IJERDInternational Journal of Environmental and Rural Development (2018) 9-2

Research article
erd

The Impact of Mimo a pigra on Local Livelihood in the
Stung Sen Core Area, Tonle Sap Biosphere Reserve
SOMALY CHAN*
National Council for Sustainable Development, Ministry of Environment, Cambodia
Email: somalychan.ca@gmail.com

MACHITO MIHARA
Faculty of Regional Environment Science, Tokyo University of Agriculture, Tokyo, Japan /Institute of Environmental Rehabilitation and Conservation, Tokyo, Japan
Received 25 Februry 2018

Accepted 13 November 2018(*Corresponding Author)

Abstract The Stung Sen Core Area is situated at the southeastern end of the Tonle Sap
Lake, and comprises an area of 6,355 ha. It was created under the Royal Decree on theestablishment of the Tonle Sap Biosphere Reserve (TSBR), dated 10 April 2001, and aims
to protect unique evergreen riverine forests and associated vegetation assemblages. Stung
Sen is the buffer zone of the three core zones within the TSBR, and provides the mostimportant inland wetland in Southeast Asia, both for biodiversity conservation and forlivelihoods based on the harvesting of aquatic resources and agricultural farming in thesurrounding areas. This core area has been interrupted by an invasive alien plant, namely
Mimosa pigra (M. pigra), which has had significant physical and economic impacts upon
the natural habitat, local community livelihoods, animals and plants, human health, jobs andthe ecosystem. This study discusses the negative impacts of the invasive M. pigra on local
livelihoods. It uses economic analysis to calculate the cost of its impact and the cost forrecovery; and then provides recommendations on how these impacts can be mitigated. The
distribution of M. pigra in core areas has been mapped, and only those areas, which have ahigh-density of M. pigra, are identified for economic analysis in this study. Face to faceinterviews were carried out with local authorities, rangers, community members, andfarmers within the Stung Sen Core Area, Phat Sonday District. The data analysis is focusedon the impact on farming land, fishing yields, local income generation, and natural habitat
distruction. This paper is developed on the basis of the results of a pilot site experiment on
methods of removing M. pigra to explore the best option for mitigating the spread of M.
pigra, and removing existing M. pigra from the Stung Sen core area.
Keywords Mimosa pigra, impact, local livelihood, Stung Sen Core Area, Cambodia

INTRODUCTION
Invasive alien species (IAS) is non-indigenous plant, animal and microorganism that have beendelivered or accidentally introduced into new areas beyond their native ranges by people, or as aresult of their activities; as well as through natural means such as wind, water, or animal movement,
and which then spreads, impacting negatively on the biodiversity, the ecosystem and economic
development (Chornesky and Randall, 2003). Mimosa pigra is a thorny invasive alien plant which
originates from tropical South and Central America and has been spreading into all tropical regions(Heard, 2009). Richard (2007) indicated that M. pigra is a branched prickly bush that can grow up
to 6 meters and can withstand low nutrient levels and a wide range of soil types. M. pigra has
invaded and subsequently become invasive across Southeast Asian countries. It is one of the mostcommon invasive species found in Cambodia, and it spreads through many parts of wetland areas,lakes and river edges, canals, ponds, floodplains and wherever water flows with its seeds.
The Royal Government of the Kingdom of Cambodia (RGKC) recognizes the Tonle Sap and
Mekong rivers as priority inland water ecosystems for management due to their significant role infood security and agricultural productivity (NBSR, 2016). The Tonle Sap is a primary source forⒸ ISERD

