Biodiversity and ecological association of tree species in special use forests huong son, my duc, ha noi

ABSTRACT The biodiversity and ecological association of tree species has an important meaning ,tree layer is decisive component of forest ecosystem but it hasn’t earn much attention in o

ACKNOWLEDGEMENTS

This study was conducted for 5 months with lot of support, guidance and encouragement from teachers, friends and beloved family members as well as relevant institutions Taking this opportunity, I would like to express my thanks to all

First of all, I would like to express my great respect and profound gratitude to my supervisor, Prof.Dr Pham Van Dien and co-supervisor, Dr Le Quoc Huy for their lucid and genial guidance, encouragement and hospitality Only with their enthusiastic guidance and encouragement, I was able to accomplish my study successfully as designed

I also would like to express sincere thanks to the Management Board, Forest ranger of Huong Son Special Use Forest, local people and especially Vietnam National University of Forest (VNUF) and Research Institute for Forest Ecology and Environment (RIFEE) - Vietnamese Academy of Forest Sciences (VAFS) for kind help and support with regard to study sites, datasets and administrative arrangement for my thesis study

Finally, I appreciate my family and classmates who were always by my side, motivate and encourage me

Due to time constrains , knowledge and capacity limitation, this study might still have some mistakes, I am really sorry for this inconvenience if any I look forward to the future endeavor with your continuos support and collaboration for my better research work

Sincerely

Ha Noi October 2nd, 2016

Le Thi Thu Hang

ABSTRACT

The biodiversity and ecological association of tree species has an important meaning ,tree layer is decisive component of forest ecosystem but it hasn’t earn much attention in our country Therefore, study on diversity and ecological association of them in natural forests takes a very important role for more understanding about this system The study was based on

18 sampling plots (1000 m2/plot), distributed on 06 fields in the special use forests of Huong Son, Ha Noi The paper determined 05 important characteristics concerning the tree communities, including: (i) important value index (IV, %); (ii) species dominance pattern; (iii) species diversity indices; and (iv) assessment of factors affecting the study site (v) ecological association of tree species and proposed some conservation measures and sustainable development The results indicated that, all plots together there are 43 species found to be ecological significance in the communities with their IV higher than 5%, and there are four species found as dominance in three plots with their IV more than 30%, made a geometric steep slope pattern in the top niche of diversity dominance (D-D) curve IV change curve by species sequence showed that, big differentiate among studied fields The value of species diversity indices also showed that, diversity of tree species in the studied sites is at medium level From results of estimating the Site disturbance index (SDI) consider that almost of study site are more or less influenced by human, in which the biggest factors affecting the biological diversity is Agriculture encroachment There were up to 11 couples of tree species found with their similarity of 80% The results showed that 120 tree species found

in the studied sites were devided into 04 ecological groups Through this approach, we could infer the relationship among them (independent, mutual, or comparative) Based on results achieved, the present study would be considered as a typically quantitative research on diversity and ecological association of tree species In addition, the paper has its significance for further understanding about tree communities of tropical natural forests in special use forests of Huong Son, Ha Noi

