MINISTRY OF AGRICULTURE AND RURAL DEVELOPMENT VIETNAM FORESTRY UNIVERSITY GRADUATION THESIS SOME STRUCTURAL CHARACTERISTICS BY TIMBER CLASSES AND DIAMETER CLASSES OF EVERGREEN BROADLEAF FOREST IN DAKRONG NATURAL RESERVE, QUANG TRI PROVINCE Major: Natural Resources Management Code: D850101 Faculty: Forest Resources and Environmental Management Student : Nguyen Thi Minh Tu Student ID : 1453090734 Class : K59B - Natural Resources Management Course : 2014 - 2018 Advanced Education Program Developed in collaboration with Colorado State University, USA Supervisor: Dr Cao Thi Thu Hien Ha Noi, September 24th, 2018 ACKNOWLEDGEMENT During months of conducting this working, I gained a variety of encouragements and assistance from many people without whom this thesis would have never been conductable First and foremost, I would like to express my such gratefulness to Dr Cao Thi Thu Hien for constant support to each step of my thesis working, giving me motives and enthusiasm as well as a wealth of knowledge The guidance was really clear with vivid images and detailed illustration, which facilitated me a lot in thesis project In another place, I would like to thank the Administration of Vietnam Forestry University, Faculty of Forest Resources and Environmental Management, Department of Environmental with sincere gratitude for enabling us all best to complete theS graduation thesis Also, I sincerely express my thankfulness to many local people and authorities, both of whom untoldly assist me in collecting data and many other related procedures In which, I am espicially thank Mr.Bui Kim Thai – Manager of Dakrong Nature Reserve, Quang Tri Province and all forest rangers in the same office for supplying me with credible data, concrete and vivid images as well as encouraging me untoldly All above, I would like to give respectful gratitude to Dakrong Residential Commune for accomodating me during the process of practicing in Dakrong Nature Reserve Finally, I also thank my family and all friends, partners for best effort to give me the best facilitations to accomplish the thesis within expectations Thank you! Hanoi, September 24th, 2018 Nguyen Thi Minh Tu TABLE OF CONTENTS ACKNOWLEDGEMENT TABLE OF CONTENTS LIST OF TABLES LIST OF FIGURES ABSTRACT CHAPTER INTRODUCTION CHAPTER II GOAL, OBJECTIVES, STUDY SITE METHODOLOGY 2.1 Goals 2.2 Objectives 2.3 Methods 2.3.1 Study site 2.3.2 Data collection 2.3.3 Data analysis CHAPTER III RESULTS AND DISCUSSION 3.1 Descriptive statistics 3.2 Frequency distributions 3.2.1 Distribution of diameter frequency 3.2.2 Distributions of height frequency 11 3.3 Species composition 13 3.4 Number of trees per diameter classess 17 The number of trees over diameter classes are listed in the Table 3.5 17 3.5 Number of trees per timber classess 18 The number of trees per timber classes was presented in the table 3.6 18 3.6 Total basal area per DBH classes 18 The total basal area per DBH classes of three forest states was shown in the Figure 3.3 18 3.7 Total basal area per timber classes 19 CHAPTER IV 21 CONCLUSION 21 4.1 Descriptive statistics 21 4.2 Frequency distributions 21 4.3 Species composition 22 4.4 Number of trees per diameter classes 22 4.5 Number of trees per timber classes 23 4.6 Total basal area per DBH classes 23 4.7 Total basal area per timber classes 23 REFERENCES 24 LIST OF TABLES Table 01 Tree measurement records Table 3.1 Descriptive statistics of 30 sample plots Table 3.2 Estimated parameters and Kolmogorov-Smirnov test Table 3.4 Density and species composition by diameter classes 14 Table 3.5 Number of trees per diameter classess 17 Table 3.6 The number of trees per timber classess 18 LIST OF FIGURES Figure 3.1 Frequency distributions of diameter for forest states 11 Figure 3.2 Frequency distributions of height for forest states 13 Figure 3.3 Total basal area per DBH classes of three forest states 19 Figure 3.4 Total basal area per timber classes of three forest states 20 ABSTRACT This study has aimed to show some structural characteristics by timber classes and diameter classes of evergreen broadleaf forest in Dakrong Nature Reserve, Dakrong district, Quang Tri province The results showed that the density of the forest state IIIA1 ranged from 570 stems/ha to 1030 stems/ha, mean