INTRODUCTION
Mangrove forests are vital to coastal ecosystems, as they stabilize sediments with their tangled root systems, preventing erosion from waves and storms They also play a crucial role in maintaining water quality and reducing pollution Additionally, mangroves are biodiversity hotspots, supporting a diverse range of marine creatures, birds, mammals, and reptiles.
Rapid population growth, expanding aquaculture activities, land reclamation for rice cultivation, and rapid urban infrastructure development have led to significant degradation of Vietnam's mangrove ecosystems Between 1943 and 1999, the mangrove forest area shrank by 62%, from 409,000 hectares to just 155,000 hectares, primarily due to war destruction and the expansion of large-scale shrimp farms.
Dong Long Commune belongs to Tien Hai District It has a total area of 7.83 km 2 and has a total population of 5010 people (Ministry of Information & Communications,
Dong Long Commune, one of four communes in Tien Hai District with significant mangrove forests, has experienced substantial environmental changes over the years Historically, extensive shrimp farming led to a reduction and degradation of mangrove areas, causing coastal dyke erosion and breaches, notably during the storm of 1996 To address these issues, projects like Program 327 and international support from the Red Cross in Denmark have been implemented to restore mangrove ecosystems, planting species such as Kandella, Rhizophora, and Sonneratia across hectares of land These initiatives not only bolster coastal dyke protection but also enhance local livelihoods through mangrove cultivation and seafood harvesting, leading to increased biodiversity and a healthier marine environment However, the ongoing impacts of climate change threaten to further complicate these efforts, underscoring the need for sustained conservation and adaptation strategies.
2 increases and sea level rises…, the mangrove forest area in Thai Binh, especially in Dong Long, needs to be protected and developed more and more
To effectively support the restoration and development of mangrove forests, it is essential to analyze the composition of plant species, their associations, and community structures, as well as their distribution within the mangrove ecosystem Understanding these factors provides insights into changes in forest structure and the processes of mangrove succession This foundational knowledge serves as a key technical basis for developing sustainable mangrove communities and implementing successful conservation strategies.
Mangrove forest in the world:
Mangrove forests distribute mainly on the equator and 2 sides tropical hermisphere However, some species expand up to 32 o 22 ’ North (Bermuda) such as Rhizophora stylosa, Kandelia candel, and Bruguiera gymnorrhiza (Le V.H, 2005)
Extensive global research has been conducted on mangrove forests, highlighting their ecological significance P.V Richard has contributed numerous studies focusing on mangrove ecosystems across South America, Central Africa, and Southeast Asia His research particularly emphasizes tropical rainforests, exploring landforms, structural features, natural components, and environmental conditions such as soil and climate that influence these vital habitats.
Rabinowitz (1975) observed that the number of young dominant mangrove species during low tide is higher than in highland areas, indicating the importance of dispersal and regeneration in these zones He noted that propagule mortality is inversely proportional to their mass, with smaller propagules experiencing higher mortality rates Once seedlings become established, their growth is typically hindered beneath the shade of tall mangrove trees, emphasizing the significance of open, sunlit areas for optimal mangrove development.
Kasawani et al (2007) conducted a comprehensive study on the forest structure, diversity index, and biomass of mangrove forests in Tok Bali, Kelantan, Malaysia, aiming to inform effective recovery and management strategies Their findings revealed that Sonneratia alba is the dominant mangrove species, with over 73 trees recorded per transect line, highlighting its significant role in the local mangrove ecosystem.
Suwa et al (2009) studied the biomass and tree height structure of a subtropical mangrove forest along the Okukubiriver in Okinawa Island, Japan Their research revealed that reductions in biomass and tree height do not necessarily indicate declines in leaf photosynthesis or overall mangrove tree development This highlights the importance of considering multiple ecological factors when assessing the health and growth of mangrove ecosystems.
Vietnam's tropical climate provides ideal conditions for mangrove forest development, contributing to its rich coastal biodiversity Historically, Vietnam boasted approximately 400,000 hectares of mangrove forests before 1943; however, by 1975, this area had dwindled to just 185,877 hectares due to factors such as war, mining activities, and unsustainable forest management practices.
