered	to	be	mean	ecosystem	root/litter	turnover.

• Average	values	for	all	fluxes	from	the	considered	literature	are	used	to	establish	a	net	soil	C	flux,	

whereas	placement	of	the	measurement	chamber	is	not	‘average’	at	all.	In	essence,	each	chamber	

measurement	should	rather	be	‘corrected’	using	root	and	litter	data	pertaining	to	the	measurement	

site	where	the	measurement	is	performed.

• A	growth	model	(Yoshimoto,	2001)	based	on	40	measurement	points	for	Japanese	timber	species	on	

mineral	soil	was	used	for	above	ground	biomass	growth.

• A	linear	model	(based	on	14	measurement	points,	Japanese	forest	on	mineral	soil)	was	used	for	below	

ground	biomass	growth.

• IPCC	values	were	used	for	soil	C	(50%).

• Data	for	the	various	pools	come	from	existing	(published)	sources	(theses,	peer	reviewed	publications,	

reports). The	reliability	of	some	(not	peer	reviewed)	sources	is	unknown.

At	 the	moment,	 this	method	is	more	 uncertain	 than	 other	methods,	as	many	assumptions	 have	 to	 be	made	

that	 have	 not	 been	 tested	 against	 direct	 measurements	 because	 of	 current	 lack	 of	 data.	 The	 lack	 of	

consideration	of	this	approach	in	the White	Paper	therefore	does	not	invalidate	the	conclusions	reached.	
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 7

DOC/POC measurements	are	discussed	briefly	in	the	White	Paper,	concluding	that	thus	far	few	measurements	

of	 DOC	 and	 POC	 concentrations	 and	 fluvial	 discharge	 rates	 have	 been	 performed	 in	 tropical	 peat-covered	

catchments.	Water	borne	carbon	losses	are	an	integral	part	of	soil	subsidence	measurements,	but	have	thus	far	

not	been	included	in	chamber	or	eddy	based	approaches	in	the	tropics.	

DOC	losses	lead	to	on- and	off	site	CO2 emissions and a	positive	relationship	has	been	found	between	DOC	and	

CO2 emissions.	Research	 has been published	 on	 the	 relevance	 of	 the	water	 borne	CO2 sources	in	 the	 tropics	

(Rixen	 et	 al.,	 2008;	 Alkhatib	 et	 al.,	 2007;	 Miyamoto	 et	 al.,	 2009;	 Yule	 and	 Gomez,	 2009), especially	 in	 the	

transitions	from	dry	to	wet	periods where	increases	of	15%	in	DOC	have	been	recorded	(Rixen	et	al.,	2008). The	

carbon	 is	 exported	 and	 rapidly	 decomposed,	 which	 may	 cause	 high	 fluxes	 of	 CO2 from	 water	 bodies	

(Couwenberg	et	al.,	2010;	Holden	et al.,	2004). The	most	recent	study	of	Moore	et	al. (2013)	concluded	that	the	

fluvial	organic	carbon	flux	from	disturbed	peat	swamp	forest	is	about	50%	larger	than	that	of	undisturbed	peat	

swamp	forest.	They	also	concluded	that	adding	these	fluvial	carbon	losses	(estimated	at	0.97	t	C	ha-1 yr-1)	to	the	

total	peatland	carbon	budget	of	disturbed	and	drained	peatlands	increases	the	total	ecosystem	carbon	loss	by	

up to	 22%.	 Jauhiainen	 and	 Silvennoinen	 (2012) used	 floating	 closed	 chambers	 to	 measure	 greenhouse	 gas	

fluxes	from	drainage	ditches	in	tropical	peatlands,	including	plantations,	and	found	that	total	GHG	fluxes	from	

canals	are	generally	higher than	from	the	neighbouring	fields.	They	found	fluxes	of	15.2	t	CO2-C	ha-1 yr-1 from

drainage	ditches	in	disturbed	peat	areas	 (ditch	area	is	2%	of	 the	 total),	which	are	somewhat	higher	 than	 the	

fluxes	found	by	Moore	et	al.	(2013),	but	on the	same	order of	magnitude.

Although	CH4 is	not	significant	in	the	carbon balance	of	ditches	(e.g.	Jauhiainen	and	Selvennoinen,2012),	CH4 is	

significant	 in	 the	 GHG	 balance of	 ditches,	 since	 the	 warming	 potential	 of	 CH4 is	 25 times	 that	 of	 CO2.	 CH4

accounted	 in	 some	 cases	 for	 over	 60%	 of	 the	 total	GHG	 balance	 (expressed	 in	 CO2-eq).	When	 using	 the	 soil	

subsidence	method,	the	carbon	losses	will	be	included,	but	the	added	warming	potential	is	not.	Therefore,	CH4

emissions	will	not	be	included	in	emission	estimates.	The	chamber	method	and	eddy	covariance	method	will	

only	 capture	 CH4 emissions	 if	 specifically	 measured.	 It	 is	 important	 to	 measure	 CH4 emissions	 from	 ditches,	

since	they	are	otherwise	not	included.	Not	addressing	these	emissions	is	conservative.

Fluvial	carbon	losses	and	losses	of	GHG’s	should	be	accounted	for	as	soon	as	the	knowledge	is	sufficient. The	

lack	 of	 consideration	 of	 water	 borne	 emissions	 in	 the	 Page	 Review is	 a	 shortcoming,	 but	 is	 understandable	

given	the	relatively	limited	evidence	base.

(Un)certainties of	frequently	used	methods

While	 some	 studies	 give	 emission	 ranges,	 methodological	 uncertainties	 and	 uncertainties	 related	 to	

calculations	and	assumptions	are	in	many	 cases	 not	addressed. Generally it	 remains	 uncertain	 how	accurate	

the	published	values	are and some	of	the	earlier	studies	on	greenhouse	gas	fluxes	are	difficult	to	interpret.	

Main,	general	pitfalls that also	have	been	satisfactory	identified	by	the	Page	Review	are:

• Short-term	(usually	<	1	y) studies (in	the	tropics,	difference	in	annual	balances	can	be	expected	between	

e.g.	dry	years	and	wet	years)

• Not	addressing	temporal	variability	(daily	to	annual)	in	a	systematic	way

• Focussing	 on	 CO2 only	 (relatively	 few	 studies	 also	 include	 N2O	 and	 CH4 in	 the	 total	 greenhouse	 gas	

balance).	Note	that	the	Page	Review	also	omitted	non-CO2 emissions	in	their	emission	factors,	which	is	

conservative.

• Not	providing	NET	emissions;	addressing	total	soil	respiration	only
8 Review of the literature on emissions from tropical peat degradation under palm oil

Observations	on	measurement	techniques

Each	 method	 of	 emissions	 estimation	 has	 strengths	 and	 weaknesses.	 These	 are	 briefly	 identified	 below	 for	

chamber	measurements,	subsidence	measurements	and	eddy	covariance	measurements.

Chamber	 measurements are	 widely	 used	 for	 estimating	 emissions	 of	 CO2,	 CH4 and	 N2O.	 If	 used	 properly,	

reliable	 (annual)	emission	estimates	can	be	made.	However,	biases	in	emission	estimates	can	easily	occur.	As	

pointed	out	in	the	Page	Review,	chamber	measurements	in	oil	palm	plantations	on	peat	have	sometimes	been	

carried	out	using	opaque	chambers.	While	these	chambers	are	well	suited	for	measuring	CH4 and	N2O	fluxes,	

they	measure	total respiration	from	roots	and	soil	combined	and	need	correction	to	arrive	at	net	CO2 emissions	

from	the	soil alone.	Main	pitfalls	for	chamber-based approaches,	which	have	been	addressed	and	discussed	in	

the	Page	Review	are:

• Lack	of	strategic	temporal	and	spatial	sampling.

• Use	of	too	long	closure	times and	not	avoiding	temperature	and	pressure	differences

• A limited	number	of	point	measurements	during	chamber	closure	time (<3)	

• Use	of	linear	interpolation	to	perform	temporal	upscaling	of	 fluxes	instead	of	using	a	regression	based	

approach.	

• No	separation	between	autotrophic	and	heterotrophic	respiration.	

As	 the	 Page	 Review	 mentions,	 so	 called	 ‘trenching’ is	 a	 method	 to	 separate	 autotrophic	 and	 heterotrophic

respiration.	However,	the	currently	used	trenching	method	cuts	off	roots	that	then	decay,	resulting	in	 (extra)	

CO2 emissions.	 Therefore,	 measurements	 should	 be	 started	 only	 after	 a	 certain	 period	 of	 time.	 Besides,	

trenching	 leads	 to	 different	 moisture	 dynamics,	 affecting	 emissions	 and	 trenching	 prevents	 not	 only	 root	

respiration	 but	 also	 rhizosphere	 priming	 by	 root	 exudates	 and	 oxygen	 that	 stimulate	 decomposition	 of	 the	

peat.	Using	the	trenching	method	has	the	risk	that	the	measured	plot	becomes	detached	from	the	system	and	

exhibits	different	properties.	For	these	reasons,	the	trenching	method	is	not	generally	supported. Another,	less	

intrusive	 method	 is	 to	 measure	 fluxes	 at	 distance	 from	 trees,	 where	 root	 respiration	 is	 not	 significant.	 This	

approach	 could	 be	 more	 reliable,	 although	 priming	 and	 oxygenation	 effects	 of	 roots,	 which	 stimulate	 peat	

decomposition,	would	then	be	underestimated.	

