Biomass and carbon sequestration prediction models for acacia mangium willd plantations in thai nguyen province, viet nam

vii Methods to Determine theAmount of Carbon Stored in the Plantation 75 Acacia Plantation Management in Thai Nguyen Province 87 Descriptive Statistics for All Variables of the Study

UNIVERSITY OF THE PHILIPPINES LOS BAÑOS Doctor of Philosophy in Forestry: Forest Resources Management

HUNG TUAN NGUYEN

BIOMASS AND CARBON SEQUE ST RATIO N PREDICT I ON

MODELS FO R A cacia m angium Willd PL ANTATI ONS

IN TH AI NGUYE N PRO VINCE, VIET NAM

This dissertation can be accessed only by those bound by confidentiality

IN TH AI NGUYE N PRO VINCE, VIET NAM

HUNG TUAN NGUYEN

JULY 2018

The dissertation attached here to, entitled “BIOMASS AND CARBON

SEQUESTRATIO N PRE DICTIO N MODELS FOR A cacia m angium

Willd PL ANTATI O NS IN TH AI NGUYEN PROVI NCE, VIET NAM ” prepared and submitted by NGUYEN TUAN HUNG in partial fulfillment of the requirements for the degree of DOCTOR OF PHILOSOPHY (FORESTRY: FOREST RESOURCES MANAGEMENT) is hereby accepted

iii

The author was born on March 29, 1980 in Thai Nguyen City, Thai Nguyen Province, Vietnam He is the eldest of two children of Mr Nguyen Van Hoi and Mrs Nguyen Thi Nhan He finished his elementary, secondary, and high school education from Thai Son, Quang Trung, and Luong Ngoc Quyen School, respectively in Thai Nguyen City, Thai Nguyen Province, Vietnam in 1998

He completed his bachelor‟s degree in Forestry from the Thai Nguyen University

of Agriculture and Forestry (TUAF), Thai Nguyen City, Thai Nguyen Province in 2002 Through the Australia Development Scholarship (ADS), he was able to earn his Master‟s degree in Forest Science and Management at the Southern Cross University, New South Wales, Australia in 2012

In 2015, the Southeast Asian Regional Center for Graduate Study and Research in Agriculture (SEARCA) granted him a scholarship to pursue his PhD degree in Forestry: Forest Resources Management at the College of Forestry and Natural Resources, University of the Philippines Los Banos (UPLB)

He is currently employed as a teacher and researcher at the Faculty of Forestry, Thai Nguyen University of Agriculture and Forestry, Thai Nguyen Province, Vietnam

He is happily married to Ms Pham Thi Hoai, with whom he is blessed with a son, Nguyen Lam Khoa and a lovely daughter, Nguyen Tue An

HUNG TUAN NGUYEN

iv

First and foremost, my sincerest thanks to my institution, Thai Nguyen University

of Agriculture and Forestry for allowing me to go on study leave and to the Southeast Asian Regional Center for Graduate Study and Research in Agriculture (SEARCA) for awarding me a scholarship to pursue a PhD degree in UPLB

Special thanks are extended to Dr Teodoro R Villanueva, Chair, advisory committee, for his intellectual and professional guidance, critical comments, encouragement and remarkable interest in supervising this study My grateful acknowledgment also to the members of my advisory committee: Dr Myrna G Carandang, Dr Wilfredo M Carangdang, and Dr Juan M Pulhin for their valuable comments, sincere concern, and understanding

I am also thankful to the rest of the faculty and administrative staff of the Institute

of Renewable and Natural Resources and the Faculty of UPLB Graduate School for their great support

A note of gratitude also goes to all the members of the Faculty of Forestry, Thai Nguyen University of Agriculture and Forestry for the support and assistance extended to

me for my study My deepest gratitude goes to my loving family for all their sacrifices and encouragements I am forever grateful to my loving wife, Mrs Pham Thi Hoai, my son,

Mr Nguyen Lam Khoa and and my daughter Ms Nguyen Tue An for their love and spiritual support

Special thanks also go to all of my sincere friends in Vietnam, as well as in UPLB who have directly or indirectly helped me during my stay at UPLB and also during the conduct of dissertation research in my country

Biomass and Carbon Sequestration of Forest Ecosystems 18

Studies on Biomass and Carbon Sequestration in the World 23 Studies on Biomass and Carbon Sequestration in Vietnam 27

Studies on Biomass and Carbon Sequestration of Acacia Species

in the World

31

Estimation of Total Aboveground Biomass and Carbon Storage

based on IPCC Method

50

Estimation of Total Aboveground Biomass and Carbon Storage

based on the Jenkins et al (2003) Method

Aboveground Biomass (AGB) Calculation from Volume 69 Biomass and Carbon Estimation of Individual Trees 70

vii

Methods to Determine theAmount of Carbon Stored in the Plantation

75

Acacia Plantation Management in Thai Nguyen Province 87

Descriptive Statistics for All Variables of the Study 92

Biomass and Carbon Estimation of Sample Tree and Stand 104

Green Biomass of Individual Tree and Stands 105 Dry Biomass and Carbon of Individual Trees and Stands 116 Percentage between Dry and Green Biomass for Sample Tree by

