Structure and regeneration characteristics of manfrove forest in tien hai district, thai binh provice

ACKNOWLEDGEMENTS Firstly, I would like to express my sincere gratitude to my advisor Dr Pham Minh Toai for constant support and valuable guidance during the time of research and writing of this thesis Secondly, I would also thank to various professors of Vietnam Forestry University and Colorado State University, especially to Professor Lee MacDonald for providing classes and guidance for this project Thirdly, I would like to thank Manager of Resources and Environment Department, Leaders of People’s Committee in Dong Long, Nam Hung, Nam Thinh commune and dwellers who live in Tien Hai district They provided good conditions when I conducted my research Last but not least, I would like to thank my family for giving birth to me and supporting me spiritually throughout my life TABLE OF CONTENTS I INTRODUCTION II GOAL AND OBJECTIVES 2.1 Goals 2.2 Specific objectives III STUDY AREA AND METHODS 3.1 Study area 3.2 Study methods 3.2.1 Preliminary survey 3.2.2 Data collection 3.2.3 Data analysis IV RESULTS AND DISCUSSIONS 4.1 Characteristics of canopy layer 4.1.1 Species composition of canopy layer 4.1.2 Density of trees in canopy layer 10 4.1.3 Canopy cover 12 4.1.4 Characteristics of the growth of mangroves 12 4.2 Characteristics of regeneration 15 4.2.1 Species composition and density of trees regeneration 15 4.2.2 Impacts of some factors on regeneration mangrove species 18 4.3 Some solutions for sustainable development of mangroves in Tien Hai district, Thai Binh province 21 ii 4.3.1 Afforestation 21 4.3.2 Forest protection 23 4.3.3 Policies in forest management and protection 23 V CONCLUSION 24 5.1 Characteristics of canopy layer 24 5.2 Characteristics of regeneration 24 5.3 Some ecological factors affect to regeneration 24 REFERENCES 25 iii LIST OF TABLES Table 3.1 Field data sheet to survey the canopy layer Table 3.2 Field data sheet to survey the regenerated trees Table 4.1 Species composition of trees in canopy layers Table 4.2 Mean density of trees in canopy layer at the study area 11 Table 4.3 Growth parameter of trees in canopy layer 13 Table 4.4 Quality of trees in the canopy layer 14 Table 4.5 Species composition and mean density of the regenerated trees 15 Table 4.6 Distribution of regenerated trees at four height levels 17 Table 4.7 Number of regenerated trees on substratum 19 iv LIST OF FIGURES Figure 3.1 Locations of study areas Figure 4.1 Mean growth of mangrove forest 13 v LIST OF PICTURES Picture 4.1 Mangrove community of Trang – Ban – Su 10 Picture 4.2 Division of branches of Trang 11 Picture 4.3 Regeneration of Trang in plant communities of Trang-Ban-Su 17 Picture 4.4 Barnacles stick on a regenerated tree 20 Picture 4.5 Dwellers in Nam Thinh digged oysters in mangrove forest 21 Picture 4.6 (a) Flower of Sonneratiasp., (b) Fruit of Sonneratiasp.; (c) and (d) Sonneratiasp 22 vi ABBREVIATION No Abbr Explaination A Good quality tree B Medium quality tree C Bad quality tree Ban Sonneratia caseolaris D1.3 Diameter at breastheight D00 Root collar diameter of a tree Dt Canopy diameter Hvn Tree height N Density 10 Su Aegyceras floridum 11 SE Standard error 12 SD Standard deviation 13 Trang Kandelia obovata vii ABSTRACT Mangrove forest plays an important role in protecting shorelines from damaging storm, hurricane, winds, waves and upgrading people’s standard of living Protecting and restoring mangrove forest will improve the life of people in the region and help cope with climate change in the coastal regions In Tien Hai district, Thai Binh Province, total area of planted mangrove forest is about 1,571.95ha This forest type is distributed at the coastal regions; include three communities of pure plantation of Trang, a mixed plantation of Trang – Ban and a mixed plantation of Trang – Ban - Su The diversity of species composition is relative simple with predominance of Trang Density and canopy cover of mangrove forest are quite high and like density and growth of regeneration The ecological elements such as water salinity, tide and soil affect the distribution of species and the growth ability of mangrove forest Key words: mangrove forest, plantation, growth, regeneration, Thai Binh I INTRODUCTION Mangrove forest ecosystem is amongst the most important and productive of ecosystems and is often found along coastal areas and offshore islands This ecosystem provides food and nursery grounds for many commercially important aquatic and terrestrial animals In addition, it stabilizes coastal lines, promotes coastal accretion and provides a natural barrier against storms, cyclones, tidal bores as well as other potentially damaging natural forces For centuries, mangroves have contributed significantly to the socio-economic lives of coastal dwellers