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Roles and Impacts of Biomass Burning in Slash-and-Burn Land Usein Tropical Mountains: A Case Study in Laos
Yoshio INOUE
National Institute for Agro-Environmental Sciences
3-1-3, Kannondai, Tsukuba, Ibaraki 305-8604, Japan.
e-mail: yinoue@affrc.go.jp

Abstract
Biomass burning is an essential part of slash-and-burn (S&B) agriculture, which is widely practiced as
an important food production system in the tropical mountains of Southeast Asia. S&B agriculture used to besustainable and carbon neutral; CO2 emissions by biomass burning were balanced with photosynthetic biomass growth, and land use was stable. However, due to drastic land-use change in the past decades, S&B
ecosystems have become a significant source of CO2 emissions into the atmosphere. The productivity of bothland and labor in S&B agriculture has been seriously affected by land-use change. This case study in Laosreveals the reality of the chrono-sequential change in land use and ecosystem management on a regional scale.
Not only the area of S&B cropping but also the frequency of biomass burning (and thus the duration of the
fallow period) had a strong influence on the ecosystem’s carbon stocks and, in turn, on the deterioration ofland and labor productivity in crop production. Historically, the indigenous people of this large area have beenhighly dependent on S&B agriculture for their living. Traditional S&B land use contributes to the sustainability of forest and water resources as well as to biodiversity. The multiple functions of biomass burning and
S&B land use have to be taken into consideration. Feasible land use and ecosystem management options
would include alternative S&B land-use scenarios that assure food security as well as carbon sequestrationand forest conservation. This paper discusses the multiple functions of S&B land use in the mountains of Laosand presents scientific approaches towards better solutions.
Key words: carbon sequestration, food security, land use, remote sensing, shifting cultivation,
Southeast Asia.

1. Introduction
Slash-and-burn (S&B) agriculture (also known as
shifting cultivation or swidden agriculture) has been
an important food production system in the tropicalmountains of Southeast Asia (Fig. 1), and is widelypracticed in the mountainous regions of Vietnam, Laos,
China, Bangladesh, Myanmar and northern India(Rasul & Gopal, 2003). In S&B agriculture, a patch ofvegetation is cleared, burned, and used to grow crops
for a few seasons, and then abandoned so that vegetation can regenerate. Biomass burning plays an essential role in the growing of crops without any artificial
inputs such as fertilizer and pesticides. S&B agriculture is a rational crop production system utilizing hilly
lands with little input, and is sustainable provided thatthe fallow period is long enough to recover plant biomass and soil fertility (Fujisaka, 1991; Roder, 2001).
Weeds and pests may be controlled to some extent byburning (Roder et al., 1997; Saito et al., 2006a).
Global Environmental Research
15/2011: 21-30
printed in Japan

Moreover, fallow biomes provide various non-timber
forest products (NTFP), such as mushrooms, medicinal plants, bamboo and insects, which constitute a
substantial part of rural livelihoods (Douangsavanh
et al., 2006). The positive role for biodiversity playedby biomass burning in traditional S&B land use wasalso suggested by Appa Rao et al. (2002), whoreported that the northern part of Laos under traditional S&B agriculture is quite rich in rice varieties.
Hence, we note that the S&B land-use system has
multiple functions in both food security and thesustainability of biological resources.
Biomass burning in S&B land use is an obvious
source of CO2 in the atmosphere (Fig. 1), but theoverall impact may be carbon neutral as long as balance is maintained between the photosynthetic biomass growth and the CO2 emissions from biomassburning (IPCC, 2003). Nevertheless, increasing population pressure and land-use regulation have forced
shifting cultivators to expand S&B areas and to©2011 AIRIES22Y. INOUE

shorten the fallow period (Pravongvienkham, 2004;
Douangsavanh et al., 2006; Fujita & Phanvilay, 2008).
Consequently, negative effects on crop productivity,
such as decreasing soil fertility and increasing weed
problems, have been reported (Fujisaka, 1991; Roder,2001), with negative impacts on biological resources(forest, NTFP, biodiversity, etc.) and the atmospherebeing serious concerns as well. The official environmental policy in Laos planned to eradicate S&B
agriculture in the upland areas to stop the degradationof natural resources (GoL, 1999). Apparently, during
the 1995-2004 period, 90% of the upland areas became
classified as forest (‘protection’ or ‘conservation’ forest) (GoL, 2005). However, the practical implementation of such policies might even have endangered bothfood security and the conservation of forest resources
through excess intensification of S&B land use(Lestrelin & Giordano, 2007; Inoue et al., 2010).
Thus, alternative land-use and ecosystem management scenarios are urgently required in order toimprove food and resource security as well as carbon
sequestration capacity in support of official policy
making and local ecosystem management practices(e.g., allocation of cropping patches, selection of crops
and cropping patterns, individual management techniques, and utilization of field and forest resources). In
this context, ecological and agronomic knowledge andtechnologies are crucial for more sustainable S&B

land use and more productive cropping systems. Geospatial information on the chrono-sequential change ofland use and ecosystem carbon stocks is required forformulating regional land-use scenarios. The multiple
functions of biomass burning should be taken into
consideration. In this review paper, the roles andimpacts of biomass burning in S&B land use are
discussed based on a case study involving the northernpart of Laos.

