Soil erosion and overland flow response to clear cutting of acacia hybrid plantation in headwater catchment of hoa binh province

MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT
VIETNAM NATIONAL UNIVERSITY OF FORESTRY

STUDENT THESIS
SOIL EROSION AND OVERLAND FLOW RESPONSE TO CLEAR
CUTTING OF ACACIA HYBRID PLANTATION IN HEADWATER
CATCHMENT OF HOA BINH PROVINCE

Major: Natural Resources Management
Faculty: Forest Resource and Environmental Management
Student: Nguyen Van Cong

Student ID: 1553090035

Class: K60 – Natural Resources Management

Course: 2015 – 2019

Advanced Education Program
Developed in collaboration with Colorado State University, USA

Supervisor: Assoc. Prof. Bui Xuan Dung

Ha Noi, 2019


ACKNOWLEDGEMENT

First and foremost, to be able to conduct this research, we would like to
express our sincere respect to our supervisor - Assoc. Prof. Dr. Bui Xuan Dung for his
enthusiastic and patient support with invaluable comments. In addition, we appreciated

the support of other lectures during the time we analyzed the data.
Not only that, many thanks are due to our friends when we started to collect
and analyze data. They always give our team the support whenever we needed. In
terms of difficulties, the transport to study sites was hard without our companions.
Lastly, I express my gratitude to local people who own the Acacia
plantation model for allowing us to conduct this research in this site. They also
informed us about the weather which extremely support us to get the data.

i


CONTENTS
ACKNOWLEDGEMENT ............................................................................................ i
LIST OF FIGURES .................................................................................................... iv
LIST OF TABLES....................................................................................................... v
ABBREVIATIONS .................................................................................................... vi
ABSTRACT .............................................................................................................. vii
CHAPTER I ................................................................................................................ 1
INTRODUCTION ....................................................................................................... 1
CHAPTER II ............................................................................................................... 4
GOAL AND OBJECTIVES ........................................................................................ 4
2.1. Goal................................................................................................................... 4
2.2. Objectives .......................................................................................................... 4
CHAPTER III .............................................................................................................. 5
STUDY SITE AND METHODS ................................................................................. 5
3.1. Study Site .......................................................................................................... 5
3.2. Methods............................................................................................................. 6
3.2.1. Legacy data ................................................................................................. 6
3.2.2. Installing monitoring plot ............................................................................ 7
3.2.3. Survey time ................................................................................................. 8

3.2.4. Rainfall and soil physical characteristics measurement. ............................. 10
3.2.5. Runoff and Soil erosion measurement ....................................................... 12
3.2.6. Vegetation observation measurement ........................................................ 14
3.2.7. Topographic survey: Slope, coordinate system and altitude of four plots are
measured by using GPS and compass. ................................................................. 14
3.2.8. Data Analysis: Data was processed by using Microsoft excel and SPSS. ... 15
CHAPTER IV ............................................................................................................ 16
RESULTS AND DICUSSION................................................................................... 16
4.1. Soil physical factors and vegetation on study sites. .......................................... 16
4.2.

Precipitation characteristics .......................................................................... 16

4.3. Response of surface runoff to clear cutting Acacia plantation. ......................... 18
4.4. Response of soil erosion to clear cutting Acacia plantation .............................. 22

ii


V. CONCLUSIONS, LIMITATION AND RECOMMENDATION .......................... 26
5.1. Conclusions ..................................................................................................... 26
5.2. Limitation ........................................................................................................ 26
5.3. Recommendation ............................................................................................. 26
REFERENCES