in Vietnam They have been not only traditionally exploited as building materials, charcoal, firewood, tannin, food, honey, herbal medicines and many other forest products which create stable jobs and income for dwellers in coastal areas This indicated that mangrove forests maintain the diversity of aquatic resources for coastal region Although mangrove forests of Vietnam are not as abundant in biological diversity as are other ecosystems such as inland tropical rainforests, they provide habitats for species which are adapted to a saline tidal environment The mangroves also provide habitats for large numbers of diverse migratory waterfowl and terrestrial animals and are very important as habitats of aquatic organisms such as algae, mollusks, Brachyura, Decapoda Tien Hai, a coastal district, is located about 23 kilometers in the southeast coastal of Thai Binh province, major estuaries flowing into sea such as Ba Lat river of Red River, Tra Ly river and Lan river, so the alluvial soil has accreted and formed more than 6,000 hectares alluvial ground, coastal wetlands with richness and diversity of fauna and flora, including Tien Hai Nature Reserve Like many other mangroves, roles and functions of mangrove ecosystem in Tien Hai are very important, especially in providing coastal protection against the actions of tidal, waves, wind and water currents, natural disasters But now, mangrove forests are threatened by climate change like natural disaster, exploitation and overuse of human activities These issues have made the changes of structure and growth of mangrove communities, which the causes of change in habitat and species composition, degradation of mangrove resources and ecological imbalance For these reasons, solutions for afforestation, reforestation and rehabilitation based on the thorough advantages of natural regeneration which are consistent with natural conditions, economic and society, are very necessary In addition, due to the importance of mangroves, many policies and projects have been developed and implemented in the coastal communes of Tien Hai district to protect and restore mangroves Therefore, research on forest structure and regeneration characteristics of mangrove forest in Tien Hai district, Thai Binh province in order to provide data and scientific research for rehabilitation and development this forest type in study areas in sustainable ways is needed Table 4.2 Mean density of trees in canopy layer at the study area Study area Trang Trang - Ban Trang – Ban - Su Tree density Transe ct Individual/plot Individual/ha 263 6,575 354 8,850 301 7,525 Mean 306 7,650 105 2,732 125 3,125 132 3,300 Mean 121 3,052 246 6,150 332 8,300 255 6,375 Mean 278 6,942 Survey results of canopy layer's tree density in study areas show that pure plantations of Trang has the mean highest density of 7,650 trees/ha, where trees grow mostly in height Survey in field work knew that with each foot of one Trang is divided into -3 branches growing and developing as an independent tree in the dense plot Picture 4.2 Division of branches of Trang 11 Besides that, mangrove community of Trang – Ban has the lowest density It may because Ban grows the largest diameter at breast-height in most of mangrove species, thus their presence limit the growth of other species and occupy a large amount of nutrient Overall, in the same species, density not only depends on the growth of species but the stages of growth and development of forests The older forest is, the less density of trees is by laws of natural selection 4.1.3 Canopy cover Canopy cover is an important structural indicator of forest status represented the coverage of forest on the soil surface, which affected to regeneration, growth and development of seedlings by light The study results showed that the pure Trang plantation has the highest coverage while canopy cover of the pure plantation of Trang is 0.92, a mixed plantation of Trang – Ban is 0.83 and mixed plantation of Trang – Ban – Su is 0.90 4.1.4 Characteristics of the growth of mangroves Study the growth in height and diameter is to find out the growth stages of mangrove species from which choose the suitable silvicultural measures to grow the yields of mangrove trees, also the change in the growth stages of mangroves In study areas, the growth characteristics of mangrove communities are shown in table: 12 Table 4.3 Growth parameter of trees in canopy layer D1.3(cm) Hvn (m) Dt (m) Study area Mean SE SD Mean SE SD Mean SE SD Trang 4.3 0.4 2.5 2.2 0.2 1.0 1.3 0.2 1.2 Trang – Ban 4.7 0.7 4.2 2.8 0.3 2.0 1.6 0.1 1.5 Trang – Ban - Su 4.0 0.5 2.6 2.5 0.3 1.7 1.3 0.3 0.7 Growth of plant communities in study areas represents in diameter at breast-height, height and diameter at canopy Growth of each community is different clearly Both of Trang and Trang – Ban