TABLE OF CONTENT

ACKNOWLEDGEMENTS

ABSTRACT

TABLE OF CONTENT

LIST OF TABLE

LIST OF FIGURE

1 INTRODUCTION 1

2 REVIEW OF LITERATURE 10

3 RESEARCH GOALS AND OBJECTIVES 15

3.1 Goals 15

3.2 Specific objectives 15

4 METHODS 18

4.1 Establish the sampling plot 18

4.2 Data collection method 18

4.3 Calculation method 18

4.4 Dominance Diversity curve (D-D) method 20

4.5 Estimating the Site disturbance index (SDI) method 21

4.6 Data analysis method 23

5 RESEARCH RESULT AND DISCUSSION 24

5.1 Important Value Index (IV%) 24

5.2 Dominance Diversity Curve of trees species in Huong Son SUF 28

5.3 Diversity indices of tree species 34

5.4 Assessment of factors affecting the study site 36

5.4.1 Agriculture encroachment 36

5.4.2 Invasive species 37

5.4.3 Tourism activities 37

5.4.5 Logging and fires 38

5.5 Ecological Association of tree species 40

5.6 Proposed some conservation measures and sustainable development 44

5.6.1 Policy and sustainable management of forest resources solutions: 45

6 CONCLUSION 48

7 SHORTCOMINGS AND RECOMMENDATION 50

7.1 Shortcomings 50

7.2 Recommendation 50 REFERENCES

LIST OF TABLE

Table 4.1 Site Disturbance Index - SDI 22

Table 5.1 Importan value index 25

Table 5.2 Diversity Indices of tree species 34

Table 5.3 Site disturbances index definition 39

LIST OF FIGURE

Figure 3.1 Map of Huong Son Special Use Forest with sites under the study (source: Huy et

al 2008, Cong 2013 17

Figure 5.1 Dominance Diversity Curve of tree species in Gieng Chen 28

Figure 5.2 Dominance Diversity Curve of tree species in Thung Sau 29

Figure 5.3 Dominance Diversity Curve of tree species in Ben Da Rung Vai 29

Figure 5.4 Dominance Diversity Curve of tree species in Hinh Bong 30

Figure 5.5 Dominance Diversity Curve of tree species in Thung Mang 30

Figure 5.6 Dominance Diversity Curve of tree species in Tuyet Son 31

Figure 5.7 Dominance Diversity Curve of all sites together under sutdy in Huong Son SUF 32 Graph 5.1 Ecological Association of tree species in stand 41

Graph 5.2 PCA graph represent for ecological association of tree species 416

Graph 5.3 Branching graph represents the relationship between the secondary plot 43

Graph 5.4 NMDS secondary sampling plot 44

INTRODUCTION

Environmental degradation is one of the most serious issues over the world today, it includes deforestation, biodiversity loss, pollution , desertification, climate change, global warming and so on The consequence of environmental degradation can be devastating on the social, economic and environmental values and systems As a cause from the environmental degradation, forests and biodiversity resources are still being declined and lost at all local, regional and global scales Around the world, biological communities that took millions of years to develop are being devastated (Sharma 2003)[1] About 20 per cent of all species are expected to be lost within 30 years and 50 per cent or more by the end of 21st century (Sharma 2004)[2] The current decline in biodiversity is largely the result of human activities, ranging from habitat destruction, over-harvesting, and pollution, to inappropriate introduction

of exotic plants and animals The diversity of natural ecological communities has never been more valued than it is now, as it becomes increasingly threatened by the environmental crises Efforts are, therefore, needed to conserve biological resources and utilize them on a sustainable basis, and maintain genes, species and ecosystems (Verma 2000)[3] the signing

of the Convention on Biological Diversity by more than 190 countries at the Earth Summit in Rio de Janeiro in 1992 put this subject at the top of international environmental agenda and brought a sense of urgency to the issue of biological conservation Biodiversity is not only fundamental to the quality of human life It is essential for human survival.( Tuxill, J., &

Bright,1998)[4] and The future of biodiversity signifies the future of humankind Its pathways

to restoration or destruction are for humans to choose By being cognisant, and by being morally alive, humanity can work to save its own body and soul (O’Riordan, T et al 2002)[5]

so maintenance of biodiversity in managed forest ecosystem is an increasing concern (Jobidon

et al 2004)[6]

In 1992, the World Conservation Monitoring Centre evaluated Vietnam as one of the

important role in the socio-economic and environmental development of Vietnam Through these services, biodiversity makes significant contribution to the national economy, providing

a basis for ensuring food security; maintaining genetic resources of animals and plants; and providing materials for construction, fuel and pharmaceutical resources However, Vietnam’s biodiversity is facing many threats (Van Huu Tap , 2015)[7]

Ecological association among species is a characteristics of forest vegetation The survival, variation and the distribution of a certain species in space and time depend not only

on the physical environment (climate, soil) but also on the mutual relationships between species coexist in the environment In nature, populations or organisms do not exsist alone, but they usually do coexistence and interaction among each other for their better exsistance and association Mutual interactions among species expressed in many aspects: competition, parasitic, symbiotic, mutualism and so on Plant community is a collection of plant species coexisted on a defined region, is characterized by a combination of species composition, structure, relationships between species with each other and with the environment Features of this reciprocal relationship are established by life forms and ecological characteristics of the plants and also by the characteristics of the habitat that is the characteristic of climate, soil and human impact, animal Biological relationships are extremely complex and diverse, and not always, we would distinguish these relationships together Study about ecological association among species, groups of species, or event among plant communities provide us with valuable information on the partern, the role, the affect each other and impact on natural ecosystems of plant species