Phan N.H (1999) documented the plant species composition of Vietnam’s mangrove ecosystems, identifying 77 mangrove species across two environmental groups with diverse life forms The "true" mangrove group (Group I) comprises 35 species from 20 genera and 16 families, while the secondary or "joiner" species (Group II) includes 42 species from 36 genera and 16 families, typically found in secondary forests and highlands Additionally, Phan Nguyen Hong was the pioneering Vietnamese scientist to research the geographic distribution and succession of mangrove communities, revealing that Vietnam hosts 45 mangrove forest communities and 6 populations spread across various regions This comprehensive study enhances understanding of Vietnam’s mangrove biodiversity and ecological structure, crucial for conservation efforts.
Recent research on Vietnam's mangrove forests highlights key findings regarding growth patterns and planting practices Vu D.T et al (2003) conducted studies across three different age groups in Giao Lac, Giao Thuy, and Nam Dinh, revealing that Kandelia mangroves aged between 4 to 6 years demonstrate optimal growth when planted at a spacing of 0.7 x 0.7 meters This planting density results in improved tree diameter and height, emphasizing the importance of appropriate management practices for sustainable mangrove forest development in Vietnam.
Dao V.T et al (2005) conducted a comprehensive study on the characteristics of mangrove plant communities in Dien Chau, Nghe An They identified a total of 40 mangrove species across 37 genera, representing 24 vascular plant families in the study area This research provides valuable insights into the biodiversity and composition of mangrove ecosystems in the region.
4 mentioned some species that participate in mangrove forest composition in Dien Chau, and divided them into 8 typical species communities with high value in the study area
Hoang V.T (2005) studied the structure of mangroves and the relationship between vegetation distribution and tidal patterns in Ca Mau mangrove forests He concluded that the area comprises 12 distinct mangrove states with 72 species across 40 families The true mangroves consist of 23 species from 12 families, while the tree participation group includes 49 species from 28 families Dominant species in the region are Sonneratia alba and Avicennia officinalis, with Rhizophora forests covering the largest area.
Recent global climate change highlights the urgent need for forest ecosystem research, particularly in riparian and coastal areas Mangrove ecosystems, as vital components of these environments, are essential for conservation, restoration, and sustainable use Studying mangrove plant communities provides crucial insights into their structure and ecological functions, which are vital for effective management Since mangrove forests undergo constant succession and change, understanding their characteristics is both scientifically important and practically significant Therefore, researching the plant communities of mangrove forests in Dong Long Commune, Tien Hai District, Thai Binh Province, offers valuable information for conservation efforts and ecosystem management.
GOALS AND SPECIFIC OBJECTIVES
Goal
To provide the scientific basic for usage, conservation and development of mangrove forest resources in Dong Long, Tien Hai, Thai Binh Province.
Specific objectives
- Determine the species composition of vascular plants and their distribution among communities of terrestrial and intertidal zones in the study area;
- Identify assemblages, plant communities, and their distribution in mangrove forests in Dong Long;
- Give a prediction about plant succession in the study area to determine whether mangrove vegetation will reach to the sea or not
STUDY SITE AND METHODS
Study site
Dong Long Commune is located in Tien Hai District, Thai Binh Province It is far from Tien Hai Town about 10km Geographical coordinate: 20 o 26’55’’ North latitude;
The East borders with sea
The West borders with Dong Xuyen and Dong Tra Commune
The South borders with Dong Hoang Commune
The North borders with Dong Hai Commune
Figure 3.1 Study site: Dong Long Commune, Tien Hai District, Thai Binh Province
Dong Long Commune covers a total area of 7.83 km 2 The population in 1999 was
5010 people, with a population density of 640 people per km 2 (Wikipedia) Dong Long is located in a tropical mooson climate However, Dong Long is also affected by coastal
The region has a coastal climate characterized by an annual average temperature of 23-24°C, with highs reaching up to 39°C It receives between 1,500 to 2,000 mm of rainfall annually, mostly occurring in summer, which accounts for approximately 80% of the yearly precipitation During the summer months, daily rainfall can range from 200 to 350 mm The dry season spans from October to March, contributing only about 20% of the annual rainfall Humidity levels fluctuate between 82% and 90%, with southeast winds prevailing in summer at speeds of 2 to 5 m/sec The area experiences storms from June to October, predominantly in August, with 4 to 6 storms annually that can have wind forces of 8 to 11, often causing significant damage to agriculture and local communities.