Eddy	covariance	methods have	not	often	been	used	in	the	tropics,	which	likely	is	the	reason	that	uncertainties	

in	emission	values	based	on	this	approach	have	not	been	addressed	in	much	detail	in	the	Page	Review.	Eddy	

covariance can	 be a	 reliable	method	 to	 estimate	 landscape	 scale	 fluxes	 of	 CO2,	 CH4 and	N2O.	 Fluxes	 can	 be	

coupled	 to	 variables	 that	 drive	emissions	 if	measured	 simultaneously	and	models	 can	 be	 created	 to	 fill	 data	

gaps	and	to	develop	future	projections.	Main	sources of	uncertainty	in	Eddy	Covariance	based	approaches	are:

• Assumptions	 made	 such	 as	 1)	 horizontal	 homogeneity	 2)	 flat	 terrain	 3)	 negligible	 mean	 vertical	 wind	

speed	

• Instruments	failure	and	improper	flux	calculations

• Model	uncertainty	in	gap	filling	procedures

• Uncertainty	in	relation	to	the	shifting	footprint

Overall,	 the	 eddy	 covariance	 method	 captures	 temporal	 variability	 better	 than	 any	 other	 method	 and	 it	 is	

expected	that	in	the	future	this	method	will	be	used	more	and	more,	either	as	a	method	to	estimate	and	model	

emissions	based	on	driving	variables,	or	to	cross-check	with	other	methods	such	as	the	chamber	based	method	

and	the	soil	subsidence	method.	
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 9

Soil	subsidence is	caused	by	several processes:	consolidation,	compaction,	oxidation,	fire, and	water and	wind	

erosion.	Consolidation	refers	to	surface	height	loss	caused	by	tighter	packing	of	the	peat	soil	below	the	water	

table.	 Consolidation	 of	 tropical	 peat	 drained	 for	 plantation	 development	 may	 result	 in	 considerable	 height	

losses,	but	ends	within	one year	 (Den	Haan	et	al.,	2012).	Like	compaction	(and	 shrinkage)	of	peat	above	 the	

water	table	it	does	not	result	in	carbon	losses.	Fires,	erosion	and	microbial	oxidation	of	peat	do	result	in	carbon	

losses	to	the	atmosphere.	Fire	related	losses	can	be	observed	from	subsidence	records,	but	the	method	does	

not	focus	on	them.	Rather	it	is	designed	to	capture	net	peat	(and	carbon)	losses	from	microbial	oxidation	and	

lateral	waterborne	 (DOC	and	POC)	export.	Wind	erosion	can	be	ignored	in	plantations	on	 tropical	peat.	As	it	

was	 believed	 that	 waterborne	 losses	 are	 small	 compared	 to	 losses	 from	 microbial	 oxidation, research	 has	

focussed	 on	 quantifying	 the	 relative	 importance	 of	 compaction	 and	 oxidation	 as	 the	 two	 main	 processes	

leading	 to	 height	 loss.	 In	 the	 first	 year	 after	 drainage,	 compaction	 and	 consolidation	 have	 a	 greater	

contribution	 to	 soil	 subsidence	 than	 in	 later	 years. Methane	 and	 N2O	 emissions	 are	 excluded	 from	

consideration	when	using	the	soil	subsidence	method.	While	chamber	methods	and	eddy	covariance	methods	

can	 give	 reliable	 annual	 estimates	 after	 a	 measurement	 period	 of	 e.g.	 2	 years,	 the	 soil	 subsidence	 method	

needs	 multiple	 years	 of	 monitoring	 to	 calculate	 annual	 CO2 emissions	 numbers	 and	 water	 borne	 losses,	 to	

average	out	the	swelling	and	shrinkage	of	the	peat	during	wet	and	dry	periods	and	because	soil	subsidence	is	a	

slow	process.	The	oxidation	fraction,	carbon	content	of	the	peat	and	bulk	density	are	the	factors	that	have	to	

be	known	to	reliably	use	soil	subsidence	as	an	indirect	measure	for	calculation	of	CO2 emissions.	Main	sources	

of	uncertainty	 for	soil	subsidence	approaches,	which	have	been	addressed	and	discussed	in	 the	Page	Review	

are:

• The	separation	between	consolidation,	compaction	and	oxidation	and	the	oxidation	component	used

• The	 assumptions	 being	 made	 with	 respect	 to	 carbon	 content	 of	 the	 peat,	 and	 bulk	 density	 used	 in	

calculations

Conclusions

Chamber	based	methods,	eddy	covariance	methods	and	 the	soil	subsidence	method	have	been	addressed	in	

great	detail,	explained	and	discussed	in	the	Page	Review.	The	main	sources	of	uncertainty	and	the	assumptions	

in	 each	 method	 have	 been	 discussed	 thoroughly.	 The	 soil	 subsidence	 method	 was	 found	 to	 be	 reliable	 and	

robust	enough	to	use	it	for	a	‘best	estimate’	for	the	emissions	factor	for	oil	palm	on peat.

Input-output	based	approaches	have	not	been	addressed	by	the	Page	Review.	Since	this	method	is	not	yet	at	

the	 stage	 of	 being	as	 certain	as	 other	methods,	 the	lack	 of	 consideration	 of	 this	approach	is	 reasonable	and	

does	not	affect	the	conclusions	reached.

Water	borne	emissions of	CO2 are	captured	by	subsidence	measurements	and	are	thus	included	in	the	emission	

factor	 for	 oil	 palm	 on	 peat	 that	 is	 given	 in	 the	 Page	 Review.	 Subsidence	 measurements	 do	 not,	 however,	

capture	non-CO2 emissions	and	thus	the	increased	warming	effect	of	potential	CH4 emissions	from	e.g.	drainage	

ditches	and	the	N2O	emissions	from	fertiliser	application	are not	included.	
10 Review of the literature on emissions from tropical peat degradation under palm oil

Chapter	3	Carbon	dioxide	emissions	

values	published

A	range	of	emission	values	for	oil	palm	plantations	on	peat	have	been	published	based	on	various	approaches.	

Chamber	based method

Table	 4	 in	the	 Page	 Review	summarizes	 available	 peat	 CO2 emission	 data	 measured	 using	 the	 (dark)	 closed	

chamber	technique	for	OP	plantations	on	peatland.	This	listing	gives	a	complete	overview	of	available	research	

at	 the	 time,	 and	 the	 assessment	 in	 that	 table	 of	 the	 quality	 of	 the	 research	 presented	 is	 fair.	 A	 few	 studies	

(Agus	et	al.,	Melling	et	al.,	Hooijer	et	al.,	 Jauhiainen	et	al.)	are	discussed	in	more	detail	below	either	because	

they	were	not	available	at	the	time	of	writing	the	review,	or	because	there	are	some	additional	comments.	

The	papers	of	Agus	et	al. (in	prep.)	and	Agus	et	al. (2012),	were	not	available	at	the	time,	but	are	based	on	the	

same	master’s	thesis	(Handayani,	2009)	as	Agus	et	al. (2010).	See	table	2	for	details.	

Table	 2.	 Details	 regarding	 land	 use,	 methods,	 sampling,	 water	 table	 (WT) and	 mean	 CO2 emissions	 in	 the	

studies	of	Agus	et	al.

Reference Land	use Method Sampling WT

(cm)

Mean	CO2	

(t	CO2	ha-1 yr-1)

Remarks

Agus	et	al.

in	prep,	and	

2012

Oil	palm	

on	peat

Modificatio

n	(30%	

correction)	

of the	

equation	

used	in	

Hooijer	et	

al.	(2006)*

no 40-60 33	 • Modification	of	the	Hooijer	

equation, because	of	

inclusion	of	autotrophic	(root)	

respiration (30%), based	on	

the	thesis of	Handayani	

(2009)

• Use	of	WT	as	a	proxy

• Including	emissions	from	fires

Agus	et	al	

2010

Oil	palm	

on	peat,	

different	

ages

Chamber 2	

measure

ments

unkno

wn

19.5	 • Short	term measurements	

extrapolated	to	annual	flux

• Underestimations	have	to	be	

expected because	of	long	

closure	times	(35	min.)	

*see	discussion	below	on	the	correction	factor	of	Agus	et	al. (2012).

Handayani	 (2009)	carried	out	 two	sets	of	 chamber	measurements	at	each	 site,	one	in	 the	wet	 season	 (MayJune)	and	one	in	 the	dry	 season	 (Oct.-Nov.).	The	 thesis	is	 focussed	on	 separation	of	auto- and	heterotrophic	

respiration	but,	as	the	Page	Review	rightly	comments,	uses	a	disputable	method:	roots	are	dug	up	and	brought	

into	 chambers	 and	 then	 covered	 by	 peat	 again,	 which	 causes	 great	 disturbance	 of	 the	 peat-soil	 and	 has	 an	

unidentified	effect	on	measured	 fluxes.	The	long	chamber	closure	times	may	lead	to	biased	estimates	 (under	

estimation)	of	real	emissions.	

The	 Page	 Review	 is	 also	 critical	 of	 the	 study	 of	 Melling	 et	 al.	 (2005).	 The	 main	 reasons	 mentioned	 are:	 1)	

measurements	 of	 undifferentiated	 CO2 emissions,	 2)	 only	 three	 replicates	 (monthly	 measurements),	 3)	

limitations	in	the	experimental	design,	4)	no	information	on	how	representative	the	measurements	were	and	
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 11

5)	two-point	linear	regression	in	estimating	fluxes	was	used.	This	criticism	is	appropriate	and	some	additional	

points	 could	 be	 mentioned	 that	 add	 to	 the	 uncertainty	 and	 possible	 underestimation	 of	 CO2 emissions	

conducted	from	this	study	(table	3).