iii


LIST OF FIGURES

Figure 3. 1. The map of study site: ............................................................................... 6
Figure 3. 2. Establishing plot model ............................................................................. 7
Figure 3. 3. Location of 2 plots .................................................................................... 8
Figure 3. 4. Harvesting Acacia process ....................................................................... 9
Figure 3. 5. Two plots before cutting ........................................................................... 9
Figure 3. 6. Two plots after cutting .............................................................................. 9
Figure 3. 7. Rain gauge site ........................................................................................ 10
Figure 3. 8. Porosity measurement process ................................................................ 11
Figure 3. 9. Surface runoff measurement process ....................................................... 12
Figure 3. 10. Soil erosion measurement process ......................................................... 13
Figure 3. 13. Excel and SPSS software ...................................................................... 15
Figure 4. 1. Storm events ........................................................................................... 17
Figure 4. 2. Precipitation, surface runoff at 2 plots before and after cutting................ 18
Figure 4. 3. Precipitation, runoff coefficient at 2 plots before and after cuttin ............ 19
Figure 4. 4. Precipitation accumulation, runoff accumulation at 2 plots before and after
cutting........................................................................................................................ 20
Figure 4. 5. Correlation of surface runoff between 2 plots before and after cutting .... 21
Figure 4. 6. Precipitation, soil erosion at 2 plots before and after cutting.................... 22
Figure 4. 7. Precipitation accumulation, soil erosion at 2 plots before and after cutting
.................................................................................................................................. 23
Figure 4. 8. Correlation of soil erosion between 2 plots before and after cutting ........ 24

iv


LIST OF TABLES

Table 4. 1. Observation plots characteristic at the study site ...................................... 16
Table 4. 2. Precipitation, API7 and rainfall intensity on study sites after cutting ........ 17
Table 4. 3. Surface runoff, runoff coefficient analysis between 2 plots before and after

cutting........................................................................................................................ 19
Table 4. 4. Independent samples t-test for the response of surface runoff to clear
cutting........................................................................................................................ 20
Table 4. 5. Soil erosion analysis between 2 plots before and after cutting .................. 22
Table 4. 6. Independent samples t-test for the response of soil erosion to clear cutting
.................................................................................................................................. 23
Table 4. 7. TCVN 5299: 2009 - Method for determination of soil erosion by rainfall 24

v


ABBREVIATIONS

API7

Antecedent precipitation index for 7 days

Cm3

Cubic centimeter

g

gram

mm

millimeter

hr

hour

df

Degree of freedom

GPS

Global position system

ha

Hectare

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

Std. Deviation

Standard Deviation

TCVN

Vietnam standard

vi


ABSTRACT
To assess the response of surface runoff generation and soil erosion to clear
cutting of Acacia plantation in headwater catchment of Hoa Binh province, 2 plots (15
m2/plot) of Acacia plantation 5- year- old were set up and monitored in 2 periods from
22 April,2018 to 12 May, 2019 (before cutting and after cutting) with 70 storm events
in Truong Son commune, Luong Son district, Hoa Binh province. The main finding
included: Surface runoff and runoff coefficient in plot 2 (0.26 mm/15m2/storm and
0.56%/15m2/storm)

were

higher

than

plot

1(0.1

mm/15m2/storm

and

0.23%/15m2/storm) after cutting. Besides, after cutting, the amount of soil erosion in
plot 2 (309.27 g/15m2/storm) was also higher than plot 1 (240.37 g/15m2/storm). The
correlation of surface runoff and soil erosion between 2 plots had strong relation after
cutting (p<0.00).
Key words: Acacia plantation model, bare land, field study, headwater,
runoff generation, soil erosion, period.

vii


CHAPTER I
INTRODUCTION
Land is not only an extremely valuable resource, but also an important
component of the natural environment.

Moreover, Land is the main source of

agriculture and forestry. However, according to the data of the Ministry of Agriculture,
the mountainous area in the North of our country is annually lost about 1cm of surface
soil. Especially in the Northwest region, it takes up to 3cm of topsoil, equivalent to
about 150 - 300 tons of land / ha (Dao Chau Thu, 2006). The amount of soil is lost, the