Methods
During a month-long survey in Dong Long commune, I conducted a comprehensive field study and selected three representative survey lines Each survey line was carefully designated to correspond with a specific plant community or assemblage, enabling an in-depth analysis of local vegetation patterns and biodiversity.
In each community, a representative area was selected to establish survey lines following the methodology of Aksornkoae and Kongsangchai (1987) Each survey line was positioned perpendicular to the sea dike, extending from the shoreline inland This systematic approach ensures accurate data collection along a consistent transect from the sea to the dike, providing valuable insights into coastal environmental conditions.
Set up standard plots on survey line
In the study, three typical locations were selected along each survey line, positioned approximately 50m, 150m, and 250m from the sea to the dike, with corresponding plots designated as Plot 03, Plot 02, and Plot 01, each covering an area of 500 m² (Nguyen V.C., 2014) The plots were precisely established using tape and right-angle measurements to ensure accuracy Boundaries were marked with four wooden stakes at each corner, and a cord was stretched around the stakes to clearly delineate each plot boundary.
Figure 3.2: S tandard plots are set up on survey line
In each plant community I set up 3 plots and determined the species component, the number of each species and total number of trees The information was recorded:
Number of standard plots, the area of survey plots, date of investigation, investigator, distance to edge (m)…
To effectively assess the vegetation, conduct detailed measurements and classifications of all wood trees, shrubs, and grasses within the surveyed plots Record every tree species and collect specimens of unidentified trees for further investigation Measure tree density by counting the number of trees per plot, and record individual tree heights, canopy heights, and canopy diameters, focusing on wood trees with a diameter at breast height (D1.3) of 3 cm or greater Document the precise location of each tree within the plots to facilitate comprehensive analysis of forest structure and composition.
This article focuses on selecting a typical forest strip for detailed analysis, with each strip measuring 10m in depth and 25m in length, parallel to the seaside The profile diagram of the forest strip is created using the established method outlined by Richards P.W and Davis T.A.W (1933-1934), ensuring an accurate representation of the forest's vertical structure These standardized measurements and methods facilitate consistent data collection and analysis across different forest strips for ecological studies and resource management.
Profile diagram is drawn on paper; it is conducted with measuring trees and drawn one by one
Standing profile: draw the near trees first and the far trees after, the trees in front are drawn solid lines and the trees in behind are drawn disjointed lines
Cross profile: draw tree canopy on all plot area, the highest trees are drawnsolid lines and shorter trees are drawn disjointed lines
To create an accurate profile diagram, it is essential to measure the tree index, including tree height and canopy dimensions in both North-South and East-West directions Additionally, record the coordinates of each tree by measuring the distance between stumps on both sides of the plot and note the shape of each tree The tree names should be clearly labeled on the profile diagram, with attention to any abbreviations used for tree names.
Take photograph and collect necessary specimens in investigation process in order to analysize and assess scientific name
+ Statistical table about components and species compositions (following to Nguyen N.T,
Assessing the scientific name of the plant involves morphological comparisons between collected specimens and authoritative references such as "Vegetation of Vietnam" by Pham H.H (1999-2000), "Forest Tree Names of Vietnam" by Vu V.D (1996), and "Plants in Mangroves of Vietnam" by Nguyen H.T (1996) These comparative analyses ensure accurate identification and classification of the plant species.
Sort tree species in family order according to the classification system of Takhtajan
Determine assemblages and communities in the study area
Analyze and evaluate the data obtained, compare with the published documents
Mangrove species are classified into three main groups: True mangrove species (MS), which are obligate and specialized to live in saline coastal environments; Mangrove associated species (MAS), which depend on mangrove ecosystems but can also thrive outside them; and Immigrating local species (ILS), comprising species that have recently migrated into mangrove areas This classification, based on Nguyen N.T et al (2001), provides a comprehensive understanding of mangrove biodiversity and ecological dynamics.