Tree Fresh Biomass Models by Separated Ages 134

Biomass Models of Branch and Leaves Combination by Separated Ages

151

Green Biomass Models for all Age Levels 159

viii

Dry Biomass Models for All Age Levels 169 Carbon Prediction Models by Separated Ages 171 Carbon Estimation Models for All Age Levels 178 Carbon and Carbon Dioxide Stock for Present Land Use and Scenarios

Plantation Management in Thai Nguyen Province

180

Carbon and Carbon Dioxide Stock of Present Land Use of

Acacia mangium Willd

180

Scenario 2: Trend in biomass and carbon of Acacia mangium

ix

1 Estimated belowground biomass and carbon models for evergreen forests in

Central Highlands of Vietnam

41

2 The estimated biomass models built for the forest types over the world 52

3 The estimated above ground biomass models built for forest types in

Vietnam

53

8 Descriptive summary of stand variables of Acacia mangium Willd 93

9 ANOVA test of diameter and tree height at different strata conditions 86

10 Descriptive statistics for sample trees of Acacia mangium Willd by ages 101

11 Average green biomass distribution in the tree (kg/tree) 106

13 Proportion of dry weight over green weight by age 122

14 Average carbon and carbon dioxide of sample trees and components 124

15 Aboveground and belowground biomass estimation from existing equations 130

16 Biomass model parameters and their performance criteria for Whole-trees 135

17 Selection of best models for whole-trees biomass estimation by age 136

18 Actual and predicted biomass for whole-tree by age 140

19 Bole biomass model parameters and their performance criteria for different

23 Selected models for biomass prediction of branch and leaves combined 154

24 Actual and predicted values of biomass for branch and leave combined

(kg/tree)

155

25 Green biomass models tested for all age classes of Acacia mangium Willd

Equation in bold font was selected as best model for biomass prediction

160

26 Total dry biomass equation tested with predicted variables at different age 163

27 The best selected dry biomass equations with predicted variables by age 164

29 Dry biomass model tested for all age classes of Acacia mangium Willd The

equation in bold font indicates the best models for dry biomass prediction

170

30 Tree carbon prediction models, parameters, and their performance criteria 173

31 The best selected equations for carbon prediction by age 174

32 Comparison of actual and predicted carbon sequestration of whole-tree by

age

175

33 Carbon model tested for all age classes of Acacia mangium Willd Model 4

(D*H) in bold font, was selected as the best model for carbon prediction

179

34 Current total carbon sequestration and three scenarios that happened 182

35 Biomass, carbon, and carbon dioxide trend values 183

xi

1 Estimated US atmospheric CO2 mitigation requirements and potential

sequestration capacities (Sundquist et al., 2008)

2

2 The global carbon cycle Fluxes shown are approximate for the period

2000-2005, as reported by the IPCC (Sundquist et al., 2008)

20

3 Principal global carbon pools Soil organic carbon (SOC) and soil inorganic

carbon (SIC) are two different forms of carbon that can be stored in the soil

(Lal 2004a)

20

5 Circle plot used in America 38

7 Analytical framework of Acacia mangium Willd biomass and carbon

model

61

8 Temporary sample plot of Acacia mangium Willd plantation 63

9 Sample plots sketch out in the Acacia mangium Willd plantation 64

10 Sample trees felled and weighed for green biomass in the field 71

11 Samples for dry biomass were calculated from green biomass 73

13 Average diameter and total height of Acacia mangium Willd at different

strata conditions by age

97

14 Sample tree variables of Acacia mangium Willd by age 103

15 Green biomass (kg/tree) changed by ages of sample trees at the different

strata (A, B, C, D) Average at bottom, side, and top biomass of the strata,

respectively)

108

16 Biomass distributions in the tree components by ages (%) 110

17 Average of green biomass by sample tree and stand by age 113

18 Correlation analysis of plantation age and green biomass 114

xii

19 Correlation analysis of relationship of total green biomass and diameter and

height

115

20 Dry biomass (kg/tree) changed by ages of sample trees at the different

strata (A, B, C, D are average, bottom, side and top biomass of the strata

respectively)