Table	3.	Details	regarding	land	use,	methods,	sampling,	WT	and	mean	CO2 emissions	in	the	study	of	Melling	et	

al

Reference Land	use Method Sampling WT

(cm)

Mean	CO2

(t	CO2 ha-1 yr1

)

Additional	remark

Melling	et	

al.,	2005

Oil	palm	

on	peat

Chamber 1	year

monthly

Annual	

average	of	

around 60	

cm

55	 • Long	chamber	closure	time

• Use	of	steel	chambers,	

which	are	temperature

sensitive

The	 studies	 of	 Hooijer	 et	 al. (2010)	 and	 Hooijer	 et	 al. (2006)	 are	 briefly	 addressed	 together	 with	 the	 metaanalysis	of	Couwenberg	et	al. (2010)	in	paragraph	5.3	on	soil	subsidence.	These	studies	present	a	relationship	

between	 water	 table	 and	 CO2 emissions	 for	 a	 water	 table	 depth	 between	 0.5	 and	 1.0,	 based	 on	 meta-data	

assessments	of	studies	carried	out	in	deforested	tropical	peatlands.	The	relationship	between	water	table	and	

GHG	 emissions found	 by	 Hooijer	 et	 al. (2012) was similar	 to	those found	 by	 Hooijer	 et	 al. (2006,	 2010)	 and	

Couwenberg	et	al. (2010).	

Although	the	relationship between	water	table	and	emissions	reported	in Hooijer	et	al	(2006)	was	partly	

compiled	from	data	with	an	unknown	autotrophic	component	to	respiration,	it	should	be	noted	that	1)	in	most	

studies	used	in	determining the	regression	(Murayama	and	Bakar, 1996;	Jauhiainen	et	al.,	2004;	Melling	et	al.,	

2005;	Ali	et	al.,	2006) it	is	likely	that	measurements	were	conducted far	away	from	trees;	3	or	4	metres	seems	

to	be	enough	to	discard	root	respiration	as	a	factor	(Dariah	et	al.	in	prep) and	2)	with	improving	insights	and	

different	measurement	techniques,	similar	values	and	relationships have	been	found.	Agus	et	al. (2012)	suggest	

correcting	the	equation	of	Hooijer	et	al	(2006)	with	a	factor	of	0.7	for	autotrophic	respiration.	However:

• In	oil	palm	plantations	roots	are	not	distributed	equally	over	the	plantation.	On	peat,	roots	grow	close	to	

stems	 and	 are	 likely	 to	 be	 absent at	 distances	 >4	 m	 (Dariah	 et	 al.	 in	 prep.).	 In	 the	 studies	 used	 to	

compile	the	equation	of	Hooijer	et	al	 (2006),	distance	to	palm	trees	is	not	mentioned,	but	it	is	likely	

that	 measurements	 were	 conducted away	 from	 the	 palm	 trees.	 In	 conclusion,	 correction for	

autotrophic	 respiration is	 not	 simply	 a	 matter	 of	 applying	 a	 single	 factor	 to	 all	 dark	 chamber	

measurements,	but	should	rather	be	made	in relation	to	where	the	 flux	measurements	were	carried	

out	relative	to	surrounding	palm	trees.

• The	correction	 factor	of	0.6, and	later	 0.7, as	 suggested	by	Agus	et	al. (2012) was	based	on	a	 student	

thesis,	which	was	not	peer	reviewed	(Handayani,	2009)	and	uses	a	disputable	method	for	separation	

between	 heterotrophic	 and	 autotrophic	 respiration	 (see	 above).	 Jauhiainen	 et	 al	 (2012)	 suggest	 a	

factor	of	0.8	for	data	gathered	close	to	trees.	Far	away	from	trees	no	correction	is	needed.	Note	that	

this	study	was	specifically	designed	to	differentiate	sources	of respiration.	

• The	publication	of	Couwenberg	et	al. (2010)	 reports	a	 similar	 relationship between	CO2 emissions	and	

water	 table	 as	 the	 studies	 of	 Hooijer	 et	 al.	 This	 independent	 study	 of	 Couwenberg	 excludes	

autotrophic	respiration.	

• The	 most	 recent	 and	 very	 extensive	 study	 of	 Jauhiainen	 et	 al. (2012)	 reports	 values	 that	 fall	 on	 the	

regression	line	of	Hooijer	et	al. (2006;	2010;	2012)	and	Couwenberg	et	al. (2010).	
12 Review of the literature on emissions from tropical peat degradation under palm oil

The	publication	of	Jauhiainen	et	al	(2012)	was still	in	preparation	at	the	time	the	Page	Review was	published.	As	

mentioned	earlier,	this	publication	contains	robust,	chamber	based	research	that	avoids	deficiencies	evident	in	

past	studies	such	as	the	inclusions	of	autotrophic	respiration and long	closure	times.	This	research	confirms	the	

conclusions	of	the	Page	Review	with	respect	to	the	emission	factor	from	the	peat	surface	in	plantations	(table	

4).

Table	4.	Details	regarding	land	use,	methods,	sampling,	WT	and	mean	CO2 emissions	in	the	study	of	Jauhiainen	

et	al.	WTD	refers	to	water	table	depth,	and	BD	refers	to	bulk	density.

Reference Land	use Method Sampling WT

(cm)

Mean	CO2

(t	CO2 ha-1 yr-1)

BD

(g	cm-3)

Remark

Jauhiainen	

et	al., 2012

Acacia	

plantations	on	

peat	(same	

plantations	as	

in	Hooijer	et

al.,	2012)

Chamber 2	years

2300	

measurements

144	locations

80 Heterotrophic

respiration:

80	(after	

correction	for	the	

effect	of	diurnal	

temperature)

(emission

=	71.40	×	WTD	+	

23.15

(R2	=	0.47,	SE	=	

197)

94	(if	not	

corrected	for	

temperature	

(emission =	74.11	

×	WTD	+	29.34	

(R2	=	0.34,

SE	=	317))

0.06–0.12	

(average	

0.09	g	

cm−3)

30–50	cm	

horizon	

from	the	

peat	

surface

• Short	

measurement	

time	(81	s)

• Linearity	

checks	on

regression

• Long	term	(2	

years)

• Frequent	

measurements	

(2-4	weekly)

• Separation	

heterotropic	

and	

autotrophic	

respiration

• Temperature	

corrected

Soil	subsidence	based method

Table	 5	 in	 the	 Page	 Review	 summarizes	 available	 peat	 CO2 emission	 data	 based	 on	 the	 soil	 subsidence	

approach	for	OP	plantations	on	peatland.	It gives	an	almost	complete	overview	of	available	research	until	the	

time	of	publishing	of	the	Page	Review and	its	judgement	on	the	appropriateness	of	the	research	described	in	

paragraph	5.3	is	fair.	The	study	of	Othman	et	al. (2011)	was	published	at	the	same	time	as	the	Page	Review and	

is	assessed	below	(Table	5):
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 13

Table	5.	Details	regarding	land	use,	methods,	sampling,	WT	and	mean	CO2 emissions	in	the	study	of	Othman	et	

al. BMP	refers	to	best	management	practices.

Reference Land	use Method Sampling WT

(cm)

Mean	CO2

(t	 CO2 ha-1

yr-1)

BD

(g	cm-3)

Remark

Othman	 et	

al., 2011 and	

Othman	 et	

al.,	 2009

(BMP	 for oil	

palm	

cultivation	 on	

peat)

old	oil	palm	

on	 peat,	

Sessang	

Sarawak,	

Malaysia

Hooijer’s	 equation	

based	 on	 water	 table	

dependency,	 cross	

checked	 with	 own	

estimates	 based	 on	 soil	

subsidence	

5	years 43	

49

53

39

44

48

Range	

0.14	 –

0.43	

Subsidence:

• 13.4	cm	yr-1

(first	 years	 after	

drainage)

• 5-6	cm	yr-1

(3-9	 years	 after	

drainage)

• 3-4	cm	yr-1

(after	 9	 years	 of	

drainage)

• CO2 calculations	

based	on	peat	C	

content,	BD and	

oxidative

fraction of	0.4

In	 the	 study	 of	 Othman	 et	 al.	 (2011),	 the	 ‘years	 after	 drainage’ need	 to	 be	 interpreted	 with	 care.	 The	 data	

collected	by	Othman shows a	sudden	decline	in	the	subsidence	 rate	between	2004 and	2006,	irrespective	of	

plantation	age and	without	explanation	and	therefore	the	observed	trend	of	decreasing	subsidence with	age	of	

the	plantation has	to	be	treated	with	care	as	well. Othman	et	al.	(2011)	do	not explain	the	40% value	for	the	

oxidative	component	of	subsidence;	this	value	is	at	the	lower	end	of	published	oxidative	fractions	(Couwenberg	

et	al., 2010)	and	likely	too	low	for	tropical	sites	(Hooijer	et	al., 2012).	Moreover,	Othman	et	al.	(2011) do	not	

present	 site-by-site	 estimates	 based	 on	 the	 subsidence method (they	 do	 estimates	 based	 on	 the	 Hooijer	

regression).	The	cross-check	with	own	observations	of	Othman	et	al.	(2011)	does	not	seem	to	have	resulted	in	

adjustment	of	the	Hooijer-based	values.	Overall,	it	is	not	very	clear	how	Othman	et	al	 (2011)	dealt	with	their	

own	 measurements.	 It	 seems	 the	 measured	 carbon	 content	 of	 25%	 was	 applied	 to	 the	 subsidence	 based	

calculations,	although	this	value	is	extremely	low	and	deserves	more	than	the	passing	discussion	in	Othman	et	

al.	(2011),	particularly	considering	that	a	carbon	content	twice	as	high	was	observed	in	an	adjacent	plot	of	the	

research	area.	The	presentation	of	the	bulk	density	numbers	in	the	paper	of	Othman	et	al. (2011)	is	opaque.	It	

is	 highly	 unlikely	 that	 bulk	 density	 would	 increase	 to	 the	 extent	 presented	 in	 the	 paper	 after	 mechanical	

compaction	of	the	peat.	The	lack	of	consideration	of	the	Othman	et	al.	(2011)	study in	the	Page	Review	does	

not	affect	the	conclusions	reached,	because	they	use	the	Hooijer	relationship between	water	table	depth	and	

CO2 emissions	for	their	final	emission	estimates.	The	cross	check	with	their	own	measurements	is	unclear	and	

also	not	relevant	for	the	comparison	in	the	Page	Review.	

