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 FORESTRYSTUDENT THESIS SOIL EROSION AND OVERLAND FLOW RESPONSE TO CLEAR CUTTING OF ACACIA HYBRID PLANTATION I

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

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

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

V CONCLUSIONS, LIMITATION AND RECOMMENDATION 26

5.1 Conclusions 26

5.2 Limitation 26

5.3 Recommendation 26 REFERENCES

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

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

Std Deviation Standard Deviation

TCVN Vietnam standard

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

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

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

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.”

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)

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)

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

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

Figure 3 4 Harvesting Acacia process

Figure 3 5 Two plots before cutting

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

( ) ( )

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

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