2. Assessing the Effects of Land-use Scenarios
on Ecosystem Carbon Stocks andLivelihoods in the Mountains of Laos:a Case Study
S&B agriculture has consitituted a major agricultural land use in the northern part of Laos, where up to
80% of the soils may be used for agriculture if all the
fallow land is included (Roder, 2001). Due to thegrowing population, the area and intensity of S&B
land use has been increasing. According to the Foodand Agriculture Organization (1985), 49% of deforestation in South and Southeast Asia was caused by
S&B agriculture. Global awareness of the negative
off-site effects may have pressed governmental policies indirectly or directly to abolish S&B agriculture.
In 1990, for example, the government of Laos planned
to replace S&B agriculture with permanent agriculture

Fig. 1 Landscapes, villagers and sky conditions during the biomass burning seasons in slash-and-burn regionsin the mountains of Laos.

Roles and Impacts of Biomass Burning in Slash-and-Burn Land Use in Tropical Mountains

by the year 2000 (Fujisaka, 1991). The government
started strongly regulating local land use to protect
forests by reducing S&B land use, but the situation
became even worse (Pravongvienkham, 2004). Therefore, alternative land-use and ecosystem management
scenarios are urgently required. However, limitedaccessibility to mountainous areas and the limited
availability of statistical data for the region have hampered scientific investigations, especially on regional
scales (Fujisaka, 1991; Roder, 2001; Shrestha & Zinck,
2001). In general, it is difficult to obtain quantitative
information, especially on land-use history (Aumtong
et al., 2009). Thus, the use of satellite imagery is a
viable option for such investigations. Due to limited
data availability, a simple approach using time-series
satellite imagery (Inoue et al., 2007, 2008) was applied
to the geospatial assessment of land use and carbon
stocks in S&B ecosystems. Information on land use
was assessed using time-series satellite imagery andwas linked with an ecosystem carbon model derived
from in situ experiments. In addition, preliminary
scenario comparisons were conducted to assess theimpact of various land-use scenarios on carbon
sequestration and food security on a regional scale.
The details of this particular case study are found inInoue et al. (2010).
2.1 Study area
The central part of northern Laos was selected as astudy area (150×150 km; Fig. 2) because S&B agri-

23

culture is the major agricultural system, and livelihoods and natural resources are seriously dependent
on S&B land use (Douangsavanh et al., 2006). The
area is centered around 102°03’48.9” E, 20°13’12.8”
N and is covered by the view of Row46/Path129of Landsat-TM. The elevation ranges from 300 to
2,000 m, with slopes from 40% to 100%. The meanannual rainfall for the area is about 1,300 mm withannual variability (SD) of 260 mm, but more than 90%of the rainfall occurs during the wet season from May
to October. The soils of most of the S&B fields areclassified as orthic acrisols, with a reddish-browncolor, clay content of >30%, and slightly acidic pH. In
general, new land patches are slashed from midFebruary to early March, burned by mid-April, seededfrom mid-April to May, and harvested from October toNovember. The most important crop in the area
is upland rice; some other crops, such as Job’s
tears, sesame, and paper mulberry, are also grown.
Major tree species include Irvingia malayana andCastanopsis echinocarpa (Kiyono et al., 2007).
2.2 Approaches
Figure 3 depicts the overall approach. The chronosequential change of land use was estimated from thetime-series satellite images with the support of groundsurveys. On-site experiments and measurements weremade to obtain basic data on biomass, yield, soil
carbon content, etc., and to derive simple empiricalmodels.

Fig. 2 Major slash-and-burn regions in the northern part of Laos as seen by earth-observing satellites(Landsat ETM+, IKONOS and QuickBird).

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Fig. 3 Approach for estimating land use and ecosystem carbon stock on a regional scale.