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jobs and incomes and around 3 million people live on or beside it. Approximately 750,000 people
live in the flooded villages, 40% of them live on the floodplains, with the remainder living
dependently on the lake (Mak, 2005). The priority occupation for those living on or beside theTonle Sap is fishing, either as a whole family business or on a smaller scale.
Stung Sen Core Area (SSCA) is one among many core areas of the Biosphere Reserve locatedin Kampong Thom Province on the lower part of the Stung Sen. Stung Sen River receives waterfrom 3 major sources: 57% from the Mekong mainstream, (52% through the Tonle Sap River, and
5% from overland flooding), 30% from tributaries of Tonle Sap Lake, and 13% from direct
precipitation (Kosal, 2011). A population of 5,252, equals to 1,164 households is living in the
SSCA, and their major incomes are from fisheries and seasonal vegetable farming. However, thechange in land use in the region, in particular an increase in rice cropping, has been a significant
factor in the spread of M. pigra, with neglected or abandoned fields being particularly susceptible
to invasion. Recently, the major pathway and spread of M. pigra surrounding the Tonle Sap Lake,especially within the SSCA, has resulted in negative impacts on the biodiversity, the ecosystem,
agriculture, socio-economic, health, and other economic activities. Therefore, this study explores
the negative impact of M. pigra on local livelihoods and the ecosystem in SSCA.
OBJECTIVE
Thi
d aim o a e and anal e he me hodologie anda egie fo in e p ing andelimina ing he nega i e impac of M. ig a ha a e ha ming he economic g o h of local
comm ni ie . The
d al o aim o in od ce applicable me hod o emo e ba ie o in a i epecie managemen in he p od c ion and p o ec ion of e land eco
em in Cambodia; i h hel ima e goal of enhancing biodi e i con e a ion and managemen
i hin p o ec ed a ea
h o gh local li elihood imp o emen .
METHODOLOGY
Data and information about the M. pigra in SSCA and around the Lower Mekong Basin (Fig.1)
was mainly collected through conducting face-to-face interviews with 80 key local authority
representatives, community members, rangers and the director and deputy director of the SSCA.

Fig. 1 M. pigra distribution map in SSCA
The consultation process for selecting these specific stakeholders was underpinned by thisstudy. Survey questionnaires and interview questions were developed to focus on the status of M.
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pigra and its distribution, the socio-economic impact, local income generation and the impact of M.
pigra on that. Best practice and/or methods used by the local community to prevent/remove M.
pigra was also taken into account. The secondary data collection focused on previous or similar
projects from scientific publications, case studies, relevant literature, the media, books, websites,
documents and other related publications, and was used to support or confirm the findings of thisstudy. A distribution map of M. pigra within the SSCA was produced according to data obtained
from GPS The dataset on the income generation status and land occupancy by M. pigra wasutilized to assist analysis of the negative impacts on socio economics and natural habitats in the
SSCA. The study also draws upon experimental results from existing projects for policy
recommendation on methods to remove M. pigra.
RESULTS
Distribution of M. pigra
M. pigra has encroached into Cambodia for decades from its neighboring countries. It was
originally considered to be a wild plant and was introduced from Indonesia to Thailand forcontrolling riverbank erosion, covering tobacco crops, and producing natural fertilizer (Napompeth& Wara, 1983). In 1949, the M. pigra was found in northern Thailand and had spread into Vietnam,
most likely before 1970 (Thi et al., 2004); it continued its advance into Long An province by 1979
(Triet et al., 2004). The weed spread into Cambodia from 1980 around the Tonle Sap Great Lakeand especially along the Mekong Rivers where it occupied thousands of hectares of flooded
wetlands and abandoned fields (Samouth, 2004). Around 1997, M. pigra had encroached into many
provinces of Cambodia, including Steung Treng, Kratie, Kampong Cham, Kandal, Kampong
Chhnang, Kampong Thom, Pursat, Battambang, Siem Reap, Prey Veng, Svay Rieng, Takeo andsome parts of Kampong Speu (GSSD, 2013). Fig. 1 shows the distribution of M.pigra within the
SSCA, however the target site for this study is Phat Sonday Commune in Kampong Thom Provine,which has a high density of M. pigra.
Socio Economics and Income Generation in the SSCA
According to the field interviews with 80 families in the SSCA and 90 families in Phat Sonday
Commune, their major income is earned from the fisheries sector. Their secondary income is basedon farming the surrounding SSCA (Table 1).
Table 1 Occupation and income generation
Major Income of Phat Sonday/SSCA

