Tree species composition and diversity in relation to altitude of closed canopy subtropical evergreen moist forest in bidoup nui ba national park, viet nam

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM NATIONAL UNIVERSITY OF FORESTRY ------ DUONG VAN HUY TREE SPECIES COMPOSITION AND DIVERSIT

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL

DEVELOPMENT

VIETNAM NATIONAL UNIVERSITY OF FORESTRY

- -

DUONG VAN HUY

TREE SPECIES COMPOSITION AND DIVERSITY IN RELATION TO ALTITUDE OF CLOSED-CANOPY

SUBTROPICAL EVERGREEN MOIST FOREST IN BIDOUP -

NUI BA NATIONAL PARK, VIET NAM

MASTER THESIS IN FOREST SCIENCE

2018

MINISTRY OF EDUCATION AND TRAINING MINISTRY OF AGRICULTURE AND RURAL

DEVELOPMENT

VIETNAM NATIONAL UNIVERSITY OF FORESTRY

- -

DUONG VAN HUY

TREE SPECIES COMPOSITION AND DIVERSITY IN RELATION TO ALTITUDE OF CLOSED-CANOPY

SUBTROPICAL EVERGREEN MOIST FOREST IN BIDOUP -

NUI BA NATIONAL PARK, VIET NAM

Major: Forest Science Code: 8620201

MASTER THESIS IN FOREST SCIENCE

ACADEMIC ADVISOR: ASSOC PROF DR BUI THE DOI

SIGNATURE:

DECLARATION

I hereby confirm that this is my own research The data and results stated

in the thesis are truthful and has not published in any one of the other studies

Duong Van Huy

First of all, I would like send special thank to my advisor Associate Prof

Dr Bui The Doi (Vietnam National University of Forestry) I want to thank for everything he did for me, for teaching, useful advice, support and encouragement He is very nice, knowledgeable and enthusiastic I want to learning many things from him

Sincerely thank to the Dr Bui Manh Hung , VNUF for his training with

me about some softwares, which I used in my study

Thank to the Board of Directors in Bidoup - Nui Ba National Park for their assistance and help to create the most favorable conditions in the process of survey and data collection at the park

Thank you to Mr Le Van Son, Mr Truong Quang Cuong, Mr Nguyen Ich Le Phuoc Thanh and Mr Bui Trung Tuyen – officers of Bidoup - Nui Ba National Park I want to thank for helping of them in field survey and data collection

I would like to send my thanks to my friends and my family for encouraging, sharing, helping and creating favorable conditions both physically, and mentally

Thank you all !

Duong Van Huy

Hanoi, 2018

ABSTRACT

Bidoup - Nui Ba National Park is one of the highest biodiversity area in Vietnam With the main area of cover by closed-canopy subtropical evergreen moist forest, this type of forest has many unique values The study was conducted at 3 altitudes: 1400-1600m; 1600-1800m; 1800m and above The research focused on the diversity of plant and forest structure at these 3 altitudes

By applying updated and current methods in forest inventory and mensuration, the research has obtained main results as follows:

The total of species in all levels is 127 species, mainly belonging to families: Fabaceae, Lauraceae, Theaceae, and Euphorbiaceae The diversity of the plant decreases when the altitude increases This phenomenon was explained

by the competition of trees in populations about light, nutrient, living space, that are harsher when going higher altitude The Simpson, and Shannon-Winer indexes were determined, with values were 0.02 and 4.05 for forest at the altitude of 1400-1600m; 0.03 and 3.86 for altitude of 1600-1800m; and 0.03 and 3.50 at the altitude of > 1800 m

Only Distance equation explains well the tree number distribution by diameter, while there is not any equation for the tree number distribution by the tree height The Cubic equation is the best to describe the relation between diameter and height of trees in forest However, this equation is very complicated, Logarithmic equation has a smaller R but it can explain quite good this relation The relation between D and H for each altitude was LnH= 1.393 + 0.427* LnDbh (1400-1600 m); LnH = 1.126 + 0.523* LnDbh (1600-1800 m) and LnH = 0.992 + 0.517* LnDbh (> 1800 m), respectively

The regeneration status of study site is very diverse with the appearance

of various species from families which are mainly participated in species composition of canopy layer, such as Fabaceae, Lauraceae, Theaceae,etc Regeneration trees with best quality (A) consists 30% at all altitudes

Although the research obtained some results to meet the research objectives and might be used for coming research in Bidoup - Nui Ba National Park in the future However, it still has some shortcomings that need to be improved Author is looking forward to receiving comments from readers, scientists and experts for the better one

TABLE OF CONTENT

DECLARATION i

ACKNOWLEDGEMENTS ii

ABSTRACT iii

LIST OF ABBREVIATIONS vi

LIST OF TABLES vii

LIST OF FIGURES ix

CHAPTER 1 INTRODUCTION 1

CHAPTER 2 LITERATURE REVIEW 3

2.1 Some related concepts 3

2.1.1 Vegetation 3

2.1.2 Forest structure 4

2.2 Some related researches 4

2.2.1 In the world 4

2.2.2 In Viet Nam 9

2.2.3 Research on vegetation at Bidoup - Nui Ba National Park 15

CHAPTER 3 RESEARCH OBJECTIVES AND METHODOLOGY 17

3.1 Goal 17

3.2 Specific objectives 17

3.3 Methodology 17

3.3.1 Study site 17

3.3.2 Data collection methods 18

3.3.3 Data analyses 20

CHAPTER 4 NATURAL CONDITIONS OF STUDY AREA 25

4.1 Natural conditions 25

4.1.1 Geographical location 25

4.1.2 Topography, geomorphology 26

4.1.3 Geology and Soil characteristics 27

4.1.4 Climate 28

4.1.5 Hydrological 29

4.2 Plant resources 29

4.2.1 Diversity of plants 29

4.2.2 Endangered and rare plant species in Bidoup - Nui Ba NP 29

CHAPTER 5 RESULTS AND DISCUSSION 32

5.1 Structural characteristics of woody plant communities at different altitudes 32

5.1.1 Tree species composition of forest vegetation at different altitudes 32

5.1.2 Forest structure 34

5.1.3 Relationship between diameter and height (Dbh-H equation) 53

5.2 Plant diversity of forest types at different altitude 63

5.3 Natural regeneration characteristics 64

5.3.1 Quality of regenerated trees in study site 65

5.3.2 The growth characteristics of regenerated trees 66

5.3.3 Plant diversity of regeneration tree 68

CHAPER 6 CONCLUSION- RECOMMEDATION 69

6.1 Conclusion 69

6.1.1 Structural characteristics of woody plant communities at different altitude 69

6.1.2 Plant diversity of forest types at different altitude 70

6.1.3 Natural regeneration characteristics 70

6.2 Recommendation 71

6.3 Limitation 71

REFRENCES 1

APPENDICES 1

LIST OF ABBREVIATIONS

FAO Food and Agriculture Organization of the United Nations

Dbh Diameter breast height

MARD Ministry of Argciulture and Rural Devlopment

FIPI Forest Inventory and Planning Institute

UNESCO United Nations Educational Scientific and Cultural Organization N/D Distribution of trees by diameter

