Runoff generation and soil erosion from different age of acaia plantation forest in truong son commune, luong son district, hoa binh province, viet nam master thesis in forest science

99999999999999999999999999999999999999999999999999999999999999
MINISTRY
OF EDUCATION AND TRAINING
MINISTRY OF AGRICULTURE AND RURAL
DEVELOPMENT
999999999999999999999999999999999999999999999999999999

VIETNAM NATIONAL UNIVERSITY OF FORESTRY
--------------------

CHIN KOLYAN
RUNOFF GENERATION AND SOIL EROSION FROM
DIFFERENT AGE OF ACACIA PLANTATION FOREST IN
TRUONG SON COMMUNE, LUONG SON DISTRICT, HOA BINH
PROVINCE, VIETNAM

MASTER THESIS IN FOREST SCIENCE

Hanoi, 2018


MINISTRY OF EDUCATION AND TRAINING

MINISTRY OF AGRICULTURE AND RURAL
DEVELOPMENT

VIETNAM NATIONAL UNIVERSITY OF FORESTRY
--------------------

CHIN KOLYAN
RUNOFF GENERATION AND SOIL EROSION FROM

DIFFERENT AGE OF ACACIA PLANTATION FOREST IN
TRUONG SON COMMUNE, LUONG SON DISTRICT, HOA BINH
PROVINCE, VIETNAM

Major: Forest Science
Code: 8620201

MASTER THESIS IN FOREST SCIENCE
Signature: ………………………
Supervisor: Assoc. Prof. Dr. Bui Xuan Dung

Hanoi, 2018
ii


ABSTRACT
Vegetation cover is the key factors that protect the soil, reduce surface runoff
and soil erosion. Present days, citizens are paying more attention to the industrial
plantation in Vietnam, especially Acacia magium plantation as it takes part in
improving the socio-economic condition. To propose a solution to mitigate the
impact of Acacia plantation, understanding about runoff generation and soil erosion
are needed. To determine the characteristic of runoff generation and soil erosion
derived at the different ages of Acacia plantation forest in Luong Son headwater of
Vietnam, four plots (15m2) were set up. Of those, 2 plots (up-hill and down-hill) in
1-year-old Acacia plantation and 2 plots (up-hill and down-hill) in 5-years-old
Acacia plantation. The main finding includes: (1) runoff coefficient at Acacia 1year-old down and up was (0.36% - 0.46%) with the average 0.41%. And Acacia 5years-old, down and up was (0.35% - 0.39%) with the average 0.37%. It shows the
slightly different between the locations of two years due to the different ground
cover. However, t-test result showed that the difference between locations in years
one and year-5 are not significant (P-value = 0.31 and P-value = 0.96 respectively).
T-test also indicated that there was no significant difference in term of an runoff at

two different ages of Acacia plantation with (P-value = 0.95 > 0.05); (2) soil erosion
is significantly different between two years of Acacia plantation (P-value = 0.004 <
0.05). Total soil erosion in year-1 and year-5 were 21.84 ton/ha/6months and 14.20
ton/ha/6months, respectively that is classified as strong erosion (level IV) base on
TCVN5299:2009; (3) both runoff and soil erosion at 2 different ages of Acacia
plantation forest has strongly depended on the amount of precipitation (R2 range
from 0.52-0.85, with P-value = 0.00). This suggests that the amount of runoff and
soil erosion at Acacia 1-year-old was a greater amount of soil erosion because of
fewer vegetation covers we need to be more concerned and apply suitable
management for reducing the negative impact of Acacia plantation forest at the
headwater of Vietnam.

i


TABLE OF CONTENT

ABSTRACT ........................................................................................................ i
TABLE OF CONTENT ...................................................................................... ii
ABBREVIATIONS ........................................................................................... iv
LIST OF TABLES.............................................................................................. v
LIST OF FIGURES ........................................................................................... vi
CHAPTER I: INTRODUCTION ..................................................................... 1
CHAPTER II: LITERATURE REVIEW ........................................................ 5
2.1. Runoff generation and soil erosion globally ................................................. 5
2.2. Runoff generation and soil erosion in Vietnam .......................................... 10
CHAPTER III: STUDY SITE AND METHODS .......................................... 13
3.1. Study site ................................................................................................... 13
3.2. Methods ..................................................................................................... 15
3.2.1. Plots design for an experiment ................................................................ 15