Occupation of Phat Sonday/SSCA

SourceNo. of family

Percent (%)

Occupation

No. of family

Percent (%)

Fisheries

53

66

Fisherman

48

53

Farmer17

21

Farmer

34

38

Animalhusbandry

3

4

Animalhusbandry

5

6

Other

7

9

Other

3

3

Total

80

100

Total

90

100

Impact Analysis of M. pigra
Table 1 shows that more than 50% of local income depends on fishing activities whilst the second
main income comes from farming. Four major factors have been identified as reasons for theⒸ ISERD

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negative impact to the fisheries yields: invasive species (M. pigra), climate change, illegal fishing,and poisoning from chemical usage in agriculture. The results of the survey suggest that M. pigra
has the most significant impact factor (60%), while illegal fishing is the secondary factor (20%),and climate change & poisoning present around 20% of the impact. Therefore, this section analyses
the impact of M. pigra on local livelihoods especially in relation to incomes earned from fishingactivities.
T o indica oTime Spen and Income ea ned f om fi he ie ha e been iden ified omeasure the impact of M. pigra on local income generation. Data on both indica o befo e andaf e p e en a ion of M. pigra have been collected by category. As shown in Figs. 2 and 3, ime
pen fo fi hing a cla ified in o 4 ca ego ie (G1 = 1-2 hrs, G2 = 2-5 hrs, G3 = 5-8 hrs, and G4 =8-10 h ), and income eceived from fishing was grouped into five categories represented by C1 =2.5-5 $, C2 = 5-10 $, C3 = 10-20 $, C4 = 20-30 $, and C5 > 30 $. The a e age income benchma k
has been set at 17 $ per day per fisherman in accordance with the data received from the interviews
with 50 fishermen as shown in Table 2. The results in Fig. 2 clearly indicated that as M. pigra
continued to spread, the fisherman had to engage in fishing activities for at least 7 more hours toearn an income at the benchmark level. Previously they had only needed to fish for 2-5 hrs toachieve that benchmark figure. This result is evidence that M. pigra has disturbed the fish habitatand its ecosystems that and has led to fish stock shortages. Fig. 3 shows the trend of local incomesfrom fisheries before and after M. pigra p e en ed. The befo e g aph ep e en income ecei edfrom fisheries before M. pigra p e en ed, and he af e g aph ep e en he po M. pigra
situation. The befo e g aph ep e en a high p opo ion of fi he men ho received a good daily
income of between $15-$25, hil he af e g aph clea l ho
i e d ama ic ed c ion in
he fi he men income o be een j $5 and $10 pe da .
25

30

b**
Number of Fisherman

Income in USD

25
20
15

Before

10

After

a**

5

Daily Income (17$)

0

20

15

a*

10

Before

5

After

b*
0

1-2 hrs

2-5 hrs

5-8 hrs

Working hours

8-10 hrs

2-5 $5-10 $** p < 0.01, * p < 0.05

Fig. 2 Change in time spent on fishing

10-20 $

20-30 $

> 30 $

IncomeFig. 3 Change in income from fishing

Table 2 Daily and annual profit loss after presentation of M. pigra in the SSCA
Description Income earned from fisheries by category Total family

IncomeC1=5$ C2=10$ C3=20$ C4=30$ C5=50$ Survey SSCA Family
SSCA
Before (family) 1
11
18
15
5
50 1,164
After (family) 16
23
7
40
50 1,164
Daily income
Income before$5 $110 $360 $450 $250 $1,175$24$27,936.00
Income after $80 $230 $140 $120
0
$570
$11
$12,804.00
Daily and annual profit loss
Daily income loss
$13.00 $15,132.00
Annual income loss
$4,745.00 $5,523,180.00Ⓒ ISERD