nutrients in the soil are also reduced, affecting the quality of local people's forests,
resulting in socio-economic losses.
Surface runoff arises when precipitation intensity is greater than infiltration. On
the other hand, when surface flow appears, it usually leads to soil erosion, so the
process of generating surface flow has certain effects on soil erosion. Soil erosion has
long been recognized as a major cause of soil degradation in mountainous areas
(Nguyen Tu Siem and Thai Phien, 1999). Soil erosion is a natural phenomenon, but
this phenomenon is happening more and more serious. It not only significantly affects
the ecosystem, degrades the structure of forest soil and watersheds, but also directly
affects the productivity of forestry cultivation and the livelihood of local people and
the people in the downstream areas. According to the results announced by H.Eswaran
et al (2001), the manufacturing capabilities of some areas in the world will be reduced
to 50% due to erosion and desertification; “In South Asia, cereal production fell by
about 36 million tons per year due to water erosion equivalent to $ 5.4 billion; At
global level, the surface of the earth loses 75 billion tons of land annually, equivalent
to the economic value of 400 dollars billion, In per capita, every citizen on Earth loses
approximately 70 USD/years” (H.Eswaran et al., 2001).
The process of generating surface runoff and soil erosion is a complex process.
The soil erosion is determined by various factors such as rainfall, rainfall intensity, soil
properties, topography and vegetation (Vo Dai Hai, 1996, Nguyen Van Dung and Tran
Duc Vien, 2005; et al., 2009).

In which, vegetation is considered an important

contributing factor in soil protection, reducing surface runoff and erosion (Pham Van
1


Dien, 1998; Vo Dai Hai, 1996; Castillo et al., 1997, Canton et al., 2001, Vo Dai Hai,
2006; Miyata et al., 2009). In general, natural forest land has the ability to penetrate

and retain water well due to its high water consumption, strong roots rooted deep into
the soil, while natural forests also have a thick mat of thick soils, from which soil
erosion was significantly reduced (Bonell, 1998; Descorix et al., 2001). The
coefficient of surface runoff where no tree is 0.23%, where no tree but having carpet is
0.085%, and where having tree is 0.028%. Soil erosion also depends on high tree
canopy layer (Pham Van Dien, 1998; Nanko et al, 2006). The more canopy layer in
forest, the more ability to retain water and soil as possible, forest with a canopy layer
has soil erosion rate three times higher than the forest with three canopy layers (Vo
Dai Hai, 1996). The previous study also showed that in species of different plants, the
ability to regulate water, reduce erosion is different (Vo Dai Hai, 1996, Chao Thi Yen,
2014; Bui Xuan Dung, 2016). There have been many domestic and foreign researches
on the importance of vegetation to reduce soil erosion and surface runoff (ex. Ligdi.
Etafa Emama, R.P.C. Morgan, (1995), Morgan, R.P.C. (2007). But when raising the
question of the impact of mining on soil erosion, the literatures and research thesis
about this issue are very limited.
In Vietnam, about 24% of the forest area is planted forest, of which Acacia
hybrid is a popular crop, bringing high economic value (Ministry of Agriculture and
Rural Development, 2012). Acacia hybrid, also known as hybrid, is a species of plants
indigenous to Northern Queensland (Australia), found in Indonesia's Irian Jaya,
Maluku (Doran and Skelton, 1982). This is a fast-growing species, which is widely
used for various purposes such as timber, firewood, agroforestry, land improvement
(Turnbull et.al, 1983). From the economic and social benefits of Acacia, Acacia
plantations are expected to increase annually (Ministry of Agriculture and Rural
Development, 2012). Besides, Acacia forest also plays an important part in protecting
the surface and structure of forest land, reducing soil erosion from heavy storms.
Truong Son commune, Luong Son district, Hoa Binh province has a total natural
area of 3,060 ha; in which agricultural and forestry land is 2,728 ha; non-agricultural
land 152 ha; Unused land is 180 hectares. Luong Son district is located in the midland

2

region - the transition area between the delta and the mountains, so the terrain is very
diverse. The low mountainous terrain has an average height of about 200 - 400m
formed by magmatic rocks, limestone and terrigenous sediments, with a dense network
of rivers and streams. Truong Son commune, Luong Son district, Hoa Binh province is
a land with suitable natural conditions

for the development of Acacia plantations.