The	study	of	Couwenberg	et	al. (2010)	is	addressed	in	 the	Page	Review,	included	in	Table	6	and	 reviewed	in	

paragraph	5.3.	Below	a	summary	is	given	(Table	6).	
14 Review of the literature on emissions from tropical peat degradation under palm oil

Table	 6.	 Details	 regarding	 land	 use,	 methods,	 sampling,	 WT	 and	 mean	 CO2 emissions	 in	 the	 study	 of	

Couwenberg	et	al.

Reference Land	

use

Method Sampli

ng

WT

(cm)

Mean	CO2

(t	CO2 ha-1 yr1

)

BD

(g	cm-3)

Remark

Couwenb

erg et	al.,	

2010

Compilati

on	of	

existing	

research	

on	soil	

subsidenc

e	and	

emission	

measure

ments	

60	–

80

Range	55-72

9	t	CO2 ha-1

yr-1 for	each	

10	cm	of	

drainage	

depth.

• Use	of	conservative	

carbon	density

• Separated between	

heterotrophic	and	

autotrophic	respiration*

• Assumed	a	conservative	

oxidation	fraction	of	40%	

(the	low	end	of	

published	values	that

range	from	40	- 90%)

*The	 paper	 uses	 a	 subsidence	 based	 approach	 that	 is	 not	 affected	 by	 the	 problem	 of	 auto- versus	

heterotrophic	respiration.	The	single	chamber	based	number	of	Melling	et	al.	2007	mentioned	in	the	study	of	

Couwenberg	et	al.	is	assumed	to	have	excluded	autotrophic	respiration.	

Couwenberg	et	al. (2010)	consider a	range	of	water	table	depths from	0	to	~70 cm	and	argue	that	emissions	

may	stop	increasing	with	water	table	depth when	water	table	depth>50	cm.	Based	on	recent	data	(e.g.	Hooijer	

et	al., 2012)	 this	hypothesis	should	be	rejected.	Couwenberg	et	al. (2010)	did	not	actually	provide	a	range	of	

values	 but	 presented	 a	 regression and	 an	 estimate	 of	 55	 t	 CO2 ha-1 yr-1 for	 a	 typical	 OP	 plantation.	 The	

extrapolation	of	the	regression	to	deeper	water	table	depths	(as	done	in	the	Page	Review)	may	be	valid,	but	it	

should	be	understood	that	these	extrapolations	were	not	presented	in	Couwenberg	et	al.	(2010).	

The	most	recent	soil	subsidence	based	research	is	that	of	Hooijer	and	Couwenberg	(accepted).	For	details,	see

Table	7	below.	

Table	7.	Details	regarding	land	use,	methods,	sampling,	WT	and	mean	CO2 emissions	in	the	study	of	Hooijer	and	

Couwenberg.

Reference Land	use Method Samp

ling

WT

(cm)

Mean	CO2	

(t	CO2	ha-1 yr-1)

BD

(g	cm-3)

Remark

Hooijer	 &

Couwenbe

rg	

(accepted)

Oil	palm

Acacia

subsidence 3	

years

56

65

70

65

58	

74	

0.106/0.082	

0.096/0.078	

0.111/0.074	

Based	 on	 steady	

state	 assumption	

and	 using	 BD of	

the	 peat	 below	

the	WT	only

This	research	confirms	 the	conclusions	of	 the	Page	Review	with	respect	 to	 the	emission	 factor	 from	 the	peat	

surface	in	plantations.	Hooijer	and	Couwenberg	(accepted)	do	not	include	the	emissions	spike	directly	following	

drainage	 in	 these	 values. Methane	 from	 ditches	 will	 add	 to	 the	 total	 greenhouse	 gas	 balance	 of	 oil	 palm	

plantations.

Given	the	relation	between	water	table	and	CO2 emissions,	lower	emissions can	be	expected	at	higher	water	

table levels.	Note	that	currently,	in	many	plantations	in	SE	Asia	the	water	table	varies between	100	cm	and	50	

cm (average	around	75	cm) below	field	level.	If	drains	are	not	spaced	properly	and	dams	have	not	been	built	in	
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 15

the	right	way,	and	because	of	the	large	seasonal	variation	of	rainfall	in	Indonesia,	over- or	under-drainage	is	a	

common	problem.

RSPO	 launched	 its	 Best	Management	 Practices	 in	 2012,	 and	 the	Malaysian	 Palm	Oil	 Board	 launched	 its	Best	

Management	Practices in	2011.	RSPO	advises	to	keep	the	water	table	between	40	and	60	cm	below	field	level,	

or	 50	 – 70	 cm	 in	 collection	 drains.	MPOB	 advices	 in	 their	management	 practices	 a	 water	 table	 of	 30-50	 cm	

below	 the	 peat	 surface	 in	 the	 field	 or	 40	 and	 50	 cm	 in	 the	 collection	 drain.	 Given	 the	 water	 table-emission	

relationship in	 Hooijer	 and	 Couwenberg,	 reducing	 the	 average	 drainage	 depth	 to	 50	 cm	 compared	 to	 the	

current	75	cm	could	potentially	lead	to	a	future	reduction	of	20	t	CO2 ha-1 yr-1 if	this	higher	water	table could	be	

maintained.	The	 reality	is	 that	maintaining	 the	water	 table	at	 40-50	cm	in	a	large	plantation	is	generally	not	

feasible	 with	 most	 current	 drainage	 lay	 outs.	 Therefore,	 RSPO	 and	 MPOB	 encourage	 plantation	 owners	 to	

optimize	their	drainage	systems.	

Eddy	Covariance	based method

The	Page	Review	did	not	review	eddy	covariance	based	research,	as	no	measurements	were	available	from	oil	

palm	plantation	sites	at	that	time.	Currently,	more	eddy	covariance	towers	in	tropical	SE	Asia	are	operational	

and	one	eddy	covariance	system	is	located	at	an	oil	palm	plantation	site.	A	tower	has	been	installed	on	an	oil	

palm	 plantation	 on	 peat,	 3-7	 years	 old, in	 Sibu, Sarawak,	 and	 has	 been	 running	 since	 2011	

(http://www.asiaflux.net/network/080SBW_1.html);	 however,	 a	 few	 years	 of	 data	 is	 needed	 before	 reliable	

estimates	can	be	presented.	If	more	research	becomes	available,	it	shall	be	cross-checked	and	eddy	covariance	

studies	shall	be	considered.	
16 Review of the literature on emissions from tropical peat degradation under palm oil

Chapter	4	Discussion

CO2	emissions	

• Heterotrophic	respiration	versus autotrophic	respiration

Flux	 measurements	 made	 using	 opaque	 closed	 chambers	 cover	 total	 soil	 respiration	 (Rtot)	 that	 includes	

autotrophic	 (Ra)	 and	 heterotrophic	 (Rh)	 components.	 Autotrophic	 respiration	 (from	 roots) needs	 to	 be	

separated	from	soil	microbial	respiration (Rh),	as	Ra represents	recycling	of	C	recently	fixed	in	photosynthesis,	

while	Rh represents	the	actual	loss	of	C	from	the	peat	substrate. Total	soil	respiration	values	have	been	used	to	

suggest	 that	emissions	 from	oil	palm	plantations	are	less	 than	 from	pristine	 forest	 (e.g.	Melling	et	al.,	2005).

Recent	studies	have	greatly	decreased	uncertainty related	to	separation	of	soil	fluxes.	An	example	of	a	recent,	

complete	 and	 robust	 study	 is	 that	 of	 Jauhiainen	 et	 al.	 (2012)	 which	 the	 Page	 Review	 rightly	 refers	 to	 as	 a	

‘benchmark’	 study.	 Based	 on measurements across	 the	 distance	 from	 Acacia	 trees	 in	 Riau (Indonesia),	 and	

supported	by	measurements	in	trenched	plots,	Jauhiainen	et	al.	(2012)	found	that	Ra at a	distance	of >	1.3	m	

from	trees	was	negligible	and	that	on	average	Ra contributed	about	20%	to	Rtot.	Agus	et	al	(2009)	report	Rh as	

40%	of	Rtot because	in	their	study	in	Aceh,	Sumatra,	they	found	that	CO2 emitted	from	the	non-rooted	zone	was	

about	62%	of	that	of	the	rooted	zone	(thesis	of	Handayani, 2009),	indicating	a	significant	contribution	of	roots

to	the	production	of	CO2. Based on	the	thesis	of	Handayani,	Agus	et	al.	(2012)	report	Ra to	be	about	14%	for	6	

year old	oil	palm and	31%	for	15	year	old	oil	palm and,	using	the	same	thesis,	Agus	et	al. (in	prep)	propose	a	

correction	 factor	 of	 0.7	 to	 derive	 Rh from	 Rtot.	However,	 the	 results	 of	Hadayani	 (2009)	must	 be	 interpreted	

with	caution,	because	of	the	methodological	issues	described	in	Chapter	3	above	and	as	discussed	in	the	Page	

Review	(paragraph	5.2).	