diameter breast height varied from 11.1 cm to 15.0 cm, mean height was 7.1 m to 11.0 m, the total basal area and volume were respectively 7.1 m – 11.0 m2/ha to 19.89 m2/ha and 28.91 m3/ha to 59.3 m3/ha These number for two forest states IIIA2, IIIB were successively: 807 stems/ha - 1330 stem/ha, 13.9 cm to 17.2 cm, 9.7 m to 12.3 m, 17.26 m2/ha - 34.23 m2/ha, 102.53 m3/ha – 191.78 m3/ha (for forest state IIIA2) and 280 stems/ha - 580 stems/ha, 18.44 cm – 24.32 cm, 0.57 m – 11.39 m, 24.31 m2/ha – 39.97 m2/ha, 247.14 m3/ha – 293.83 m3/ha (for forest state IIIB) The forest state IIIA1 leaded in the number of species with 68 tree species per hectar, followed by the forest state IIIB with 62 tree species per hectar The number of tree species of forest state IIIA2 went down to the last place with only 35 tree species The number of dominant tree species among diameter classes of the forest state IIIA1, IIIA2 and IIIA3 was successively 5,7,6,0 tree species, 4,5,5,6 tree species and 7,6,5,7 tree species The number of trees per diameter classes of the two forest states IIIA1 and IIIA2 concentrated mostly on diameter of -15 cm and the density of forest state IIIB concentrated mostly on diameter within 15-30 cm In all forest states, the number of trees concentrated on timber class VIII reflexes that a majority of trees in Dakrong Nature Reserve is lowly-qualified for economic and utilization use The total basal area of forest state IIIA1 and IIIA2 concentrated on the first DBH class (6 cm the forest state IIIB concentrated on the second DBH class (15 cm D D 15 cm) and of 30 cm) For the forest state IIIA1, the total basal area mainly focused on two timber classes VII For the forest state IIIA2, the total basal area was the largest on the last timber class (VIII), followed by timber class II, IV, VI For the forest state IIIB, the total basal area of timber class VIII and V was the highest Key words: timber classes, diameter classes, evergreen broadleaf forest, species composition, CHAPTER INTRODUCTION According to inventory results in May 2018, the total area of forested land in Quang Tri Province is 254.000 ha, in which the coverage accounts for 50% (MARD, 2018) Until now, there are natural reserves established in districts, in which Dakrong Natural Reserve located in Dakrong District was discovered leading nature ones of the whole province in the capacity of natural resources including forests Bordering on Phong Dien Natural Reserve in Thua Thien Provinve, Dakrong Natural Reserve in Quang Tri Province has an area of 40.526 ha, including regional part of communes: Ba Long, Hai Phuc, Trieu Nguyen, Ta Long, Huc Nghi, Hong Thuy in Dakrong district With variety and diversity of forest ecosystems and limestone, watersheds here are home to many species of fauna and flora In addition, Dakrong reserve is also “The important Green Corridor” connecting the network of the north of Bach Ma – Hai Van, Bach Ma Phong Dien, Phong Nha – Ke bang, Vu Quang, Pu Mat and other natural reserves of Eastern Phu Rieng, Hin Nam No of neighboring country – Laos Moreover, Dakrong reserve also provides people with spectacular landscape and many attractive sites for ecotourism Dakrong natural reserve is in the low mountainous region, with sharp separation and high slope Now, it is reported that 1412 species of flora have been found, 24 species of them are listed in the Red Book There are types of forests in this vegetational cover: closed evergreen sub-tropical broadleaf forest and closed evergreen tropical broadleaf forest rainforest In which, the former one possesses the greatest area of the same type in the central provinces In terms of closed evergreen broadleaf forest in Dakrong, it owns an area of 5000 hectares, accounting for 12% of total reserve area, distributed in the height from 800 m to 1400 m above sea level, mainly in mountain range from Pa Le to A Doa, with mass of A Pong cave mountain This is the forest type that is not muchly affected and basically still maintains its primitiveness Its coverage reaches 70% Vegetation cover mostly grows broadleaf species belonging to Fagaceae, Loraceae, Euphorbiaceae, Fabaceae, Sapotaceae, ect In which, there are some trees playing the key role in setting up main communities such as Castanopsis