2.2.1 Estimating S&B land use based on time-series
satellite imagery
The S&B land-use areas consist of a variety of
cropping and fallow (C+F) patterns, and their area
ratios constitute a crucial basis in this study. However,
only qualitative information was available fromobservation and interviews (e.g., Roder, 2001;
Douangsavanh et al., 2006), so we quantified croppingand fallow patterns using satellite imagery. We used
Landsat-MSS, TM and ETM+ satellite images(Row46/Path129), and high-resolution images fromIKONOS and QuickBird satellites taken over a span of
33 years. Since the S&B patches each year can bediscriminated with a high-accuracy polygon-basedclassification (Inoue et al., 2007, 2008), vector layersof polygons were generated from individual satellite
images based on segmentation procedures. Next, thepolygons were used to extract S&B cropping patches
based on supervised classification. The accuracy ofthis classification procedure proved as high as 0.95-1.0
for S&B land use (Inoue et al., 2007). The binary
images over consecutive years were stacked and used
to trace the chrono-sequential change of S&B land use
on a pixel basis. Consequently, the C+F land-use patterns (community age of fallow vegetation as well as
timing and duration of S&B cropping) were derived ona pixel basis from the time-series analysis of satellite
imagery. This method proved useful in this type of
ecosystem.
2.2.2 Estimating ecosystem carbon stocks on aregional scale
In this approach, the community age of fallow
vegetation derived from the analysis of time-series
satellite images was used as a clue to link the land-use
patterns and in situ measurements for estimating
ecosystem carbon stocks. This approach is rather simple but useful and robust. Regional ecosystem carbon

stocks CR (MgC ha-1) were estimated from the area
A (ha), area ratio Rk (%), and ecosystem carbon stock
CEk (MgC ha-1) for each land-use pattern (C+F cycle) k
using the following equations:
(1),
(2),
where CV (MgC ha-1) is the carbon stock in crop or fallow
vegetation, including biomass, dead biomass, litter fall
and roots, and CS (MgC ha-1) is the carbon stock in thesoil at a depth of 0.3 m. Ecosystem carbon stocks CEk invarious C+F cycles (k) were estimated by combining
simple semi-empirical models for CV and CS, both ofwhich were expressed as a function of community age. Rk
was estimated from the polygon-based classification oftime-series satellite imagery. These partial models were
derived respectively from the concurrent experimental
studies on site. Details are reported in Kiyono et al.
(2007) and Asai et al. (2007, 2009). These semiempirical models for CV and CS were synthesized andlinked with Rk by way of the community age. Thisapproach successfully provided the information necessary to infer the dynamics in regional ecosystem carbon
stock as affected by land use.
2.2.3 Ecosystem surface conditions at biomassburning
In our study area, the slashed biomass is usuallyburned twice. In general, the fallow vegetation is slashed,dried and burned during late February to mid-March. The
embers after the first burning are gathered and burned
again. Indigenous knowledge on S&B agriculture may be
the most important inheritance for villagers, since not
only critical cropping practices such as slashing, seeding,
weeding and harvesting, but also effective and safe

Roles and Impacts of Biomass Burning in Slash-and-Burn Land Use in Tropical Mountains

2.3 Major results and insights
2.3.1 Chrono-sequential change in the S&B land-use
area
The cropping area by S&B practice in each year
increased rapidly from around 5% in the 1970s to 12% in
the first decade of the 21st century (Fig. 4). The increaseduring the 1990s was remarkable, while it was still small
before the mid-1980s. The annual increment rate during
the decade after 1990 was about 3.8% for the study area.
Similar analyses conducted in several other areas within
the whole study area showed an annual rate of 3%-5% for
the decade. Although the recent trend suggests somestabilization, no decreasing trend has been found during
the period of analysis. These data support descriptive
information from reconnaissance at various sites in theregion (e.g., Roder, 2001; Douangsavanh et al., 2006).
2.3.2 Community age of fallow vegetation: a clue forlinking land use and carbon models
The history of S&B or non-S&B land use could betraced on a pixel basis for the area of interest, so important land-use parameters, such as duration of consecutive
cropping periods or community age of fallow vegetation,
were derived systematically from the dataset. This was
the most crucial role of time-series satellite images in thisanalysis. On average, 75% of the S&B area each year

consisted of newly slashed patches, 76% of which wereabandoned after a single year of cropping. Long S&B
consecutive use (>4 years) was very minor. These results
agreed well with previous reports on trends in regional
land use and on the drastic decrease in crop yield duringconsecutive cropping (e.g., Roder, 2001; Douangsavanh
et al., 2006; Saito et al., 2006a; Asai et al., 2009).
The community age of fallow vegetation could also
be derived on a pixel basis by tracing back to the last
S&B use on each pixel (Fig. 5). The most common fallow
length was three years (20%) followed by two years(17.5 %), that is, the major C+F cycle was a pattern of
one-year cropping and three-year fallow (1C+3F), followed by a 1C+2F pattern. The short-fallow area (1-3Fyears) was up to 45%, whereas the five- to elevenyear-fallow area was 27%. These findings agreed wellwith the general information from ground-based reconnaissance, which also supported the qualitative descriptions on the overall trend of S&B land use in the region(Fujisaka, 1991; Roder, 2001; Pravongvienkham, 2004).
General trends in S&B land use have been reported basedon observations, but the present results are the first of thiskind based on chrono-sequential analysis of time-series
satellite imagery.