N/H Distribution of trees by height

IUCN International Union for Conservation of Nature and Natural Resources GPS Global positioning system

LIST OF TABLES

Table 4 1 Botanical composition in Bidoup - Nui Ba NP in Viet Nam Red

Book and IUCN Red List 30

Table 5 1 Tree species composition in 1400-1600m altitude 32

Table 5 2 Tree species composition in 1600-1800m altitude 33

Table 5 3 Tree species composition in 1800m and above 33

Table 5 4 Diameter growth of forest at different altitudes 35

Table 5 5 Height growth of forest at different altitudes 35

Table 5 6 N/D distribution at altitude of 1400-1600m 40

Table 5 7 N/D distribution at altitude of 1600m-1800m 42

Table 5 8 N/D distribution at altitude of 1800m and above 44

Table 5 9 N/H distribution at altitude of 1400-1600m 48

Table 5 10 N/H distribution at altitude of 1600m-1800m 50

Table 5 11 N/H distribution at altitude of 1800m and above 51

Table 5 12 Model Summary and Parameter Estimates for D-H relation for the forest at altitude of 1400-1600m 54

Table 5 13 Model Summary and Parameter Estimates for D-H relation for the forest at altitude of 1600-1800m 55

Table 5 14 Model Summary and Parameter Estimates for D-H relation for the forest at altitude of >1800m 56

Table 5.15 Descriptive Statistics of variables in 1400-1600m 58

Table 5 16 Model Summary( 1400-1600m) 58

Table 5 17 Coefficients (1400-1600m) 58

Table 5 18 Descriptive Statistics of variables in 1600-1800m 59

Table 5 19 Model Summary (1600-1800m) 60

Table 5.20 Coefficients (1600-1800m) 60

Table 5 21 Descriptive Statistics of variables in 1800m and above 61

Table 5 22 Model Summary (1800m and above) 61

Table 5 23 Coefficients (1800m and above) 62

Table 5 24 Plant diversity at different altitudes 63

Table 5.25 Natural regeneration trees in 3 altitudes 64

Table 5 26 Quality of regenerated trees surveyed in sample plots 65

Table 5 27 The growth of expected trees in regeneration layer 66

Table 5 28 Diversity of regeneration trees 68

LIST OF FIGURES

Figure 3 1 Map of study site 17

Figure 3 2 Setting survey plots in the research site 19

Figure 3 3 Measure the diameter and identify species 20

Figure 5 1 Tree position at the altitude of 1400-1600m 36

Figure 5 2 Tree position at altitude of 1600-1800m 37

Figure 5 3 Tree position at the altitude of 1800m and above 38

Figure 5 4 Distribution by diameter in altitude 1400-1600m 39

Figure 5 5 Distribution by diameter in altitude 1600-1800m 39

Figure 5 6 Distribution by diameter in altitude in 1800m and above 40

Figure 5.7 a Meyer distribution for N/D relation at altitude of 1400-1600m 41

Figure 5.7 b Weibull distribution for N/D relation at altitude of 1400-1600m 41 Figure 5.7 c Distance distribution for N/D relation at altitude of 1400-1600m 41 Figure 5.8 a Meyer distribution for N/D relationship at altitude of 1600-1800m 43

Figure 5.8 b Weibull distribution for N/D relationship at altitude of 1600-1800m 43

Figure 5.8 c Distance distribution for N/D relationship at altitude of 1600-1800m 43

Figure 5.9 a Meyer distribution for N/D relationship at altitude of 1800m and above 45

Figure 5.9 b distribution for N/D relationship at altitude of 1800m and above 45 Figure 5.9 c Distance distribution for N/D relationship at altitude of 1800m and above 45

Figure 5.10 N/H distribution at the altitude of 1400-1600m 46

Figure 5 11 N/H distribution at the altitude of 1600-1800m 47

Figure 5 12 N/H distribution at the altitude of 1800m and above 47

Figure 5.13a Meyer distribution for N/H relationship at altitude of 1400-1600m 49

Figure 5.13b Weibull distribution for N/H relationship at altitude of

1400-1600m 49

Figure 5.13c Distance distribution for N/H relationship at altitude of 1400-1600m 49

Figure 5.14a Meyer distribution for N/H relationship at altitude of 1600m-1800m 50

Figure 5.14b Weibull distribution for N/H relationship at altitude of 1600m-1800m 51

Figure 5.14c Distance distribution for N/H relationship at altitude of 1600m-1800m 51

Figure 5.15a Meyer distribution for N/H relationship at altitude of 1800m and above 52

Figure 5.15b Weibull distribution for N/H relationship at altitude of 1800m and above 52

Figure 5.15c Distance distribution for N/H relationship at altitude of 1800m and above 53

Figure 5 16 Describe relationship between diameter and height by 10 different equations at the altitude of 1400-1600m 55

Figure 5 17 Describe relationship between diameter and height by 10 different equations at the altitude of 1600-1800m 56

Figure 5 18 Describe relationship between diameter and height by 10 different equations at the altitude of 1800m and above 57

Figure 5.19 Regression histogram (1400-1600m) 59

Figure 5.20 Regression histogram (1600-1800m) 61

Figure 5.21 Regression histogram (1800m and above) 63

Figure 5.22 Distribution of regeneration trees into height classes for forest at three altitudes 67

CHAPTER 1 INTRODUCTION

The forests are extremely important to every creature on Earth, which considered as a green lung of the Earth By photosynthesis, plants absorb carbon dioxide and produce oxygen into the atmosphere Moreover, forests are the habitat of almost terrestrial wildlife species and for human life, the role of forests is more clearly expressed Recognizing that, policymakers, scientists, and sociologists have been carrying out many environmental protection campaigns around the world However, the forest environment has been negatively impacted by human activities, such as over-exploitation, shifting cultivation, conversion of forested land to other landuse, etc We are witnessing the rapid disappearance of natural forests With the massive development of industries, the exploitation and use of fossil fuels, deforestation along with the large amount of emissions has made the effects on climate change more pronounced

in the 21st century

Viet Nam is a country located in the tropical monsoon region, and has a large area of natural forest and high biodiversity value, including valuable species and abundant resources However, due to negative impacts and improper management, the natural forests of the country have been declining in both area and the quality of the forests