tonkinensis, Lithocarpus dinhensis, Quencus fleuryi, Archidendron tonkinensis, and some species of Cinnamonum genus of Lauraeae family From the height of 1200 m above sea level, there are some other species as Archidendron tonkinensis, Michelia tonkinensis, ect Especially Dacrycarpus imbricatus, Dacrydium elatum, Podocarpus neriifolius, of which occupying the emergent layer of stand, leading to formation of some mixed stands with broadleaf and needleleaf forest Tree species belonging to this type of forest own diameter of 25-30 cm, height of 20m, some others’ diameter is even up to 50-100cm Despite great effort in management, protection and research investigation on biodiversity in this area, there are still drawbacks on the work of managing and protecting until now, scientific data have not been completed yet, biodiverisity has yet to be investigated adequately and systematically Besides, living condition of ethnic minorities is still very difficult, especially Van Kieu, Pa Co In order to provide a scientific basis for proposing solutions to sustainable managing natural forest in general and natural evergreen broadleaf in Dakrong nature reserve – Quang Tri Province in particular, it is necessary to study “Some structural characteristics by timber classes and diameter of evergreen broadleaf forest in Dakrong nature reserve, Quang Tri province” CHAPTER II GOAL, OBJECTIVES, STUDY SITE METHODOLOGY 2.1 Goals The goal of this study is to analyze some structural characteristics by timber classes and diameter classes of evergreen broad-leaved forest in Dakrong nature reserve, Quang Tri Province 2.2 Objectives - To provide some statistic characteristics of natural forests in the research area - To analyze forest structural characteristics of overstorey in the research area - To find species composition in the study area - To find number of trees by diameter classes and timber classes - To find the total basal area by diameter classes and timber classes 2.3 Methods 2.3.1 Study site Dakrong Nature Reserve is located in the southern part of the Dakrong district of Guizhou Province, and has a geographical coordinates of 16023 '- 16009' north latitude106052’ – 107009 east longitude Dak Krong Nature Reserve covers an area of 40,526 ha, including part of communes of Ba Long, Hai Phuc, Trieu Nguyen, Ta Long, Huc Nghi and Hong Thuy of Da Krong district The annual average temperature is from 22 to 23 degrees Celsius, the average annual rainfall is from 2500 mm to 3000 mm, the average humidity is from 85% to 87% 2.3.2 Data collection In this study, forest states namely IIIA1, IIIA2 and IIIB were selected 30 sample plots were established, 10 sample plots in each forest state Each plot covers 1000m2 (40m of length x 25m of width) For trees in overstorey: In each plot, all of the individual trees found in diameter at breast height (D1.3) greater than or equal to 6cm was marked, local and scientific names identified, their diameter was measured at 1.3 m from the ground All trees in each plot were measured total tree height by Blumeleiss All data will be recorded on the field forms as the following: Forest state IIIA1 No trees 140 Frequency (fact) Frequency… 120 100 80 60 40 20 Height (m) 11 13 15 17 19 Forest state IIIA2 No trees 180 160 140 Frequency (fact) 120 Frequency (theoretical) 100 80 60 40 20 Height (m) 11 13 15 17 Forest state IIIB 12 19 21 23 25 No trees 45 40 Frequency (fact) 35 Frequency (theoretical) 30 25 20 15 10 Height (m) 11 13 15 17 19 21 23 25 27 Figure 3.2 Frequency distributions of height for forest states as fitted by Weibull (3) distribution 3.3 Species composition Results of density and species composition in the study area are summarized in Table 3.4 In view of the total, the number of trees per (No.trees/ha) of forest state IIIA2 was the highest with 1141 individuals/ha (Table 3.4) While number of trees per of forest state IIIB was the lowest with only 437 stems/ha, nearly three times as low as that of forest state IIIA2 and twice as low as forest state IIIA1 with 793 trees/ha However, forest state IIIA1 leaded in the number of species with 68 tree species per hectar, followed by the forest state IIIB with 62 tree species per hectar The number of tree species (No.species) of forest state IIIA2 