119

21 Dry biomass distribution in sample tree components (%) by age 120

22 Average dry biomass of Acacia mangium Willd sample trees (kg/tree) and

stand (ton/ha) in Thai Nguyen Province

121

23 Correlation analysis of log-transformation of D, H and dry weight of

Acacia mangium Willd sample trees in all age levels

121

24 Average carbon and carbon dioxide of sample trees and stands 125

25 Correlation analysis of Acacia mangium Willd plantation age and carbon

stock

128

26 Actual versus predicted whole-tree biomass using the best equations for

separated different ages The R2 value indicates the goodness of fit for

fitted regression line

142

27 Actual and predicted whole-tree biomass using the best equations for all

age levels The R2 value indicates the goodness of fit for fitted regression

30 Tested actual and predicted biomass by ages using linear regression scatter 158

31 Residual analysis plotted of all sample trees for the best selected models 161

32 Correlation analysis between measured and predicted dry biomass by age 168

33 Correlation analysis between whole-tree dry biomass and diameter, total

xiii

36 Correlation between whole-tree carbon with diameter and total height of

sample

178

37 Residual plotted analysis of all sample trees for the best selected models 180

38 The trend of biomass and carbon of Acacia mangium Willd in Thai

Nguyen

184

xiv

Hung Tuan Nguyen, University of the Philippines Los Banos, July 2018 Biomass and

Carbon Sequestration Prediction Models for Acacia Mangium Willd Plantations in

Thai Nguyen Province, Vietnam

Major Professor: Dr Teodoro R Villanueva

The study developed a model to estimate current biomass and carbon stocks as well as

predict future biomass and carbon sequestration potential for forest plantations of Acacia mangium Willd in Thai Nguyen Province, Vietnam Specifically, the study: 1) characterized the Acacia mangium Willd plantation in Thai Nguyen Province, Vietnam; 2) estimated the current biomass and carbon stocks of tree and stand for Acacia mangium Willd plantations; 3) developed

a biomass and carbon models for tree of Acacia mangium Willd; 4) determined the future

conditions of plantation based on the programs and policies of the government; and 5) recommended appropriate management strategies to improve the forest plantation development and management

A total of 126 plots representing various ages of plantations were established at the bottom, hillside, and hilltop of the plantation Data collected from each plot included age of plantation, spacing, density, diameter, total height, basal area, and volume Estimates of the various plantation characteristics showed significantly higher values in the bottom compared with those in the other parts of the plantations sampled

The data for biomass and carbon estimation and development of prediction model came from 54 destructive sampled trees of different diameter classes (big, medium, and small) of the different ages Six candidate non-linear regression equations using variables as diameter, total height, and age of plantation were tested and assessed for statistical validity and accuracy in biomass and carbon prediction Data analysis was carried out in Excel and STATA 14 PM software The study showed that the major biomass and carbon of tree are boles, followed by branches and leaves Biomass and carbon models were tested for separated ages (each age class

was tested by the model), as well as all age levels from ages 2 to 7 Acacia mangium Willd

plantation (all age classes from 2 to 7 were tested by the model) In terms of separated ages, the model with one variable as diameter (D) showed the better values than variable height (H) and two variables (D, H) combined due to the high correlation efficiency (R2), small standard error (SE), and higher F values As for the models tested for all age levels combined with the addition

of the variable age (A), there was no significant difference observed between single predictor and combined predictors The accuracy of the values was tested by chi-square and residual analysis to compare between observed and predicted biomass and carbon

The prediction equations were used to assess future biomass and carbon sequestration in the province Scenarios of biomass and carbon change were assessed based on the programs and policy of the government

CHAPTER I

INTRODUCTION

Background of the Study

Climate change is one of the most pressing issues in the world today Human activities, especially the burning of fossil fuels, have caused an increased concentration of carbon dioxide (CO2) in the atmosphere, which is a large contributor to climate change It

is generally thought that reducing dependency on fossil fuels and using renewable resources like biomass are ways that can reduce CO2 emissions (Adams et al., 2002)

Carbon sequestration in trees and soil as a means of minimizing atmospheric carbon stores is a concept that has been undervalued as a means to help prevent global climate change However, it has been shown that forests and soils have a large influence

on atmospheric levels of CO2 Moreover, geologic sequestration and ocean sequestration are also effective in CO2 storage (Adams et al., 2002)

Demand for carbon dioxide mitigation in the United States (such as carbon) and potential absorption capacity: (1) Reducing CO2 emissions and CO2 emissions in the United States to stabilize atmospheric CO2 at 550 ppm Model of the United States Climate Change Science Program); (2) Estimated absorption capacity of the United States (Figure 1) According to estimates by the US Department of Energy, an estimated 3,400 gigatons of carbon for potential geological reserves is equivalent to 12,600

a vital part of a comprehensive strategy to offset anthropogenic CO2 emissions and minimize future climate change (Adams et al., 2002)

Figure 1 Estimated US atmospheric CO2 mitigation requirements and potential

sequestration capacities (Sundquist et al., 2008)

The report of IPCC in 2007 indicates that about 100 billion metric tons of carbon over the next 50 years could be sequestered through forest management, which would offset 10-20% of the world‟s projected fossil fuel emissions These models indicated the

need to reduce annual global emissions by more than 75% during the next century in order to stabilize atmospheric CO2 at about 550 parts per million (Sundquist et al., 2008) For the US, McCarl and Schneider (2001) cited in Sundquist et al., (2008), suggested that between 50 and 150 million metric tons of additional carbon sequestration per year could

be achieved through changes in agricultural soil and forest management Enhancing the natural processes that remove CO2 from the atmosphere is one of the most cost effective means of reducing atmospheric levels of CO2 and cutting down dependency on fossil fuels