3.2.2. Measure runoff ....................................................................................... 19
3.2.3. Measure soil erosion ............................................................................... 20
3.2.4. Measure precipitation ............................................................................. 21
3.2.5. Soil moisture measuring ......................................................................... 21
3.2.6. Measure porosity of the soil .................................................................... 22
3.2.7. Soil texture ............................................................................................. 23
3.2.8. Vegetation observation ........................................................................... 25
3.2.9. Topographic survey ................................................................................ 25
3.3. Data analysis ............................................................................................. 25
CHAPTER IV: RESULTS ............................................................................. 26
4.1. Runoff generation at 2 different ages of Acacia plantation......................... 26
4.2. Soil erosion at 2 different ages of Acacia plantation .................................. 30
4.3. The relationship among runoff, soil erosion, and precipitation ................... 35
4.4. Suggested solution ..................................................................................... 39

ii


CHAPTER V: DISCUSSION ......................................................................... 41
5.1. Runoff generation at two different ages of Acacia plantation forest ........... 41
5.2. Soil erosion at two different ages of Acacia plantation forest .................... 44
CHAPTER VI: CONCLUSION ..................................................................... 49
ACKNOWLEDGMENT ................................................................................... 50
REFERENCES
APPENDIX

iii


ABBREVIATIONS

1-Down

Plot 1-down at Acacia 1-year-old

1-Up

Plot 1-up at Acacia 1-year-old

5-Down

Plot 5-down at Acacia 5-years-old

5-Up

Plot 5-up at Acacia 5-years-old

API7

Antecedent precipitation index for 7 days

C

Carbon

Cm3

Cubic centimeter

df

Degree of freedom

FAO

Food and Agriculture Organization

Fig.

Figure

GIS

Geography Information System

GPS

Global position system

ha

Hectare

N-P-K

Nitrogen - Phosphorus - Potassium

P-value

Probability

R2

Coefficient of determination

RUSLE

Revised Universal Soil Loss Equation

SPSS

Statistical Package for the Social Sciences

USA

United States of America

USDA

US Department of Agriculture

iv


LIST OF TABLES

Table 3.1. Observation plots characteristic at the study site ........................................ 17
Table 3.2. Soil texture at study site follow FAO classification 2006 ......................... 17
Table 4.1. The summary result from SPSS (Appendix table1) ................................... 30
Table 4.2. The summary result from SPSS (Appendix table 1). ................................. 34
Table 4.3. Summary of correlation analysis between runoff, soil erosion, and both

rainfall and soil moisture characteristics ........................................................................ 38
Table 4.4. TCVN5299: 2009 Method for determination of soil erosion by rainfall . 39
Table 5.1. Comparison the runoff coefficient with other studies (the unit for first
two columns are %/6months while the rests are a %/1 year) ...................................... 43
Table 5.2. Compare the soil erosion among Acacia plantation forest year-1, year-5
(ton/ha/6months) with other land types (ton/ha/year for the rest) ............................... 47