By 2016, Viet Nam had 14,377,682 hectares of forestland Of which, natural forest is 10,242,141 hectares, and plantation forest was 4,135,541 hectares Compared to the total natural area of 33,095,250 hectares, the up-to-date coverage rate was 41.19% Although the rate of forest cover in Viet Nam has increased in recent years, biodiversity and forest quality have declined significantly Besides, Viet Nam is still facing natural threats such as storms, floods, forest fires, and pests This is also one of the causes of deforestation and forest degradation.[1]

Once, understanding on natural forests is very important for scientists and policymakers, in which, research on forest structure and species diversity in a given area is very essential This is the basis for raising solutions for the rehabilitation and improving the degraded natural forest, and ensuring sustainable forest development In addition, the study on the structure of the

forest may help scientists to address characteristics of forests for development and in specific areas

Bidoup - Nui Ba National Park is one of four biodiversity centers in Viet Nam, one of 221 internationally endemic bird areas (EBA) with three important bird areas (IBA); is the bio-geographical region of Gymnosperm species and is also the number one conservation priority in the Biodiversity Conservation Strategy for the South Truong Son (WWF, 2003) biodiversity zone This area is extremely rich in biodiversity values, including many rare species listed in the Red Book of Viet Nam and the Globe Bidoup - Nui Ba National Park is also the core zone of the Langbiang Biosphere Reserve, which was recognized by UNESCO in 2015.[2]

The area of closed-canopy subtropical evergreen moist forest type occupied the biggest area of Bidoup - Nui Ba national park This is a typical forest type of the Southern Truong Son mountain range In the national park, this forest type covers an area of 20,937.32 hectares, accounting for 32.36% of the total area The forest is located at an altitude of 1,000 m and above, with an annual average temperature of less than 180C, with a higher rainfall in the area around Da Lat city, from 2,300 to 3,000 mm / year, with a humidity of 89% to 95% During the dry season (December to March next year), there are often cloudy and light rain.[2]

Located in a strictly protected area, the closed-canopy subtropical evergreen moist forests in Bidoup - Nui Ba National Park are less affected by humans This is a necessary condition for studying the structure of natural forests in Viet Nam as well as in the world However, due to insufficient time and resources, the author focuses on the study “Tree species composition and diversity in relation to altitude of closed-canopy subtropical evergreen moist forest in Bidoup - Nui Ba National Park, Viet Nam” It will be a document for the further study of the natural forest structure at Bidoup - Nui Ba National Park

CHAPTER 2 LITERATURE REVIEW

The formation of forest types is closely related to the formation of associations of plants in natural with geographical regions and climatic conditions In each associations of plants group, climate, soil and moisture determine the composition and potential of forest development Forest types of allocation are essentially unaffected by human impacts The fragmentation of plant communities is mainly based on the dominance ecological

Universally, the tropical rainforest has the highest biodiversity, distributing mainly in the equatorial regions, such as the Amazon basin (South America), Congo River (Africa), India, Malaysia, in which the Indian-Malaysian forest belt has a high biodiversity There are 2,500-10,000 species of plants in a narrow area and up to 7 layers of trees with precious plants By large variation in rain, wind and heat regimes, tropical forests are often complicated in both species composition and structure of the forest.[2]

2.1 Some related concepts

2.1.1 Vegetation

The principal components of vegetation are individuals of plant species, but the study of vegetation is a group of plants formed by a large or small number of individuals There are two different directions in the world The first one consists of a few researchers: Negri (Italy); Gleason, Curtis (USA); Whitaker, Brown (England); Fournier, Lenoble (France) and Ramenxki (Soviet Union, before 1953) suggested that individual species of plants are the only entity in nature and deny the existence of populations From this point of view - also called individual view, vegetation is a continuous variation, which means that it consists of random sets of individuals of always changing tree species and without clear boundaries

Second trend includes most prestigious scientists from many countries in the world such as: Braun - Blanquet, Pavillard (France); Du Rietz, Rubel (Scandinavian); Weavar, Clements (England); Walter (Germany); Shoo, Tuxen

(Hungarians); Pavlovxki (Poland); Sukasov, Lavrenko ( Soviet Union), agreed that the basic object of vegetation is plant population From this point of view - also called populations view, the vegetation consists of specific units that have the shape, structure, composition, boundary, dynamics, and distribution areas

2.1.2 Forest structure

Forest structure is an arrangement of the species composition of vegetation in spatial and time The structure of the forest expresses the ecological relationship between the trees and the surrounding environmental factors, including: ecological structure forming trees species, life forms, layers; morphological structure of forest canopy; vertical structure; structure in horizontal plane (density and distribution of trees in the population); structure over time (by age).[3]

2.2 Some related researches

2.2.1 In the world

2.2.1.1 Principles of vegetation classification

The vegetation on the earth is very rich and varied; they are formed, existed and developed in different conditions and interactions such as geography

- topography, rock - soil, climate - hydrology, elements of flora, fauna, and microorganisms Until now, scientists have not found common standards to classify vegetation Based on different viewpoints and research methods, the principles of classification and development of different classification systems were introduced There are scientists who identified tree species composition as the main factor to classify the vegetation Other scientists based on the characteristics of the exterior and structure of the vegetation, or based on the characteristics of soil and soil classification criteria to classify

There are currently four main types commonly used by scientists in the study of vegetation:

a, Principle of vegetation classification based on tree species composition

This principle was laid down by Hult R (1881) and completed by Schroter J and Brockmann-Jerosch (1916) Later, French botanists expanded

and added to the principles of vegetation classification, which was widely applied in the 20th century Braun - Blanquet (1928) was typical of this type The basic classification system for vegetation is an association The term was first used by Humboldt A.F in 1807 to refer to certain groups of plants in spatial Later, it was supplemented by Braun - Blanquet, which was further clarified and used as the basis for the classification of the vegetation

b, Principle of vegetation classification based on external appearance characteristics

Representatives of this principle were Humboldt A.F (1804 - 1859), Grisebach A.H.R (1838), Warming E (1896), Schimper A.F.W (1898), Rubell