Slash-and-burn area (%)

fire-management necessitate sophisticated methods
based on long experience (Roder, 2001; Douangsavanh
et al., 2006).
According to the preliminary measurements by Asaiet al. (2007), the burning efficiency (BE) at the first burning was 74% and 38% in plots with three-year andten-year fallow periods, respectively. The above-groundbiomass just before the first burning was 8.5 and45.7 MgC ha-1 in the three-year and ten-year plots,
respectively. The BE value was much lower in theten-year plots because of the higher ratio of thick trunks
and twigs. However, the overall BE reached as high as
99% and 88% for the three-year and ten-year periods,
respectively, after the second burning. Therefore, themajor part of the above-ground biomass is emitted into
the atmosphere as CO2, soot, and other trace gases
through burning. The other parts are degraded gradually
afterwards and/or are further gathered and combusted asfuels. Note that, in general, the BE values may have large
variability among areas and countries due to climatic,
geophysical, biological and cultural conditions (e.g.,
Prasad et al., 2001). It is assumed that a large part of theunderground biomass would also be decomposed into thesoil, although the ratio is rather uncertain. During thefield experiment, soil temperature was measured at
depths of 0, 1.0 and 2.5 cm during biomass burning by
Thermo Crayon. Soil temperatures at depths of 1.0 and
2.5 cm never exceeded 100°C, although soil surface
temperature reached as high as 400°C. Hence, theinfluence of burning on the gaseous emission of soilorganic matter was assumed to be negligible.

25

Year

Fig. 4 Temporal change of slash-and-burn cropping area eachyear in the intensive study area (350 km2) in Luang
Prabang Province. (Inoue et al., 2010)

Fig. 5 Relative areas of land patches with different fallow
lengths. This graph indicates the average values for two
years, 2003 and 2004. Data were derived from thechrono-sequential analysis of time-series images. (Inoueet al., 2010)

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2.3.3 Ecosystem carbon stock capacity as affected bycropping-fallow patterns
Figure 6 shows the chrono-sequential changes inecosystem carbon stocks under some typical C+F cycles.
The initial value was set to be a typical value measured
just before cropping (42.0 Mg ha-1), estimated fromin situ measurements (Asai et al., 2007); this value iscomparable with the reported range, i.e., 38-61 Mg ha-1
(Bruun et al., 2006). Obviously, the major increase inecosystem carbon stocks was brought by biomass growthof fallow vegetation (secondary forest), while the drastic
drop was caused by biomass burning in S&B practice.
Even within some selected C+F patterns in this figure,the average value over 35 years varied by up to 33 MgC
ha-1. In the case of the 1C+3F pattern (i.e., a cycle of
one-year cropping with three-year fallow), the temporal
average during 35 years was 41.7 MgC ha-1, which isnearly the same as the initial value. In the 1C+2F cycle,
however, the temporal average of 34.9 MgC ha-1 waslower than the initial carbon level by 7.1 MgC ha-1. For
example, the temporal average of carbon stocks in the
2C+10F cycle was larger than that in 1C+3F by 21 MgC
ha-1; this amount could be sequestered into the ecosystemfrom the atmosphere by changing the land-use patternfrom 1C+3F to 2C+10F. The bottom points in each line
indicate the carbon level just after S&B practice. The
decreasing trend was obvious in short fallow patterns, butsome slight decreasing trend was still found even underten-year fallow patterns (e.g., 1C+10F). According to ourfield observations, interviews with villagers andhistorical records (e.g., Fujisaka, 1991; Roder, 2001), as
well as our satellite image analysis, the major C+F
combinations are quite simple. Hence, this simulation
assumed that the simple C+F combinations would
sufficiently represent the real situation in the region.
Nevertheless, because of a serious decrease in crop yield

due to the repeated short- fallow cycles, it may not be
possible to repeat such short-fallow cycles as 1C+2F overthe long term. In fact, some villages have already given
up S&B land use because soil fertility has been
completely depleted. This type of serious land degradation will expand in the near future unless alternativeland-use options are introduced. The results will be
useful in inferring the impact of land use on ecosystemcarbon stocks and the potential for sequestering carbon
by changing land-use and ecosystem management
practices.
2.3.4 Comparison of regional carbon stocks andincome under various land-use scenarios
The above analysis allows systematic comparisons to
be made of the effects of land-use scenarios on regional
carbon stock capacities and income (Fig. 7). These
simplified land-use scenarios include the major factors
affecting regional carbon stocks and income, such as
cropping-fallow cycles, inputs and outputs in the cultivation of rice and cash crops, and labor productivity. The
normal market prices of products and labor were used.
According to field experiments and surveys (Saito et al.,2006a), rice yields could be increased by 50% using
improved rice cultivars, and coupling with nitrogenfixing legume species (e.g., Stylosanthes guianensis)
could support soil fertility to sustain the rice yield (Saito
et al., 2006b). Weeding labor made up more than 50% of
the total labor spent for S&B cropping, and the input of
weeding labor would increase with decreasing fallow
periods (Roder et al., 1997).
The regional average of carbon stocks increases witha longer fallow period (S4 scenario) compared with therecent status (S1). Regional carbon stocks decrease whenlonger fallows are reduced (S2). Ecosystem carbon
stocks will increase by 10.5 MgC ha-1 if the 1C+5F pat-Fig. 6 Chrono-sequential changes in ecosystem carbon stock under some typical land-use patterns as assessed by acoupled model of carbon in the soil and fallow vegetation. “C” and “F” denote cropping and fallow,
respectively, so that “1C+10F” means a pattern of one-year cropping and ten-year fallow. The arrow andnumber attached to each line indicate the temporal average of carbon stocks. (Inoue et al., 2010)