+ Determine the distribution of mangrove vegetation following to 5 main groups: regular intertidal zone, irregular intertidal zone, sands sludge formation and improvements,
10 improvement sand area less tidal and coastal shrimp farms, road and sea dike based on separation of Phan K.L and Nguyen T.H (1998)
+ Analyze data by excel 7.0 software
Determine coefficient composition of each species calculated by:
With: K is coefficient composition n is the number of individual species in the study area
N is total individual species in communities
From that give the composition formula of each
⁄ = With: N: is number of individual species or total individual species in standard plot S: is area of plot (m 2 )
3.2.2.3 Predict Plant succession in the study area
Predicting plant succession in the study area was assessed based on Vu T.T (2000) Based on these results from plant composition, distribution, communities… will predict the plant succession in study area
RESULTS AND DISCUSSIONS
Species composition of vascular plants and their distribution
The intertidal zone along the coast is characterized by its swampy, expansive, and silty terrain, yet it lacks native mangrove forests Key factors preventing the development of mangrove forests in these areas include monsoons and storms, which disrupt the establishment and growth of these ecosystems (P.N Hong and H.T San, 1993).
Through investigating and interviewing local people I saw that the mangrove forest in Dong Long is forest planting For a long time, coastal people here planted stands of
Sonnaeratia, Kandelia candel, Aegiceras corniculatumand Acanthus ebrateatusto protect dykes, houses and farms After a few years these mangrove plants grow and regenerate naturally and quickly in the intertidal zone
4.1.1 Species composition of vascular plants in Dong Long commune
The research results have identified 51 species of plants; belonging to 49 genera, 13 families of 2 phyla: Polypodiophyta, Magnoliophyta The research result is presented in appendix 01
Species composition of mangrove appendix shows that MS group includes 7 species, which belong to 6 plant families; accounting for 13.7% of total species MAS group includes
15 species, which belong to 14 plant families; accounting for 29.4% of total species Remaining is 29 immigrant local species which belong to 10 families, accounting for 56.9% of total species
Dong Long's mangrove species composition is less diverse compared to Phan N.H's 1999 plant list, which documented 106 mangrove and associated species Specifically, Dong Long hosts 51 out of the 106 species, representing approximately 48.1% of Vietnam's total mangrove species, excluding immigrant local species.
Based on the criteria established by Pham Nhat et al (2003) and FAO (2007), the mangrove forest in Dong Long exhibits low species diversity, with only 1 to 3 mangrove species present Generally, a mangrove forest with more than 10 species is considered to have high diversity Therefore, it can be concluded that the mangrove plants in Dong Long have low biodiversity.
12 less diverse In there, 7 main mangrove species arranged in descending order of quantity are
Sonneratia caseolaris (Bần chua), Kandelia candel (Trang), Aegiceras corniculatum (Sú),
Acanthus ebrateatus (Ô rô), Acrostichum aureum (Ráng đại), Excoecaria agallocha (Giá),
Rhizophora stylosa (Đước vòi) Sonneratia caseolaris, Kandelia candel, Aegiceras corniculatum, and Acanthus ebrateatusare 4 typical species with high quantity and belong to
Table 4.1 True mangrove species in 3 lines
Survey lines Line 1 Line 2 Line 3
Note: 0: absent; +rare; ++ average; +++ abundant
Analysis of Table 4.1 indicates that Sonneratia caseolaris, Kandelia candel, and Acanthus ebrateatus are the species consistently found across all three sampling lines, demonstrating their adaptability to the local environment Aegiceras corniculatum appears in two lines, further highlighting its resilience In contrast, Rhizophora stylosa is only present in a single line with a solitary tree, suggesting limited distribution in the area These findings confirm that Sonneratia caseolaris, Kandelia candel, Acanthus ebrateatus, and Aegiceras corniculatum are the key species well-adapted to the natural conditions in Dong Long commune.
4.1.2 Diversity of flora in Dong Long
Dong Long's mangrove ecosystem comprises not only true mangrove species but also associated and immigrant local species, resulting in a diverse environment with various structures and life forms According to the Ministry of Agriculture and Rural Development (2000) in "Forest Tree Names of Vietnam," this biodiversity enhances the ecological richness and resilience of the mangrove forest.