As part of the SUF system in Vietnam, the Huong Son SUF is an important natural reserve for biodiversity, landscape and curtural conservation as well as local livelihoods However, the forests and biodiversity there are currently affected negatively by both human activities and natural incidents and degradations Therefore, the conservation of biodiversity, protection of precious gene pool as well as other natural resources are concerned There were

already some itnitial research on forest enventories and assessment for values, significances and potentials of the protected area, however, a number of important issues has not been done systematically and scientifically with regard to vegetation and biodiversity partern examination, biodiversity and vegetation quantification, their valuation and so on, those would be the important basis for knowledge and understanding, for later application studies and soluation development, as well as other issues of decision makers for its sustainable management and utilization

All together, there is an urgent need to carry out studies to understand biodiversity and ecological association We should find its uses and conservation, planning and management for concept of sustainable management and development In view of the situation and requirements, the study” Biodiversity and Ecological Association of tree species in special use Forests Huong son, My Duc, Ha Noi “ was formulated to conduct This present study as a topical issue, would meet the gap of requirement and would contribute well for the development of measures and solution as mentioned above

1 REVIEW OF LITERATURE Biodiversity conservation

Vietnam is one of the most biodiversity rich countries in the world, comprising only 1% of the earth’s surface but being home to 10% of all species Nevertheless, many threats to biodiversity in Vietnam that are existing Being introduced in 1992, the Convention of Biological Diversity (CBD) is considered as a principal comittment of signed state members

to conserve and utilise the world biodiversity in a sustainable way and to equally share benefits provided by this resurce The Strategy has been released, serving as a basic orientation for the long-term development of forest resources in Vietnam In 1995, the first National Biodiversity Action Plan (NBAP) of Vietnam that was approved by Prime Minister This plan has become a legal document that directed biodiversity conservation activities in Vietnam (report to the biodiversity convention secretariat) Ingeneral, Vietnam has been acknowledged as a country with high biodiversity, and as one of the prioritized nations for global conservation so need to national biodiversity strategies and section plans for biodiversity conservation and sustainable management

Biodiversity measurement and quantification

Research biodiversity and the biodiversity of the areas of study that has long been the world's scientists particularly interested, so has a lot of studies have been published Biodiversity attracted the interest of all communities and the scientists by the need to learn and its importance to human beings Biodiversity attracted the interest of all communities and the scientists by the need to learn and its importance to human beings Regarding quantitative biodiversity research

The diversity of species in tropical rainforests is expressed by the formula Weiner (1971) as a parameter to compare the density of each species with H = 6.0 (6.2 = 97% maximum) is greater than 10 times temperate broadleaf forests (0.6) This index decreases from the tropics to two poles, and depends on different continents In the result of research

Shannon-Pandey (Shannon-Pandey et al 2002)[8] when researching biodiversity index H 'of vegetation in some study site of moist temperate forests ecosystems in western Himalayan , considered that , biodiversity index H’ of this study site is relative lower than humid tropical forests, H index

of tree species reached maximum is 2.25 , shrub is 2.31, herbaceous plants is 2.69

Risser and Rice (1971)[9] reported that, tropical rain forests were found to have a much higher plant species diversity than temperate forests In temperate forests, highest values for Shannon diversity were recorded at 2.0 to 3.0 while Braun (1950)[10] reported tree diversities between 1.7 and 3.4 in forest in eastern North America For tropical rain forests, a higher diversity (5.4) was found by Knight (1975)[11] Besides H index also depend on other factor such as climate condition, atitude, altitude, the level of environmental pollution H index of the humid tropical rain forests is very high 5.06-5.40 than 1.16-3.40 for temperate forests (Braun 1950); Monk 1967; Riser and Rice, 1971; Singhal et al., 1986)[10][12][9][13]