v


LIST OF FIGURES
Fig 2.1. Soil erosion effect by human impact in Madagascar, (Source: US news) ....8
Fig 2.2. Soil erosion by water globally (ton/ha/year) .................................................9
Fig 2.3. Soil erosion in Lai Chau after heavy rain in June 2018 ...............................12
Fig 3.1. The map of the study site: a) Location of Hoa Binh province on Viet Nam
map, b) Contour line map of four plots location; c) Acacia 1-year-old; d) Acacia 5years-old. ...................................................................................................................14
Fig 3.2. Picture a). Contour line map shows the location of four plots, b). Model
illustrates elevation, slope, and distance of 4 plots at the study site .........................16
Fig 3.3. Picture plot 1-down and 1-up of Acacia 1-year-old and, plot 5-down and
plot 5-up of Acacia 5-years-old planation forest at study site. .................................16
Fig 3.4. The model of plot and experiment conducted, a). gutter, b). plastic tube, c).
aluminum sheet, d). plastic container ........................................................................18
Fig 3.5. A measured amount of runoff ......................................................................19
Fig 3.6. Took eroded soil to dried and weighted in the Laboratory..........................20
Fig 3.7. US standard plastic rain gauge ....................................................................21
Fig 3.8. (a) Bulk density tube, (b) took a soil sample, (c) soil sample keep in zipper
plastic bag, (d) measured wet soil .............................................................................23
Fig 3.9. (A) Removed fraction, (B) rock and roots, (C) soil after grind and
(D)pipette ..................................................................................................................24
Fig 4.1. Runoff generation and precipitation at the study site ..................................26

Fig 4.2. Runoff coefficient from four plots ...............................................................27
Fig 4.3. Runoff accumulation and precipitation from four plots ..............................28
Fig 4.4. Runoff generation box chat plot ..................................................................29
Fig 4.5. Precipitation and soil erosion from four plots .............................................31
Fig 4.6. Soil erosion accumulation from four plots ..................................................31
Fig 4.7. Soil erosion box chat plot ............................................................................33

vi


Fig 4.8. The model illustrates the result of runoff and soil erosion at two different
ages of Acacia plantation forest from April to September 2018 ..............................34
Fig 4.9. Correlation between precipitation and runoff from four plots ....................35
Fig 4.10. Correlation between soil erosion and precipitation from four plots ..........36
Fig 4.11. Correlation between soil erosion and runoff from four plots ....................37

vii


CHAPTER I: INTRODUCTION
Runoff and erosion are considered the main cause of soil and water resources
degradation (Clement et al., 2006; Yang et al., 2003). Runoff is a process of water
surface flow, other sources flow over the earth’s surface. Runoff is one of the main
factors that support for non-point source pollution. It’s also the main cause of
sediment delivery to stream and river (Braskerud, 2002). However, sometimes
runoff can start before all surface depressions have been filled (Moore and Larson,
1979).
Erosion is the action of the surface process of soil due to a water drop and
wind, under the impact of gravity on earth (Ellison, 1945). Previous researches
indicated that runoff and erosion have a close relationship with precipitation

(Ramos‐ Scharrón and MacDonald, 2007). Soil erosion is a natural phenomenon
but this phenomenon is becoming more serious (Hudson, 1995). It not only directly
affects the agroforestry production activities but also affects the environment and
the life of the downstream communities as land degrades rapidly in all aspects:
chemistry, physics, and biology (Joseph, 2005). The characteristics of runoff and
erosion will have a direct impact on soil quality, stream health and water quality. In
the rapid developing speed of the world, the environmental problem has emerged as
one of the most important challenges that the world together must face.
Industrialization and agriculture activities have left behind serious impact on the
natural condition.
Globally Soil erosion has been an environmental concern in such countries as
China and those bordering the Mediterranean Sea for millennia (Morgan, 2009).
The potential of soil loss estimated is about 0.38mm/year. The most seriously
affected region in the world in Southeast Asia. It nearly 60% of present soil erosions
are induced by human activity, global warming, the increasing trend of precipitation
and population (Yang et al., 2003). Erosion happens quite frequently in Asia, Africa
and South America with the soil mass from 30 to 40 tons per hectare for every year
(Barrow, 1991). In Cambodia, the degradation of soil and water quality will lead to