Hoang Chung (1980) about plant’s life form, I divided them into 4 life forms: Wood, Shurb, Herb and Liana The research results are shown in table 4.2
Table 4.2 The life form of mangrove vegetation in Dong Long
The table indicates that herbs represent the most prevalent life form, accounting for 43.1% of the total species, with the dominant species belonging to the Asteraceae and Amaryllidaceae families commonly found along dyke edges, coastal shrimp farms, and roads Shrubs make up 31.4% of the species, with key species including Aegiceras corniculatum, Acanthus ebrateatus, Clerodendrum inerme, and several from the Solanaceae family.
Wood life forms account for 21.6% after Herb and Shrub group and main species belong to True mangrove species as Sonneratia caseolaris, Kandelia candel, Excoecaria agallocha
(Giá) and Mangrove associated species like Hibiscus tilliaceus (Tra làm chiếu) Liana just accounts for 3.9% includes Ipomaea pes carpae and Canavalia lineate
4.1.3 The valuable uses ofvegetation in Dong Long
Research in Dong Long has revealed the presence of 50 mangrove species, each with valuable applications including medicinal uses, food, timber and firewood, bonsai cultivation, and production of attar.
Table 4.3 The valuable uses of vegetation in Dong Long
Tamin, Attar (tinh dầu), dye (thuốc nhuộm) A
Note: Total does not equal 51 species because one species can have many valuable uses M: Medical; TF: Timber, firewood; B: Bonsai; F: Food; A: Attar; T: Toxic; D: Different
In Dong Long commune, nearly 86.3% of local plants possess medicinal properties, primarily comprising herbs and shrubs that thrive along dykes and highland areas Additionally, plants used for bonsai cultivation and food purposes make up 21.6% of the total, while those valued for timber and firewood represent 17.6% Other uses of plants in the region account for approximately 6% to 12%, highlighting the diverse utilitarian significance of the local flora.
4.1.4 Distribution of vegetation in Dong Long
Research findings from Appendix 01 indicate that the distribution of vascular plants in Dong Long commune is categorized into five main groups: the regular intertidal zone, irregular intertidal zone, areas with sands sludge formation and improvements, less tidal improvement sand areas, and coastal shrimp farms along with roads and sea dikes.
Table 4.4 Distribution of vegetation in Dong Long commune
Sands sludge formation and improvements 3 4 7.8
Improvement sand area less tidal 4 12 23.5
Coastal shrimp farms, road and sea dike 5 45 88.2
Note: Total does not equal 51 species because one species can live in many regions
Vegetation in Dong Long is primarily distributed along coastal shrimp farms, roads, and sea dikes, accounting for 88.2% of the area, with the dominant species being immigrant local species The irregular intertidal zones and island areas with less tidal influence make up 19.6% and 23.5%, respectively Additionally, low-density vegetation is found in sand sludge formations and areas of shoreline improvement, representing 7.8% and 9.8% The main mangrove species in these regions include true mangroves such as Sonneratia caseolaris and Kandelia candel, highlighting the area's diverse coastal vegetation.
Acanthus ebrateatus and Aegiceras corniculatum.
Assemblages and mangrove forest communities and their distribution in Dong Long 15 1 Species density
To determine mangrove communities at Dong Long commune, I conducted an investigation species composition of 3 lines that is perpendicular to seaside The results were showed in table 4.5
Table 4.5 Composition some mangrove lines follow to plots
Line Plot Species Rate Composition formula
Average 6.2Ac + 2.9Kc + 2Ae+ 0.22Sc
Note: Ac: Aegiceras corniculatum; Ae: Acanthus ebrateatus; Sc: Sonneratia caseolaris;
Based on data composition in 3 line surveys, I determined 3 mangrove communities corresponding with the lines 1, 2, 3 are:
- Line 1: Sonneratia caseolaris - Kandelia candel - Acanthus ebrateatus
- Line 2:Acanthus ebrateatus - Aegiceras corniculatum - Sonneratia caseolaris
- Line 3:Aegiceras corniculatum - Kandelia candel - Acanthus ebrateatus - Sonneratia caseolaris
Table 4.6 Mangrove plant communities in 3 lines
Communities Sc- Kc- Aelines on first transect line and the results show that there are