The	Ra value of	20%	of	Rtot reported	by	Jauhiainen	et	al. (2012)	is	lower	than	previous	values	suggested	for	oil	

palm	plantations	on	peatland,	which include 31-46%	 (Melling	et	al.,	2007),	36%	 (Murdiyarso	et	al.,	2010)	and	

29% (Hergoualc’h	 and	 Verchot,	 2011).	 The	 latter	 two	 studies	 are	 meta-analyses	 that	 include	 data	 from	

plantations	on	mineral	soil	as	well.	Most	research	used	the	so	called	‘trenching’	method.	If	not	applied	properly	

and	with	care,	the	disturbance	of	the	peat	soil	ecosystem	related	to	the	cutting	of	the	roots	may	have	a	great	

impact	(increase)	on	the	respiration	values.	It	has	to	be	noted	that	Jauhiainen	et	al.	(2012)	also	partly used	the	

trenching	method	in	their	study.	

Not	specifically	mentioned	by	the	Page	Review	is	that	applying	a	correction	for	Ra on	published	chamber	based	

data	 is	 not	 without	 risk,	 because	 it	 is	 not	 known	what	 location	 exactly	 has	 been	 sampled	 and	 thus	 it	 is	 not	

known	if	Ra is	partly	or	entirely	included	in	measured	emissions.	If	samples	are	taken	>3-4	meters	 from	palm	

trees	on	peat,	the	influence	of	autotrophic	respiration	will	be	close	to	0.	Close	to	trees	(<	1	m),	the	influence	of	

autotrophic	respiration will	be	at	a	maximum.	The	most	reliable	way	for	determining	emission	default	values	is	

to	use	research	that	avoids	inclusion	of	autotrophic	respiration	(e.g.	Jauhiainen	et	al.,	2012;	Couwenberg	et	al.,

2010)	and	to	compare	more	than	just	one	study.

Soil	subsidence	

• oxidation	versus compaction

Drainage	of	peatlands	leads	 to	 soil	 subsidence	 resulting	 from	peat	oxidation,	 shrinkage	and	compaction.	The	

Page	Review	states	that	after	a	stage	with	rapid	subsidence	rates	 (1-2	years)	caused	mainly	by	consolidation,	

subsidence	rates	stabilize	and	slow	down	to	a	constant	rate.	Recently	this	conclusion	was	confirmed	by	Hooijer	

& Couwenberg	 (accepted)	and	Den	Haan	et	al.	(2012).	They	report	that	in	tropical	peatlands	soil	stabilisation	

occurs	within	1	year	after	drainage.	The	initial	or	primary	subsidence	depends	on	the	type	and	depth	of	peat	
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 17

and	the	drainage	level	and	rates	can	be	more	than	50	cm	yr-1 in	drained	tropical	peatlands	(Hooijer	et	al.,	2012;	

Wösten	et	al.,	1997).	Most	 recent	and	extensive research	of	Hooijer	et	al.	 (2012)	and	Hooijer	& Couwenberg	

(accepted)	shows	that	constant	long-term	subsidence	rates	are	around	4	to	5	cm	yr

-1

,	4.5	cm	yr-1 on	average.	

Stephens	 et	 al.	 (1984)	 report	 that	 peat	 surface	 subsidence	 continues	 at	 a	 constant	 rate	 for	 many	 decades,	

which	is	explained	by	the	dominance	of	oxidation,	the	limited	(but	continued)	role	of	compaction and	the	lack	

of	consolidation. Over	18	years	of	drainage,	75%	of	cumulative	subsidence	in	Acacia plantations	was	found	to	

be	caused	 by	 peat	oxidation by	Hooijer	et	al.,	 2012. The	 same	 study	estimated	 92%	oxidation	in	an	oil	 palm	

plantation	in	 Jambi	over	a	period	of	19	years	after	drainage.	Values	of 85-90%	were	reported	 for	subtropical	

peatlands	by	Stephens	et	al. (1989)	based	on	over	76	years	of	measurements and	the	earlier	published	value	of	

78%	oxidation	by	the	same	author	based	on	55	years	of	measurements	(Stephens	and	Speir, 1969).	Wösten	et	

al.	 (1997),	 based	 on	 DID	 and	 LAWOO	 (1996),	 report	 average	 subsidence	 rates	 of	 4.6	 cm	 yr

-1 for	 oil	 palm	

plantations	 in	 Johor,	 14	 to	 28	 years	 after	 drainage of	 which	 60%	 was	 estimated	 to	 be	 caused	 by	 oxidation.	

Wösten	 et	 al.	 (1997)	 also	 report	 cases	 of	 complete	 peat	 loss.	 Couwenberg	 et	 al.	 (2010)	 assumed	 a	 40%	

oxidative	component	to	subsidence	based	on	a	global	review	that	includes	data	from	temperate	climate	zones.	

The	 oxidative	 fraction	 may	 be	 expected	 to	 be	 higher	 in	 the	 tropics	 as	 oxidation	 is	 temperature	 dependent	

whereas	compaction	is	not	 (or	only	secondarily via	oxidation).	Hooijer	&Couwenberg (accepted)	report	~80%	

for	two	oil	palm	plantations.	

It	seems appropriate	to	separate	soil	subsidence of	the	first	year from	subsequent	years.	Immediately	following	

drainage,	consolidation	plays	a	large	role	in	subsidence,	but it ceases	within	a	year (Den	Haan	et	al.	2012). After	

that, compaction	of	the	drained	peat	layer	may	be	larger	than	afterward,	but	stabilizes within	5	years	(Hooijer	

& Couwenberg,	accepted).	The	value	of	92%	oxidative	contribution	as	proposed	by	Hooijer	et	al. (2012)	is	on	

the	 high	end	 of	 published	values,	 but	 until	 now	it	is	 the	most	 robust	 study	 that	was	 specifically	 designed	 to	

determine	the	contribution	of	oxidation	to	soil	subsidence	since	drainage	started.

Note	that	in	the	method	set	out	by	Hooijer	& Couwenberg	(accepted)	an	estimate	of	the	oxidative	component

is	not	needed	to	determine	emissions.	Only	subsidence	rate,	bulk	density and	carbon	content	of	the	peat	below	

the	 water	 table	 have	 to	 be	 known.	 Nevertheless,	 the	 authors	 did	 calculate	 an	 oxidative	 contribution	 to	

subsidence	of	80%.

Carbon	content	of	the	peat

Table	 5	 of	 the	 Page	 Review	 summarizes	 estimates	 of	 peat	 carbon	 emissions	 based	 on	 a	 review	 of	 soil	

subsidence,	including	the	carbon	density	used	in	calculations.	It	quotes	carbon	densities	of	0.068	and	0.138	g	C	

cm-3.	The	value	of	0.068 is	taken	from	Couwenberg	et	al.	(2010),	who	later	corrected	this	value	to	0.061	for	CKalimantan	and	 0.044	 for	 coastal	peat	 swamp	 forests (Dommain	et	al.	 2011).	Note	 that	 this	 value	would	 be	

applicable	 to	 the	peat	below	 the	water	 table only	and	is	 (very)	conservative	when applied	 to	 the	upper	peat	

layer.	The	value	of	0.138	g	C	cm-3 is	taken	from	Ywih	et	al.	(2009)	at	very	high	peat	bulk	densities	of	~0.300	g	

cm-3.	

Carbon	concentration	values	on	a	dry	weight	basis	of	around	55%	were	found	to	be	representative	for	hemic	

and	 fibric	 tropical	 peat	 in	 SE	 Asia.	 Similar	 values	 were	 reported	 by	 Couwenberg	 et	 al.	 (2010),	Wösten	 et	 al.	

(1997),	Warren	et	al.	(2012),	Hooijer	et	al.	(2012),	Dommain	et	al.	(2011),	Page	et	al. (2004)	and	Yulianto	et	al.

(2007).	Hergoualc’h	and	Verchot	(2011) used	a	value	of	50%	(IPCC,	2003)	if	no C	concentration was	provided	in	

a publication.	Overall,	carbon	content	of	tropical	peat	ranges	between	40%	and	60%	depending	on	the	nature,	

mineral	content	and	location	of	the	peat.

Lower	values	of	23.8%	(Jaya,	2007)	and	26.0% (Sajarwan	et	al.,	2002)	are	associated	with samples	taken	near	

the underlying	mineral	substrate	or	for	peaty soils	with	a	large	proportion	of inorganic material. Lower	values	

that	 have	 been	 found	 in	 the	 past	 can	 be	 attributed to	 the	 method	 that	 was	 used	 to	 determine	 the	 carbon	

fraction.	 The	 basic	 principle	 for	 the	 quantification	 of	soil	organic	 carbon	 relies	 on	 the	 destruction	 of	 organic	

matter,	which	can	be	performed	chemically	(which	was	often	used	in	the	past)	or	via	heat	(which	is	currently	

used).	In	studies	where	chemical	destruction	was used the carbon	fraction	was underestimated	with	reported	
18 Review of the literature on emissions from tropical peat degradation under palm oil

values	of	20-30%	in	tropical	peat.	Currently,	the	method	with	elevated	temperatures (loss-on	ignition) is	most	

common	 to	 determine the	 C	 fraction.	 Warren	 et	 al. (2012)	 suggest	 using	 values	 established	 by	 elemental	

analysers	only.	

If	the	soil	subsidence	method	is	used	to	estimate	CO2 emissions,	carbon	density	either	has	to	be	measured,	or	a	

(conservative,	low)	default	value	has	to	be used	to	translate	subsidence	into	CO2 emissions.	For	peat	with	a	low	

mineral	content	(low	ash	peats,	which	dominate	plantation	sites)	the	carbon	fraction	of	the	peat	will	be	on	the	

high	end	of	published	values,	while	 for	peat	with	a	considerable	mineral	content	 this	will	be	on	 the	low	end	

(Warren	et	al., 2012).	