Roles and Impacts of Biomass Burning in Slash-and-Burn Land Use in Tropical Mountains
tern and those with shorter fallows are all replaced with
1C+6F, whereas it will decrease by 8.8 MgC ha-1 iflonger fallows are diminished, leaving only 1C+3F or
shorter fallow patterns. The exclusion of 20% of the areafrom S&B land use as conservation forest (S3 and S5) isalso effective at increasing regional carbon stocks since
the area is never used again for S&B in the future.
In this comparison, the land-use scenarios in 1980 and1990 were included based on data on the S&B area andthe most probable S&B patterns inferred from interviews
with old villagers as well as previous reports (Fujisaka,
1991; Roder, 2001). The difference in carbon stocks
between 1980 and 1990 was small, but the differentialfrom 1990 to the recent status (S1) was as large as 41.6
MgC ha-1for the ecosystems in the region. This change
was caused by an increase in S&B area and by shortened
fallow periods. The amount of carbon released from theecosystems into the atmosphere was affected by the
structural change in S&B land use.
Food and resource security (sustainability of forests,
NTFP, drinking water, biodiversity) is of the highest
priorities for livelihoods in the region (Rasul & Gopal,
2003; Douangsavanh et al., 2006). In other words,
alternative land-use and agricultural options cannot be
accepted without some merits for food and resource security, even if such options are effective for carbon
sequestration. There might be some incentive for carbon
sequestration by ecosystem management if some carbon
trading system could be applied to S&B land use, but it is
not feasible to date. In fact, we sometimes witnessedlong-fallow or conservation forest areas (community age>15 years) being incorporated into S&B cropping. This is
illegal in principle, but villagers cannot avoid expanding
the S&B area to such protected areas due to decreasing
land and labor productivities under recent land-use
conditions. The conflict between forest conservation andthe people’s food security is serious. The majority of the
S&B region will suffer similar problems sooner or later.
Therefore, balancing food production and environ-27

mental remediation is of increasing importance in ecosystem management and policy making, especially indeveloping countries (Pravongvienkham, 2004; Grau
et al., 2008). In S&B land use, environmental remediation is closely linked with the recovery of carbon stocks,
soil fertility and forest products, so livelihood security(income) and carbon stocks are key indicators of thebalance. Figure 7 compares gross regional income andcarbon stocks under a few selected scenarios based on
preliminary simulations. The gross gain in regional
income in S2 is estimated to be comparable with that in
S1, while ecosystem carbon stocks are lowered by
1.0 Mg ha-1. In the S3 scenario, a relatively large increasein carbon levels is expected, but income is seriously
reduced. If the possible reduction in crop yields due torepeated short fallow cycles is included, the results may
be worse in reality under short-fallow scenarios (e.g.,
S1 and S2). The S4 and S5 scenarios would create
significant increases in regional carbon stocks (14.1 and20.4 MgC ha-1, respectively). The S4 scenario provides
the highest gain in gross income as well as relatively highcarbon levels, but does not reduce the total area of S&B.
The S5 scenario shows the highest increase in carbon
levels, while gross income is also improved to someextent. Hence, some reasonable scenarios for balancing
food security and carbon sequestration may exist
between the S4 and S5 scenarios. The experimental
studies in the region suggest that an alternative cropping
system based on a combination of high-yielding ricecultivars, green manure plants (e.g., Stylosanthes
guianensis), and cash crops (e.g., paper mulberry) might
be the most promising option for allowing the 2C+10F
pattern in the S4 and S5 scenarios to be realized (Asaiet al., 2007). Although these simulations may be affectedby various conditions such as the market price of
products, these results should help local government in
the design of regional land-use and ecosystem management scenarios, taking account of both the gross regional
benefit and the carbon stock capacity of the region.