Currently, global warming is considered a major problem that is negatively influencing organisms and ecosystems worldwide Moreover, as a consequence of global warming, climate change has brought about damages to all components of the environment as evidenced by rising sea levels, drought, changing microclimate, increasing occurrence of different types of diseases, water shortage, decreasing biodiversity, and increasing extreme weather phenomena (IPCC, 2000)

The climate change related to greenhouse gas emissions into the atmosphere (mainly CO2) due to the economic activities of human society is a priority concern in many countries all over the world Thus, a study on CO2 sequestration will contribute in stabilizing greenhouse gas concentrations in the atmosphere at a safe level and also prevent damages on the earth‟s environment that are caused by human activities such as forest fire, deforestation, illegal logging etc Moreover, a study on carbon sequestration and commercial value of forest carbon is an important part of the environmental value of

Vietnam and 160 countries around the world have adopted and signed the Framework Convention of the United Nations on Global Climate Change (UNFCCC) which was confirmed by the Kyoto Protocol in 1997 The framework aims to establish a legally binding protocol on greenhouse gas emission reductions for developed countries and come up with mechanisms to help developing countries achieve socio economic development in a sustainable manner through the implementation of the "clean development mechanism" (CDM) CDM has opened up great opportunities for the forestry sector in the trade of carbon accumulation by the forest ecosystem to create livelihoods for people and reinvest development (Prime Minister 2010)

Vietnam‟s genuine interest on the issue of climate change has led it to become one

of the pioneering countries in Southeast Asia to apply payment for forest environmental services In 2008, the Prime Minister of Vietnam issued Decision No 380/QD-TTg on policies to pilot payment for forest environmental services Decision No 380/QD-TTg was piloted in two provinces, namely: Son La and Lam Dong (Prime Minister Decision, 2008)

In 2010, Vietnam Government issued Decree No 99/2010/ND-TTg on policies for forest environmental payments (Prime Minister, 2010) According to this decree, organizations and individuals that benefit from forest environmental services have to pay for forest environmental services to owners of forests that create supply services including CO2 absorption and retention of forest carbon

In 2014, the Ministry of Agriculture and Rural Development (MARD) issued Decision No 774/ QD dated 18-4-2014 -BNN -TCLN which aims to Approve Action Plan to improve productivity, quality, and value of plantation production phase in 2014-

2020 in order to develop large timber production plantation (MARD, 2014) In addition, Vietnam Government continues to support large timber plantations with a higher fund under Decision No 147/2007 / QD-TTg dated 10-9-2007

In the North East region where Thai Nguyen Province is located, the group

species for large timber production forests include Acacia species, Eucalyptus, Ficus

Religiosa, Pinus, Chukrasia tabularis, Canarium album Raeusch, Melia azedarach Linn

In particular, Acacia species is still the dominant species selected for planting, accounting for about 80% of the area (MARD, 2014)

According to MARD (2015), the forest area in Vietnam is close to 14.062 million hectares including natural forests which account to more than 10.175 million hectares, and more than 3,886 hectares of plantation The area of forest cover reaches 39.5%, while the area of perennial crops grown on forestland accounts to just over 1.3% As a result,

Acacia is a large genus with over 1,300 species widely distributed throughout the tropics and subtropics Most species are found in the Southern hemisphere while the main centre of diversity is located in Australia and the Pacific Acacia is found, sometimes dominant, in primary and secondary forest, forest margins, savannah, grassland, and savannah woodland, on poorly drained floodplains, and along fringes of mangrove forest,

where it is sometimes associated with Melaleuca and Rhizophora spp (PROSEA, 1995)

Acacia mangium Willd is found in areas of high rainfall in Northern Australia,

New Guinea and some adjacent islands The prevailing climate in these areas is usually strongly seasonal, with rainfall of less than 50 mm/month in June–October, in contrast to the average annual rainfall of 1,450–1,900 mm in Southern New Guinea, and 2,100 mm

in Northern Queensland, Australia (PROSEA, 1995)

Fast growing, nitrogen fixing, ever-green with phyllodes that serve as leaves

(NFTA, 1987), Acacia mangium Willd is a medium-sized to fairly large tree measuring

Acacia mangium Willd is an important multipurpose tree for the tropical

lowlands It is one of the most widespread of the fast-growing tree species used in plantation forestry programmes throughout Asia, the Pacific, and the humid tropics like Vietnam (Chaw Chaw Sein, 2011)

Acacia mangium Willd has been playing an increasingly important role in efforts

to sustain a commercial supply of tree products whilst reducing pressure on natural forest ecosystems Fast-growing Acacia plantations provide industrial wood for Vietnam‟s wood-processing, pulp and paper industries, and woodchip exports, as well as household fuelwood supplies in rural areas Currently, 80% of the total requirement of Vietnam‟s wood-processing industries must be imported Acacia plantations are also nitrogen fixing

species and its leaves provide an effective litter layer, making the species a favoured

plantation genus in Vietnam (Chaw Chaw Sein, 2011)