Bulk	density	of	the	peat

Page	et	al.,	(2011b)	presented	a	comprehensive	overview	of	bulk	density	 (BD)	values	of	 tropical	peat.	In	 the	

given	overview,	only	the	study	of	Melling	et	al	(2007)	provides	values	for	BD	in	oil	palm	plantations	(mean	0.20	

g	 cm-3,	 SD	 0,007	 g	 cm-3).	 The	 lowest	 average	 bulk	 density values	 below	 the	 water	 table	 reported	 for	 large	

plantation	 areas	 are	 those	 in	Hooijer	et	 al.	 (2012)	 and	Hooijer	 and	 Couwenberg	 (accepted)	 which vary	 from	

0.073	to	0.078	g	cm-3 and	are well	within	the	range	suggested	by	Page	et	al.	(2011b).	Overall,	in	many	studies	a	

BD	of	around	0.1	g	cm-3 is	assumed	as	the	most	comprehensive	value	for	the	BD	of	tropical,	drained	peat.	

Note	 that	 plantation	 development	 on	 peat	 requires	 compaction	 before	 planting	 of	 trees	 to	 create	 optimal	

conditions	to	anchor	the	roots	of	palm	trees.	The	compaction	by	heavy	machinery	starts	after	removal	of the	

vegetation	and	is	in	many	cases	practiced	over	a	period	of	years	before	planting	starts.	Therefore,	the	density	

of	the	upper	soil	is	higher	in	plantations	compared	to	undisturbed	peat	soils.	Othman	et	al. (2011)	reported	BD	

values	before	and	after	land	development	for	oil	palm	of	0.14	- 0.09	g	cm-3 and	0.26	- 0.16	g	cm-3,	respectively.

At	least	two	different	techniques	are	used	for	determining	the	BD of	peat:	the	auger	method	as	used	in	most	

earlier	studies	and	 the	‘pit’	method	as	used	in	Hooijer	et	al.	 (2012)	and	Hooijer	and	Couwenberg	 (2012);	 the	

‘pit’	method	has	been	suggested	to	be	a	better	method	because	less	compaction	and	less	variation	is	expected	

during	 sampling.	The	augers	 can	 cause	 overestimation	 because	 of	 compaction	 during	 sampling,	 but	 can	also	

cause	underestimation	when	coarse	fragments	or	high	water	content	cause	incomplete	recovery.

Soil	subsidence	measurements to	estimate	CO2 emissions

The	emission	 values	as	estimated	 by	Hooijer	et	al. (2012)	are	within	 the	 range	 of	 other	 published	estimates	

based	on	soil	subsidence	(Couwenberg	et	al.,	2010;	Hooijer	et	al.,	2010;	Hooijer	& Couwenberg,	accepted)	for	

water	table	depths	in	the	range	60-85	cm	and	are	supported	by	the	chamber	based	research	of	Jauhiainen	et	

al.	 (2012).	 Table	 8	 shows	 other	 available	 studies	 that	 report	 on	 soil	 subsidence	 in	 tropical	 peat,	 and	 the	

corresponding	oxidation	component.	

Table	8. Reported	values	for	soil	subsidence	rates,	oxidation	components	and	peat	thickness.	

Source Subsidence	rate Oxidation	

component

Peat	thickness Region Duration

(cm	yr-1) (%) (m) (years)

Hooijer	et	al., 2012 4.8	– 5.4 75	and	92 6 Riau	and	Jambi 5-18	

Wösten	 et	 al., 1997

and	 DID	 and	 LAWOO,

1996

2	– 4.6 60 Johor 14
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 19

DID	Sarawak, 2001 5 60 Johor >	2

Andriesse, 1988 Up to	6

Othman	et al., 2011

Othman	et al., 2009

2.5	– 4.3 >3 Sarawak 8

Couwenberg	 et	 al.,

2010

Compilation	 of	

different	sources

40-60

Hooijer	 and	

Couwenberg	

(accepted)

4.1	– 4.6	 80* 6-9 Jambi	and	Riau 2-3

*As	mentioned	previously,	for	the	method	as	set	out	by	Hooijer	& Couwenberg	(accepted)	an	estimate	of	the	

oxidative	component is	not	needed.	Only	subsidence	rate,	bulk density (of	lower	peat)	and	carbon	content	of	

the	peat	have	to	be	known.	

The	study	of	Hooijer	et	al.	 (2012)	is	 thus	 far	 the	only	study	 that	explicitly	addresses	carbon	losses	during	 the	

initial	years	after	drainage.	Consolidation	is	assumed	to	be	restricted	to	the	first	year	after	drainage	(Den	Haan	

et	al., 2012)	and	is	calculated	to	amount	to	56	cm.	The	study	then	uses	the	difference	in	bulk	density	between	

the	upper	compacted	and	the	lower	uncompacted	peat	layers to	assess	the	contribution	of	compaction	to	the	

total	observed	subsidence	over	 the	 first	years;	the	 remainder	of	 the	subsidence	is	 then	ascribed	 to	oxidative	

losses.	 As	 demonstrated	 by	 Hooijer	 & Couwenberg	 (accepted),	 bulk	 density	 profiles	 show	 little	 variation	 at	

larger	 depth	 and	 the	 assumption	 (used	 in	 subsidence	 studies	 worldwide)	 that	 lower	 peat	 layers	 are	

representative	 for	 near	 surface	 peat	 before	 it	 was	 compacted	 is	 valid.	 While	 uncertainties	 remain,	 the	

approach	of	Hooijer	et	al.	(2012)	to	calculate	C	losses	over	the	first	years	after	drainage	is	convincing.

The	conclusion	of	the	above	discussions	on	carbon	content,	bulk	density	and	oxidation	fraction	is	that	the	Page	

Review	provides	a	representative	review	of	these	 factors,	taking	into	account	the	uncertainties	that	still	exist	

and	by	using	justified	estimates	for	the	factors	that	are	needed	to	calculate	the	emissions	from	soil	subsidence.	

The	 use	 of	Hooijer	et	al. (2012)	as	the	most	 robust	and	most	 complete	 study	at	 this	 time	 is	justified, and	 is	

further	 validated	 by extensive	 cross-checks	 with	 other	 research	 and	 by	 discussion	 where conclusions	 from	

other studies differ.

The	soil	subsidence	method	is	a	strong	approach	for	assessing	average	emissions	from	oil	palm cultivation	on	

peat.	 If	 the	 peat	 is	 over-consolidated	 and	 compaction	 and	 oxidation	 are	 the	 major	 processes	 determining	

subsidence,	the	method	can	be	used	for	the	water	table	depths	that	are	needed	for	oil	palms	to	grow	(40+	cm),	

including	 less	 deeply	 drained	 peats.	 The	 soil	 subsidence	 method	 should be	 used	 with	 caution	 if	 drainage	 is	

gradual	(like	in	drainage	affected	forested	areas)	and	consolidation	may	still	play	a	role	over	multiple	years. The	

soil	 subsidence	 method	 of	 Hooijer	 and	 Couwenberg	 (accepted)	 avoids	 the	 use	 of	 oxidation	 fraction	 and	 is

therefore	less	uncertain	than	the	soil	subsidence	based	emission	calculations	that	need	the	oxidation	fraction	

as	an	input.	
20 Review of the literature on emissions from tropical peat degradation under palm oil

Chapter	5	Questions	and	Answers

Can	the	default	CO2 emission	as	published	by	the	Page	Review be	replaced	by	a	more	recent	number?

No	recently	published	information	can	be	deemed	more	reliable	and	replace	the	emission	factors	of	the	Page	

Review.	The	Page	Review	recommends	a	default	emission	factor	of	86	t	CO2 ha-1 yr-1 (annualised	over	50	years)	

for	oil	palm	plantations	on	peat	with	a	water	table	at	70-80	cm	(which	is	currently	BAU).	This	value	is	based	on	

the	 work	 of	 Hooijer	 et	 al.	 (2012)	 and	 includes	 an	 initial	 spike	 in	 emissions	 after	 land	 use	 change.	 Whereas	

derivation	 of	 the	 initial	 spike	 in	 emissions	 (178	 t	 CO2 ha-1 yr-1)	 is	more	 difficult,	 the	 assessment	 of	 ongoing	

annual	emissions	more	than	5	years	after	drainage	(73	t	CO2 ha-1 yr-1)	is	seen	as	solid.	Using	average	values	for	

subsidence	rate	(4.5	cm	yr-1),	bulk	density	of	the	peat	(0.10	g	cm-3),	C	fraction	of	the	peat	(55%)	and	oxidative	

component	to	subsidence	(75%),	emissions	amount	to	70	t	CO2	ha-1 yr-1,	which	is	close	to	the	value	of	Hooijer	et	

al.	 (2012).	 Methane	 emissions	 from	 ditches	 amount	 to	 ~3	 t	 CH4 (~80	 t CO2-eq)	 per	 ha	 ditch	 area	 and	 year	

(Jauhiainen	&Silvennoinen 2012),	which	contributes	an	additional	~1.5	t	CO2eq	per	ha	plantation	area	and	year.	

The	emission	factor	in	the	Page	Review	does	not	address	these	methane	emissions	and	in	that	respect	it	must	

therefore	be	seen	as	a	conservative	(low)	estimate.

Hooijer	et	al. (2012)	is	a	complete	and	well	designed	assessment	of	the	oxidative	portion	of	peat	subsidence.	

Hooijer	et	al. (2012)	assessed	the	initial	BD	based	on	two	different	approaches:	they	determined	BD	just	below	

the	 water	 table	 and	 they	 compared	 BD	 values	for	 plantations	 at	 different	 years	 after	 drainage	 (2-18	 years).	