Fig. 7 Comparison of regional carbon stocks and gross regional income under a few selected land-use andecosystem management scenarios based on simulation for 35 years. Each scenario is summarized asfollows: S1: same S&B area and land-use patterns as present; S2: same S&B area as present, butwith the longest fallow limited to 8 years; S3: reserve 20% for conservation forest, but otherwise
same land-use pattern as present; S4: same S&B area as present, but with alternative twelve-year
cycle of land-use management; S5: reserve 20% for conservation forest and alternative twelve-year
cycle of land-use management. (Inoue et al., 2010)

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3. Roles and Impacts of Biomass Burning in
Slash-and-Burn Land Use
S&B agriculture has been the major livelihood activity of villagers in the tropical mountains. It is considereda suitable land use for hilly regions, and is sustainable
provided that the fallow period is long enough toregenerate vegetation cover and soil fertility (Warner,
1991; Roder, 1997). It was a reasonable land-use option
for rural people with low incomes and low access tomodern inputs and infrastructures when the population
density was low. Although its productivity is low, it provides high returns to labor with low input requirements.
Upland rice is the most important crop in S&B food production; in Laos, for example, rice accounts for about
70% of total calorie intake across the nation (Maclean
et al., 2002). According to Roder et al. (1997), the major
constraints to rice production in S&B cropping are weeds,
diseases, insects, drought stress, soil fertility and labor
availability. In general, soil organic matter plays animportant role not only as a pool of plant nutrients, butalso as a source of better physical, chemical and biological soil properties. Biomass burning has an essential rolein S&B crop production because the mineralization ofsoil organic matter after burning is the major source ofsoil fertility. Since soil organic matter is provided fromthe biomass growth during the fallow period and from theash deposits by biomass burning at the end of the fallow
period, the amount of biomass, i.e., the fallow length, iscritical for crop production. In fact, a positive correlation
has been shown between rice yield and fallow length (e.g.,
Sanchez et al., 1982; Saito et al., 2006b). In summary, themost important function of biomass burning in S&B land
use is to provide the fertility for growing crops undersuch adverse geographic conditions (e.g., Warner, 1991;
Roder, 1997).
Roder et al. (1997) also pointed that weed control,
among the above constraints, is the most important issue

in rice cropping since labor productivity is highly
dependent on weeding requirements. The requirement forweed control is related to fallow periods, presumably
because the frequency of burning affects the species
composition of fallow biomes (e.g., Roder et al., 1997;
Saito et al. 2006a). In general, weeding labor has increased significantly with the shortening of the fallow
period. Thus, biomass burning and its frequency (fallow
period) have a strong influence on land and laborproductivity in crop production.
On the other hand, biomass burning in S&B land use
affects ecosystem functions such as carbon stocks andbiological resources, as well as the impact on atmospheric quality via CO2 emissions. These functions areinevitably linked with the issue of food security. In general, the carbon balance in S&B land use was once
considered neutral (IPCC, 2003), but the changes in S&B
cropping patterns and land-use intensity could havesignificant impacts on carbon emissions and/or sequestration through ecosystem management practices. This is
one of the hot issues in relation to the global carbon cycle
and the carbon trade in the context of the Kyoto Protocol(e.g., IPCC, 2003; Houghton, 2005). Biomass burning in
S&B agriculture is also one of the major sources of othertrace gases such as NOx (Prasad et al., 2000).
Figure 8 summarizes the major roles and impacts ofbiomass burning in S&B land use. These multiple functions should be taken into consideration in the development of alternative ecosystem management options
towards solutions to food and environmental security.
As a basis for a range of scientific analysis andoperational projects, spatio-temporal assessment of ecosystem dynamics is required because of the large diversity and heterogeneity of ecosystems. Nevertheless, thestatus of ecosystem carbon stocks and possible changes
by ecosystem management have not been well investigated quantitatively (Inoue et al., 2008). Therefore, theuse of satellite images and geoinformation, especially in

Fig. 8 Interactions of biomass burning in slash-and-burn agriculture with food andenvironmental security through agronomic and bio-geo-physical processes.

Roles and Impacts of Biomass Burning in Slash-and-Burn Land Use in Tropical Mountains

29

combination with in situ data, is crucial for such purposes.
The regional case study in Laos in the previous section
should provide some useful insights for similar ecosystem issues in methodological, conceptual and operational
aspects.

models derived from in situ measurements. Further research efforts should be dedicated to finding possible
solutions to this serious agro-environmental problem.

4. Conclusions

This review is based on the outcome papers of a
project supported in part by the Global Environment
Research Fund, Ministry of the Environment of Japan.