went down to the last place with only 35 tree species 13 Table 3.4 Density and species composition by diameter classes Forest state IIIA1 Variable Total cm < DBH < 15 cm 15 cm < DBH < 30 cm 30 cm < DBH < 45 cm No.trees/ha No.species Dominant species 793 68 Ficus religiosa, Tapiscia sinensis, Knema saxatilis, Lithocarpus … 545 64 Tapiscia sinensis, Knema saxatilis, hibbertia, Ficus religiosa, Euphorbia tirucalli, Typha orientalis 226 50 Knema saxatilis, Ficus religiosa, Tapiscia sinensis, Lithocarpus, Typha orientalis No.trees/ha No.species Dominant species 1141 35 Cirsium japonicum, Fagraea fragrans, Hymenodictyon excelsum, Cinnadenia paniculata, Burretiodendron hsienmu 437 62 Gironniera subaequalis Planch, Eberhardtia Aurata, Hydnocarpus nana, Hydnocarpus obtusa, Vatica odorata, Peperomia obtusifolia 744 32 Cirsium japonicum, Pseuderanthe mum carruthersii reticulatum, Diospyros rubra, Cinnadenia paniculata 235 35 Ficus religiosa, Lithocarpus, Tapiscia sinensis, Lysidice rhodostegia Hance, Vernicia montana, Knema saxatilis 275 24 Fagraea fragrans, Cinnadenia paniculata, Hymenodictyon excelsum, Nageia fleuryi, Euphorbia tirucalli, Burretiodendron hsienmu IIIA2 No.trees/ha No.species Dominant species IIIB 168 48 Eberhardtia Aurata, Vatica odorata, Knema globularia, Diospyros rubra, Hydnocarpus obtusa, Gironniera subaequalis Planch, Hydnocarpus nana 14 213 40 Gironniera subaequalis Planch, Eberhardtia Aurata, Hydnocarpus nana, Hydnocarpus obtusa, Vatica odorata, Peperomia obtusifolia 312 27 Cirsium japonicum, Pseuderanthemum carruthersii , Diospyros rubra, Fagraea fragrans Cinnadenia paniculata 47 24 Peperomia obtusifolia, Gironniera subaequalis Planch, Hydnocarpus nana, Cissa chinensis, Eberhardtia Aurata DBH > 45 cm 418 28 Fagraea fragrans, Hymenodictyon excelsum, Cinnadenia paniculata, Burretiodendron hsienmu, Nageia fleuryi 20 13 Aphanamixis grandiflora Blume, Cissa chinensis, Vatica odorata, Eberhardtia Aurata, Canarium album Raeusch, Physalis angulata, Cinnamomum parthenoxylon The number of dominant species of the forest state IIIA2 was out of 35 tree species (Table 3.4), accounting for 14.3 % including: Gironniera subaequalis Planch, Eberhardtia Aurata, Hydnocarpus nana, Hydnocarpus obtusa, Vatica odorata, and Peperomia obtusifolia In contrast, the number of dominant tree species in the forest state IIIA1 was the lowest with out of 68 tree species, accounting for 5.88 %, including: Ficus religiosa, Tapiscia sinensis, Knema saxatilis, and Lithocarpus The number of dominant trees in the forest state IIIB species took up 9.6% with out of 62 tree species, they are: Gironniera subaequalis Planch, Eberhardtia Aurata, Hydnocarpus nana, Hydnocarpus obtusa, Vatica odorata, and Peperomia obtusifolia For the forest state IIIA1, the number of trees per hectar gathers most highly on diameter class of 6-15 cm with 545 individuals/ha Meanwhile, there is no species owning diameter over 45 cm The number of trees within 15 cm - 30 cm and 30 cm - 45 cm in diameter were closely equal with 235 and 226 stems/ha Also, the number of tree species was the highest at diameter class of cm - 15 cm with 64 tree species and there was no tree species owining diameter over 45 cm Diamter class of 15 cm - 30 cm jumped up to the highest at number of dominant tree species with out of 35 tree species (accounted for 20%), including: Ficus religiosa, Lithocarpus, Tapiscia sinensis, Lysidice rhodostegia Hance, Vernicia montana, and Knema saxatilis Going after is the number of dominant tree species of cm D 15 cm and 30 cm D 45cm with successively species (10%) and species (9.3%) The number of dominant tree species over 45cm in diameter was 0, the lowest of all dominant tree species that were distributed most in diameter classes are Cirsium japonicum, Pseudseranthemum carruthersii paniculata 15 reticulatum and Cinnadenia For the forest state IIIA2, diameter class of cm - 15 cm kept leading in the number of trees per hectar with 744 stems and standing in the least was number of trees of 15 cm - 30 cm in DBH with 275 trees, twice as high as than that of IIIA2 There were 418 trees over 45 cm in diameter (just going after the number of trees in diameter of cm - 15 cm) The number of tree species within diameter class of cm - 15 cm remained