E (1926), Clements F (1928), Schmithusen J (1939), Walter H (1960) and others (cited by Tran Dinh Ly, 1998) The external features are expressed in the form of life Because the form of life is not just about appearance, it is the result

of long-term interaction between the plant and the environment First of all, the effects of climate change and soil Thus, in a unit of vegetation classification there may be many plant species that are very different, but due to the similarity

of habitat conditions that lead to the convergence of external characteristics The morphology of the vegetation also reflects their ecological characters

The basic classification of this principle is the formation which corresponds to the vegetation The concept of population is defined by Grisebach A H.R in 1838 (Thai Van Trung, 1970)

c, Principle of vegetation classification based on spatial distribution

The basis of this classification principle is the causal relationship between the vegetation and its spatial distribution Therefore, the study of the rules and their distribution causes must begin with studying each classification unit of the vegetation Researchers believed that three main reasons for the spatial distribution of vegetation were:

 The separation of the kingdom by genetic causes was related to the history

of the earth

 Spatial distribution of habitats and differences between potential spatial, habitats of vegetation due to biological factors

 Human impact - by to these impacts, that the local vegetation often has special characteristics related to the history of human culture

d, Principle of vegetation classification based on factors arising tree populations

In principle, the factors such as geography - topography, climate - hydrography, rocks - soil, biological factors, flora were selected as main factors The vegetation type is the basic unit of this classification The vegetation type is considered to be equivalent to the populations in the principle of external characteristics (Thai Van Trung, 1970)

2.2.1.2 Study on forest structure and species composition

Forest structure has been studied by various foresters around the world using different methods to meet a specific objective However, there are two main directions to describe the forest structure: qualitative and quantitative

a, Study on forest structure by qualitative methods

According to P.W Richards (1952)[9] Thai Van Trung, M Forster, and Rollet B (1972), the study of the structure of tropical forest stands stopped in the draw the vertical image With this method, the authors tried to draw a unique image of the standing structure This method has been widely used so far, even though it had a problem that its rules could not be clarified

Richards P.W (1968) argues that "A plant association consists of different species of trees, different forms of life but creates a certain ecological condition and has an external structure, and is arranged in a natural way and reasonable in space" The arrangement is considered both vertically and horizontally By this arrangement, an association will be distinguished from other plant association, and described by diagrams This method can quickly identify a forest type through cross-section diagrams Based on this, the silviculturalists can determine the technical measures to make the forest more

According to Baur G.N (1961) , rainforest is a closed canopy, consisting

of trees that are essentially moist, evergreen, broad-leaved, with two or more layers of trees and shrubs or more of different life forms - creepers and secondary plants (cited by Nguyen Van Them, 2009) This refers to tropical rainforests that have certain characteristics of humid, multi-layered, and other life forms that are complex in a forest type.[4]

According to Assmann (1968), "a forest of trees is the overall forest trees

to grow and develop in a given area being made up of certain circumstances, and

it has an external structure as well as inside, different with the other forest areas (cited by Tran Manh Cuong, 2004) With this view, a forest type must have a certain number of forest trees to create a canopy layer that distinguishes it from another forest

b, Study forest structure by quantitative methods

With the development of science and technology, researchers could apply mathematical statistics and modeling to study forest structure, establishing relationships among forest survey elements Many recent researches were implemented on the structure of spatial and time of the forest by quantitative methods that we can list some as below:

According to Meryer (1940), the standard forest has been constructed with the regression equation to calculate the steady number of trees and diameter classes; Richards P.W (1952) in "Tropical Rain Forests" also mentioned the distribution of trees by diameter, which he attributed to a typical distribution of mixed forest In the book "Tropical Forest Ecosystems" published by FAO (1978), the author also considered the distribution of trees by diameter classes Rollet (1980) devoted an important chapter to establishing the regression equation the number of trees-diameter (cited by Nguyen Van Truong, 1983).[8]

Above authors have developed regression equations for different forest types (number of trees by diameter) From the investigators, it is possible to deduce the other variables through the regression relation This is an important basis for the application of forest management to find some useful conclusions

for silvicultural activities aimed at the development and improvement of forest resources in terms of quantity and quality

According to Prodan (1952), the study of the forest distribution law mainly based on the D1.3 diameter (Dbh) associated with the development stage and the business measures According to the author, the distribution of trees by diameter is most valuable to the forest, especially mixed forest, which reflects the silvicultural characteristics of the forest (cited by Tran Manh Cuong, 2007).[6]

Unidentified natural forest distribution has been proven in many parts of the world It is the distribution of trees according to the diameter of the natural forest with a left skew The number of trees are more concentrated at the small diameter classes due to the fact that there are many different species and many generations coexist in the forest type Regarding a species, due to its ecological characteristics, adjacent trees (small trees) are always larger than the larger classes due to the competition rules of nutrient space and natural elimination; the favorable places in the forest, trees will rise to survive and develop

The distribution of trees by height in natural forests often shows many peaks due to multiple generations coexist, and genetic characteristics of some forest species that grow to a certain size, the not growing more At the same time, the distribution of many peaks is also the result of inappropriate selection harvest

2.2.1.3 Research on natural regeneration

Forest regeneration is a unique and continuous biological process of the forest ecosystem The emergence of seedlings of trees growing under forest canopy, gaps in the forest after selective cutting, after slash and burn to farm The important role of this regeneration class is to replace the aged tree, which is the restoration of the basic forest composition

Forest trees are often regenerated when they have favorable conditions of environmental factors; seeds are able to germinate when the light conditions, the

ground, etc are favorable Understanding the forest regeneration is a basic to propose proper silvicultural measures for sustainable forest management

2.2.2 In Viet Nam

Viet Nam was ranked as the 16th country in terms ofthe highest biodiversity in the world It has the stretching mainland and locates in the convergence place of three main flows of plant migration from China, India – Himalaya and Malaysia – Indonesia, The chapter “Natural forest ecosystems of Viet Nam” of the Forestry Handbook (MARD, 2006) shows the detailed descriptions about every type of natural forest in Viet Nam Forest structure has always been an interesting topic for forestry researchers.[3]

2.2.2.1 Studies on vegetation classification

a, Forest classification system according to current status

Since 1960 the Forest Inventory and Planning Institute (FIPI) has applied the classification of forests based on the current status of Loschau to propose appropriate silvicultural measures Under this system, Viet Namese vegetation is divided into four major categories:

 Type I: Bare land with bare hills or without forests

 Type II: Young forest

 Type III: Natural forest has been affected at different levels and are in the phase of differentiation