have an equal growth ability In pure plantation of Trang, mean growth of mangrove species in D1.3= 4.3m, Hvn = 2.2 m and Dt = 1.3m In a mixed plantations, mean growth of mangrove species in D1.3 = m, Hvn = 2.5m and Dt = 1.3 m while mixed plantation of Trang – Ban has the most mean growth of mangrove species with D1.3= 4.7m, H = 2.8m and D.canopy = 1.6m 5.0 4.5 4.0 3.5 3.0 Trang 2.5 Trang - Ban 2.0 Trang - Ban - Su 1.5 1.0 0.5 0.0 D13 H D.canopy Figure 4.1 Mean growth of mangrove forest Research results in the Figure 4.1 shows that the growth of mangrove species in the different mangrove communities is represented by diameter at breast-height, diameter of 13 canopy and height The more growth in height grows, the more growth in diameter at breast-height grows In which the growth in plant communities of Trang – Ban is the largest, and plant community of Trang – Ban – Su is the lowest Quality of trees in the canopy layer plants is shown in table 4.4 In pure plantation of Trang, the percentage of good quality trees is 53%, bad quality trees 11 % and medium quality trees 36% In a mixed plantation of Trang – Ban, the percentage of good quality trees is the lowest 35 %, bad quality trees 17% In a mixed plantation of Trang – Ban – Su, the percentage of good quality trees is the highest 55 %, bad quality trees 13% Therefore, the majority of trees have the good quality There is a small proportion of bad quality trees remaining in the community Table 4.4 Quality of trees in the canopy layer Quality (%) Study area A B C Trang 53 36 11 Trang – Ban 35 48 17 Trang – Ban - Su 55 32 13 Survey results show that the mangrove forests are still developing in study areas However, the difference in density leads to the difference clearly in formation of forest, due to the difference site conditions, such as soil texture, thickness of sediment, salinity, and tidal fluctuation from which the characteristics of the tree growth reflect the difference in density, make a difference in the difference conditions of forest In status of the thick forests, trees must compete with other trees for nutrition, sunlight so trees grow higher than in the thin forests And in the thin forest of plant community of Trang - Ban, trees have enough nutrition and light to develop in diameter, have many branches, broaden canopy, 14 typically Sonneratia caseolaris Besides, a mixed community of Trang – Ban –Su is flooded in water in a long time, the roots of trees are broaden because spongy tissues absorb water from the pore-water of roots 4.2 Characteristics of regeneration 4.2.1 Species composition and density of trees regeneration With mangrove ecosystem, tree regeneration formed by propagates growing before dropping from the parent trees, which each propagate may be lying horizontally on the sediment or standing up and covered by water during this time When the seedling falls from the parent tree, it seems to plant itself in the sediment under the parent tree, but more often it is dispersed further away by the tidal action as the method of dispersal to avoid crowding of young plants The position where propagates stranded finally will be a place for regenerated trees to develop Table 4.5 Species composition and mean density of the regenerated trees Study area Trang Trang – Ban Trang – Ban -Su Transect Density (trees/ha) Species composition 745 10Trang 685 10Trang 785 10Trang Mean 738 10Trang 780 9.27Trang + 0.73Ban 775 9.74Trang + 0.26Ban 710 9.80Trang + 0.20Su Mean 755 9.60Trang + 0.40Su 740 9.31Trang + 0.69Su 715 9.74Trang + 0.26Su 800 9.44Trang + 0.56Su Mean 752 9.50Trang + 0.50Su 15 a Species composition Survey indicated that regenerated trees in three study areas are mainly in the stage of propagates Regenerated trees’ height is differentiated clearly at height level The number of regenerated trees grows mainly regeneration of Trang under the parent trees, distributed at sea edge and dike edge There is no regeneration of Ban in plant community of Trang – Ban – Su due to high density of canopy layer trees, small seedlings, poor growth in cold weather; only grow in low salt concentrations (5-15𝑜⁄𝑜𝑜 ) On transect number 02 of plant communities of Trang – Ban and Trang – Ban - Su, the high growth and density are causes of less regenerations Clearly, most saplings in canopy layer are representing in the regenerated trees layer And there is not significant change in mangrove species-community in the future b Density In wetlands, mangrove trees have the different forms of regeneration Su and Trang regenerated by propagules beneath the parent trees, there is no regeneration of Ban Survey results on transect number 03 of plant communities of Trang – Ban – Su has the highest density of regeneration is 800 trees/ha and all three study areas, tree regeneration grows the high density inward of