3 species Sonneratia caseolaris, Kandelia candel and Acanthus ebrateatus Sonneratia caseolarisis dominant species, accounting for 7.6 ÷ 10, Kandelia candel accounting for 1.2 ÷
2.4 and Acanthus ebrateatusaccounting for 0.4 Moreover, plot 1 just only apprear Sonneratia caseolariswithout having the appearance of the other species Plot 2 has the the appearance of Sonneratia caseolaris, Kandelia candel and dominant species is also Sonneratia caseolaris with 7.6, Acanthus ebrateatus is absent in this plot
The second line includes 3 species Acanthus ebrateatus, Aegiceras corniculatum, Sonneratia caseolarisand Acanthus ebrateatus is dominant species accounting for 5.5 ÷ 8.9, Aegiceras corniculatumaccounts for 2.3 ÷ 8.8 and Sonneratia caseolaris has low rate with
1.1 ÷ 2.3 Plot 4 appears 2 species are Aegiceras corniculatumand Sonneratia caseolariswithout having Acanthus ebrateatus and in this plot Aegiceras corniculatumis dominant accounting for 8.8 Plot 6 appears Acanthus ebrateatus and Sonneratia caseolaris
18 without appearing Aegiceras corniculatumand the dominant species isAcanthus ebrateatusaccounting for 8.9
The third line features the highest species diversity, with four key species: Aegiceras corniculatum, Acanthus ebrateatus, Sonneratia caseolaris, and Kandelia candel Among these, Aegiceras corniculatum is the dominant species, representing approximately 3.2% to 8.6% of the area, while Kandelia candel accounts for about 1.1% to 6.6% Acanthus ebrateatus makes up around 2%, and Sonneratia caseolaris has a low occurrence rate of 0.16% to 0.3% Notably, only Plot 9 includes all four species, whereas Plots 7 and 8 contain only three species: Aegiceras corniculatum, Kandelia candel, and Sonneratia caseolaris, indicating varying species distribution across different plots.
Forest density is a crucial factor influencing forest formation and the potential habitat for various species It plays a vital role in shaping site conditions and overall ecosystem health Throughout the processes of forest growth and development, tree density is a dynamic variable that constantly evolves, impacting the structure and sustainability of the forest ecosystem Understanding and managing forest density is essential for promoting healthy forest development and ensuring optimal living space potential.
Through investigation on structure density of mangroves in research area, the results are summarized in the table 4.7
Table 4.7: Tree density in communities, assemblages in Dong Long commune
From statistic table of mangrove forest density, we know that:
The Community Ac-Kc-Ae-Sc (Sú- Trang- Bần chua) exhibits a high tree density of 5,193 trees per hectare, predominantly consisting of Aegiceras corniculatum (Sú), which forms dense, thick stems, leading to a greater number of trees compared to other plots In contrast, the communities Sc-Kc-Ae (Bần chua- Trang- Ô rô) and plot 06 within the Ae-Ac-Sc community (Ô rô- Sú- Bần chua) display lower tree densities, dominated by Sonneratia caseolaris (Bần chua) This dominance by Sonneratia caseolaris, the largest mangrove species in the area, limits the presence of other species due to its extensive size and significant space and nutrient requirements.
The research concentrates on stratified structure with forest separation into different tree layers following to vertical section and cross section
In three mangrove communities in Dong Long Commune, tree component participating in mangrove forest is less, species composition is relatively simple, so stratified structure in here is also simple
Sonneratia caseolaris - Kandelia candel - Acanthus ebrateatus community: A stratified property of this community is quite clear Community includes 2 main species are
Sonneratia caseolaris and Kandelia candel and the structure includes 2 distinctive layers
Sonneratia caseolaris represents the tallest and most prominent tree species within the mangrove forest, reaching an average height of 7.8 meters and a diameter of 28 centimeters, establishing it as the uppermost layer in this ecosystem In contrast, Kandelia candelis occupies the second layer, with an average height of 1.6 meters and a diameter of 4 centimeters, playing a secondary role in the mangrove community structure.