 Type IV: Primary forest has not been impacted or forest with slight impact This classification system has been widely used in forestry production from the mid-twentieth century to the present The forestry sector has been supplemented and improved gradually to meet the development needs of the sector However, this classification system is intended only for the classification of forests according to timber volume for trading purposes, timber extraction, without regard to ecological basis, development, or structure of trees species composition.[3]

b, Classification of forest vegetation according to ecological factors

Tran Ngu Phuong (1970) proposed the Northern Viet Nam Forest Classification, which combined land, climate, altitude, and forest characteristics

to classify forests in northern Viet Nam into three categories: (1) Tropical rainforest; (2) sub-tropical rainforest; (3) high mountain sub-tropical rainforest This simple forest classification has initially been applied in the process of forest restoration in Viet Nam The most obvious disadvantage of this classification is not highlighting the causal relationship between the vegetation and the conditions of the environment

Thai Van Trung based on the ecological view of plant communities to classify Viet Nam's forest vegetation into 14 vegetation types (1970) In each type of vegetation, the author divides into sub-types which depends on the trees species, soil conditions, and the effect of human So, the forest ecology of Viet Nam is very diverse and rich.[3]

Ecosystems, plant populations, and external factors are constantly interacting with one another to survive and develop according to their own rules:

* Geography - topography: At altitude, the topography of Viet Nam can

be divided into two major areas: (1) low and medium land areas; (2) The upland area consists of mountains with altitudes of over 1000 m in the South and over

700 m in the North Such topographic features have a great influence on climatic conditions of forest vegetation

Thai Van Trung divided into two groups of vegetation: plant population according to latitude and altitude and to distinguish areas over 1000 m in the South and over 700 m in the North The lowlands are less than 1000 m in the South and less than 700 m in the North

* Climate - Hydrology: Viet Nam has a typical tropical climate, with the exception of some areas in the South are equatorial and some areas in the North are subtropical with unusually cold winters The average temperature of Viet Nam is relatively high (20 - 250C), relatively high humidity and abundant rainfall (average annual rainfall is 1500-2000 mm) In one year, there are two distinct seasons: rainy season and dry season In the high mountains where there

are different vegetation belts According to Thai Van Trung, Viet Nam's high mountains are divided into three main belts:[3]

- From 1000 m to 1800 m in the South and from 700 m to 1600 m in the North, the lowland subtropical belt has an annual average temperature of 15 - 200C The dominant species belong Fagaceae, Lauraceae, Theaceae, Magnoliaceae, Juglandaceae, Rosaceae In addition, there are also Pinus kesiya, Pinus lasteri or Ketelaerta daudiana (in the south)

- From 1800 - 2600m in the South and 1600 - 2400m in the North is the lowland temperate humid belt, with an average annual temperature of 10-150C Includes many temperate species mixed with conifers This is the belt of Pinus dalatensis and Pinus kremfii which is endemic to Viet Nam

- From 2600 m and above in the South and 2400 m or more in the North)

is the medium mountain temperate belt This area is less studied Plants include shrubs, Ericaceae family and conifers such as Abies pindrow, Tsuga yunnanensis

* Bedrock - soil: This group of factors has a decisive effect on the formation of soil vegetation types and climatic conditions The soil types of Viet Nam are very diverse In varied climatic and terrain conditions, various types of soil have been formed In low and medium areas, Ferralsols predominates in the formation of red soils (Ferralsols soil) In the high mountains, the Ferralsols process is weak, which creates the yellow soil similar to China's subtropical

Especially in the high mountains (usually above 2800m) it can form high humus soils All soil conditions are the basis for the classification of soil - climates or sub-soil types forest vegetation in Viet Nam

* Flora factors: flora factors group have decisive tree species composition and forest vegetation types Particularly indigenous species are critical to the formation of plant sub-types There are three main migration flows are recorded

as follows:

- Migration flows from the south (from Malaysia to Indonesia) accounts for about 15% of all plant species

- Migration flows from northwest included temperate species originated from the bottom of the Himalayas, southern China The plants in this group account for about 10%

- Migration flows from the West and South West to or from the dry regions of India - Burma The plants of this migration account for about 14%

Thus, the indigenous component (50%), migrants included all three flows (39%), the rest has origin from temperate zones, tropical zones, and other regions

* Biological and human factors: regarding this group is the role of plant organisms such as animals, micro-organisms, and humans Animals and micro-organisms have a strong impact on the growth and development of forest trees Many insects play an important role in pollinating Animals involved in spreading seeds extend the area of the plant Microorganisms play a major role

non-in the decomposition of organic substances that provide nutrients to plants

c) The classification system of Viet Nam's forest vegetation according to UNESCO classification (1973)

Nguyen Nghia Thin (1997) based on the vegetation classification of UNESCO (1973) to divide the vegetation of Viet Nam into 4 classes: forests, woodlands, scrub and grassland.[3]

d) Classification of Viet Nam's natural forest ecosystems according to the Forestry Handbook (2006)

Based on five groups of ecological factors, Viet Nam forest vegetation has been divided into 8 main ecological systems: 1) closed-canopy tropical evergreen moist forest; (2) closed-canopy semi-deciduous tropical moist forest; (3) evergreen broadleaved limestone mountains forest; (4) Natural coniferous forest; (5) Dipterocarp forest; (6) Mangrove forests; (7) Melaleuca forest; (8) Bamboo forest

The classification system of forest plantations according to the Forestry Handbook has a scientific basis, which is deeply studied and the approach is not too complicated

2.2.2.2 Study on forest structure and species composition

Thai Van Trung (1963, 1970, 1978) studied closed-canopy tropical evergreen moist forest and presented structural model layers such as Emergent layer (A1), Canopy layer (A2), understory (A3), forest floor (B) and the grass layer (C) Thai Van Trung has applied and improved David-Richard’s vertical mapping method to study the structure of Viet Nam forest, in which shrub layer and forest floor are magnified with smaller scale and notation the species composition of the population with the ecological characteristics, climate chart, geographic location, and terrain.[3]

Nguyen Van Truong (1983) studied the structure of mixed forest with a quantitative way and stratified by mechanical height From the results of previous authors, Vu Dinh Phuong (1987) observed that the determination of the level of evergreen broad-leaved forest is perfectly reasonable, but only in the case of distinctly stratified forest layer This means that when the forest has grown steadily, it uses the quantitative method to determine the limits of the tree layers

