145

Expansion of Rubber Mono-cropping and its Implications for
the Resilience of Ecosystems in the Face of Climate Change inMontane Mainland Southeast Asia
Jefferson FOX1*, Jean-Christophe CASTELLA2, Alan D. ZIEGLER3 andSidney B. WESTLEY1
1

The Research Program, The East-West Center
1601 East-West Road Honolulu, HI, 96848-1601, USA
2
The Institute of Research for Development (IRD) France,2
the Centre for International Agriculture Research (CIRAD) France, based in Laos
3
The Geography Department, National University of Singapore*e-mail: foxj@eastwestcenter.org

Abstract
Farmers in montane mainland Southeast Asia (MMSEA) have long practiced shifting cultivation withplots of land cultivated temporarily and then allowed to revert to secondary forest for a fallow period. In recent years, shifting cultivation has given way to more intensified forms of mono-cropped agriculture,including cultivated crops, orchards and, of increasing importance, rubber tree plantations. Today, more than
one million hectares have been converted to rubber plantations. By 2050, the area under rubber trees in
MMSEA is predicted to increase fourfold (Fox et al. 2012). This massive conversion of primary or secondary
forests to rubber mono-cropping could threaten the resilience of both ecosystems and livelihoods. Despite
environmental concerns and market fluctuations, both local farmers and outside entrepreneurs are likely tocontinue expanding rubber plantations because of their high economic returns. We argue that more diversified
agroforestry systems that provide an optimal balance between economic returns and environmental
sustainability are needed to improve the long-term outlook for the region in the face of climate change.
Key words: carbon, rubber, Southeast Asia, water

1. Introduction: Massive Land Use
Conversion in Montane Mainland
Southeast Asia
With “montane” defined as land above 300 meters
elevation, montane mainland Southeast Asia (MMSEA)
covers about one-half of the combined land area ofCambodia, Laos, Myanmar, Thailand, Vietnam andChina’s Yunnan Province (Fig. 1). The region is home togreat biological and cultural diversity that is threatened
by deforestation, commercial agriculture driven by regional and global markets, and the rapid expansion ofurban and periurban landscapes (Fox & Vogler, 2005).
The region’s high seasonal, interannual, and multidecadal climate variability and the resulting long historyof catastrophic floods and droughts, with their impacts onregional socioeconomic wellbeing and political stability(Buckley et al., 2010), are also of major consequence.
These factors create a unique setting in which presentday human-environment interactions in MMSEA offer apreview of future challenges throughout the developing
Global Environmental Research
18/2014: 145-150
printed in Japanworld.
For centuries, farmers in this region have practiced diverse systems of shifting cultivation, in which plots ofland are cultivated temporarily and then allowed to revert
to secondary forest for a fallow period. The staple crop is
typically upland rice, but cultivated plots may include a
range of secondary food and cash crops such as maize,
cassava, banana, sugarcane, ginger and cardamom(Mertz et al., 2009). Fruit trees or other useful tree
species may be planted on fallow plots leading to complex agroforestry systems, or they may be left entirely
regrow naturally. These practices produce a unique landscape mosaic combining small agricultural plots withsecondary forests. Studies conducted in the region largely
agree that these traditional land-use systems are environmentally sustainable, protecting the region’s richbiodiversity and soil and water resources (Ziegler et al.,2011; Fox et al., 2012).
Over the past half century, the five countries of
MMSEA have witnessed a major shift from predominantly subsistence agrarian economies to industrialized©2014 AIRIES146

J. FOX et al.

societies. These changes have been accompanied by
growing urban populations and establishment of a number of regional megacities. Simultaneously, the agricultural frontier has advanced as demand for land andresources from the growing population, both within the
sub-region and from outside, has increased (Fox &Vogler, 2005).
A central dynamic of this change has been the rapid
growth of boom crops (Hall et al., 2011). Among themany types of commercial products promoted and grown
are numerous tree-based products such as rubber, coffee
and cashews, and fast-growing tree species for pulp andpaper. Between 2000 and 2010 the amount of the landscape occupied by tree crops grew at an annual rate of
4.32% per year (Li & Fox, 2011).
In recent years, entrepreneurs from China, Vietnam,
Malaysia and Thailand have invested heavily in the
expansion of rubber plantations to new areas of Laos,
Cambodia and Myanmar, as well as portions of their own
countries (Fox & Castella, 2013). One impetus for the
expansion of rubber in the highlands has been the widespread shift from rubber to oil-palm production in morehumid areas where rubber was grown before. By 2012,rubber plantations covered more than one million hectares of non-traditional rubber-growing areas of China,
Laos, Thailand, Vietnam, Cambodia and Myanmar (Li &Fox, 2012). By 2050, the area under rubber plantations ispredicted to increase fourfold, largely replacing secondary forests and land currently under shifting cultivation(Fox et al., 2012).