1


serious consequences for human life in the natural ecosystem as well as ecology,
social and economic aspect. Erosion is the most serious because of the sediments
transport from China to the Mekong basin. In 1997 during the flood season on lower
forest and floodplain in Cambodia, 84.6 million ton of soils were washed from the
lancing Jiang to the lower Mekong (Kelin and Chun, 1999). The annual sediment
load of the basin was estimated around 67 x 106 tons/year at Chiang Saen (Hården
and Sundborg, 1992). In recent years, in the mountainous areas in Vietnam has lost
a huge amount of soil due to erosion. According to land use analyzed, Vietnam has

about 25 million for steep land, with huge potential for erosion, about 10
ton/ha/year (Vinh TQ and Minh HT, 2009). According to systematic monitoring
from 1960 until now, there is 10-20% of area affected by erosion from moderate to
strong (Xiem NT and Phien Thai, 1999). Runoff generation and soil erosion from
mostly occurs at headwater area (Miyata et al., 2009). Headwater systems are the
areas of originated water within a channel network, are characterized by interaction
with the hydrologic, geomorphic and biological process. It varies from hill slopes to
downstream channels (Hack and Goodlett, 1960).
Runoff generation and soil erosion from headwater area are often governed by
several factors such as climate, human activities and animal, terrain, rainfall
intensity, topology, soil characteristics, and especially vegetation cover (Huang et
al., 2002; Miyata et al., 2009). Vegetation cover is the key factor that protects the
soil and it reduces runoff and soil erosion (Castella et al., 2006; Descroix et al.,
2001a; Pham Van Dien, 2006). In a natural forest, undisturbed perennial forestlands
generally produce the least amount of runoff and soil erosion among all land use
systems. Soil erosion from undisturbed forest soil normally ranges from 0.02 to 1.2
Mg ha (Wagenbrenner et al., 2006). Normally in the forested zone, the amount of
runoff and erosion are negligible because of well-vegetated forest land has high
infiltration rate because it was protection by trees, understory vegetation cover, and
leaf litter, it should be noted that well-managed forest land can maintain higher
storage capacity (Descroix et al., 2001a). According to (MacDonald et al., 2001), in

2


a natural forest, overland flow only presented during large storms. When the forest
is being extracted, it can produce more surface runoff as well as soil (Imeson and
Vis, 1982). The amount of sediment varied according to the status of vegetation
cover, in particular, sediment from bare land was 133g/m2, area without a tree but
have litter was 30g/m2 and the forest area was 1.1g/m2 (Descroix et al., 2001b). In

the clear-cutting or disturbed forest land, the amount of Runoff and soil erosion are
significantly higher, because of the lacks of vegetation cover such as grass, shrub.
Runoff and soil erosion is also dependent on the canopy cover (Nanko et al.,
2008). Forests with more canopy layers, the ability to retain water and soil is higher,
forest with one canopy layer, the amount soil erosion will be three times higher than
the forest with three canopy layers. The different ages of the tree in plantation forest
also impact on the process of runoff generation and soil erosion in different ways.
Previous studies have also shown that the ability to regulate water and reduce
erosion is varied with different tree species (Dung. B.X, 2011). And for plantation
forest different age of trees planting even though the same types of forest plantation
but it could be different the amount of runoff and soil erosion, because of it
different vegetation cover.
In Vietnam, about 24% of the forest area is planted forest, in which Acacia
mangium is a popular crop, which brings high economic value (Ministry of
Agriculture and Rural Development, 2012). Acacia mangium is a native species in
northern Queensland (Australia), found in Iran Jaya, Maluku, Indonesia (Doran and
Skelton, 1982). This is a fast-growing species, which is widely used for various
purposes such as timber, firewood, tannery, and agroforestry and soil improvement.
From the economic and social benefits of acacia, the acacia plantation area is
expected to increase every year. The area of plantation forest tends to increase
annually (Ministry of Agriculture and Rural Development village, 2012). However,
the lack of a database reflects the relationship between Acacia plantations and the
generation of surface runoff and erosion in Vietnam, leading to difficulties and