dike footing 16 Picture 4.3 Regeneration of Trang in plant communities of Trang-Ban-Su c Distribution of regenerated trees Table 4.6 Distribution of regenerated trees at four height levels Study areas Trang Trang – Ban Trang – Ban - Su Transect Distribution (%) ≤ 0.5 0.5 ÷≤1.0 1.0÷ 1.5 >1.5 63.5 35.6 0.9 42.7 48.6 0 73.9 25.2 0 Mean 60.0 36.5 0.3 57.4 40.5 2.1 65.7 33.7 0.6 60.9 39.1 0 Mean 61.3 37.3 0.9 66.4 31.4 2.2 70.8 28.3 0.9 75.2 24,1 0.7 Mean 70.8 27.9 1.3 17 Number of regenerated trees is mainly at height level ≤ 0.5 m, next at height level from 0.5m to 1m, and then number of regenerated trees at height level from to 1.5m is very few, but there are no regenerated trees at height level ≥ 1.5m Because regenerated trees grow beneath the under-layer plants, lack sunlight and nutrient, they only grow at the smallest height level (≤ 0.5m) Number of regenerated trees at height level ≤0.5m occupy the highest rate 70.8 % in a mixed plantation of Trang – Ban – Su 4.2.2 Impacts of some factors on regeneration mangrove species a Impacts of canopy layer Due to the dense growth of canopy layer, the regenerated trees have poor nutrition and low intensity full sunlight light to grow, the propagates not fall down directly on ground , but be held on tree-trunk or tree root, and then water swept away other places Thus, the number of regenerated trees is poor b Impacts of tidal fluctuation According to study of characteristics of tidal related to distribution and development of mangroves in Vietnam, Phan Nguyen Hong (1991) commended “without the difference in climate and soil conditions, mangroves grow better in semi-diurnal tidal than diurnal tidal” In study area, the highest tidal is 3.2m, the lowest tidal is 0.4m; the tide is rising slower than ebbing Tidal fluctuation influences the salinity of the surface and ground, which in turn affect the survival of the propagules and the distribution and development of regenerated trees In study areas with non-regular tidal regimes, plants in intertidal zones also affect the respiration, transpiration and photosynthesis process Here strong influenced by wave action, the number of regenerated trees is less near shore 18 Tidal amplitude affects on the distribution, growth of mangrove trees In study areas, the average tidal amplitude is relative high (1.5-1.8m), the highest tidal amplitude is 3.5m; the lowest tidal amplitude is 0.25m Thus, status of mangrove forests is distributed widely inland; distribution of tree regeneration concentrated on onshore and along canals and creeks c Impacts of substratum Substratum also affects regeneration of mangrove trees When propagules fall down clay and sandy clay have the ability of good growth Through survey shows substratum changes from clay and sandy clay to silt according to rules from dike edge to shore Impacts of substratum to mangrove regeneration are shown in the following table: Table 4.7 Number of regenerated trees on substratum Study areas Trang Trang - Ban Trang – Ban -Su Transect Substratum Trees/plot Clay 29 Sandy clay 27 Silt 31 Clay 48 Sandy clay 35 Silt 55 Clay 32 Clay 28 Silt 43 The above table showed that the ability of regeneration of three communities grows and develops on substratum is silt d Impacts of other factors to regeneration - Hot and humid climate, appearance frequently of thunderstorm and tropical low 19 pressure causes of collapsed trees, broken branches, buried under sand, washed seedlings away or dead trees due to bad weather - Sea-weed and marine-fouling organisms, barnacle in particular, are suggested to be an important factor affecting the survival and growth of mangrove seedlings At the edge of sea with high salinity of sea water, the regenerated trees are influenced by barnacle, caused slow development in the growth and stem diameter Barnacles grow very quickly, often make hard coat around stem, leaves and twigs Concurrently, due to high salinity of sea water, the growth of trees is poor Also, sea-weed forms a large plaque, which cover seedlings, cause for drooping of seedlings Picture 4.4 Barnacles stick on a regenerated tree - Human activities: Mostly dwellers in these study areas live on catching fish and seafood caused uprooted, falling and broken of seedlings by trampling down and exploiting clams and Vạng everyday for a living as well as grazing (ducks and buffaloes) In addition, the annual population growth, conversion of mangrove forests for agriculture expanded the 20 activities of agricultural production affect to mangroves such as rice production Shrimp aquaculture increases, replacing mangroves with ponds, has dramatically affected to mangroves On the other hand, dwellers usually impact on mangrove ecosystem without control of managers such as cutting timber, overexploitation or indiscriminate exploitation, also affect