Fig. 1 Montane mainland Southeast Asia.

In addition to boom crops, heightened concern forenvironmental conservation has led state actors to zone
large amounts of land as off-limits to agriculture and,increasingly, to try to enforce that zoning. In 1990, there
were 115,759 km2 of protected areas in these five countries (IUCN & UNEP-WCMC, 2014). By 2010 this area
had more than doubled to 252,698 km2. In the lower
Mekong countries of Thailand, Laos, Cambodia andVietnam this figure represents 22% of the landscape, thelargest proportion of national land area demarcated forconservation zones of any region of the world (PADP,
2003). Despite this protection, forest cover in MMSEA
fell from 50.7% to 45.7% between 1990 and 2010, as aresult of losses in Cambodia, Laos and Myanmar(Meyfroidt & Lambin, 2009). In Thailand, the agricultural frontier has closed and forests are beginning toregrow on former cropland while in Vietnam large
government-supported afforestation and reforestation
programs are resulting in forest expansion, but poor forest quality is still an issue (Hoang et al., 2011).
One factor driving the transition toward more intensive agriculture has been the expansion of road networks
and markets, making it easier for farmers to purchaseagricultural inputs and sell their crops. Finally, cropsubstitution programs, designed to eliminate the cultivation of opium poppies, have motivated a shift toward
rubber and other cash crops. National governments in theregion have accelerated this trend by formulating explicit
policies to replace traditional shifting-cultivation systems
with other forms of land use, including the permanentcultivation of annual crops, rubber and other tree-crop
plantations, and greenhouse-based horticulture (Ziegler
et al., 2009). Policies have included the outright banningof shifting cultivation, declaring areas to be forest
reserves and excluding the people who had lived there for
centuries, moving them into more crowded settlements inthe lowlands. Attracted by the opportunity to convert
traditional farming areas into high-value commercial
operations, outside entrepreneurs, corporations and governments have sought to gain control of land in the region
through schemes ranging from joint ventures with local
farmers to outright dispossession. Some farmers haveenhanced their income by switching to intensive cash
crop production. Others have been forced into contracts
with unfavorable terms or have lost their land entirely(Fox et al., 2009).
While more intense agricultural production may posea threat to fragile local environments, it is not possible toturn back the clock. Rubber plantations, in particular,
have proven highly profitable (Jumpasut, 2014). Given
financial realities, neither local farmers nor outside
entrepreneurs are likely to return to subsistence forms ofagriculture. As a response to the changing situation, theChinese have gone as far as to redefine rubber plantations
as forests, thereby increasing the area they have declaredunder forest cover. But are rubber plantations really as
beneficial to the environment as natural forests? Are they
more or less beneficial than the traditional systems ofshifting cultivation that they are replacing? Given theExpansion of Rubber in Montane Mainland Southeast Asia

current pace of expansion, it is particularly critical toanswer these questions and determine the environmental
implications of this large-scale change in land use in theface of a changing climate. The sequential drought andflood events in mainland Southeast Asia in 2010 and2011 exemplify the potential vulnerability of current
land-use systems to extreme climate events.