S&B agriculture is an important food production system in hilly regions, and is widely practiced in the tropical mountains of Southeast Asia. Biomass burning is an
essential part of S&B agriculture and is an obvious
source of CO2 in the atmosphere, but basically the impact
may be carbon neutral as long as photosynthetic biomass
growth and CO2 emissions by biomass burning arebalanced. However, the case study in Laos clearly
showed significant changes in land-use conditions andquantified the changes in ecosystem carbon stocks due tothe increased S&B area and shortened fallow periods.
The large decrease in ecosystem carbon stocks had been
emitted into the atmosphere through biomass burning.
This suggests, in turn, the potential capacity of land-use
and ecosystem management for carbon sequestration.
Nevertheless, to reduce the atmospheric impact of biomass burning and/or increase ecosystem carbon stocks,
the multiple functioning of biomass burning and S&B
land use has to be taken into consideration. Historically,
indigenous people in large areas have been highly
dependent on S&B agriculture for their living. Biomassburning and its frequency (fallow period) are strongly
related to land productivity and labor productivity in crop
production; for example, mineralization of soil organic
matter after burning is the major source of soil fertility,
and weeding labor is related to the fallow period. Moreover, traditional S&B land use contributes to thesustainability of biodiversity, forest products (including
NTFP) and water resources. Therefore, the eradication of
biomass burning, as declared in the official environmental discourse, is unlikely to be achieved no matter how
many years pass by. Alternative S&B land-use scenariosthat couple positive effects on food security, natural resources and carbon sequestration would be the mostfeasible solution for the moment. In other words, any
land-use and ecosystem management scenario for carbon
sequestration should be beneficial to regional livelihood
since addressing poverty, i.e., food security, is of thehighest priority for villagers.
Spatio-temporal information is essential to the designing of more productive and sustainable land-use andecosystem management scenarios on regional scales. The
vital role of earth-observing satellite images and geoinformation in spatio-temporal assessment has been clearly
demonstrated. The use of time-series satellite images has
proven useful in deriving the chrono-sequential changeof land use, relative areas of consecutive S&B uses,
community age, and C+F patterns. Note that long-termarchives of satellite images are crucial in assessing
dynamic land-use history. Satellite-based information iseffective especially when combined with process-based

Acknowledgements

References
Asai, H., K. Saito, B. Samson, K. Vongmixay, Y. Kiyono, Y. Inoue,
T. Shiraiwa, K. Homma and T. Horie (2007) Quantification ofsoil organic carbon dynamics and assessment of upland riceproductivity under the shifting cultivation systems in northern
Laos. Proceedings of the 2nd International Conference on Ricefor the Future, November 5-9 2007, pp.201-205, Bangkok,
Thailand.
Asai, H., K. Saito, B.K. Samson, K. Songyikhangsuthor, K.
Homma, T. Shiraiwa, Y. Kiyono, Y. Inoue and T. Horie (2009)
Yield response of indica and tropical japonica genotypes to soil
fertility conditions under rainfed uplands in northern Laos. Field
Crops Research, 112: 141-148.
Appa Rao, S., C. Bounphanousay, J. Schiller and M. Jackson(2002) Collection, classification, and conservation of cultivatedand wild rices of the Lao PDR. Genetic Resources and Crop
Evolution, 49: 75-8.
Aumtong, A., J. Magid, S. Bruun and A. de Neergaard (2009)
Relating soil carbon fractions to land-use in sloping uplands innorthern Thailand. Agriculture, Ecosystems and Environment,
131: 229-239.
Bruun, T.B., O. Mertz and B. Elberling (2006) Linking yields ofupland rice in shifting cultivation to fallow length and soil
properties. Agriculture, Ecosystems and Environment, 113:
139-149.
Douangsavanh, L., A. Polthanee and R. Katawatin, R. (2006) Food
security of shifting cultivation systems: Case Studies from
Luang Prabang and Oudomxay Provinces, Lao PDR. Journal of
Mountain Science, 3: 48-57.
FAO (Food and Agriculture Organization) (1985) Tropical
Forestry Action Plan, Rome, FAO.
Fujisaka, S. (1991) Diagnostic survey of shifting cultivation innorthern Laos: targeting research to improve sustainability andproductivity. Agroforestry Systems, 13: 95-109.
Fujita, Y. and K. Phanvilay (2008) Land and forest allocation in
Lao People’s Democratic Republic: Comparison of case studies
from community-based natural resource management research.
Society and Natural Resources, 21: 120-133.
GoL (Government of Lao PDR) (1999) The Government's
Strategic Vision for the Agricultural Sector, Ministry ofAgriculture and Forestry, Vientiane.
GoL (Government of Lao PDR) (2005) Forestry Strategy to theYear 2020, Government of Lao PDR, Vientiane.
Grau, H.R., N.I. Gasparri and T.M. Aide (2008) Balancing foodproduction and nature conservation in the Neotropical dry
forests of northern Argentina. Global Change Biology, 14:985-997.
Houghton, R.A. (2005) Aboveground forest biomass and theglobal carbon balance. Global Change Biology, 11: 945-958.
Inoue, Y., J. Qi, A. Olioso, Y. Kiyono, Y. Ochiai, T. Horie, H. Asai,
K. Saito, T. Shiraiwa and L. Douangsavanh (2007) Traceabilityof slash-and-burn land-use history using optical satellite sensor
imagery: a basis for chrono-sequential assessment of ecosystemcarbon stock in Laos. International Journal of Remote Sensing,
28: 5641-5648.