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Table 2 shows daily and annual incomes from the fisheries sector and the profit loss of the
1,164 families in the SSCA. This figure is based on the results of the interviews with 50 selectedfamilies in the target area.
DI=Nf1x + Nf2xC2 + NfxC3 + Nf4C4 +Nfx5C5
TNf

Eq. (1)

Where DI = daily income; Nf = Number of family/category
C = Value/category; TNf = Total number of family for survey

Income generation

50%
40%
30%

a*

20%

Before M. Pigra invasion

10%

After M. Picra invasion

b*

0%
2-5 $

5-10 $

10-20 $

20-30 $

> 30 $

Income* p < 0.05

Fig. 4 Change in daily income from fishingThis assignment used the Eq. 1 to estimate local incomes in each category identified in Table
2. According to this calculation, when M. pigra had not yet presented, each family in around 3035% of the total population, was able to generate a daily income of between $ 20 to $ 30; but after
M. pigra had presented, each family in nearly half of the total population was only able to earn $ 10
per day. Therefore, each family had experienced a loss of more than 50% of their income to a rateof $ 13 per day and an overall loss of $ 4,745 annually due to the fish habitat being interrupted by
M. pigra. In addition, the total profit loss for the SSCA amongst 1,164 families has been the hugeamount of more than 5.5 million dollars annually.
RECCOMENDATIONS
Experiment and Control Methods to Remove M. pigra
Several methods have been applied in the developed countries to control the quick invasion of M.
pigra, including physical controls, chemical controls, re-vegetation, and biological controls (Marko,
1999). Each method has always had its pros and cons. In Cambodia, three methods have been
applied and one method is currently under assessment.
1. Physical methods: Hand clearance was the first method used by local people to deal with M.
pigra; this included cutting stumps, uprooting seedlings and stumps, and burning them. Thismethod was very labor intensive and thus expensive, because a significant seed store in the soil
appeared and the plants would geminate in the next rainy season and re-infest the cleared areas; somore labor was required to go back and deal with the new emerging seedlings. The longer the plant
was allowed to grow, the more costly it became to clear them because the plants just grew bigger
which made it more difficult every time, and it took much longer to destroy them. According to theresults of an experiment conducted by the biodiversity department team (BDB) of General
Secretariat of the National Council for Sustainable Development (GSSD) in 2013, this form ofcontrol can only be cost effective when undertaken on a small scale.

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2. Chemical methods: Foliar spraying of herbicides, specifically glyphosates, on weeds like M.
pigra is a method that is often used in Cambodia. However, this method has been attempted within
the SSCA by applying glyphosates onto the cut stumps of the plant, which is a combination
technique of both physical and chemical methods. This technique is also very labor intensive but it
provides significant results in terms of destroying the M. pigra compared to just using the physicalcontrol method alone. The chemical method is usually applied during the dry period, when bark
spraying, stem injection and soil treatments are followed by burning. Unfortunately, due to the
SCCA being located inside the Tonle Sap Protected Areas, herbicide usage is not recommended,and this method could provide negative impacts on the water quality and natural habitat, especially
if there is over-usage of the herbicides or their use is uncontrolled.
3. Biological controls methods: Biological con ol i he e Bio-Agene o de o he em ,flowers, leaves, seeds, or roots of M. pigra. These agents include phytophagous insects, species that
attack roots, stems, leaves, flowers, and fruits, either as larvae or as adults or in both stages, andfungal pathogens. Four hundred and forty-one phytophagous insects have been found on M. pigra
in Central and South America (Harley et al., 1995; Marko, 1999). Based on a survey report (DBD,
GSSD/MoE, 2013), even though this method has been applied in Thailand and Vietnam on M.
pigra, there is no evidence that biological controls succeed in eliminating the weed. When DBD,
GSSD conducted a survey of insects in the SCCA and the 8 provinces that surround the Tonle Sap
Great Lake, the results showed that different insects and larvae are damaging the stems, leaves andflowers of M. pigra, but there is no proof that those insects are bio-agene to M. pigra and thisrequires further research.
4. Re-vegetation methods: This is a method of rehabilitating native species or installing
plantations of local vegetation in degraded land to prevent the sunlight reflecting on the buried M.
pigra seeds. It can be rehabilitation of degraded ecosystem, plantations of fast grow vegetables andplantations of native trees. Re-vegetation produces better results with fast growing species. Part ofthis method includes local people using water hyacinth and water spinach to suppress new
seedlings and the sprouting of M. pigra on their agricultural land. This practice is very common
and costs less through just capturing and keeping water hyacinth and water spinach in agriculturalland during the flooding season. When the water recedes, all of the trapped water hyacinth dies
before it is able to spread and cover the agricultural land. People are then able to grow crops suchas maize and pumpkins by cultivating small patches of the land.