2. Climate-driven Vulnerability
The monsoon regime dominates the atmospheric circulation in mainland Southeast Asia, resulting in highly
seasonal precipitation, with 80%-90% of total precipitation falling during the six-month summer monsoon
season (approximately May-October). The time of onset,
duration, intensity and frequency of breaks in the summer
monsoon circulation and precipitation can vary significantly, resulting in a relatively high frequency of extreme
precipitation years, both low and high (Lim et al., 2012).
Drought due to deficient monsoon rainfall can produce
widespread crop failure and famine. Excessive rainfall
often produces flooding in densely populated low-lying
cities, such as Chiang Mai and Bangkok, which experienced large floods in 2005 and 2011, respectively (Wood& Ziegler, 2008; Ziegler et al., 2012). Over the pastmillennium, numerous multi-year “megadroughts” areknown to have occurred in the region with devastatingconsequences, ranging from political upheavals, e.g.,during the 1756-1768 drought, to massive death tolls(e.g., during the drought of 1876-1878 (Cook et al.,2010). Extreme monsoon rainfall variability, including
lengthy droughts, during the 14th and 15th centuries, isthought to have contributed to the fall of the Khmer
Empire based at Angkor (Buckley et al., 2010).
Variations in monsoon timing and intensity are known
to be associated with Pacific- and Indian Ocean-based
coupled ocean-atmosphere oscillations, viz. the El NiñoSouthern Oscillation (ENSO) and Indian Ocean Dipole(IOD), respectively (Ummenhofer et al., 2011). Many of
the historical megadroughts affecting the region, forexample, were associated with severe El Niño events(Davis, 2001; Cook et al., 2010). Indian Ocean sea
surface temperature (SST) changes produce regional
drought (or heavy rains) during the positive (or negative)
phase of IOD (Saji et al., 1999; Ashok et al., 2001). In the
future, global climate change is expected to have significant effects on the Asian monsoon circulation withconsequences for the mean and variability of the regional
climate in mainland Southeast Asia.
Expectations are that climate warming will cause
intensification of the monsoon, resulting in greaterinterannual and multi-decadal variability in the form of
more frequent and more severe droughts and floods(Overpeck & Cole, 2007). Ashfaq et al. (2009), using
regional downscaling of CMIP3 global model simulations, projected a reduction in monsoon precipitation inSouth Asia, resulting from a delayed onset and more
frequent monsoon breaks associated with weakened local
Hadley circulation. Upward trends in temperature and the147

frequency of high temperature extremes have been detected in the region; significant rain days have decreasedin number and the proportion of annual rainfall derived
from extreme events has increased (Manton et al., 2001).
Observations indicate a shift toward a drier climate in theregion that began in the mid-1970s (Cook et al., 2010),
along with a weakening of the relationship between
ENSO and the Asian monsoon. These findings may belinked to a higher frequency of positive IOD events inrecent decades (Ummenhofer et al., 2011). Due to theanticipated climate changes in mainland Southeast Asia,
the dry season is expected to lengthen and intensify. In
contrast, the rainy season is expected to shorten andintensify, with dramatic increases in rainfall occurring in
the wettest months. Thus, both seasonal water shortages
and floods may be exacerbated (Mainuddin & Kirby,2009).
The role that forests and other plant communities may
play in mitigating climate change has put a premium on
efforts to measure the carbon content of plants in forestsand in various agricultural systems (Gibbs et al., 2007;
Ziegler et al., 2012). Particular concern is focused on
areas where land-use systems are changing, resulting in
carbon gains or losses. The limited available data suggest
a substantial overlap between below-ground carbon
stored under traditional systems of shifting cultivation
and under rubber plantations (Ziegler et al., 2012; Yuen
et al., 2013; Fox et al., 2013). This overlap in measures ofabove-ground and below-ground carbon suggests that atransition from traditional shifting cultivation to rubber
plantations will probably not lead to substantial increases
or decreases in levels of carbon sequestration. Maintenance or expansion of protected forests could certainly
increase carbon sequestration. Yet it is difficult to set landaside when populations in the region are growing andboth local farmers and outside entrepreneurs are beginning to profit from a booming rubber industry.

3. Trans-boundary Environmental Issues
Forest conversion and agricultural intensification not
only contribute to carbon emissions and high costs associated with more irrigation and fertilizers, but generate
other major issues that threaten the resilience of ecosystems and livelihoods at the landscape scale and thatagroforestry can mitigate. These issues are explored in
the four subsections that follow.
3.1 Accelerated drought and flooding indownstream areas because of water and land-use
change upstream
Both an increase in intensive rain-fed annual crops
and areas of commercial tree crops will require more
off-season water for cultivation. A projected drier climate
with increased rainfall variability makes the water supply
less predictable. Increased buffering of water storage isthus needed. The buffering capacity of landscapes, however, has been declining because of reductions in rainfall
recharge resulting from changes from land-cover types of