regeneration of mangrove trees Picture 4.5 Dwellers in Nam Thinh digged oysters in mangrove forest 4.3 Some solutions for sustainable development of mangroves in Tien Hai district, Thai Binh province 4.3.1 Afforestation - Promote afforestation and reforestation activities, priority the predominant species, some species with advantage of cold tolerance as Ban Myanmar or some species reduce soil erosion - Expanding zones of alluvial ground and hybridize some new species in other places to to enrich the forest and species diversity 21 - Mangrove forests are extremely productive ecosystems that provide numerous good and services both to marine environment and people: sea dike protection, preventation form natural disaster Thus, the Managers should guide planting trees, strictly control in selecting the good quality mangrove species to plant and directly supervise in afforestation b a c d Picture 4.6 (a) Flower of Sonneratiasp., (b) Fruit of Sonneratiasp.; (c) and (d) Sonneratiasp 22 4.3.2 Forest protection Depend on the real situation of afforestation in local, forestry scientists should propose some solutions for reduction of barnacle infestation to the regenerated trees; should scientific research to create biological products to exterminate barnacle, harmless to environment Also, forest protection combined with the interests of the mass in afforestation and propaganda in forest protection legislation for local people and in school 4.3.3 Policies in forest management and protection - Identifying the needs of people in forest conservation, restoration and management to build up plans of management which work for the good of the community - Scientists should research and technology transfer to help dwellers in using effective the models production in agriculture, forestry and fisheries combined sustainable methods in order to improve human’s life as well as reducing pressures on mangrove ecosystems - Strengthen the role of management, inspection and forces to patrol the forest in order to have a thorough grasp of the facts of mangrove land use in aquaculture land, prevent from overexploitation affecting to natural regenerating development, promptly stop cases of adverse impacts on mangrove forest 23 V CONCLUSION 5.1 Characteristics of canopy layer Composition values of Trang species in canopy layers in all three mangrove communities always revealed the highest values (8.75 ÷ 10) Next, Su get values of 0.47 ÷ 0.97 While Ban get the lowest values ( 0.12 ÷ 0.83) Most mangrove communities have the great density, typically the density of the pure plantation of Trang is 8,850 trees/ha Mangrove communities grow more than 50% good quality trees The canopy cover of the pure plantation of Trang is 0.92 while the canopy cover of a mixed plantation of Trang – Ban is 0.83; the canopy cover of a mixed plantation of Trang – Ban – Su is 0.9 In addition, a mixed plantation of Trang – Ban grows the largest diameter at breast-height and height of mangrove trees 5.2 Characteristics of regeneration Regeneration of Trang is the largest in species composition in each community Distribution of regeneration is at sea edge and dike edge In the regeneration layer, the height of trees is clearly different height level Most regenerated trees mainly grow at height level ≤ 0.5 meter and concentrated distribute on shore and dike edge 5.3 Some ecological factors affect to regeneration By analyzing the results, some main factors affected the distribution and the ability of regeneration mangrove trees such as canopy layer trees, tidal fluctuation and substratum In addition to climate, sea-weed, marine-fouling organisms and human According to the research results, propose some solutions to sustainable management such as afforestation, forest protection and policies in management and protection 24 REFERENCES Chung, N.V (Master thesis, 2014), Forest structure and regeneration characteristics of some mangrove communities in Xuan Thuy National Park, Nam Dinh province Dinh H.T (student thesis, 2011) Status of mangrove forest and solutions in restoration and development in Nghia Hung district, Nam Dinh province Hong, P.N., San, H.T (1993), Mangroves of Vietnam , IUCN, Bangkok Hong, P.N., (2005), Roles of mangrove forest in protecting coastal areas Li, S.W., Maxwell, G.S., (2006), Barnacle infestation on the bark of Kandelia candel (L.) Druce and Aegiceras corniculatum (L.) Blanco, Electronic Journal Marchel Marchand (2008), Report “ Mangroves restoration in Vietnam” Ministry of Agriculture and Rural Development Project “Restoration and development mangrove forest in coastal, stage 2008-2015” P B Tomlinson (1986), The botany of Mangroves To P.T.T (Student thesis,2013), Solutions in mangrove forest sustainable management in Bai Tu Long National Park, Van Don district, Quang Ninh province 25