Forest structure is the arrangement of species composition of forest vegetation by spatial and time, including both ecological and morphological (Phung Ngoc Lan, 1986) Studying the forest structure is important for the application of silvicultural solutions and long-term forest business planning

Tran Van Con (2001) used the Weibull model to simulate the number of trees by diameter of the Dipterocarp forest and suggested that when the forest was young, the decreased distribution, and inn contrast, when the forest older, the peak of distribution moves from left to right

Regarding the quantitative study of forest structure, the modeling of D1.3 diameter structure has been studied by many authors, and presented in different types of probability distribution Following Dong Si Hien (1974), the Meyer function and the Poisson curve were used to determine the experimental distribution of trees by diameter (N/D) for natural forest.[6]

Nguyen Hai Tuat (1982, 1986) used the distribution decreased function, distance distribution to perform structured secondary forests and applied Poisson curve on forest populations structure

2.2.2.3 Research on regeneration capacity

Forests in Viet Nam are affected differently in terms of intensity such as illegal logging, harvesting, shifting cultivation, etc According to studies of forest vegetation of Thai Van Trung (1978) in Viet Nam: "lighting is ecological factors dominate and control the process of natural regeneration of forest vegetation" If other environmental conditions such as forest soil, temperature, humidity under the forest canopy change, the composition of regenerated trees

do not change much and do not happen a cyclic way in space and time The way

of regeneration is the rule of causality between plants and the environment

The study of gaps in IIIa1 forest - Ba Vi National Park (2009), the characteristics of the regeneration layer in the gaps fluctuate according to the gap size: large gap size, the number of regenerated tree species increases The temperature is related to the number of regenerated species in the gap When the height of the regenerated tree increased, the moisture increased The increased cover and height of forest floor increased the height of regenerated trees decreased

Nguyen Huu Hien (1970) has proposed a method for assessing tropical forest tree species composition, which suggests that the number of tree species is abundant, with an area of one hectare of up to hundreds of species Therefore, it

is only the species with the highest number of individuals in the important layers (in terms of dominant species or dominant species groups).The author has formulated the formula: XTB ≥N/a with X being the individuals' average value

of a species; N is the number of trees surveyed and a is the number of species surveyed A species called the major component of a species must have an individual number that is equal to or greater than X This is a convenient way of analyzing the distribution of species or the distribution of association tree species

2.2.3 Research on vegetation at Bidoup - Nui Ba National Park

Considered as a standard sample of the subtropical rainforest ecosystem, Characteristics of ecological factors such as climate and terrain have contributed significantly to the richness, diversity of the flora of Bidoup - Nui Ba National Park

Research result of Luu Hong Truong and Diep Binh Phong in 2012 shows that Bidoup - Nui Ba National Park is divided into four types of natural ecosystems as follows: Closed-canopy subtropical evergreen moist forest; Closed-canopy subtropical broadleaves mixed conifer moist forest; Conifer subtropical woodland forest; and bamboo mixed forest and bamboo forest.[7]

(1) Closed-canopy subtropical evergreen moist forest:

This is a typical forest type of the Southern Annamites; covering an area

of 22,634 ha, accounting for 34.7% of the total area of the national park Forests distributed from altitude 1000m or more This type has 2 typical sub-types:

- Moss forest sub-type:

At an altitude of 1,900 m, Bidoup , and Chu Yen Du Peaks, represents a special regime of precipitation on high slopes, where rainfall is as high as 3,000

mm per year and often cloudy It creates a favorable environment for moss and lichens, along with species such as Orchidaceae, Rubiaceae, Araliaceae, etc

- Pygmy forest sub-type:

The pygmy forest occupies a narrow area on the top of Gia Rich, Hon Giao and Nui Ba mountain peaks, with an altitude of 2,100 m or more, steep slopes, eroded soil, rocky outcroppings, and strong winds The tree species involved in the main canopy are of the low height, with an average height of 10-

15 m, with many branches, moss covered the trunk and many beautiful orchids The common species belong to Fagaceae, Theaceae, Lauraceae, etc Here often meet Rhododendron exelsum, which has very beautiful flowers.[7]

(2) Closed-canopy subtropical broadleaves mixed conifer moist forest:

This type of forest covers an area of 14,340.78 ha, accounting for 22.16%

of the total area of the NP, occurring at altitudes above 1,000 m, species

composition of Fagaceae, Lauraceae still play the main role, Magnolia and Theaceae play a secondary role Especially in this forest type with species gymnosperms accounted for a significant proportion, grow mixed with broadleaf trees, forming discontinuous forest on the slopes and the eastern mountain Rich, Bidoup Chu Yen Du and Cong Troi, in which species: Pinus krempfii and Pinus dalatensis are extremely endemic and only found in the NP and in the vicinity

The species composition of this forest type with the coniferous species mainly of Pinus krempfii and Pinus dalatensis becoming the most unique forest type in Viet Nam only occurs in Bidoup - Nui Ba National Park and the NPs These are Chu Yang Sin (Dak Lak) and Phuoc Binh (Ninh Thuan)

(3) Conifer subtropical woodland forest:

Pine forests in Bidoup - Nui Ba are mainly Pinus kesiya, which dominate the forest, forming the most unique and largest forest in the country with an area

of 19,645.16 ha, accounting for 30.36% of the total area of the NP Characteristics of this forest type are mainly mixed with some species of Theaceae and Fagaceae grows under the canopy is the average height of less than 4 m and a diameter 15 cm below average and have good fire resistance as some species as Heliconia niligirica, Lyonia ovalifolia, Quercus lanata

(4) Bamboo mixed forest and bamboo forest:

This type of forest consists of bamboo mixed forest and bamboo forest occupying a very small area of about 1,808.39 ha, accounting for 2.8%

CHAPTER 3 RESEARCH OBJECTIVES AND METHODOLOGY

3.1 Goal

Determine tree species composition and diversity of closed-canopy subtropical evergreen moist forest Bidoup - Nui Ba National Park at the different altitudes

3.2 Specific objectives

- To study structural characteristics of woody plant communities at different altitudes

- To assess of plant diversity of forest types at different altitudes

- To determine some natural regeneration characteristics of woody plant communities at different altitudes

3.3 Methodology

3.3.1 Study site

Figure 3 1 Map of study site

Bidoup - Nui Ba National Park (12°00 to 12°19’N, 108°21’ to 108°44’E) which lies within the administrative boundaries of Lam Dong province, southern