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high infiltrability (e.g., undisturbed forests) to those thatgenerate substantial surface runoff, including intensely
cultivated hillslopes, where accelerated erosion occurs(Ziegler et al., 2004, 2007, 2009). Technical approaches
to increasing water storage through construction of dams
and reservoirs provide water for hydropower generationand downstream irrigation, but may result in a reduced
capacity to absorb unexpected rainfall towards the end of
the rainy season, as seen in the 2011 Bangkok floods(Ziegler et al., 2012). Reservoirs in northern Thailand
often have no storage capacity left as their operationalrules prescribe maximum water supply for the dry season.
Their total economic costs have been huge (Cook et al.,2010). Reducing the risk of droughts during dry seasons
and years, and floods during wet months requires technical plus natural buffering to secure downstream ecosystems and livelihoods.
3.2 Reduction of agro-biodiversity
The increasing prevalence of rubber monocultures onland that used to have agro-diverse land uses has reduced
the biological buffering against pests, weeds and diseases
and increased the risk that farmers are exposed to in theface of climate variability and market fluctuations(Aratrakorn et al., 2006). Agro-biodiverse, intermediateintensity agroforestry options at farm and landscapescales could increase farmers’ capacity to deal with economic and climatic shocks as well as natural (andhuman-induced) disasters (Qiu, 2009; Hoang et al., 2011).
Such practices, however, remain blind spots for muchongoing research and development because they are
misunderstood as being of only ‘traditional’ value, rather
than dynamic responses to contemporary pressures thatbuild on local knowledge and practice.
3.3 Erosion and depletion of the soil organic carbon
sink
Conversion of natural forest to cultivated land generally leads to a reduction of soil organic carbon stocks
because of reduced litter inputs, higher top soil temperatures that lead to higher decomposition rates, and soil
disturbance that increases decomposition due to increased aeration and destruction of physiochemical protection mechanisms (Brunn et al., 2009). Intensificationof rubber monocultures and rain-fed rice on steep slopes
may cause accelerated erosion (Sidle et al., 2006; Ziegler
et al., 2009). When the soil surface layer is eroded, the insitu carbon and various nutrients are washed away andoften exported from the hillslope and even outside thecatchment (Brunn et al., 2009). Subsoils with lower soilorganic carbon content and water-holding and infiltration
capacity are then exposed, further increasing surface
run-off. Groundwater dynamics are potentially affectedby dry-season water use of rubber as a commercial tree
crop (Guardioloa-Claramonte et al., 2008, 2010). Thisillustrates how land productivity may be reduced at alandscape scale by efforts to increase economic gains
locally and hence why there is a need for cross-scale
approaches to landscape management. Such approaches

need to foster the development of social capital at thescales at which ecosystem services manifest if they are tobe effectively managed.
3.4 Long-term impacts and complexity at thelandscape scale
It usually takes time before unintended effects ofhuman changes in agro-ecosystem functions can be seen.
This is because interactions involve lag times before
ecosystem resilience reaches a tipping point. For example, irrigation of a commercial agricultural landscape wasseen to affect water quality and quantity adversely in thedelta area of northwestern Mississippi after 20 years ofmonitoring (Coupe et al., 2012). Accelerated drought
during the dry season due to mono-cropping of rubber in
the Upper Mekong river basin was found after 15 years ofsystematic observation (Zhang et al., 2012). Furthermore,policies aimed at one sector in one part of MMSEA may
cause unintended ecological consequences in other sectors and places (Coupe et al., 2012). The complexity ofsocio-ecological systems needs to be better captured as abasis for multi-stakeholder negotiations of development
trajectories that work for all. This requires a long-term,
integrated landscape approach to research, development
and monitoring at multiple scales ranging from the local
to the regional.

4. Conclusions and Recommendations
New, site-specific assessments are needed for a better
understanding of the environmental implications of rapidly expanding rubber plantations in MMSEA. Assessments at multiple sites will improve understanding ofland-use changes across this highly diverse region.
Transition from some short-fallow systems of shifting
cultivation to rubber plantations could improve carbon
sequestration, but the gains may be difficult to measure
and, in any case, are not likely to be dramatic. Specifically, it is doubtful whether a REDD+ scheme could be
devised to support these sorts of transitions because thecarbon volumes involved may be too limited to interest
investors, and payments to farmers may be too small tomotivate a switch from rubber. Given the economics atplay, it seems inevitable that strong demand and highprices for natural rubber will continue to drive a transition from traditional farming systems in the highlands ofmainland Southeast Asia to landscapes dominated byrubber plantations. In a more ideal world, farmers would
transition to more diverse agroforestry systems combining both crop and tree production in ways that improveclimate change mitigation through carbon sequestration
and adaptation through resilience to unexpected climatic
events or market fluctuations.
For example, a study in Xishuangbanna found that
tea-rubber intercropping systems sequestered atmospheric CO2 and increased soil organic carbon better thanrubber planted alone (Zhang et al., 2007). Leguminous
cover crops planted between rubber trees can also
substantially increase carbon accumulation in addition toExpansion of Rubber in Montane Mainland Southeast Asia