the greatest with 32 tree species However, the number of species in diameter class of 15 cm 30 cm, 30 cm - 45 cm and over 45 cm tended to be roughly equal with successively 24, 27 and 28 tree species On the contrary, the number of dominant tree species among diameter classes were just slightly fluctuating, with tree species (accounting for 12.5%, cm D (18.5%, 30 15 cm, the lowest one), tree species (17.8%, D D 45) and tree species (25%, 15 cm D 45 cm), tree species 30 cm, the greatest one) In which, Cinnadenia paniculata was mostly distributed in all diameter classes For the forest state IIIB, there was a fluctation among the number of trees per of diameter classes Whereas there were up to 213 trees/ha within diameter class of 15 cm 30 cm (the highest of DBH classes), there is only 20 trees/ha over 45 cm in diameter (the lowest of DBH classes) The number of trees per of cm D D 15 cm and 30 cm 45 cm also strikingly fluctuated with successively 168 trees/ha and 47 trees/ha The number of tree species in diameter classes are successively 48, 40, 24 and 13 tree species With respect to dominant tree species, there was 6, 7, 6,5 and tree species from the first to the fourth DBH class Gironniera subaequalis Planch, Eberhardtia Aurata, Hydnocarpus obtusa, Vatica odorata Peperomia obtusifolia were the four most-distributed dominant species in all diameter classes In general, the forest state IIIA2 tended to lead in the number of trees per hectar and the forest state IIIA1 tended to lead in the number of tree species 16 3.4 Number of trees per diameter classess The number of trees over diameter classes are listed in the Table 3.5 Table 3.5 Number of trees per diameter classess Forest state DBH classess IIIA1 IIIA2 IIIB (no.trees/ha) (no.trees/ha) (no.trees/ha) cm < DBH < 15 cm 545 744 168 15 cm < DBH < 30 cm 235 275 202 30 cm < DBH < 45 cm 13 98 47 DBH > 45 cm 17 15 The Table 3.5 illustrated that the density of the two forest states IIIA1 and IIIA2 tended to decrease gradually by the increase of diameter classes Specifically, the number of trees per hectar of the two forest states IIIA1 and IIIA2 concentrated mostly on diameter of -15 cm, with 545 stems/ha and 744 trees/ha Successively going after was the number of trees per hectar of 15 cm D 30 cm, 30 cm D 45 cm, D 45 cm with 235 (trees/ha, in forest state IIIA1) and 275 (trees/ha, in forest state IIIA2), 13 (trees/ha, in forest state IIIA1) and 98 (trees/ha, in forest state IIIA2), ( trees/ha, in forest state IIIA1) and 17 (trees/ha, in forest state IIIA2) Particularly in the forest state IIIA1, there was no tree with diameter over 45cm So, it can be seen that the density of the forest state IIIA1 and IIIA2 concentrated highly on diameter within -15 cm This means the number of young-aged trees of the two forest states IIIA1 and IIIA2 accounted for the largest percent of all In contrast, the density of the forest state IIIB concentrated mostly on diameter within 15-30cm with 202 trees/ha, followed by was the number of trees of cm cm with 168 trees/ha The number of trees in DBH class D 15 45cm kept the lowest with 15 cm (greater than that of forest state IIIA1 but smaller than that of forest state IIIA2) To generalize, the majority of trees owned diameter of cm - 15 cm and 15 cm - 30 cm, the number of trees per hectar in diameter of 30 cm - 45 cm and over 45cm of all three forest states was still limited 17 3.5 Number of trees per timber classess The number of trees per timber classes was presented in the table 3.6 Table 3.6 The number of trees per timber classess State Timber classess IIIA1 IIIA2 IIIB (no.trees/ha) (no.trees/ha) (no.trees/ha) I II 160 34 III 15 29 IV 22 129 16 V 52 28 101 VI 61 97 52 VII 78 22 VIII 563 704 193 The density distribution of forest states in timber class I, II and III (3 of which are regarded as the most valuable) was rather little and even equal to (in timber class II of state IIIA1 and timber class III of state IIIA2, for example) Only the class II of forest state IIIA2 owned more excessive density than other states in timber class I, II, III with 160 trees/ha In those timber classes which are listed in medium value as IV, V, VI and VII, the number of trees per hectar were rather fluctuating, and not uniform among all forest