In Vietnam, the study of Acacia species entirely focuses on Acacia hybrid This

present study focused only on the growth, the structure, tree composition, and current

biomass of Acacia magium Willd, particularly in Thai Nguyen Province where it

dominates almost all forest plantations Existing prediction models that estimate the current and future biomass and carbon sequestration potential of plantations were not

used in this study Furthermore, the biomass and carbon estimation of Acacia magium Willd plantation in Thai Nguyen Province, Vietnam were not tested in the consecutive

age levels

Statement of the Problem

Characteristics of forest plantation, such as tree density, basal area, tree frequency, stand height, species composition, and volume are part of any silvicultural stand investigation However, in various tree attributes, diameter and total tree height are probably of the greatest importance (Kleinn et al., 2004) and are the most widely used descriptors of biomass and carbon assessment Diameter is, in most cases, easily and directly measured to calculate the biomass and carbon sequestration of forest trees In forest inventory, total biomass and carbon of trees and stands can be estimated based on diameter and total tree height

Forests play an important role in the global carbon cycle In tropical timberlands,

up to 50% of the carbon is found in vegetation and 50% in the soil (Dixon et al, 1994; Brown, 1997; IPCC, 2000; Pregitzer and Euskirchen, 2004; Phan Minh Sang and Lưu Canh Trung, 2006) This was one of the reasons for their inclusion in the Kyoto Protocol (UNFCCC, 1997) Therefore, forests have the greatest potential for reducing CO2

emissions in the atmosphere (Brown, 1997; Munishi et al., 2000; Munishi, 2001; Munishi and Shear, 2004)

Thus, elucidating on the potential of carbon sinks and the role of forest ecosystems in the carbon cycle, measures to increase the contribution of forest ecosystems in combatting global climate change is now of global scientists‟ interest

The amount of carbon absorbed actually depends on forest types, forest conditions, species, and age levels; however, the current concern is how to estimate and forecast the ability of forests to absorb carbon as a basis to pay for environmental services These are the outstanding issues being researched in Vietnam especially in the current period, when the area of planted forests is increasing To encourage forest investment units, a research that would quantify the environmental value of forests is essential

Estimates of biomass and carbon stocks and CO2 sequestration are important information and inputs for monitoring the volatility of absorbing CO2 emissions in carbon pools for each state of the forest types, and regions with different ecological conditions There are relationships between biomass, carbon and silvicultural investigation factors

(diameter at breast height (DBH), tree height (H)) and ecological factors, structural factors such (forest species composition, basal area, density) which are important variables for biomass and carbon estimation and prediction methods (Bao Huy et al.,

2012 cited in Bui Hien Duc, 2014)

Mathematical models for estimating biomass and carbon vary between sites and species as a function of growth conditions and species composition In recent years, efforts to develop correlation equations from global to local equations have been increasing in the tropics (Brown, 1997; Chave et al., 2005) However, the use of global allometric equations can lead to significant errors in vegetation biomass and carbon estimations compared to local equations due to the specific condition of the study areas

In Vietnam, one model has been developed to quantify the amount of biomass

for some common species, including Acacia mangium Willd, for plantations based on

the ecological condition of the regions Despite of the presence of allometric models for

estimation of biomass in Acacia mangium Willd in the country, the model cannot be used

yet in a wide range of specific conditions, ages, elevations, and soil types because of the following reasons: 1) the allometric model was developed for the whole ecological condition of the region and only focused on the biomass rather than on carbon model; 2) the model was developed for different densities, site classes, and growth conditions of the plantation; and 3) the model was based on plantation of 6 and 7 years of age which is about the rotation age of the plantation in Vietnam

These suggest the need to develop local reliable biomass and carbon models for

Acacia mangium Willd that can account for the biomass and carbon variation as a

function of diameters, age classes, total height The biomass and carbon models developed would be of great assistance to forest managers in their management planning In addition, biomass and carbon models are important for emerging carbon market mechanisms such as Reducing Emissions from Deforestation and Forest Degradation (REDD+) and for the role of conservation and sustainable management of forest and forest biomass and carbon stocks and clean development mechanism (CDM) The key idea of REDD+ is the role of conservation, sustainable forest management, and enhancement of forest reserves in multi-level (global-national-local) forest systems through payments for environment service (PES)

Managing forest plantations has greatly increased the demand for biomass and carbon sequestration on forest plantation management Hence, this study essentially sought to answer the following questions:

1) What are the characteristics of Acacia mangium Willd plantation in Thai Nguyen

Province, Vietnam;

2) What is the potential biomass and carbon sequestration of Acacia mangium Willd

plantation at different ages?;

3) What are the models of biomass and carbon sequestration that will best represent

Acacia mangium Willd plantations at different ages?;

4) How much is the difference between actual biomass and predicted biomass?; and

5) What is the trend of biomass and carbon of Acacia mangium Willd plantation in

Thai Nguyen Province based on the programmes and policies of the local government?