Through the local people, most of the people in the area depend on afforestation.
Currently, there are 75 households in the village, 322 people mainly live on forest
planting.
Acacia is a high-value forestry tree, trusted by many people and planted on a
large scale. But in one place, if planting many continuous cycles can lead to soil
degradation, poor nutrition, then will affect crop yields. In addition, in many places,
the exploitation method for Acacia forests is mostly clear cutting, so there will be a
long time when the land is vacant and insufficient coverage. During recovery process,
the soil is easily washed away, eroded when rainfall and storms. But nowadays, there
is no study and data related to effects of harvesting forest on soil erosion. To further
clarify this issue, i have conducted a study on: “Soil erosion and overland flow
response to clear cutting of Acacia hybrid plantation in headwater catchment of
Hoa Binh province.”

3


CHAPTER II

GOAL AND OBJECTIVES

2.1. Goal
The goal of this project is contributing to provide scientific and practical basis to
minimize the generation of surface runoff and the amount of soil eroded by forest
planting and harvesting activities in Headwater catchment of Vietnam.
2.2. Objectives


Identify the effects of forest harvesting on the generation of surface runoff in

the study area.


Identify the effects of forest harvesting on soil erosion from Acacia hybrid

plantation model in the study area.


Proposing solutions to minimize the negative impact of clearly cutting Acacia

forest on soil and water environment in the study area.

4


CHAPTER III
STUDY SITE AND METHODS
3.1. Study Site
The study was conducted in Truong Son commune, Luong Son district, Hoa Binh
province. Truong Son commune covers an area of 30.64 km², with a population of
1871 people in 1999 and a population density of 61 persons / km².

About topography, Luong Son district in the midland - where the transition
between the delta and mountainous, so the terrain is very diverse. The low
mountainous terrain is approximately 200-400m in height, formed by magma,
limestone and terrigenous sediments, with a dense network of rivers and streams.
Luong Son climate is tropical monsoon, with cold winters - less rainfall; hot
summer - heavy rain. The average temperature of the year is 22.9 - 23.30°C. The
average rainfall is from 1,520.7 to 2,255.6 mm / year, but unevenly distributed during
the year and even during the season is very erratic. “The average precipitation is 276 –
322 mm/month. Each year, there are at least 2 Typhoons that affect the area, the wind
velocity is about 30m/s. The rainfall is unevenly distributed, mainly occurs on in some
months during the rainy season, it can generate huge amount of runoff, causing flood
and seriously landslide and erosion.” (Linh, 2017).

5


Figure 3. 1. The map of study site:

a) Location of Hoa Binh province on Viet Nam map; b) Location of Luong Son
district on Hoa Binh map; c) Location of Truong Son commune on Luong Son district
3.2. Methods
3.2.1. Legacy data
The data was inherited from previous science thesis: “Runoff generation and soil
erosion from different age of Acacia Plantation forest in Truong Son Commune,
Luong Son district, Hoa Binh province, Vietnam” (Chin Kolyan, 2018)

6


3.2.2. Installing monitoring plot

Figure 3. 2. Establishing plot model

a. Aluminum trough (collect soil erosion); b. Plastic pipe (conduct water
from trough to bucket); c. Border (prevent water outside); d. Bucket
(contain surface runoff)
We took 2 plot samples, standard plots were protected and had clear boundaries.
The area of each plot is 15m2 (3m x 5m).
The border of plots was built by aluminum plates. The aluminum plates’ foot was
buried at least 10cm deep to ensure it can withstand heavy winds and heavy rains.
Aluminum plates was 30cm high to prevent rain splash, held and reinforced to stand
upright by steel wires and bamboo piles. The plots were perpendicular to the contour
line. At the down slope end of each plot, an aluminum trough was inserted connecting
to a plastic pipe to transport overland flow and sediment to the buckets used to hold
water and soil after each storm. The aluminum trough had a plate to cover the trough

7


in order to prevent rain splash and rainfall from outside. After finished establishing
plot, we set the rain gauges beside these plots to measure the precipitation. The rain
gauges were set far from the tree canopy to avoid interception from overlying canopy.
3.2.3. Survey time
I set up 2 plots of Acacia plantation 5 –year –old and then, I divided survey
process into 2 phases: In Phase 1, the data was collected by Mrs. Chin kolyan in 6
months (from 22 April to 3rd September, 2018); in this phase, the trees in 2 plots was
not cut. In phase 2, the data was collected by Mrs. Ngoan (student at Standard
program) and me in 3 months (from 21st February to 12 May, 2019); when the trees in
plot 1 was not cut, besides the trees in plot 2 was clear cut; In phase 2, I implemented
full steps of harvesting process (cutting trees, burning and planting new trees).