3


challenges in the development of plantation forest models to achieve the best
environmental performance.
In the mountainous area of Vietnam, due to the sloping hilly terrain combined

with large annual precipitation, surface runoff and erosion are serious issues in the
management of land and water resources. Behind, the indigenous people are tending
to growth more industrial plantation – especially Acacia as it can improve their
livelihood. Although there have been many studies on the protection of soils from
Acacia mangium, it is still a lot of unclear information. Specifically, the effect of
different ages of Acacia mangium in term of reducing the surface flow and against
soil erosion remain unknown. To further clarify this issue, and present the solutions
I conducted my final thesis “Runoff generation and soil erosion from a different
age of Acacia plantation forest in Truong Son commune, Luong Son district,
Hoa Binh province, Vietnam”
Afterward, step by step quantify these relationships to develop Acacia
plantation models not only for the research area, but also for another similarity area,
and to provide the basis for science and further research to develop solutions to
regulate water and protect land resources. Here, we hypothesize that vegetation
cover significantly plays an important role in protecting soil and reducing the
amount of runoff and soil erosion. For the main goal of this study is a strong
characterize the process of runoff generation and soil erosion from a different age of
Acacia plantation forest in Truong Son commune, Luong Son district, Hoa Binh
Province, Vietnam. Hence the objectives of this study were to:
1) To determine runoff generation at 2 different ages of Acacia plantation forest
1-year-old and 5-years-old
2) To determine the amount of soil erosion at 2 different ages of Acacia
plantation forest
3) To propose some suggested solution to reduce the negative impact of runoff
and soil erosion from Acacia plantation forest.
4


CHAPTER II: LITERATURE REVIEW
2.1. Runoff generation and soil erosion globally

The soil is one of the most important things to support every element in the
ecosystem. In addition, Altieri, (1999) stated that 90% of all human foods are
produced on land is a process from the natural ecosystem. Presently the ecosystem
was changed by many driven factors such as socioeconomic forces, land use
change, and decreasingly of land cover. It has to be more challenging for
researchers to know the crucial factor of the problem. For instance, the decreasingly
soil quality because of human activities and natural disaster is unknown. In the
world, twenty-three percent of the land surface has been affected by soil erosion it
about 5-10 million hectares were affected every year (Bui Xuan Dung, 2017; Van
De et al., 2008). In Asia the population grew rapidly, land-use changes and
degraded land it’s the cause of soil erosion (Ha et al., 2012; Lal, 2004). For the
highest percentage of degraded land is about 31% in the history of Asia, followed
by Africa at 27% (Oldemal, R.L, 1994). In developing countries, the cost of land
degradation may be more than 15% of the Gross National Product (Barbier and
Bishop, 1995). In Western Europe, there was a growing realization from the 1970s
that soil erosion could have a major effect on soils, even on lowland arable areas
(Morgan, 2009). According to Yang et al. (2003) stated that watershed management
must be done carefully because it should control the runoff and erosion which are
two of the most serious problems in the world.
Runoff and soil erosion are often not only the primary consequences and
symptoms of land mismanagement but contribute to negative downstream off-site
impacts such as flooding pollution and siltation of water bodies and reservoirs
(Bruijnzeel, 2004). Previous researches Maglinao and Leslie, (2001) said that
erosion is regarded as a major type of environmental damage in South-East Asia.
Erosion is the phenomenon of surface erosion under erosive forces of water or
wind. Soil erosion is a natural phenomenon, but this phenomenon is happening
more and more serious (Ellison, 1944). Soil erosion from land areas is widespread
5

land degradation at the global scale in term of loss soil fertility, water quality and
adversely affects all natural and human-managed ecosystems, including agriculture
and forestry. Its effects are pervasive, and its damages are long lasting (Pimentel
and Kounang, 1998). It is generally hypothesized that increased exploitation of land
resources in headwater catchment areas, even as small as km2

< 1, with the

associated fragmentation of native forest vegetation, can result in increased
sediment discharge and elevated nutrient loads that act to reduce water quality and
availability to downstream users (Bruijnzeel, 2004).
There have been some attempts to study the dynamics of the natural resources
in the Himalayas and other mountainous areas of the world. Sharma et al. (2001)
evaluated the fluxes of overland flow, sediment output, and nutrient losses. Eighty
percent of the sediments delivered to the world’s oceans each year came from Asian
rivers and amongst these Himalayan rivers are the major contributors (Chorley,
1969). In mountain zones, overland flows are influenced by surface features, slope
value and vegetation affect runoff and erosion according to (Nguyen Trong Ha,
1996). The rainstorms often generate substantial surface runoff with the potential
for accompanying soil and nutrient losses (Wells, 1981). These changes in rainfall
patterns and intensities may result in greater amounts of overland flow and a
concomitant increase in the quantities of C and N removed from hill slopes
(Edwards and Owens, 1991). Furthermore, Negi et al. (1998) studied three highaltitude forested watersheds in Nandadevi