states However, a majority of trees per hectar concentrated on timber class VIII (which was considered low at economic and utilization values), successively with 563 (trees/ha, in forest state IIIA1), 704 (trees/ha, in forest state IIIA2) and 193 (trees/ha, in forest state IIIA3) Clearly, that most density concentrated on timber class VIII reflexes that a majority of trees in Dakrong Nature Reserve is lowly-qualified for economic and utilization use Meanwhile, the number of trees per hectar in timber class I, II and III were still limited in comparison with that of timber class VIII 3.6 Total basal area per DBH classes The total basal area per DBH classes of three forest states was shown in the Figure 3.3 18 Total basal area 16 15 14 13 12 11 10 6 cm < DBH < 15 cm IIIA1 (m2/ha) IIIA2 (m2/ha) IIIB (m2/ha) DBH classes 15 cm < DBH < 30 cm 30 cm < DBH < 45 cm DBH > 45 cm Figure 3.3 Total basal area per DBH classes of three forest states The total basal area of forest state IIIA1 concentrated on the first DBH class (6 cm D 15 cm) with 8.83 m2/ha, followed by the second DBH class (15 cm D 30 cm) with 3.81 m2/ha and the third place was the third DBH class with 0.21 m2/ha DBH class over 45 cm equaled m2/ha For the forest state IIIA2, the total basal area focused on the first DBH class with 13.87 m2/ha, the total basal area continuously showed a decrease trend from the second to the fourth DBH class with 5.13 m2/ha, 1.83 m2/ha, 0.32 m2/ha, respectively The total basal of the forest state IIIB concentrated on the second DBH class (15 cm D 30 cm) with 15.43 m2/ha, followed by the first DBH class with 12.84 m2/ha The total basal of the third and the fourth DBH class was 3.59 m2/ha and 1.15 m2/ha, respectively 3.7 Total basal area per timber classes The total basal area per timber classes of three forest states was illustrated in the Figure 3.4 For the forest state IIIA1, the total basal area mainly focused on two timber classes VII (1.26 m2/ha) and VIII (9.12 m2/ha) (Figure 4.4) The total basal area at timber classes I, II accounted for a tiny number, even timber class II had no tree For the forest state IIIA2, the total basal area was the largest on the last timber class (VIII) with 13.04 m2/ha, followed by timber class II (2.96 m2/ha), IV (2.39 m2/ha), VI (1.80 m2/ha) The total basal area of timber class VII and V was 0.41 m 2/ha and 0.52 19 m2/ha, respectively Timber class II had no tree, that means the total basal area of this timber class was zero For the forest state IIIB, the total basal area of timber class VIII and V was the highest with 14.58 m2/ha and 7.63 m2/ha, followed by timber class VI (3.93 m2/ha), II (2.57 m2/ha), III (2.19 m2/ha) The first timber class (I) had the lowest total basal area with 0.23 m2/ha Total basal area 16 15 14 13 12 11 10 I IIIA1 IIIA2 IIIB Timber classes II III IV V VI VII VIII Figure 3.4 Total basal area per timber classes of three forest states 20 CHAPTER IV CONCLUSION This study has aimed to show descriptive statistics, analyze some characteristics of forest structure, assess the species composition, find number of trees by diameter classes and timber classes, the total basal area by diameter classes and timber classes in the natural forest in Dakrong nature reserve, Quang Tri province 4.1 Descriptive statistics The density per ranged from 870 to 1330 trees/ha Forest state IIIA2 had the highest number of trees per hectar (from 807 stems/ha to 1330 stems/ha) (Table 3.1) This was closely followed by forest state IIIA1 with 570 stems/ha - 1030 stems/ha The third place was forest state IIIB with 280 stems/ha - 560 stems/ha Forest state IIIB had the largest mean diameter at breast height (dbh) (from 18.44 cm to 24.32 cm) while the smallest mean dbh (from 11.1 cm to 15.0 cm) was recorded for forest state IIIA1 The highest mean tree height belonged to the forest state IIIA2 (ranged from 9.7 m to 12.3 m), meanwhile, the shortest mean height of trees was found in the forest state IIIB, lied between 6.30 m and 11.39 m The total basal area per hectare in forest state IIIB was the highest (24.31 m2/ha – 29.97 m2/ha), this was followed by forest state IIIA2 with basal area per of 17.26 m2/ha - 34.23 m2/ha The lowest basal area per of forest state sIIA1 was 7.00 m2/ha – 19.89 m2/ha