Hooijer	 measured	 BD’s	 after	 drainage,	 at	 32	 locations	 in	 Acacia	 and	 palm	 oil	 plantations	 and	 based	 on	 the	

comparison	 between	 their	 assumed	 initial	 BD	 and	 the	 BD	 after	 drainage,	 they	 estimated	 an	 oxidative	

component	 of	 75%	 and	 92%	 respectively.	 Since	 (as	 discussed	 before),	 in	 the	 first	 years	 after	 drainage,	

consolidation	 as	 well	 as	 compaction	 and	 oxidation	 play	 a	 role,	 while	 after	 stabilization	 the	 influence	 of	

consolidation	is	reduced	to	zero,	at	least	two	numbers	shall	be	given for	the	oxidative	component (one	for	the	

first	years	after	drainage	and	one	for	the	stable	situation).	For	the	first	years	after	drainage,	Hooijer	assumed	

the	 oxidation	 component	 at	 75%	 based	 on	 ‘farmers	 records’	 of	 soil subsidence	 and	 measurements	 of	 BD	

profiles	at	10	locations (pits).	By	assuming	the	BD just	below	the	water	table	to	be	the	initial	BD,	the	oxidative	

losses	were	calculated	by	subtracting	losses	by	consolidation	and	compaction	from	the	total	soil	subsidence.

The	method	as	proposed	by	Hooijer	and	Couwenberg	(accepted)	avoids	the	use	of	an	oxidative	component	by	

using	the	BD	of	the	peat	below	the	water	table	as	a	proxy	for	the	original	BD	of	the	peat	above	the	water	table.

This	method	thus	integrates	the	effect	of	initial	consolidation.	Compaction	continues	to	work	on	consolidated	

peat	once	it	reaches	the	aerated	zone	above	the	water	table.	As	noted	above,	the	estimate	for	long	term	rate	

of	emissions	with	70	cm	drainage	(slightly	shallower	than	the	75	cm	average)	is	comparable	to	the	value	of	73 t	

C	ha-1given	in	Hooiijer	et	al.	(2012).	

RSPO	and	MPOB	use	the	independently	published	relationships	between	water	table	and	emissions	of	Hooijer	

et	al. (2012),	Hooijer	et	al. (2006;	2010)	and	Couwenberg	et	al.	 (2010).	The	peatland	working	group	of	RSPO	

(part	 of	 the	 GHG	 working	 group)	 has	 been	 working	 recently	 on	 an	 assessment	 of	 available	 research	 and	

determining	which	 numbers	 shall	 be	 used	 for	 emission	 calculations	 for	 oil	 palm	 on	 drained	 peat.	 This	 work	

group	has delivered	the	following	publications	in	2012 (some	are	in	press	at	the	moment):

• The	 RSPO	 manual	 on	 best	 management	 practices	 (BMPs)	 for	 existing	 oil	 palm	 cultivation	 on	 peat	

(Published	June	2012,	available	on	RSPO	website).	

• A	scientific	review	on	Environmental	and	social	impacts	of	oil	palm	cultivation	on	tropical	peat	(in	press,	

available	on	request).
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 21

• RSPO	manual	on	best	management	practices	for	management	of	natural	vegetation	and	rehabilitation	of	

degraded	 sites	 associated	 with	 palm	 oil	 cultivation	 on	 peat	 (Published	 October	 2012,	 available	 on	

RSPO	website).

The	Greenhouse	gas	working	group	of	RSPO	is	currently	developing:

• The	PalmGHG	Calculator	(final	draft	ready,	to	be	launched	for	use	soon)

The	 GHG	 Calculator has	 been	 developed	 so	 that	 palm	 oil	 producers	 can	 estimate	 the	 net	 greenhouse	 gas	

emissions	produced	during	the	production	chain.

RSPO’s	scientific review	has	listed	the available	research	related	to	emissions	from	tropical	peat.	They	provide	

an extended	list,	slightly	different	from	the	research	highlighted	by	the	Page	Review, however	the	conclusions	

are	 similar.	 They	 cite	 in	 their	 BMP:	  ́Page	 et	 al	 (2011)	 reviewed	 a	 large	 number	 of	 assessments	 of	 GHG	

emissions	from	peatlands	in	SE Asia	and	concluded	that	the	best	available	estimate	of	GHG	emissions	from	oil	

palm	plantations	on	peat	was	86	tonnes	of	CO2-eq	per	ha	per	year	(annualized	over	50	years)’.	For	the purpose	

of	calculating	oil	palm	plantation	specific	green	house	gas	emissions	a	GHG	 tool	is	currently	being	developed	

which	 uses	 the	 equations	 of	 Hooijer	 et	 al. (2010)	 and	 Couwenberg	 et	 al. (2010) for	 emissions	 from	 peat	

drainage	(an	emissions increase	of	around	9 t	CO2 per	10	cm	of	drainage	depth).	Also	the	Malaysian	Palm	Oil	

Board	has	adopted	the	9	t	CO2 per	10	cm	of	drainage	depth	for	emission	calculations	in	plantations	(Othman	et	

al.,	2011;	BMP	of	MPOB).	

Hergoualc’h	and	Verchot	(2012)	arrived	at	lower	estimates	for	CO2 emissions.	The	gain-loss	method	they	use	is	

currently	 still	 fraught	 with	 assumptions	 (see	 Chapter	 2,	 e.g.	 estimates	 for	 belowground	 biomass	 inputs,	

estimates	 for	litter	inputs,	 dead	wood	inputs,	assumption	 on	 similarities	 of	 root:	 shoot	 ratio’s	 between	 peat	

and	 mineral	 soils,	 etc).	 Uncertainty	 because	 of	 these	 assumptions	 is	 high,	 and	 has	 not	 been	 tested	 yet.	

Although	 the	 method	 is	 promising,	 it	 is	 currently	 less	 certain	 than	 chamber	 measurements	 and/or	 soil	

subsidence	measurements.	

Could	 Best	 Management	 Practices	 (BMP)	 such	 as	 advised	 by	 e.g.	 the	 MPOB	 and	 the	 RSPO	 change	 this	

emissions	default	value	in	the	near	future?

If	 the	 peat	 is	 managed	 according	 to	 the	 advice	 of	 for	 example	 the	 RSPO	 and	 the	 MPOB,	 emissions	 from	

plantations	might	be	reduced.	However,	the	implementation	of	BMPs	is	far	from	reality.	Below	the	descriptions	

of	the	two	BMP	guidelines	developed	by	RSPO	(2012)	and	MPOB	(2011)	are	given:

MPOB’s	best	management	practices,	Othman	et	al. (2011),	state	that	a	high	ground	water	table	is	required	to	

reduce	emissions.	For	that	purpose	a	denser	network	of	drains	is	needed	in	sapric	peat,	while	in	fibric	peat	a	

less	dense	 network	is	 deemed	 optimal.	The	 recommendations	 for	 optimum	water	 table	 depths	vary	with	 oil	

palm	age	and	peat	development	stage	as	shown	in	Table	9.	MPOB	suggests	 that	 the	 rate	of	subsidence,	and	

thus	 emissions,	 can	 significantly	 be	 reduced	 by	 increasing	 the	 ground	 water	 table	 up	 to	 30-40	 cm	 from	 the	

surface	during	the	early	years	of	development.	An	average	groundwater	table	at	43	cm	reduced	the	estimated	

CO2 emissions	to	levels	below	40	t	CO2 ha-1 yr-1 compared	to	the	86	t	CO2 ha-1 yr-1 that	is	reported	by	Hooijer	et	

al. (2012)	at	groundwater	levels	of	80	cm.	However,	the	emission	estimates	presented	in	Othman	et	al.	(2011)	

are	not	in	accordance	with	observed	subsidence	rates.	

Table	9.	Water	management	for	oil	palm	planting	on	peat	in	Sarawak	(Othman	et	al., 2009)

Development	stage Drainage	intensity Water	level	from	ground	surface

Oil	Palm Peat number	of palm	 rows	 Groundwater	 table	 in	 Water	 level	 at	
22 Review of the literature on emissions from tropical peat degradation under palm oil

between	drains field	(cm) collection	drain	(cm)

Immature Fibric >	8 30-40 35-40

(1	-3	years	old)

Young	mature Hemic 8 40-45 45-55

(4-7	years	old)

Fully	mature Sapric 4 40-50 50-60

(>	8	years	old)

RSPO	Recommendations	for	reducing	greenhouse	gas	emissions	from	oil	palm	on	peat	are	given	in	Table	10.

Table	 10. Recommendations	 for	 existing	 oil	 palm	 plantations	 on	 peat	 as	 described	 in	 the	 RSPO	 Best	

Management	Practices	Guide,	which	is	recently	published	(cited	from	the	BMP	Guide	of	RSPO).

Water	management

In	 the	 case	 that	 a	 plantation	 is	 developed	 on	 peat,	 good	 water	 management	 is	 the	 key	 factor	 to	 keep	

greenhouse	gas	emissions	as	low	as	possible.	Every	10	cm	of	drainage	causes	an	emission	of	around	9	tons	of	

CO2 per	 hectare	 annually.	 Flooding	 has	 to	 be	 avoided	 because	 this	enhances	 the	 formation	 and	emission	 of	

methane	and	reduces	yields.	This	Manual	recommends	maintaining	water	levels	in	the	field	drains	at	40-60	cm.	

However,	if	palms	are	immature,	even	water	levels	of	35-45	cm	are	sufficient	to	obtain	high	yields	and	this	will	

reduce	the	greenhouse	gas	emissions	further.	