Biosphere Reserve of Central

Himalayas. This study indicated a significant role of tree physiognomy on the
relative partitioning of total rainfall into infiltration and overland flow. McDowell
and Sharpley, (2002) studied the effect of flow path length on phosphorus (P) loss
in overland flow with and without localized dairy manure application at two sites

within an agricultural watershed in Pennsyl vania, USA. Most early studies Malmer,
(1996) as well as current work, focus on presented experimental data on
hydrological effects and nutrient losses of forest plantation in an experimental
catchment in Sabah, Malaysia Mandal et al. (2012) compared soil nutrient data from

6


different land uses across Amazonia. Patterns were identified regarding nutrient
concentration and variation with the type of land use (McGrath et al., 2001).
Runoff occurred after a storm event and it is one of the main sources of nonpoint pollution at stream ecology. Previous researches indicated that runoff has a
close relationship with precipitation (Ramos‐Scharrón and MacDonald, 2007). Van
De et al. (2008) the major cause of runoff is not only rainfall but also depend on
other factors such as slope, gradient, terrain, and under vegetation story considered
as a method of runoff prediction (Hudson, 1995). For example, research has
provided evidence for the result from field studies describing the effect of slope on
runoff are contradictory (Chaplot and Le Bissonnais, 2000; Fox et al., 1997).
Sharma et al. (1983) stated that some case increases the amount of runoff.
Moreover, Poesen, (1984) claimed that runoff decreases. On the other hand Mah et
al. (1992) as slope gradient increase runoff, it not significantly different. As has
been previously reported in the literature the concept of Horton, (1933) developed
that overland flow or surface runoff occurs when rainfall rates exceed soil
infiltration rates. The coefficient of surface runoff where no tree is 0.23%, where no
tree but having carpet is 0.085%, and were having a tree is 0.028% (Descroix et al.,
2001b). Previous studies have emphasized, in the catchment area, the saturation
overland flow and subsurface flow were dominant processes in rainfall-runoff
processes (Bonell, 1998). In additionally Bonell, (1998), in the forested zone or a
natural forest, the amount of runoff is negligible because of the structure of the tree,
leaf litter, and understory vegetation cover.

7


Fig 2.1. Soil erosion effect by human impact in Madagascar, (Source: US news)
Vegetation cover are plays an important role to control erosion by canopy, roots
system, litter component for reducing the power of runoff and soil erosion from the
environmental condition (Zuazo et al., 2004). In the same fashion, numerous studies
have reported vegetation have influence reducing erosion, sediment processes with
spatial scales Xu, (2006) and eco-environmental changes. For globally during the
past, concerning to re-establishing perennial vegetation cover that is a good way to
protect environmentally, reduces runoff and soil erosion (Davie and Lant, 1994). In
other words, Wilcox et al. (2003) quote that related to eco-hydrology the effects of
vegetation scale on runoff and erosion will be different depending on the degree of
disturbance. However, many researchers have done about vegetation cover related
to soil erosion (Nguyen Trong Ha, 1996; Xu, 2006; Zheng, 2006; Zuazo et al.,
2004). Additionally, there are many studies found that the stems of plants can trap
runoff then reduces the amount of soil eroded (Dung. B.X, 2011; Ligdi and Morgan,
1995).

8


Fig 2.2. Soil erosion by water globally (ton/ha/year). Source: Nachtergaele et
al. (2010)
In summary: Runoff and soil erosion are growing globally, soil performs a
range of key functions, including the production of food, the storage of organic
matter, water and nutrients, the provision of a habitat for a huge variety of organic
matter, water and preserving a record of past human activity. fortunately, there is a
strong correlation between runoff, soil erosion, and vegetation cover. Thus, increase
the vegetation cover can control soil erosion and runoff.