Central Viet Nam (Central Highlands) covers almost the entire Lam Vien Plateau The national park has a diverse topography ranging from 700- 2200 m with an average altitude of 1500-1700 m and many mountain ranges above 2000

m The three highest peaks are Bidoup (2287 m), Lang Biang (2167 m) and Hon Giao (2060 m) (FREC-FIPI, 2008) Bidoup - Nui Ba National Park has a high altitude tropical climate with an average temperature of 180C and humidity range of 75-85% The average annual precipitation is 1755 mm, varying with an altitude between 1650 and 3750 mm per year (Tixier, 1966), and September is the month with the highest precipitation There are three main types of forest in this national park, including needle-leaf forest, evergreen broadleaf forest and mixed needle-leaf and broadleaf forest (FREC-FIPI, 2008)

3.3.2 Data collection methods

3.3.2.1 Field survey

Setting up plots for survey:

- Setting up 9 surey plots with the area of 400 m2 (20m x 20m) at attitude 1400-1900m The standard plots were set up at 3 altitudes (1400-1600m and 1600-1800m and above 1800 m) In each plot, all trees were recorded with their species name and diameters with DBH of 5cm and more, the height of trees to track the development of the forest Besides, the research inherited 07 available plots from Bidoup - Nui Ba NP

- In each plot, setting up 5 subplots (25m2, 5 x 5 m) There were totally

150 subplots to be investigated with all information about regenerated trees with DBH less than 5cm

- Using GPS and a map to locate the survey plots

Figure 3 2 Setting survey plots in the research site

3.3.2.2 Forest structure inventory

- In the survey plots (20m x 20m) Tree species with a minimum Dbh ≥ 5

cm were numbered, marked and measured with the species name, DBH, height and crown diameter

Specifically as follows:

+ Tree species: Identify in the field by the support of local experts In case

of unidentifiable trees, collect the botanical specimens (leaves, flowers, fruits and even bark) for further identification at the laboratory

+ DBH: Use a tape to measure with millimeter precision Measure at a height of 1.3m above the ground level

+ Tree height : Using the Blume-Leiss to measure the total height of each trees

- In sub-plots (25m2):

+ Investigating regenerated trees: all of the woody tree species were numbered and marked Recorded information about species name, diameter, and height The quality of each tree was recorded; and determined the origin of small trees; finally investigated the distance between regenerated trees

Figure 3 3 Measure the diameter and identify species

3.3.2.3 Secondary data

The study inherited documents from Bidoup - Nui Ba National park

office, which include:

- 7 survey plots for biodiversity monitoring (20x20m) in altitude 1800m

1400 Biodiversity monitoring report in Cong Troi

- Biodiversity monitoring report in Hon Giao

- Biodiversity and ecological characteristics in Bidoup - Nui Ba National Park

3.3.3 Data analyses

Data were processed on software Stata, SPSS and microsoft Excel:

Percentage tree composition

Based on the formula of Daniel Marmillod, Vu Dinh Hue (1984), and Dao Cong Khanh (1996) to identify the Important Value (IV%)

Which:

IV% : Important Value of species i

N% : percentage of species i in the population

G% : percentage of the basal area of species i in the population

The species with IV%  5% is really ecologically significant in the forest stands According to Thai Van Trung (1978), in a stand of some tree species> 50% of the total number of tall trees, the species is considered the dominant group It is necessary to calculate IV% of species with this value higher than 5% and stops when the total IV% reaches 50%

- Density:

⁄

Which:

n: the population of trees in the sample plot

S0: The area of the typical standard plot (m2)

Plant diversity

Simpson's Index (D) measures the probability that two individuals randomly selected from a sample will belong to the same species (or some category other than species) There are two versions of the formula for calculating D Either is acceptable, but be consistent

∑ ( ) Or:

∑

n = the total number of organisms of a particular species

N = the total number of organisms of all species

The value of D ranges between 0 and 1 With this index, 0 represents infinite diversity and 1, no diversity That is, the bigger the value of D, the lower the diversity

- Shannon- Winner index and the Shannon’s measure of evenness

Species evenness refers to the proportion that each species comprises of the whole The Shannon-Weiner Species Diversity Index is calculated by taking the number of each species, the proportion each species is of the total number of

individuals, and sums the proportion times the natural log of the proportion for each species Since this is a negative number, we then take the negative of the negative of this sum The higher the number, the higher is the species diversity

In the ideal situation, one should compare populations that are the same size in numbers of individuals

The formula is as follows:

Meyer distribution equation:

Is the probability distribution of continuous random variables The density function has the form:

Y= αe-βX

(3.6)

In which: Y is the observed frequency; X is the observed quantity; α, β are two parameters The β parameter represents the level of graph Concavity, and the larger the β, graph Concavity is greater and in contrast

Weibull distribution equation:

Is the probability distribution of continuous random variables on the domain values (0 → + ∞)

Density equation form: P(x) = αλXα-1exp(-λxα) (3.7) Distribution equation form: F(x) = 1-exp(-λxα) với x ≥ 0 (3.8)

Where α, λ are two parameters of the Weibull distribution α characterizes the deviation of the distribution λ denotes the sharpness of the distribution

In which: γ and α are two parameters

Distance distribution is a j-shaped form, one vertex corresponds to the value x = 1 (when γ + α <1) Distance distribution after reaching the top peak will decrease as x increases The parameters of the distance distribution are estimated as follows:

If Di is the median value of the i-th dimension, Dmin is the smallest diameter, k

is the distance group diameter, Xi is defined as:

Study on the correlation between diameter (D) and height (H): From Hvn and D1,3 of forest stands, established D-H relationship function by some equations which were available in SPSS software Select the most appropriate equation according to the correlation coefficient R and evaluate the relationship between height and diameter growth of forest stands

Regeneration characteristics

The density of regenerated trees is calculated according to the following formula:

M = n (trees/ha) (3.13)

In which:

M: density of regenerated trees (trees / ha)

n: total number of regenerated trees in the sub-plots

S: total area of regenerated tree plots (sub-plots)

The quality of regenerated trees is divided into 3 levels: good (grade A), medium (grade B) and bad (level C)

Quality of regenerated trees

In which:

N%: percentage of good, medium and bad trees

n: total of good, average, bad trees

N: total number of regenerated trees

CHAPTER 4 NATURAL CONDITIONS OF STUDY AREA

4.1 Natural conditions

4.1.1 Geographical location

The territory of the Bidoup - Nui Ba National Park includes Da Chais, Da Sar, Da Nhim, Dung K’No, Lat, Lac Duong town and a part of Da Tong commune of Dam Rong district