Hypothesis of the Study

The hypotheses of the study were:

H 1 Changes in the plantation parameter and geographic variables can be used to

explain the variations in biomass and carbon of Acacia mangium Willd in

different ages;

H 2 Biomass and carbon models developed through statistical tools can be used to

predict current and future biomass and carbon sequestration of Acacia mangium

Willd tree and stand in Thai Nguyen Province, Vietnam;

H 3 Biomass and carbon models can be used to identify the best biomass and carbon

growth of Acacia mangium Willd plantation; and

H 4 Biomass and carbon of Acacia mangium Willd can be improved through

appropriate management strategies and policies

Objective of the Study

The general objective of this study was to develop a biomass and carbon

sequestration prediction model for Acacia mangium Willd plantations in Thai Nguyen

Province, Vietnam

Specifically, the objectives of the study were:

1 to characterize the Acacia mangium Willd plantation in Thai Nguyen

Province, Viet Nam;

2 to develop prediction model for predicting biomass and carbon sequestration

of Acacia mangium Willd plantations in Thai Nguyen Province, Viet Nam;

3 to test the efficiency of the developed models in predicting current and future

biomass and carbon of Acacia mangium Willd plantations;

4 to assess the current biomass and carbon sequestration of Acacia mangium

Willd plantation;

5 to assess the future biomass and carbon change in Acacia mangium Willd

plantation in Thai Nguyen Province, Vietnam;

6 to determine future capacities of Acacia mangium Willd plantations to

sequester carbon based on programs and policies of the government; and

7 to recommend appropriate management strategies and policies to improve

biomass and carbon sequestration of Acacia mangium Willd plantations in Thai

Nguyen Province, Vietnam

Importance of the Study

Forests play an important role in the global carbon budget because they dominate the dynamics of the terrestrial carbon cycle (Tan et al., 2007; Zhao and Zhou, 2005)

Biomass from plants and vegetation constitutes a significant carbon stock and is the main conduit for CO2 removal from the atmosphere through photosynthesis Consequently, the UNFCC and its Kyoto Protocol have recognized the role of forests in carbon sequestration The amount of carbon sequestered by a forest can be inferred from the biomass accumulation since approximately 50% of forest dry biomass is carbon (de Gier, 2003) Change in forest biomass is influenced by natural succession, anthropogenic actions such as deforestation, harvesting, plantation, silviculture, and natural disturbances

by pests, fire and climate change (Brown, 1997; IPCC, 2006) Thus biomass assessment

is important to understand changes in forest structure as well as carbon sequestration of the forest ecosystems

Aboveground biomass (AGB) is one of five forest carbon pools (IPCC, 2006) which is measurable and reportable for forest carbon projects operating under existing voluntary or future international compliance carbon sequestration markets Structural attribution estimation such as aboveground woody biomass is an important step towards reliable monitoring of the carbon pools in these ecosystems to help us better understand the global carbon cycle

Study on biomass density of forest ecosystem is an important ecological variable for understanding the evolution and potential future changes of the climate system Consequently, assessment of biomass and its dynamics is a crucial input variable to develop climate change projection models and mitigation and adaptation strategies (GTOS 2009) In addition, estimation of forest biomass is also very important for harvest planning (production of forest timber) Estimating forest biomass from a larger area than the stand (from the management unit to all stands) is likewise important in the development of a strategic planning on using renewable energy sources from wood biomass (ELVIS et al., 2009).

Moreover, forest biomass is an important variable for estimating carbon stocks in the forest and studying other biochemical cycles (Husch et al., 2003, Rötzer et al., 2009)

In addition, it is necessary to evaluate reality production (Rötzer et al., 2012) The importance of biomass estimates has increased since the adoption of the Kyoto Protocol

in 1997 (Repola, 2013)

Understanding absorption, reduction, and sequestration of carbon and carbon dioxide associated with forest ecosystems is an important mechanism for mitigating global warming (Husch et al., 2003) Estimation of carbon sequestration in forest ecosystems should include measurements in all relevant carbon sinks (Brown 1999; Brown 2002b; IPCC 2006; Pearson et al., 2007; Wiese et al., 2015); aboveground biomass (AGB) (tree and non-tree vegetation) below ground biomass (BGB), dead organic matter (dead wood biomass and waste), and soil organic matter

Biomass equations are preferred to access representative sample of trees data from the target forest ecosystems (Somogyi et al., 2006) The biomass specific estimation equations from local sites are considered accurately in forestry applications The Good Practice Guidance (IPCC, 2003) and the Guidelines for National Greenhouse Gas Inventories (IPCC, 2006) by the Intergovernmental Panel on Climate Change (IPCC) preferred the selection and use of species-specific allometric equations from local to national and to global scale Hence, development of a local biomass equation can be helpful in the evaluation of the precision of biomass estimates instead of using alternative models

Forest biomass and carbon models are also tools used by forest managers to predict the current and future status of biomass and carbon sequestration of the forest resources which they are managing in order to understand the interactions between biology and physical capacity of forest ecosystem and management activities