The similar trend to volume, the volume of three forest states IIIB, IIIA2, and IIIA1 was 247.14 m3/ha – 293.83 m3/ha, 102.53 m3/ha – 191.78 m3/ha, 28.91 m3/ha – 59.30 m3/ha, respectively 4.2 Frequency distributions The Kolmogorov smirnov test indicated that the Weibull (3) distribution can provide good fit for the diameter and height data, because its calculated D-values with pvalue was higher than 0.05 in all forest states This implies the null hypothesis was accepted for the Weibull (3) distribution, meaning the data followed the specified distribution There was virtually no difference in the frequency distributions of the DBH across the three forest states In addition, forest state IIIA1 was lacked of large stems Trees with a DBH greater than 70 cm were only found in two forest states IIIA2 and IIIB 21 4.3 Species composition The forest state IIIA1 leaded in the number of species with 68 tree species per hectar, followed by the forest state IIIB with 62 tree species per hectar The number of tree species of forest state IIIA2 went down to the last place with only 35 tree species The number of dominant species of the forest state IIIA2 was out of 35 tree species, including: Gironniera subaequalis Planch, Eberhardtia Aurata, Hydnocarpus nana, Hydnocarpus obtusa, Vatica odorata, and Peperomia obtusifolia In contrast, the number of dominant tree species in the forest state IIIA1 was the lowest with out of 68 tree species, including: Ficus religiosa, Tapiscia sinensis, Knema saxatilis, and Lithocarpus The number of dominant trees in the forest state IIIB species was out of 62 tree species, they are: Gironniera subaequalis Planch, Eberhardtia Aurata, Hydnocarpus nana, Hydnocarpus obtusa, Vatica odorata, and Peperomia obtusifolia For the forest state IIIA1, the number of tree species was the highest at diameter class of cm - 15 cm with 64 species and there was no tree species owining diameter over 45 cm The number of dominant tree species of three diameter classes was 5, and tree species, respectively The number of dominant tree species over 45cm in diameter was For the forest state IIIA2, the number of tree species within diameter class of cm 15 cm remained the greatest with 32 tree species However, the number of tree species in diameter class of 15 cm - 30 cm, 30 cm - 45 cm and over 45 cm tended to be roughly equal with successively 24, 27 and 28 tree species The number of dominant tree species among diameter classes were just slightly fluctuating, with 4, 5, and tree species from the first to the fourth DBH classes For the forest state IIIB, the number of species in diameter classes are successively 48, 40, 24 and 13 tree species With respect to dominant tree species, there was 7, 6, and tree species from the first to the fourth DBH class 4.4 Number of trees per diameter classes The number of trees per DBH classes of the two forest states IIIA1 and IIIA2 tended to decrease gradually by the increase of diameter classes The number of trees per diameter classes of the two forest states IIIA1 and IIIA2 concentrated mostly on diameter of -15 cm, with 545 stems/ha and 744 trees/ha The density of the forest state IIIB concentrated mostly on diameter within 15-30cm with 202 trees/ha 22 4.5 Number of trees per timber classes The density distribution of forest states in timber class I, II and III (3 of which are regarded as the most valuable) was rather little and even equal to (in timber class II of state IIIA1 and timber class III of state IIIA2, for example) In all forest states, the number of trees concentrated on timber class VIII reflexes that a majority of trees in Dakrong Nature Reserve is lowly-qualified for economic and utilization use 4.6 Total basal area per DBH classes The total basal area of forest state IIIA1 and IIIA2 concentrated on the first DBH class (6 cm D 15 cm) with 8.83 m2/ha and 13.87 m2/ha, respectively Then, the total basal area continuously showed a decrease trend from the second to the fourth The total basal of the forest state IIIB concentrated on the second DBH class (15 cm D 30 cm) with 15.43 m2/ha, followed by the first DBH class with 12.84 m2/ha The total basal of the third and the fourth DBH class was 3.59 m2/ha and 1.15 m2/ha, respectively 4.7 Total basal area per timber