H index is decrease from the equator to the north pole and a south pole and from low mountain to high mountains H index of polluted water basins is only 1 or less, while in the water basin can be 2, 3 or higher

Vietnam has been acknowledged as one of the most prioritized countries for global conservation due to its richness in biodiversity Since 1994, Vietnam has officially joined the Convention of Biological Diversity (CBD), the “ecosystem approach” which endorses principles of negotiated local governance and adaptive management (Vermeulen and Koziell 2002)[14] and committed itself to conserve and utilize its biodiversity in a sustainable, thus the result of research about quantitative biodiversity also interested by researchers It is basis for conservation measures and sustainable development of biodiversity resources According

to the result of biodiversity report (H’) in Huong Son SUF, H’ ranged 3.83 -5.50 This result

is suitable for current time, the result considered that: Shannon-Wiener (H’) ranged 2.63-5.08 The major difference in Shannon H 'in the study site to reflect the differences in ecological conditions and site disturbance condition The maximum value of H’ index achieve is site

In “Growth , demorgraphy and stand structure of scaphium macropodum in differently

managef forests in Vietnam ” ( Le Quoc Huy, 2012)[15] quantified species diversity of S

macropodum plant communities at four sites: Cattien, Bachma and M’drak ,Dakuy, with

different level off disturbance Across these sites, the Shannon-Wiener index (H’) ranged

from 2.63-5.08; IVI values for S macropodum ranged from 17.5-80.0 (IVI total: 300) The

highest values of H’ were found at the medium disturbance sites, where the D-D curve strongly suggests a lognormal series and S macropodum seems to thrive best Research also found that relationship between H’ and the site disturbance index (SDI) strongly fitted a quadratic regression model (r2 = 0.76, p< 0.001) and the H’ diversity peaked at moderately disturbance (SDI of 0.45) in the study sites

Pham Thi Kim Thoa[16] 2012 research biodiversity of tree species in Son Tra – Da Nang nature conservation area for that in study site, H’ index is high, it ranged 1.62-4.76 However level of biodiversity in communities tended to decrease due to impacted by environment and human activities

Le Thanh Cong et al 2009[17] assessed biodiversity by calculate biodiversity index : IVI, H’, Cd, A/F for Huong Son SUF given the result for species diversity index H( Shannon-Weiner) of tree species is relative high , ranged 3.83-5.50 belong to scope of humid tropical natural forest , whereas H 'of the shrub is 3.02-5.20 and herbaceous plants ranged 1.98-4.12

The number of tree species, which has ecological significance in communities varied from 12 to 15 species (among total of 88 and 73 species in OTC1 and OTC2, respectively)

Among them, five species such as Khao vang (Machilus bonii), Mo (Manglietia conifer), Gioi xanh (Mangletia sp), Sai dat (Wedelia chinensis) and Rang rang (Ormosia pinnata) are in top

five species Diversity of tree species in the study site is at medium level (represented by S, d, H' and D indices)was showed in Biodiversity and Ecological Association of tree species in natural forest Ba Vi national park Ha Noi by Pham Van Dien (2016)[18]

Ecological association

In the study of tropical rain forest, many hypothesis have been proposed to explain the coexistence of species The Janzen-Connell hypothesis explained that additional plants far from mother plant would avoid the effects of harmful organisms living around the mother plant Thus, species with similar habitat but different resistant level on various harmful organisms would get the benefit to expand its range Expanded from the Janzen-Connell hypothesis, the species herd protection supposed that many different species living together will limit the impact of harmful organisms Therefore, the mutual relations can be maintained even in the case of competition

Neutral theory supposed that all individuals, regardless of species difference, are equal

in the process of reproduction, growth and death Uriarte et al (2004)[19] when studying the rainforest in Barro Colorado Island, Panama has found the evidence supporting this theory However, Chave (2004)[20] suggested that this theory is true only in a limited number of cases Obviously not all species are ecologically equivalent Niche theory hypothesized that the combination of spatial and environmental changes will be reflected in the morphology, physiology and characteristics of life stages of each species In tropical rain forests, which have high species diversity and low species density, interaction among species and with other species is also more complex than other forest types