30

Y. INOUE

Inoue, Y., J. Qi, A. Olioso, Y. Kiyono, Y. Ochiai, S. Saito, H. Asai,
T. Horie, T. Shiraiwa and L. Dounagsavanh (2008) Reflectancecharacteristics of the major land surfaces in slash-and-burn
ecosystems in Laos. International Journal of Remote Sensing,
29: 2011-2019.
Inoue, Y., Y. Kiyono, H. Asai, Y. Ochiai, J. Qi, A. Olioso, T.
Shiraiwa, T. Horie, K. Saito and L. Dounagsavanh (2010)
Assessing land-use and carbon stock in slash-and-burn ecosystems in tropical mountain of Laos based on time-series satellite
images. International Journal of Applied Earth Observation andGeoinformation, 12: 287-297.
IPCC National Greenhouse Gas Inventories Programme (2003)
Good Practice Guidance for Land-use, Land-use Change andForestry, pp.1-275, Institute for Global Environmental
Strategies, Hayama.
Kiyono, Y., Y. Ochiai, Y. Chiba, H. Asai, T. Shiraiwa, T. Horie, V.
Songnoukhai, V. Navongxai and Y. Inoue (2007) Predicting
chronosequential changes in carbon stocks of pachymorph
bamboo communities in slash-and-burn agricultural fallow,
northern Lao People's Democratic Republic. Journal of Forest
Research, 12: 371-383.
Lestrelin, G. and M. Giordano (2007) Upland development policy,
livelihood change and land degradation: interactions from a
Laotian village. Land Degradation and Development, 18: 55-76.
Maclean, J.L., D.C. Dawe, B. Hardy and G.L. Hettel, eds. (2002)
Rice Almanac, International Rice Research Institute, West
Africa Rice Development Association, International Center for
Tropical Agriculture, Food and Agriculture Organization.
Prasad, V.K., P.K. Gupta, C. Sharma, A.K. Sarkar, Y. Kant, K.V.S.
Badarinath, T. Rajagopal and A.P. Mitra (2000) NOx emissions
from biomass burning of shifting cultivation areas from tropicaldeciduous forests of INDIA – estimates from ground-based
measurements. Atmospheric Environment, 34: 3271-3280.
Prasad, V.K., Y. Kant, P.K. Gupta, C. Sharma, A.P. Mitra and K.V.S.
Badarinath (2001) Biomass and combustion characteristics of
secondary mixed deciduous forests in Eastern Ghats of India.
Atmospheric Environment, 35: 3085-3095.
Pravongvienkham, P. (2004) Upland natural resources management strategies and policy in the Lao PDR. In: H. Furukawa, ed.,Ecological destruction, Health, and Development: Advancing
Asian Paradigms, pp.481-501, Center for Southeast AsianStudies, Kyoto.
Rasul, G. and G.B. Gopal (2003) Shifting cultivation in the mountains of south and Southeast Asia: Regional patterns and factors
influencing the change. Land Degradation and Development,
14: 495-508.

Roder, W., S. Phengchanh and B. Keoboulapha (1997) Weeds inslash-and-burn rice fields in northern Laos. Weed Research, 37:
111-119.
Roder, W. (2001) Slash-and-burn rice systems in the hills ofnorthern Lao PDR: Description, challenges and opportunities
pp.1-201, IRRI, Los Banos.
Saito, K., B. Linquist, G.N. Atlin, K. Phanthaboon, T. Shiraiwa andT. Horie (2006a) Response of traditional and improved upland
rice cultivars to N and P fertilizer in northern Laos. Field Crops
Research, 96: 216-223.
Saito, K., B. Linquist, B. Keobualapha, K. Phanthaboon, T.
Shiraiwa and T. Horie (2006b) Stylosanthes guianensis as ashort-term fallow crop for improving upland rice productivity innorthern Laos. Field Crops Research, 96: 438-447.
Sanchez, P.D., D.E. Bandy, J.H. Villachia and J.J. Nicholaides(1982) Amazon Basin soils: management for continuous crop
production. Science, 216: 821-827.
Shrestha, D.P. and J.A. Zinck (2001) Land-use classification in
mountainous areas: integration of image processing, digital
elevation data and field knowledge (application to Nepal).
International Journal of Applied Earth Observation andGeoinformation, 3: 78-85.
Warner, K. (1991) Shifting cultivators: local technical knowledge
and natural resource management in the humid tropics.
Community Forestry Note 8, 1-20. Rome, FAO.

Yoshio INOUE
Dr. INOUE leads research at the National Institutefor Agro-Environmental Sciences, Japan. He has
also served as a Professor at the Graduate Schoolof Life & Environmental Sciences, University ofTsukuba since 1995. He has been involved inecosystem informatics with the interdisciplinaryinterests in plant ecophysiology, micrometeorology, remote sensing, andregional studies. His recent research has focused on methodological studies
on remote sensing of biophysical and ecophysiological variables in plantand ecosystems, and regional assessment of agro-ecosystem dynamics
using remote sensing, modeling and geospatial information systems.

(Received 15 March 2011, Accepted 7 October 2011)