Figure 3. 3. Location of 2 plots

8


Figure 3. 4. Harvesting Acacia process

Figure 3. 5. Two plots before cutting

Figure 3.6. Two plots after cutting

9


3.2.4. Rainfall and soil physical characteristics measurement.
a. Precipitation measurement
Rainfall was monitored by using US standard plastic rain gauge. Precipitation
was recorded each storm event in amount of water fall into the rain gauge from the
beginning to the end of the storm. An inter-storm period was defined as a period of at
least 6 hours without rain (Yen, 2014). Because the amount of overland flow decrease
quickly after precipitation, a 6-hr period without precipitation was sufficient to
distinguish storm events (Dung et al, 2011).

Figure 3.7. Rain gauge site

b. Soil moisture measurement
Using the Antecedent precipitation index for 7 days (API7) to determine the soil
moisture for each storm event was also figured out.
(

()

10

)


API (i): Precipitation index of the i dates
i: Daily number of days to calculate precipitation index (before) (API) (I € 1-n)
i, j must satisfy condition 0 ≤ i - j ≤ 10
n: number of days in whole observation period
Pj: The corresponding rainfall of rainy day j. If there is much rain on the jth day, it will
be equal to the total number of rains on that day. Any Pj that satisfies the condition 0 ≤
i - j ≤ 10 will be accrued into the API of the i th date in accordance with the above
equation. Outside this area, the rainy day will not affect the API of the ith day.
c. Soil properties measurement
We use Dry Bulk Density Tube to collect soil in order to determine bulk density.
Firstly, remove grass on the surface, use a hammer to close the density pipe with a
height of 6cm and a diameter of 6cm to the ground, note that the edges should be
closed and closed in the vertical direction. Then dug that land up into a tight plastic
bag to mark the location of the standard plots, weigh and record it all and then dry it
up.

Figure 3. 8. Porosity measurement process

i)

Dry Bulk density (D) is the weight of a unit volume of a loose material (such as a

powder or soil) to the same volume of water (g/cm3). Calculated by using the formula:

D=
In which:
D: Dry Bulk density (g/cm3)
M: Weight of dry land in its natural state (g)

11


V: The volume (cm3)
ii)

Porosity of the soil is the ratio of the pores in the soil compared to the volume

of soil. The porosity of the soil is determined by the particle density and the Dry Bulk
density of the soil. Porosity is calculated by using the formula:

X% =

* 100

In which:
d: is the particle density (g / cm3)
D: is the bulk density (g / cm3)
Because we only knew bulk density, so we can assume particle density is equal to 2.56
g/cm3 (Liesch, 2013)
Soil moisture content (%): Determination of soil moisture following steps
Step 1: Weigh the aluminum box, (W1) (g)
Step 2: Weigh soil and aluminum box, we got W2 (g)
Step 3: After 24 hours drying in an oven at a temperature of 105⁰C, weight soil and

aluminum and we got W3 (g). Calculated according to the following formula:
W% =

* 100

Soil depth was measured by measuring tape, we excavate the soil profile (surface cut
straight from the ground down to the bare rock layer.) then used the tap to have the
depth of soil.
3.2.5. Runoff and Soil erosion measurement
a. Surface runoff measurement

Figure 3. 9. Surface runoff measurement process

12


We collected water from buckets after each storm then use graduated cylinder to
directly measure amount of runoff from each plot.
Surface runoff coefficient = (𝑇𝑜𝑡𝑎𝑙 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑠𝑢𝑟𝑓𝑎𝑐𝑒 𝑟𝑢𝑛𝑜𝑓𝑓) / (𝑇𝑜𝑡𝑎𝑙
𝑝𝑟𝑒𝑐 𝑝 𝑡𝑎𝑡 𝑜𝑛) * 100%
b. Soil eroded measurement
Soil eroded also came with surface runoff to the buckets, so after each storm, we
waited for soil to settled down to the bottom of the bucket then took the water to
cylinder to measured, the soil was left in the bucket would be collected then bring to
the laboratory as well as the soil from troughs and pipes in each plot. The soil then
dried in laboratory and weighted to determine the amount of soil erosion.