9


2.2. Runoff generation and soil erosion in Vietnam
Soil erosion is a hazard traditionally associated with agriculture in the tropical
and semi-arid area and important for long-term effects on soil productivity and
sustainability. Morgan, (2009) reported that it is a problem of wider significance
occurring additionally on land devoted to forestry, transport, and recreation. Erosion
also leads to environmental damage through sedimentation, pollution and increased
flooding. In watershed management, the most common and critical problem directly
impact on soil quality, hydrology, stream health and water quality are runoff and
soil erosion. According to the previous study of Lal, (1998) quote that in southeast
Asia the major type of environmental damage with dramatic consequences in term
of water quality and soil fertility is erosion on sloping land. In Vietnam since the
mid-eighties, agricultural start to the development and the population growth of the
peoples also increased frequently. In addition due to rapid human population
growth, the cropping areas have expanded to more marginal lands such as
mountains and the fallow periods have been shortened or even abandoned (Clement
et al., 2006).
Natural forest was destroyed by illegal logging to get the timber production and
then they convert forest to become agriculture land or forest plantation. Plantation
holds an important part in water regulation via its impact on the hydrological
process. Among other factors such as soil, precipitation, slope, road length,
plantation also controls the amount of runoff and soil erosion. By way of example
Castella et al. (2006) from the mid-70s until 1998, villagers in Vietnam cultivated
cassava, arrowroot, taro, maize, eucalyptus plantation on the upland. After that in
2005 five agro-system were dominated such as Acacia mangium plantation, cassava
planted, bracharia ruzziensis planted, Venicia Montana planted and Eucalyptus
plantation (Orange et al., 2007). As a matter of fact, Dien, (1996) quote that

different land use system directly affects the physical structure and biochemical
characteristics of the soil. In order to estimate soil and nutrient losses under
different land use management on sloping land under intense cultivation in Southern
10


Vietnam. Van De et al. (2008) using the Revised Universal Soil Loss Equation
(RUSLE) standard it can apply many land use situations for prediction the amount
of soil erosion. Example erosive farming practice, climate with intense rainfall and
sloping topography are often cited as the main cause of soil erosion such as
reduction in biodiversity, loss of topsoil, flash floods frequent occurrence during
rainy season and droughts during the dry season. Moreover, Tran and Le, (1999)
concentrated 80% of intense rainfall during the rainy season, increased the runoff
process and high soil erode ability make upland fields prone to erosion and diffuse
pollution of river networks.
Ngo et al. (2015) reported that different land use type varied strongly water
yield was 376.9 mm in 2005 and 72.0 mm in 2010. Base flow also increased 189.4
mm and 63.9 mm, respectively. Moreover, while surface runoff increase strongly
water yield was also increasing. Similarly, sediment yield from soil erosion
increased from 101.3 ton-ha-year to 148.1 ton-ha-year during (1995-2005) was a
similar trend to runoff. All sediment delivery to rivers or streams can cause flooding
and reservoir sedimentation as well as negative effects on water quality and aquatic
resources (Chappell et al., 2004; Gomi et al., 2006). As an illustration in northern
Vietnam, soil loss varies greatly with land use and location. In 1999, soil losses by
water erosion (runoff erosion) on upland areas were estimated at about 3.022 billion
ton/ha/year for the whole 22 million ha area that represents approximately 70% of
the total country area (Tran and Le, 1999). The amount of the total soil loss in a 250
ha forested land and watershed covered by agricultural ranged from 16.3 to 172.2 g
/m2/year in Vinh Phuc province (van Keulen et al., 2013). As well as according to
Ha et al. (2012) soil losses were reported in Hoa Binh province is about 14 to 150

g/m2/year. Other studied reported soil losses of up to 1305 g/m2/ year in Hoa Binh
Province (Podwojewski et al., 2008). Additionally for maize fields soil erosion up to
17,000 g/m2/year in Son La province (Tuan et al., 2014). One case study said that
the annual soil loss recorded before 2002 through bed load measurements have
decreased from 3.6 t ha−1 year−1 to 0.1–0.3 t ha−1 year−1 in 2004 (Orange et al.,

11


2007). The highest amount of soil losses will lead to increasing the need for
chemical fertilizers and decrease land productivity (Lal, 1998). Not only that
problems but socioeconomic also decreases, including regional poverty, food
insecurity, lower household incomes and so on (Ananda and Herath, 2003).

