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 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:

Hanoi, 2018


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

i


ACKNOWLEDGEMENTS
I started to study Tropical Forestry program in Vietnam National
University of Forestry (VNUF) in 2016. It was a difficult time for me. Because
my knowledge was limited. It was very hard for me to complete my study without
the support of many people. From inner of myself, I want to thank you all.
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

ii


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.
iii


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
iv

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

v

LIST OF ABBREVIATIONS
NP

National Park

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

vi


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
vii


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

viii


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 16001800m .................................................................................................................. 43
Figure 5.8 c. Distance distribution for N/D relationship at altitude of 16001800m .................................................................................................................. 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
ix


Figure 5.13b. Weibull distribution for N/H relationship at altitude of 14001600m .................................................................................................................. 49
Figure 5.13c. Distance distribution for N/H relationship at altitude of 14001600m .................................................................................................................. 49

Figure 5.14a. Meyer distribution for N/H relationship at altitude of 1600m1800m .................................................................................................................. 50
Figure 5.14b. Weibull distribution for N/H relationship at altitude of 1600m1800m .................................................................................................................. 51
Figure 5.14c. Distance distribution for N/H relationship at altitude of 1600m1800m .................................................................................................................. 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

x


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-todate 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

1


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.

2

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

3


(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
4


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.
5


 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
stable.
6


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
7


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
8


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
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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
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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.
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- 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 nonplant 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
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.
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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]
13