The study of diversity and ecological relationships of tree species in natural forests has always been considered a topical issue, with major implications for the conservation and sustainable management of the few remaining natural forest ecosystems on Earth At the same time, the development of "close to nature" farming systems is seen as a “wise” solution to not only obtain high economic efficiency but also to ensure the durability of those farming systems ( Pham Xuan Hoan et al, 2011)[21]

“The results of the study about biodiversity and ecological association of tree

the similarity from 80% or greater, there are nine couples of tree species which have closely relationship with each other, but there is no any couple of secondary plot which formed These are findings, which have ecological significance and open the new way for deeply studying on forest ecosystem characteristics in general as well as on the special use forest such as in Ba Vi national park in particular

In the study - Spatial pattern and associations of tree species in tropical evergreen broad-leaved forest a Luoi, Thua Thien Hue-Pham Van Dien, Nguyen Hong Hai [22] finded suggest that dispersal limitation was the main process controlling intra-specific distribution patterns Inter-specific association could be affected by species herd protection Neutral interaction was minor part of species associations Habitat heterogeneity plays an important role for species distribution patterns, and the spatial segregation occurs at a scale around 15 m

in this forest Ecological similarity also contributed to positive associations of tree species

3 RESEARCH GOALS AND OBJECTIVES 3.1 Goals

The outputs and outcomes of the study are expected to contribute for the sustainable management and ustilization of the forest and biodiversity resources of the Huong Son

Special Use Forest

3.2 Specific objectives

(i) To examine the species biodiversity and its patterns with quantitavite indices of tree

species in the Huong Son Special Use Forest (SUF) under different site disturbance impacts,

(ii) To study for determination of the ecological association of the tree species in the Huong Son SUF under the study

(iii) To propose practical interventions and measures for the sustainable management and utilization of the forests, landscapes and biodiversity resources of the Huong Son SUF

3.3 Study site and scope

Huong Son Special-use forest locate on Huong Son commune, My Duc district, Hanoi geographical location : 23O29’ to 20O34’ North latitude and 1050

41’East longitude the northern abuts with Hung Tien and An Tien commune , the eastern is Ha Nam provice, the west is Hoa Binh provice

Huong Son commune is a junction between the delta and mountain of Hoa Binh province, the most of area belong to limestone mountains, exist of hill and low mountain terrain with the highest peak is 381m The division was created for the Huong Son Mountain has diverse topography, majestic scenery it's worth ecotourism and landscape more interesting to attract tourists

Topography of Huong Son is formed by two groups of factors including:

- Casto topographic : massif is mainly consists surface Casto and underground Casto which creat caves such as Huong Tich, Tien Son, Hinh Bong, Long Van and so on

- Casto field interleaved: the field has a thick layer Casto, the local people took advantage to agricultural cultivation and fruit growing

Soil is formed and developed on the limestone mountain The process of direct impact on the surface is the process of erosion, landslides and sedimentation processes in the slot and valleys

There are 3 kind of soil :

- Black humus soil on limestone

- Feralit soil develope on limestone

- Silt

Huong Son has been afected by tropical monsoon climate , the region has relatively high temperatures The average annual temperature is 23-30C Average annual rainfall from 1800- to 2000 mm with the number of rainy days 140-150 days / year The rainy season from April to October reached 81-91% of the annual rainfall The dry season from November to March next year Notably, the rainy season is concentrated in the June, July, August, it causes erosion and landslides, which affect soil erosion when the vegetation destroyed However in Huong Son, although there are 2 distinctive seasons, due to the dry season is not too harsh to create favorable conditions for the restoration and development of forest vegetation

About the history of formation and development, Huong Son SUF was named in a list

of special-use forests in Vietnam under the Decision No 194 / CT, dated 09.08.1986 of the President of the Council of Ministers, the Cultural and Historical Huong Tich Pagoda zone has an area of 500 ha (MARD, 1997)[23] The objective of these SUFs is: "Protecting the forest on limestone and famous landscapes of the region" (Sung 1994)[24] Huong Son SUF

is a museum of life; there are mountains, lakes, caves, trees and wildlife The main area is 4,355 hectares and the buffer zone is 1,191 hectares There are 85 families, 577 genera, 873 species of flora in Huong Son SUF, of which 25 rare plant species are listed in the Red Book There are also 288 species of fauna belonging to 84 families, 26 genera, including 40 rare animal species that have high economic value and there is a new species discovered in 2011