Fire	prevention

Burning	 of	 biomass	 for	 clearance	 and	 burning	 of	 drained	 peat	 in	 dry	 years	 is	 the	 second	 largest	 source	 of	

greenhouse	 gas	 emissions	 in	 peat	 swamp	 areas.	 The	 implementation	 of	 zero	 burning	 and	 fire	 prevention	

measures	 will	 help	 to	 reduce	 emissions	 due	 to burning.	 Pulverization	 of	 old	 palms	 is	 a	 technique	 that	 is	

commonly	used	to	clear	old	plantations	 for	replanting.	The	pulverized	material	can	be	applied	in	the	 field	 for	

protection	 of	 the	 soil	 for	 drying	 and	 for	 fertilizing	 the	 soil,	 limiting	 carbon	 loss. In	 particular,	 it	 has	 been	

suggested	 to	 use	 high-tech	 field	 shredders/chippers/mulchers	 (for	 sample	 technology,	 see	 http://www.faeap.com.au/content.asp?L=3&idMen=317)	 to	 accelerate	 decomposition	 (and	 at	 the	 same	 time	 reduce	

incidences	of	oil	palm-related	diseases)	during	replanting.	

Soil	compaction

The	compaction	of	the	peat	soil	before	planting	has	been	reported	to	lead	to	lower	CO2	emissions	compared	to	

no	compaction	 before	 planting	of oil	 palms.	The	oxidation	of	 the	 peat	will	 be	 reduced	 due	 to	 the	 decreased	

porosity	of	 the	soil	 (Witjaksana,	2011).	Maintenance	of	grasses,	 ferns,	mosses	 (natural	vegetation)	and	other	

soft	 vegetation	 on	 bare	 soil	 will	 add	 to	 the	 reduction	 of	 decomposition of	 the	 peat	 soil	 due	 to	 drainage	 by	

reducing	the	soil	temperature	and	reducing	the	evaporation	from	the	soil.	

Fertilizer	practices

The	 use	 of	 ‘coated’	 nitrogen	 fertilizer	 will	 help	 to	 reduce	 N2O	 emissions.	 It	 is	 recommended	 to	 implement	

fertilizer	 practices	 that	 optimize	 N-fertilizer	 and	 maximize	 organic	 fertilizer	 use	 including	 composting	 and	

careful	fertilizer	application	during	rainy	seasons.	In	addition,	fertilizer	can	increase	the	breakdown	of	the	peat	

soil	 by	 bacteria	 accelerating	 oxidation	 and	 subsidence. Reduction	 of	 fertilizer	 use	 can	 thus	 reduce	 the	 CO2

emissions.	

Carbon	stock
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 23

Carbon	 stocks	can	be	maintained	and	increased	 through	maintenance	and	 rehabilitation	of	buffer	 zones	and	

High	Conservation	Value	Areas,	planting	other	crops	and	optimal	oil	palm	planting	density.	Conserving	adjacent	

(or	where	appropriate,	within	plantation)	forested	areas	will	increase	the	carbon	stock	of	the	area.	For	further	

information	they	refer	to	the	Rehabilitation	Guide.	

The	 reality	is	 that	 currently	most	 plantations	 that	are	joining	 RSPO	 or	MPOB	 have	water	 tables	at	 75	 cm	 on	

average.	Moreover,	also	many	plantation	owners	and	small	holders	are	not	members	of	MPOB	or	RSPO.	The	

BMP	guidelines	of	RSPO	and	MPOB	provide	voluntary,	not	mandatory	criteria.	Besides,	to	maintain	the	water	

table	 at	 40-60	 cm	 below	 field	 level	 within	 plantations,	 a	 very	 sophisticated	 drainage	 systems	 is	 needed,	

especially	 in	 drier	 areas,	 and	 it	 could	 be	 that	 in	 drier	 areas	 (mainly	 in	 Indonesia)	 for	 parts	 of	 the	 year	

maintenance	of	the	high	water	table	is	almost	impossible.	It	is	unlikely	management	practices	will	change	on	a	

large	scale	in	the	near	future.	

If	BMPs	would	be	implemented	in	 the	 future	additional	 research	would	be	welcome	before	adapting	default	

emission	 factors.	 For	 example,	 Witjaksana (2011)	 suggests	 that	 compaction	 reduces	 emissions,	 but	 robust	

scientific	evidence	needs	to	be	provided.

Fires	in	forest	and	peat	are	the	second	largest	greenhouse	gas	source	after	emissions	resulting	from	drainage	of

peatlands.	Undisturbed	peat	swamp	forests	usually	do	not	burn,	but	become highly	susceptible	to	fires if	they	

are	drained.	The	 fire	 risk	in	oil	palm	plantations on	peat	is	generally	low compared	 to	abandoned,	degraded	

peatland,	because	of	1)	artificial	soil	compaction	during	land	preparation	to	provide	strong	anchorage	for	the	

palm	 trees,	and	2)	intensive	monitoring	and	control	of	 fire incidence. However,	many	plantation	owners	and	

smallholders	do	not	have	fire	control	and	still	use	fire	for	clearance	of	newly	developed	land.	Besides,	peat	and	

forest	fires	often	occur	near	plantation	areas	because	drainage	effects	extend	outside	plantations.	Currently	no	

recommendations	 are	 provided	 by	 RSPO	 and	 MPOB	 to	 prevent	 off-site	 impacts.	 Emissions	 from drainagerelated	fires	would	add	to	the	emission	factor	given	in	the	Page	Review.	

Can	emissions	estimates	for	Acacia	plantations	be	translated	to	emissions from	oil	palm	plantations?

If	 conditions	are	 the	 same	 (equal	 climate,	 peat	 type,	water	 table),	emissions	 from	Acacia	 plantations	 can	 be	

considered	 to	 be a	 good	 estimate	 for	 emissions	 from	 oil	 palm	 plantations.	 Hooijer	 et	 al.	 (2012) show	 that	

integrated	 total	 C	losses	 over	longer	 time	 scales	 from	 oil	 palm	 plantations	and	Acacia	are	 similar.	Below are

listed	some	similarities	and	some	differences:

• Inputs	of	fertiliser	in	oil	palm	plantations	are	higher	(higher	N2O	emissions).	

• Acacia	 has	 harvest	 rotations	 of	 5	years,	 compared	 to	 the	 25	years	 rotation	 cycles	 of	 oil	 palm.	This	 likely

causes	higher	disturbance	emissions and	longer	periods	with	‘bare	soil’	and	thus	increased	decomposition	

of	peat.	Jauhianen	et	al. (2012) report	similar	high	soil	temperature	in	the	absence	of	a	closed	canopy	layer

• Peat	emissions (heterotrophic	respiration)	at	the	same	drainage	depth	 (range	0.5	– 1.00	m)	are	similar if	

canopy	cover	is	similar.	The	two	crops	require	similar	drainage.	

• The	 proportion	 of	 autotrophic versus	 heterotrophic respiration	 is	 dependent	 on	 the	 tree root-density	

within	 the	plantations.	There	is	no	 research	on	distribution	of	 roots	of	oil	palm	and	Acacia	and	 thus	 the	

difference	remains	unknown.	

Currently	only	Hooijer	et	al. (2012)	and	Hooijer	&	Couwenberg	(accepted)	have	published	a	direct	comparison	

of	 emissions	 from	 Acacia	 vs	 Oil	 Palm,	 however,	 in	 the	 future	 more	 research	 is	 expected	 to	 report	 on	

comparisons	of	emissions,	similarities	and	differences.
24 Review of the literature on emissions from tropical peat degradation under palm oil

Chapter	6 Recommendations	and	

conclusions

The	Page	Review	is	comprehensive	and	can	be	considered	applicable.	Fire	related	emissions,	off-site	emissions	

and	non-CO2 emissions	such	as	CH4 ditch	emissions	are	not	taken	into	account	and	therefore	the	value(s)	are	

conservatively	low.

The	emissions	factors	given	by	the	Page	Review	are	recommended	as	appropriate	for	use	in	the	modelling	of	

indirect	land	use	change	emissions,	although	it	should	be	noted	that the	calculation	of	the	initial	spike	directly	

after	drainage	is	less	robust	at	this	time	than	the	calculation	of	long-term	stable	emissions.	In	the	case	that	land	

is	 newly	 developed	 and	 drained	 for	 oil	 palm	 the	 initial	 spike	 should	 be	 accounted	 for	 (the	 Page	 Review	

recommended	 86	 t	 CO2 ha-1 yr-1 annualised	 over	 50	 years).	However,	 if	emissions	are	 calculated	 for	existing	

plantations	on	peat,	many	years	after	drainage,	one	should	exclude	the	initial	peak	and	use	the	emission	factor	

for	ongoing	exploitation	of	73	t	CO2 ha-1.

If	in	 the	 future	 the	adoption	of	Best	Management	Practices	as	 recommended	by	MPOB	and	RSPO	leads	 to	a	

significant	decrease	in	drainage	depth	in	oil	palm	plantations,	emission	factors	should	be	re-assessed	based	on	

additional	research	or	based	on	published	relationships	between	emissions	and	water	table	depth.	Currently,	

the	 implementation	 of	 best	 management	 recommendations	 has	 not	 been	 achieved,	 and	 most	 plantations	

maintain	water	tables	at	75	cm	below	field	level	on	average.	

It	has	to	be	noted	that,	although	‘good’	management	practices	(e.g.	adaptation	of	the	water	table)	can	reduce	

emissions,	they	will	never	turn	oil	palm	systems	on	peat	into	a	carbon	and/or	GHG	sink,	and	peat	drainage	will	

always	cause	a	‘carbon	debt’.	Also,	soil	subsidence	due	to	drainage	can	cause	agricultural	problems,	because	it	

can	lead	to	flooding	and	to	salt	water	intrusion.
Review	of	the	literature	on	emissions	from	tropical	peat	degradation	under	palm	oil	 25

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