Fig 2.3. Soil erosion in Lai Chau after heavy rain in June 2018. Photo:
Prokeraia.com
In summary: The study on runoff generation and soil erosion in Vietnam is
poorly known while Vietnam is the most impacted by soil loss and flooding. It is
the cause of food security, poverty of the country. Recovering of the forest is
important to protect the soil that indirectly protects the national food security and
reduce the poverty.

12


CHAPTER III: STUDY SITE AND METHODS
3.1. Study site
The planted Acacia forests in Chanh village, Truong Son commune, Luong Son
district, Hoa Binh province were chosen to be the monitored area. The study site
belongs to Truong Son commune which is located in a mountainous area. The

coordinate is 20°51'N 105°27'E. The study area belongs to Lam Son Forestry
Company (Figure 3.1). The total area of this commune is 3060 ha, in which forest
account for 2610 ha with the total area of Acacia plantation forest is up to 1359.86
ha occupied 13.9% of total manage areas of Lam Son company (Hoa Binh forest
company, 2016).
The study site belonging to Hoa Binh province, with the basic characterized of
geography as a hilly area situated between mountains and the red river plain. The
altitude ranges from 0 to 1,510 m above sea level. The elevation decreases from the
northwest to the southeast. Located at Hoa Binh province, the study site is also
influenced by the monsoon weather characterized by hot, rainy, and dry seasons.
According to observations over the last decade, the coldest month was January with
an average temperature of 14.9 °C, and the hottest month being July with an
average temperature of 26.7 °C. The rainy season is normally from May to October
with both a high frequency and intensity of rainfall. In August and September,
rainfall peaks at values from 300 to 400 mm per month. The rainfall during this
period accounts for 84–90% of the yearly rainfall. The frequency and intensity of
the rainfall are concentrated over a short period where rainstorms and super
rainstorms are major contributions to the landslide hazard in the area (Bui et al.,
2012). Generally, average precipitation range from 1400-1900mm per year (Ngo et
al., 2015). Due to the hilly terrain and a large amount of precipitation, runoff,
erosion, and landslide become a serious issue in Truong Son commune. Behind,
indigenous people mostly earn a living from agroforestry activities, so they also
disturbed to the natural forest and with the poor management and monoculture of

13


only Acacia or Eucalyptus plantation forest is the problem which leads to the sharp
increase in the amount of runoff and soil erosion.

Study site

-b-

-a-

-c-

-d-

Fig 3.1. The map of the study site: a) Location of Hoa Binh province on Viet Nam
map, b) Contour line map of four plots location; c) Acacia 1-year-old; d) Acacia 5-yearsold.

14


3.2. Methods
3.2.1. Plots design for an experiment
Four plots were installed at two Acacia plantation forest at different ages, in
detail: plot 1 was set up in down-hill is called plot 1-down and second plot up-hill is
called plot 1-up at 1-year-old Acacia plantation forest; the third plot is set up in
down-hill is called plot 5-down and fourth plot is set up up-hill is called plot 5-up at
5-years-old Acacia plantation forest. At each forest stage, in order to see the amount
of runoff and erosion at different elevations, one plot was set up at the upper-hill
part and the other one was located at the down-hill part (Fig 3.2). For the general
information from four plots in detail at (table 1&2).

-a-

15

-b-

Fig 3.2. Picture a). Contour line map shows the location of four plots, b). Model
illustrates elevation, slope, and distance of 4 plots at the study site

1-down

1-up

5-down

5-up

Fig 3.3. Picture plot 1-down and 1-up of Acacia 1-year-old and, plot 5-down and
plot 5-up of Acacia 5-years-old planation forest at study site.
16