Figure 3. 10. Soil erosion measurement process

13

3.2.6. Vegetation observation measurement
Canopy and vegetation cover were determined by using GLAMA and Canopy
Cover Free application. We took the picture from the canopy and the vegetation cover
(standing in the central of each plot) and inserted to the program to process then
recorded the results.

Figure 3. 11. Canopy cover, vegetation cover measurement process

3.2.7. Topographic survey: Slope, coordinate system and altitude of four plots are
measured by using GPS and compass.

Figure 3. 12. GPS and compass tool

14


3.2.8. Data Analysis: Data was processed by using Microsoft excel and SPSS.

Figure 3. 13. Excel and SPSS software

To determine the response of surface runoff and soil erosion to clear cutting
Acacia plantation, I applied paired – plots analysis. In this method, 2 plots were
observed in the same natural condition (precipitation, weather condition,
topography, …) in 2 periods (before and after cutting trees). Plot 1 was controlled and
maintained all of trees in both periods, while plot 2 was clearly cut all of trees in
second period. I compared the changing and correlation of surface runoff and soil
erosion between 2 plots before and after cutting. So, I could assess responses of
surface runoff and soil erosion to clear cutting trees.

15


CHAPTER IV
RESULTS AND DICUSSION
4.1. Soil physical factors and vegetation on study sites.
Table 4. 1. Observation plots characteristic at the study site

Parameters
Slope ( o)
Elevation (m)
Canopy cover (%)
Ground cover (%)
Porosity (%)
Number of trees
Average of DBH
(cm)
Average of height (m)

Before cutting
Plot 1
Plot 2
(Tree)
(Tree)
26
27
60
72
85.89

86.9
36.2
38.9

After cutting
Plot 1
Plot 2 (No
(Tree)
tree)
26
27
60
72
89.72
0

56
5

59
5

30.1
55
5

8.5
6.2

8.0

6.1

8.7
6.3

0
52
0
0
0

Generally, some parameters (canopy cover, ground cover, porosity) significantly
changed after cutting tree in plot 2. There was a slight decrease in porosity from 59%
to 53% in plot 2. It means that the porosity of soil decreased after clear cutting. The
canopy cover and Ground cover equal to zero after cutting. But in plot 1, these
parameters change slightly.
4.2. Precipitation characteristics
The total observed data is 70 storm events, in which, there are 55 storm events
observed from 22 April to 3rd September, 2018 (before cutting), and 15 storm events
observed from 21st February to 12 May, 2019. The average amount of rainfall is 35.90
mm, ranging from 2.3 mm to 117.5 mm. The lowest rainfall was 2.3 mm on
20/06/2018, the highest one was 117.5 mm on 19/06/2018.

16


Figure 4. 1. Storm events
Table 4. 2. Precipitation, API7 and rainfall intensity on study sites after cutting

No.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Date
02/03/2019
16/03/2019
19/03/2019
23/03/2019
01/04/2019
04/04/2019
07/04/2019
09/04/2019
15/04/2019
17/04/2019
23/04/2019
28/04/2019
04/05/2019

05/05/2019
12/05/2019

Precipitation (mm)
56
44
57
54
62
54
26
24
16
45
34
39
60
32
24

API7 (mm)
0
0
14,67
20,54
0
20,67
28,33
23,8
4

8
7,5
6,8
6,5
65,57
4,57

17

Rainfall intensity (mm/hr)
28,00
22,00
28,50
27,00
4,13
4,91
26,00
3,00
16,00
15,00
22,67
13,00
15,00
16,00
24,00