Fig. 5 Re-vegetation through native plant
5. Policy recommendations: This study demonstrates that M. pigra negatively impacts not only on
natural habitats, but also on local income generation. Although there are four methods that can be
introduced to tackle the weed, very few of the methods have been effective in its complete
eradication. The re-vegetation method proved to be the more feasible option for larger scaleattempts to suppress and kill M. pigra, and this method was the least costly; while physicalⒸ ISERD

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methods have proven to be too expensive and unsustainable. Chemical methods have been effective
but have produced negative side effects and result in negative consequences on the ecosystem andwater quality. In this regard, any policy recommendation should consider both short and long termsolutions. Supporting and encouraging local people to continue their practice of using water
hyacinth and water spinach to suppress new seedlings and the sprouting of new M. pigra on
agricultural land can only be a short term solution to the problem. Longer term solutions should
concentrate on the development of plantations and the planting of native species to rehabilitate
degraded ecosystems and land.
CONCLUSION
According to the results and discussions conducted through this study, it can be concluded that the
SSCA is not only rich in biodiversity, but it has contributed enormously to national and local
economic growth. Each family living in Phat Sonday commune has the ability to earn around$8,760 annually from fisheries alone; and they are also able to generate an additional income fromagriculture and farming the surrounding areas. Unfortunately, the SSCA has been effected by theInvasive alien species M. pigra which was introduced into Cambodia from 1980 and which has
rapidly spread, surrounding the Tonle Sap Great Lake as well as along the Mekong Rivers. The
impact of this IAS on the ecosystem and fish stock at the SSCA has led to profit losses of at least
5.5 million dollars annually; and this does not include the impact on agricultural production andfarming yields. In order to respond to the rapid invasion of M. pigra, four methods of control havebeen introduced in an attempt to eradicate M. pigra. These have included physical controls,chemical controls, biological controls, and re-vegetation controls. Based on the geographical areaof the SSCA and the limited research available on bio-agenes, chemical and biological controls are
not a recommended method going forward. Therefore, only the physical and re-vegetation controls
should be applied, even though the physical method can be costly and M. pigra is not permanently
removed through utilising that method.
Aware of serious impacts from the spread of M. pigra to local livelihoods, ecosystems, andnatural habitats, this study highlights two possible policies recommendations: 1) for the short term
strategy, continue use local methods to suppress new seedlings and sprouting of M. pigra on
agricultural land with local vegetable cover such as water hyacinth and water spinach to suppress
growth; and 2) develop and implement rehabilitation programs to replant native species onabandoned agricultural land and degraded ecosystem areas as a long term strategy.
ACKNOWLEDGEMENTS
The authors would like to thank the General Secretariat of the National Council for Sustainable
Development, Ministry of Environment for supporting this study, and recognizes the participationof local community in the SSCA in providing information during the survey. Thanks also go tocolleagues from the Biodiversity Department for their support during the field study and sincere
thanks to the Institute of Environmental Rehabilitation and Conservation as well as Tokyo
University of Agriculture, for the support on this paper.
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