Bidoup - Nui Ba National Park has geographic coordinates:

- From 12000'04 "to 12052'00" North latitude

- From 108017'00 "to 108042'00" East longitude

It is bordered by the Serepok River and Da Nhim Watershed Forest in Lam Dong Province, the north is adjacent to Chu Yang Sing National Park, Dak Lak province; Phuoc Binh National Park, Ninh Thuan and Khanh Hoa provinces This is a transition zone between three eco-regions: the South East Coast, the South East and the Central Highlands and also between the lowland coastal highlands This is why the National Park has the typical biodiversity values of both mixed broadleaf and coniferous forests Furthermore, it is a natural biodiversity corridor for both animals and plants that creates continuity

in lowland areas as well as in high and mountainous areas

This area is considered to be the "middle" of a large and highly valuable primary forest area, extending from Chu Yang Sing National Park in northern Dak Lak province through Bidoup - Nui Ba NP to the Hon Ba nature reserve, Khanh Hoa province, and Phuoc Binh NP, Ninh Thuan province With an area

of several hundred thousand hectares, it is an ideal condition for the coordination

of forest protection and biodiversity protection in Central Viet Nam - Central Highlands of Viet Nam

Moreover, with the geoscientific stratification, this large area contains the tremendous value of biodiversity, which is considered standard samples for research in Southeast Asia

The total area of the core zone of the national park is 70,038.75 hectares,

of which special-use forests occupy 56,436 hectares and protection forests are 13,602.75 hectares

Bidoup - Nui Ba National Park is divided into 03 subdivisions:

- Strictly protected zone: 33,583 hectares

- Ecological rehabilitation zone: 22,854 hectares

- Administrative and service center: 13,601.75 hectares

The buffer zone is 33,966 hectares

4.1.2 Topography, geomorphology

Bidoup - Nui Ba National Park surrounded by arc-shaped mountains around the lower northwest and south The north is bounded by mountains that originate from the Hon Giao peak, which runs through the watershed of the Serepok River to the west To the south is the 1,800 - 1,900m high mountain range that starts from Gia Rich in the east, runs east-west and ends at Langbiang Mountain To the east are the Hon Giao, Gia Rich and Bidoup mountains The west is Chu Yen Du mountain which connected to Langbiang, gradually lower and limited by the Serepok River Overall, the topography of Bidoup - Nui Ba National Park can be divided into the following areas:

- Central area: average altitude from 1,400 m to 1,700 m, the difference is relatively high in the region ranges from 50 m to 100 m, with a slope of 80 to

150

- East and south are high mountains 1,900 m - 2,200 m with Hon Giao (2,060 m), Gia Rich (1,922 m), Bidoup (2,287 m), Lang Biang (2,167 m)

- To the west, there are Chu Yen Du (2,051 m) and Cong Troi (1,882 m)

in the north of Da Lat city

Due to the difficult terrain, Bidoup - Nui Ba NP has the shape of "n", so the boundary becomes more and more complicated and prolonged

The topography of Bidoup - Nui Ba National Park is the dominance of medium and high mountains The height of the mountains ranges from 1,000 m

to 2,287 m ( Bidoup in the southeast) In addition, there are some important

mountains in the national park that are significant in terms of local biological geography (Gia Rich 1,923 m and Hon Giao 2,062m)

4.1.3 Geology and Soil characteristics

Research results from the Viet Nam-Russia Tropical Center show that the geology of Bidoup - Nui Ba National Park was formed at the end of the Jurassic period, the beginning of Kreta, about 130-150 million years ago From the Paleocene period, the area has been at a stable stage, although the tectonic activity Northern and Central Annamites is relatively strong This was the opportunity for exchanges and convergence of plant and animal from the north, west, and south to the Himalayas, India, Burma, Indonesia and Malaysia which formed the edemic and unique factors of the classification unit Thus, this is a very significant place to study, preserve the integrity and uniqueness of genetic diversity and the diversity of wildlife

Geological foundation is relatively homogeneous (in terms of area ratio) with a predominantly granite rock formation In addition, the area also has metamorphic rocks, slate, and limestone The soil of the area is mainly gray soil developed on the mother stone Granite and Dacid In general, the area is quite fertile; the mechanical composition varies from slit to clay

With an area no larger and less differentiation of complex geological conditions in the area so there are not many soils

- Humic Acrisols: Widely distributed throughout the NP up to the altitude

of about 2,000 m The soil is characterized by a relatively strong ferralsol process combined with surface humus accumulation (creating humus layers 10-

20 cm thick) This soil is high soil moisture and spongy The erosion process is slow and depends on the topography and vegetation cover

- Ferralic Acrisols: Distribution is concentrated in the upstream Krong

Kno River The soil has a thick layer and varies depending on the slope and the separation of the terrain In general, the soil layer is about 50 cm thick with high humus in the surface layer and most of the area is still maintained primary forest vegetation

- Alisols: Distribution mainly on some mountain peaks higher than 2,000 m

- Dystric Gleysols: This type of soil scattered in the whole territory of the

NP, especially in the wide valley This is a group of soils formed and developed

on the washout and accretion of soil on the foot and slopes (mainly Humic Acrisols ) Therefore the soil morphology is very different

- Fluvisols : This type of soil is scattered into narrow areas along Da

Nhim River and Krong Kno River

4.1.4 Climate

a, Climate characteristics

Although located in the tropical monsoon climate of the South East and Central Highlands, but due to the geographic location and topography, Bidoup - Nui Ba National Park has a sub-tropical climate

- The total solar radiation is 114.8 Kcal / cm2 / year, the largest in March, decreasing in rainy season, the lowest in October

- The air of the East Sea is dominated from November to April, The climate is low temperature at night, low humidity, no rain Since April, the Northeast monsoon has been declining and took over by the southwest monsoon From May to October, climate is high humidity, cloudy, more rain

- The average annual air temperature is 180C January is the coldest month

of the year, with average temperature is 15.60C May is the hottest month of the year, with average temperature is 19.60C Daily temperature amplitude in the dry season: 11.20C - 13.20C Daily temperature amplitude in rainy season: 60C -

70C The average ground temperature is: 20.60C

b, Rainfall regime

Bidoup - Nui Ba National Park has annual rainfall varies from 2,800 mm - 3,000 mm / year January rainfall is the lowest 6 mm The dry season average only 5.7 mm Rainy day rainfall range from 50 mm - 80 mm September rainfall

is the highest (300 mm) Rainfall in rainy season accounts for 80% of the whole year

c, Humidity