Composition of insect of the Huong Son SUF is also very rich with 374 species on 65 Families, 13 genera This is the great potential of the ecosystem for research, conservation and sustainable development of eco-tourism, community tourism and sightseeing

Huong Son SUF is a special forest ecosystem develope arid on limestone mountains in which has a very low of humus Huong Son forest is evergreen forest, tropical rainforest there are many valuable plants in the conservation of genetic resources in scientific research and environmental landscape Previously forest over exploited , currently with efforts of management forest are being protected and tend to recover well

Figure 3.1 Map of Huong Son Special Use Forest with sites under the study (source:

Huy et al 2008, Cong 2013

4 METHODS 4.1 Establish the sampling plot

In each study site (6 sites) are selected with different level of impact, a set of 3 sampling plots (quadrats) was established for necessary data collection The total sampling plots are 18 The size of each sampling plot was 1,000 m2 (25 m x 40 m) The plots were layed out in an uphill direction in 3 positions: a plot low on a hill, in the middle part of a hill and high on a hill

4.2 Data collection method

Basic data collection was shared from the research on “Biodiversity Inventory of Huong Son Special Use Forest” done by Research Center for Forest Ecology and Environment, Forest Science Institute of Vietnam, and the additional data collection from the study sites was done recently in 2015

In each sampling plot, we assessed the following variables:

(i) Name of all tree species occurring in the sampling plots; specimens of unidentified plant species were collected for identification

(ii) Number of individuals of each occurring tree species

(iii) Total height (H) and Diameter at breast height (DBH) or D10cm of each individual stem with height ≥ 1 m

(iv) Canopy cover, degree of disturbance, topographic features

These data were used to calculate relative density, abundance and dominance of the species; and from those values the Importance Value Indices (IV%) and Species diversity indices were calculated

4.3 Calculation method

- The factors structure and growth, such as: (density - N, trees / ha), average growth, basal area was calculated according to the instructions in the forest inventory (Vu Tien Hinh, Phạm Ngoc Giao, 2003)[25]

Applied the practical research methods by quantitative analysis of biodiversity in order

to determine the index : Shannon index (H) , Importance Value Index ( IV% ) If the value of the index is high, it means high diversity corresponds with high biological value This research method is necessary to create database for solution for conservation , policy and planning sustainable use of biodiversity resources

To identify indicators of biodiversity of Huong Son SUF , using survey methods according to plots At each plots, measure and collect information on :

- Species composition ; determine the name of the trees

- The number of individuals for each species , diameter of each individual

- The important value of tree species (IV, %) is defined by the formula of Curtis, 1959, according to Whittaker leads, R.H 1975)[26][27]

(4-1) Where:

- IV%: Important value index of tree species

- N%: Percentage of the number of tree species

- G%: Percentage of basal area of tree species

Basal area ( BA) = pi * ( DBH/2)2

- Identification of species diversity index, include:

 Margalef (d)

(4-2) Where :

d: Diversity indicator Margalef

N: Total individual in the plot

 Shannon - Wiener (H’)

(4-3) Where :

H’: Indicator Shannon - Wiener

S: the number of species in the plot

Pi = ni / N

N: Total individual in the plot

ni: The number of individual of i specie

 Simpson (L - Lambada)

(4-4) Where :

D is Simpson index

P is the proportion (n/N) of individuals of one particular species found (n) divided by

the total number of individuals found (N)

S is the number of species

4.4 Dominance Diversity curve (D-D) method

To analyze species dominance patterns and ascertain the resource apportionment among the species at a site, Dominance Diversity curves (D-D) were developed wherein the IVI was used as a measure of the niche of a species its and resource apportionment thus was treated as an expression of the relative niche size This is based on the assumption that there is some correspondence between the share in community resources and community space utilized by a species (Whittaker 1975, Pandey et al 2002, Huy 2012)[27][8][15]