Reliable biomass and carbon predictions are important for sustainable forest management of regrowth forest plantation, in policy formulation, in strategic planning, and in operations management (Brown, 1999)

This study focused on the aboveground biomass and carbon sequestration of

Acacia mangium Willd plantation at consecutive different ages from 2 to 7 and sought to

predict how the potential biomass and carbon of the plantation changed as management condition changed in Thai Nguyen Province, Viet Nam

Furthermore, this study proposed to compare the predicted and actual biomass and

carbon of Acacia mangium Willd plantation at the different ages

The biomass and carbon models of Acacia mangium Willd plantation that were

developed and the results from the study supported and improved forest management decision-making in Thai Nguyen Province, Vietnam

Last but not least, the results from this study can be used for future studies on Acacia species plantation in provinces and countries having similar problems and conditions

Scope and Limitation of the Study

This research was conducted to study the Acacia mangium Willd plantations in

Thai Nguyen Province, Vietnam and concentrated on estimating the aboveground

biomass and carbon sequestration of Acacia mangium Willd plantation (dominant tree only) at ages 2, 3, 4, 5, 6, and 7 All the data and information pertaining to Acacia mangium Willd plantation were taken from the fields, internet sources, the Office of

Forest Department, and related institutions in Thai Nguyen Province

On the other hand, the other pools of Carbon (soil, litter, dead wood…) of the

Acacia mangium Willd plantation were not included in this study because of resources

limitation

CHAPTER II

REVIEW OF LITERATURE

Biomass and Carbon Sequestration of Forest Ecosystems

Forests play a vital role in recycling of air in the lower atmosphere Forests store and release carbon dioxide through natural processes As a tree grows, it takes in CO2 from the atmosphere and releases oxygen in the process of photosynthesis The carbon that is taken from the air is incorporated into sugars, which become the building blocks for production of wood About one-half the weight of dry wood is carbon that carbon is stored or sequestered as long as the wood is in existence When trees die, decay or burn they release carbon stored in the soils and biomass (organic matter such as stems, stumps and slash) as CO2 into the atmosphere Carbon is also released as CO2 when trees are harvested, although considerable carbon is stored in wood put into long-term use such as in houses, furniture, and books (World Climate Change Report cited in Patel K.N et al 2017)

Since the industrial age, the concentration of carbon dioxide in the atmosphere has increased from about 280 parts per million (ppm) to 377ppm, a rise of 35 percent Carbon dioxide accounts for only 0.035 percent of the atmosphere, but is most abundant of the greenhouse gases including methane, nitrous oxide, ozone, and chlorofluorocarbons (CFCs) All greenhouse gases play a role in protecting the earth from rapidly losing heat during the night time, but the unusually high concentrations of the gases are thought to cause entire

warming of the global climate Currently, governments around the world are pursuing strategies to prevent the increase in the concentration of carbon dioxide and other greenhouse gases (World Climate Change Report cited in Patel K.N et al 2017)

Carbon sequestration refers to the natural and deliberate processes through which carbon dioxide (CO2) is either removed from the atmosphere or diverted from emission sources and stored in the ocean, terrestrial environments, and geologic formations (Sundquist et al., 2008) Oceans, which mainly store carbon in sediments and dissolved carbonates, are by far the largest global carbon store (Figure 2) Terrestrial carbon sequestration, hereafter referred to in this paper as carbon sequestration, is the process through which CO2 is absorbed from the atmosphere through photosynthesis and stored in biomass and soils (Sundquist et al., 2008)

Figure 2 The global carbon cycle Fluxes shown are approximate for the period 2000-2005,

as reported by the IPCC (Sundquist et al., 2008)

Figure 3 Principal global carbon pools Soil organic carbon (SOC) and soil inorganic carbon

(SIC) are two different forms of carbon that can be stored in the soil (Lal 2004a)

Vegetation is a carbon sink which stores more carbon than it emits In the global carbon cycle, the amount of carbon stored in the vegetation and ground is about 2.5 terra ton (soil, green biomass, and litter), the atmosphere contains only 0.8 terra ton Carbon exchanged by the respiratory and photosynthesis of plant is 0.61 Terra ton and exchanges between air flow and ocean is 0.92 terra ton (Lal 2004a)

Forest ecosystems are sources and sinks of carbon (Watson et al., 2000) In addition,

forest is the best carbon sink since it stores large amounts of carbon (IPCC, 2006) Therefore, forest ecosystems have been playing an important role in controlling climate change Reducing forest will reduce the amount of carbon that is stored and absorbed by

forest ecosystems

According to the IPCC (2006), there are 5 major carbon pools in forest ecosystem including: 1) Aboveground biomass defined as all of the living vegetation biomass, both woody and herbaceous, above the ground including stems, stumps, branches, bark, seeds and foliage (Figure 4); 2) Belowground biomass defined as all biomass of live roots Fine roots of less than 2 mm diameter (the suggested minimum) are often excluded because these often cannot be distinguished empirically from soil organic matter; 3) Litter is all non-living biomass with a size greater than the limit for soil organic matter (the suggested minimum is