classes For the forest state IIIA1, the total basal area mainly focused on two timber classes VII (1.26 m2/ha) and VIII (9.12 m2/ha) For the forest state IIIA2, the total basal area was the largest on the last timber class (VIII) with 13.04 m2/ha, followed by timber class II (2.96 m2/ha), IV (2.39 m2/ha), VI (1.80 m2/ha) For the forest state IIIB, the total basal area of timber class VIII and V was the highest with 14.58 m2/ha and 7.63 m2/ha, followed by timber class VI (3.93 m2/ha), II (2.57 m2/ha), III (2.19 m2/ha) 23 REFERENCES Archibald, E.E.A, 1940 The specific character of plant communities II A quantitative approach Journal of Ecology 37, 260-274 Blanc, l., G Maury-lechon & J P Pascal 2000 Structure, floristic composition and natural regeneration in the forests of Cat Tien National Park, Vietnam: an analysis of the successional trends Journal of Biogeography Bui Manh Hung, 2015, Structure and restoration of natural secondary forests in the Central Highlands, Vietnam Bui Thi Diep, 2012 Some silvicultural characteristics of forest in Dong Nai Nature and Culture Reserve Bui The Doi, 2001 Some structural characteristics and natural regeneration of forests in lime stone mountains in locations in the North of Vietnam Campbell, D G., J L Stone & J A Rosas 1992 A comparison of the phytosociology and dynamics of three flood plain forests ofknown ages, Rio Jurua, western Brazilian Amazon Botanical Journal of the Linnaean Society 108: 213-237 Cao Thi Thu Hien, 2016, Change in tree species diversity over time in tropical rainforests of central region, Vietnam Duran, E., J A Meave, D J Lott & G Segura 2006 Structure and tree diversity patterns at landscape level in a Mexican tropical deciduous forest Boletinde Sociedad Botanica de Mexico Edward F Connor et al Species – Area relationships, San Francisco State University and University of South Florida 10 Gleason, H.A, 1992 On the relation between species and area Ecology 3, 158-162 11 Hamann, A., E B Barbon, E Curio & D A Madulid 1999 A botanical inventory of a submontane tropical rainforest on Negros Island, Philippines Biodiversity and Conservation 24 12 Kessler, M., P J A Keber, S R Gradstein, K Bach, M Schmull & R Pitopand 2005 Tree diversity in primary forest and different land use systems in Central Sulawesi, Indonesia Biodiversity and Conservation 14: 547-560 13 Kimmins, J.P.,1998 Forest ecology, Prentice – Hall, Upper Saddle River, New Jersey 14 Klaus v Gadow, 2012 Forest Structure and Diversity 15 Knight, D H 1975 A phytosociological analysis of species rich tropical forest on Barro Colorada Islands, Panama Ecol Monogra 16 Losose, C & G Leigh 2004 Tropical Forest Diversity and Dynamism: Findings from a Large-Scale Plot Network Chicago University Press, Chicago 17 Lü, X T., J X Yin & J W Tang 2010 Structure, tree species diversity and composition of tropical seasonal rainforests in Xishuangbanna, south-west China Journal of Tropical Forest Science 22: 260-270 18 Margalef, F R 1958 Information theory in ecology Gen Syst., 3:36–71 19 Mohd Nazip Sutatunan, 2008, Tree Species Diversity and Forest Stand Structure of Pahang National Park, Malaysia 20 Nguyen Dinh Truong, 2011 Some structural characteristic on high mountain forests bordering the National Park Bi Doup-Nui Ba, Lam Dong province and Company limited liability the member forest products, Khanh Hoa province 21 Rao, B R P., M V S Babu, M S Reddy, A M Reddy, V S Rao, S Sunitha & K N Ganeshaiah 2011 Sacred groves in southern eastern ghats, India: Are they better managed than forest reserves? Tropical Ecology 22 Richards, P W 1952 The Tropical Rain Forest, Cambridge University PressS 25 APPENDICES 26 ... composition, find number of trees by diameter classes and timber classes, the total basal area by diameter classes and timber classes in the natural forest in Dakrong nature reserve, Quang Tri province. .. evergreen broadleaf in Dakrong nature reserve – Quang Tri Province in particular, it is necessary to study ? ?Some structural characteristics by timber classes and diameter of evergreen broadleaf forest. .. classes and diameter classes of evergreen broad-leaved forest in Dakrong nature reserve, Quang Tri Province 2.2 Objectives - To provide some statistic characteristics of natural forests in the