Niche space partitioning and resource sharing

We followed Naveh and Whittaker (1979), Verma (2000) and Pandey (2002)[28][3][8] for the analysis of the vegetation stands in terms of two dominance pattern models, as follows:

- Geometric series: this kind of D-D curve is typical for sites where one species

highly dominates the site This highly dominant species thus possesses a high IVI value and is considered to occupy the top niche It takes a large share to the available resources The next important species takes a similar proportion of the resources left by the first species, and so

on This is the so-called niche preemption hypothesis (Whittaker 1975, Pandey et al 2002)[27][8] This kind of curve represents a geometric series with a very steep slope: the dominant species is the most competitive, followed by the other species that are subsequently proportionally less competitive and thus take proportionally less of the total resources Communities with this pattern usually have a low species diversity (Preston 1948, Naveh and Whittaker 1979)[29][28] This geometric series would also suggest that the vegetation of the site is not stable, and often other species can invade the community (Pandey et al 2002,Huy 2012).[8][15]

- Log-normal distribution: this kind of D-D curve occurs on sites where none of the

species possess high IVI values and none strongly dominates the site Plant communities showing a log-normal distribution, are thought to more equally share the resources in a gradual ranking order from the most important species to the least important one This log-normal distribution also suggests that at the site species are fairly equally competitive Such communities have high diversities, and the vegetation of the site is considered rather stable

(Verma 2000, Pandey et al 2002, Huy 2012)[3][8][15]

4.5 Estimating the Site disturbance index (SDI) method

Conducing assess of Site Disturbance Index for study sites : Agriculture encroachment, Invasive species , Tourism activities , Firewood and medicinal collection, Logging and fires Define level of site disturbance of factor Correspon: 0.30, 0.20, 0.20, 0.15

và 0.15 (table 1) according to (Naveh and Whittaker 1979, Acharya 1999, Huy

Table 4.1 Site Disturbance Index - SDI

Site Disturbance Index (SDI) was assessed as follows: SDI >0,5 is high level of site disturbance , 3 < SDI <=0,5 is medium level of site disturbance SDI <=0,3 is low of site disturbance

4.6 Data analysis method

- Using Excel for statistical calculation and analysis

- Ecological association between tree species in the communities was identified through three tools: branching diagram (dendrogram cluster), graphs NMDS (non-metric multidimentional scaling), graph PCA (principal component analysis - analysis the main component area) These indicators are determined by the R software installed on computers

5 RESEARCH RESULT AND DISCUSSION 5.1 Important Value Index (IV%)

The results of Important Value Index (IV%) of 18 sampling plots are represented in appendices from 1 to 6 List of species has Important Value Index (IV%) > 5% are shown in

table 5-1

Table 5.1 Importan value index

Local

Name Latinh Name

GIENG CHEN THUNG SAU

BEN DA- RUNG VAI HINH BONG

THUNG

31 Sòi Sapium sebiferum - 5.5 5.3 - - - -

Importance Value Index (IV% ) of a species represents the relative dominance of the species in a community, which further indicates how important the species is with respect to its associates in terms of resource utilization

According to Thai Van Trung (1971, 2001)[31][32], in a community, species with its

IV of 5% or more, it should have a real ecological significance to join the forest stand in the community From the results in Table 1, it showed that in 6 studied sites, the Important Value Index and its sequency changed significantly with forest and stand

All together from 18 sampling plots of 6 studied site, there are 43 species found with their IV more than 5%, of which 13 specis found in Gieng Chen site, 11 species in Thung Sau,

17 species in Ben Da- Rung Vai, 12 species in Hinh Bong, 12 species in Thung Mang and 13 species in Tuyet Son site Number of ecological significance species found highest in plot 3 (11 species) and lowest in plot 1 (2 species)

The highest values of IV% were found for Gao (Bombax malabarica) with 47.4% at the plot 6 of Thung Sau site ( and 38.1% in plot16) , followed by IVs of other three species as Buong (Sinocalamus flagellifera) with 32.4 % in plot 14, Sung (Ficus racemora) with 35.5%

in plot 14

5.2 Dominance Diversity Curve of trees species in Huong Son SUF

Figure 5.1 Dominance Diversity Curve of tree species in Gieng Chen