2 mm) and less than the minimum diameter chosen for deadwood (10cm) lying dead and in various states of decomposition above or within the mineral organic soil; 4) Dead wood refers to all non-living woody biomass not contained in the litter, either standing, lying on the ground, or in the soil Deadwood includes wood lying on the surface, dead roots, and

stumps larger than or equal to 10 cm in diameter; and 5) Soil organic carbon is the organic carbon in mineral soils to a specified depth chosen and applied consistently through a time series Live and dead fine roots within the soil (of less than the suggested minimum for below ground biomass) are included wherever they cannot be empirically distinguished from the soil organic matter

Figure 4 Five carbon pools in the forest ecosystem

Sources: Winrock international, 2012

Carbon is stored by vegetation through the process of photosynthesis, the results of which are carbohydrates (C6H12O6) which are the building blocks of vegetation

Studies on Biomass and Carbon Sequestration in the World

Biomass and carbon of forest ecosystem are the problems that have caught the interests of several researchers Forest ecosystems are huge reservoirs of the earth In the tropical forests, up to 50% of the carbon are stored in vegetation and 50% of reserves are stored in the soil (Dioxon et al., 1994; IPCC, 2000; Pregitzer and Euskirchen, 2004)

It is estimated that forest operations and reforestation in the world have a CO2

absorption rate in biomass from 0.4 to 1.2 tons/ha/year in the north pole, about 1.5-4.5 tons/ha/year in temperate regions, and 4-8 tons/ha/year in the tropics (Dioxon et al., 1994; IPCC, 2000)

DuyiHo (nd) mentioned that the annual sea plants photosynthesis is about 3x1010tons of organic material, and is about 5,3x1010 on the ground Particularly, the net dry matter yield in tropical forest ecosystems is 10-50 tons/ha/year, with an average of 20 tons/ha/year while dry biomass ranges from 60-800 tons/ha/year with an average 450 tons/ha/year (cited in Le Hong Phuc, 1994)

Canell (1982) had a publication on "biomass and primary productivity of the world forests" which features 600 works on the dry biomass, coal, branches, leaves, and some other components, in 1,200 primary forests of 46 countries around the world

Brown et al (1993) estimated that in 1980, the average biomass density of tropical forests in Asia was 144 Mg/ha (megagram/ha) of biomass, and 148 Mg/ha in soils (up to

100 cm) that is corresponding to 42 and 43 picogram (Pg), respectively, for the entire area

A similar study by Iverson et al (1993) reported an average maximum C stock of 185

Mg C/ha with a range from 25 to over 300 Mg C/ha in the current forest lands in tropical Asia Conversely, Palm et al (1986), cited in Houghton (1991), found that tropical forests in Asia have C density of 40-250 Mg/ha and 50-120 Mg/ha in the same vegetation and soil application Brown et al (1991) reported that the Southeast Asian forests biomass was from 50-430 Mg/ha (25-215 Mg C/ha) and from 350-400 Mg/ha (175-200 Mg C/ha) before the penetration of human beings For inventory of national greenhouse gases, IPCC (1996) proposed a default value of 275 Mg C /ha for the wet forests of Asia

Murdiyarso (1995) cited in ICRAF (2001) researched and found out that Indonesian forests absorbed carbon from the amount of 161-300 tons/ha in the above ground biomass

Brown et al (1996) estimated the total amount of carbon that forest operates can absorb up to 5 years (1995-2000) at about 60-87 Gt C, with 70% in the jungle tropical, 25%

in temperate forest, and 5% in the northernmost forests (Cairns et al., 1997)

In 2002, Van Noordwijk studied the possibility of secondary forest carbon accumulation, the agroforestry systems, and intensive perennials in Indonesia Results showed that the amount of carbon absorbed was 2.5 tons/ha/year on the average

Lasco (2001) reported that secondary natural forest in the Philippines ranged 86-201 tons of C per hectare (equivalent to 370-52 tons of dry biomass/ha, accounting for 50% of estimated carbon biomass)

According to McKenzie (2001), carbon in forest ecosystems is normally concentrated in four main parts of trees: the vegetation on the ground, litter, roots, and soil The determination of carbon in forests is usually done through identifying forest biomass This work is relatively comprehensive and systematic accumulation of forest carbon

According Rodel (2003), although forests cover only 21% of the earth's surface, its biomass, however, accounts for 75% compared with terrestrial biomass and annual growth accounts for 37%

An issue of interest to many researchers is the method used in determining biomass The method used is very important because it relates to the accuracy of the results of the research Depending on the conditions, each method will be used to determine biomass Some of the studies which used different methods of biomass determining include the study

of Newbuold (1967) who proposed the use "sample tree" to study the biomass and productivity of forest plots This method is the international program as indirect back pointer(IBP) applied uniformly

Forest biomass can be identified quickly based on the relationship between the size

of tree and biomass, and components of tree as the form of mathematical functions This method is commonly used in North America and Europe (Whitaker, 1966) Sampling methods to determine root biomass was described by McKenzie et al (2001)