improving soil quality and fertility. An enabling institutional environment is necessary for increasing the inclusion of rubber in mixed agroforestry systems. Policymakers responsible for managing the current rubberboom must recognize the competing views and diversityof actors in environmental decision making and actively
seek to include local people in decision-making processes. Such a multi-stakeholder landscape approach has
historically been lacking in the interactions between
policymakers and farmers throughout much of montane
mainland Southeast Asia.
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Jefferson FOX
Jefferson FOX is a senior fellow at the East-WestCenter in Honolulu. He studies land-use andland-cover change in Asia and the possible
cumulative impact of these changes on the regional and the global environment. His ongoing
research includes ‘Forest, agricultural, and urban
transitions in Mainland Southeast Asia: Synthesizing knowledge and developing theory’ and ‘Community-based forest
management within a globalized economy: Examining local and distantdrivers of forest cover change in the Middle Hills of Nepal.’ Both projects
are funded by NASA. He has worked in Bangladesh, Cambodia, China(Yunnan), Indonesia, Laos, Myanmar, Nepal, Thailand and Vietnam.

Jean-Christophe CASTELLA
Jean-Christophe CASTELLA is a senior researcher at the Institute of Research for Development(IRD, France). He has investigated changes inland use and livelihood systems in Montane
Mainland Southeast Asia during the past 20
years through successive secondments to theInternational Rice Research Institute (IRRI,
Philippines), the Centre for International Forestry Research (CIFOR,
Indonesia), and most recently, the Centre for International Agronomic
Research for Development (CIRAD, France). He is now involved in the
Eco-Friendly Intensification and Climate Resilient Agricultural Systems(EFICAS) Project in Lao PDR, under the Global Climate Change Allianceof the European Union and French Agency for Development (AFD). He isdeveloping a landscape approach to sustainable intensification of agriculture towards ‘climate resilient villages’ in the mountains of northern
Laos. He is also contributing to methodological development ofcommunity-based natural resource management and policy mechanisms
related to climate change mitigation and adaptation.

Alan D. ZIEGLER
Prof. ZIEGLER’s research addresses the interactions among physical and ecological systems inSoutheast Asia, with water resources serving as
a common nexus. His work typically involves
developing environmental monitoring programs
that facilitate understanding catchment processes, as they vary both naturally and anthropogenically over different spatial and temporal scales. He seeks to workwith others who have an interest in various aspects of water resource
management, environmental health, natural hazards or hillslope/catchmenthydrology. He is currently interested in exploring environmental impactsof land-cover change, the risks to rural populations in developing areas ofingesting contaminated drinking water, exposure to anthropogenic contaminants (heavy metals and pesticides) and exposure water-borne
pathogens (e.g., parasites, bacteria). This type of research is a multidisciplinary balancing act, grounded in science, but with an interest inincorporating elements of human geography.

Sidney B. WESTLEY
Sidney B. WESTLEY has worked as a writer,
editor and publications director for more than 40
years, including 22 years in East Africa. Before
joining the East-West Center in 1994, she
worked for research organizations in the fields offorestry and agroforestry, immunology andmolecular biology, animal science, development, and African history. At the East-West Center, she has worked on avariety of publication projects, including The future of population in Asia(with Robert D. Retherford) and Asia's energy future: Regional dynamics
and global implications (with Kang Wu and Fereidun Fesharaki). From1994 to 2004, she was the series editor and principal writer for the
East-West Center’s quarterly publication, Asia-Pacific Population &Policy, and she is currently the series editor for the National Transfer
Accounts (NTA) Bulletin. From 1996 to 2011, Ms. Westley coordinated anannual workshop on communicating with policymakers about populationand health as part of the East-West Center's Summer Seminar on
Population. She holds a B.A. in government from Smith College.

(Received 26 June 2014, Accepted 2 November 2014)