Figure 4.1 Vertical profile in line 1
Figure 4.2 Cross profile in line 1
Acanthus ebrateatus - Aegiceras corniculatum - Sonneratia caseolariscommunity: A stratified property of this community isclear Community includes 2 main species are
Sonneratia caseolaris, Acanthus ebrateatus and Aegiceras corniculatum High layer is
Sonneratia caseolaris, average height is 10m and average diameter is 25.5cm The second
21 layer includes Acanthus ebrateatus and Aegiceras corniculatum They belong to shrub and have nearly same in height about 1.2m
Figure 4.3 Vertical profile in line 2
Figure 4.4 Cross profile in line 2
The mangrove community comprising Aegiceras corniculatum, Kandelia candel, Acanthus ebrateatus, and Sonneratia caseolaris exhibits a clear stratified structure This community consists of three distinct layers, with Sonneratia caseolaris forming the uppermost layer, reaching an average height of 13.3 meters and a diameter of 39 centimeters The second layer is dominated by Kandelia candel, which has an average height that distinguishes it within the community.
3.9m and average diameter is 9.6cm The third layer includes Aegiceras corniculatumand Acanthus ebrateatus, both of them have nearly same in average height are 1.5m
Figure 4.5 Vertical profile in line 3
Figure 4.6 Cross profile in line 3
Dong Long commune features a true mangrove community characterized by a simple species composition, primarily dominated by key species such as Sonneratia caseolaris, Kandelia candel, Acanthus ebrateatus, and Aegiceras This dominant mangrove group plays a vital role in maintaining the ecological balance of the coastal ecosystem Understanding these characteristic species is essential for conservation efforts and sustainable management of mangrove habitats in the area.
23 corniculatum Especially Sonneratia caseolaris is dominant species appearing in 3 communities and 9 plots
4.2.3 Distribution of mangrove forest communities in Dong Long
The study identified three distinct mangrove communities along three survey lines, including Sonneratia caseolaris - Kandelia candel - Acanthus ebrateatus, Acanthus ebrateatus - Aegiceras corniculatum - Sonneratia caseolaris, and Aegiceras corniculatum - Kandelia candel - Acanthus ebrateatus - Sonneratia caseolaris The Sonneratia caseolaris - Kandelia candel - Acanthus ebrateatus community is the most prevalent in Dong Long Commune, primarily distributed along line 01 near the Tra Ly River Additionally, the Aegiceras corniculatum - Kandelia candel - Acanthus ebrateatus - Sonneratia caseolaris community borders the Dong Hoang Commune, with the third community situated between these two.
Predict plant succession in Dong Long
Plant succession is the natural process through which one ecosystem replaces another over time, shaping the landscape's ecological dynamics Among various types, mangrove succession in tropical estuaries, such as the southern Vu Trung Tang region, exemplifies primary succession, marking the initial establishment and development of mangrove ecosystems in these environments This process is crucial for understanding coastal habitat regeneration and biodiversity conservation in tropical estuarine regions.
The distribution of mangrove species varies significantly across different coastal zones, with species composition and abundance differing from seaside to dike areas Initially, pioneer mangrove species establish at low densities in the estuarine regions, gradually developing into dense forested areas within the regular intertidal zone As the environment shifts towards irregular intertidal zones and dike edges, mangrove density tends to decrease, demonstrating an uneven distribution pattern across the coastal gradient.
Table 4.8 Species compositions in three communities
Community Plots Species Number of trees/plot Total
Looking at the table above, we can divide succession into 3 stages: pioneer, mixed community and degradation In estuary, slush is not suitable for life of many tree species;
Sonneratia caseolaris and Aegiceras corniculatum are the sole pioneer species thriving in this environment, owing to their ability to withstand high salinity, strong waves, and wind Their extensive root systems effectively trap and collect sediments, including organic matter from decaying plant material, which leads to the soil becoming more compact and stable over time As sediment accumulation continues, it promotes habitat development and supports further ecological succession in the area.
Mangroves, particularly 25 species, can invade and outcompete early colonizers like Aegiceras corniculatum, Kandelia candel, and Acanthus ebrateatus, leading to the development of mixed mangrove communities These pioneer species do not compete with each other initially and tend to migrate seaward as the land elevates and consolidates Over time, this process results in the degradation of the mixed forest, as pioneer species move to new areas, creating a dynamic and evolving mangrove ecosystem Additionally, environmental conditions in these areas support the growth of other species such as Cyperus malaccensis and Acanthus ebrateatus, contributing to the biodiversity of mangrove forests.
Future predictions indicate that the intertidal land will gradually expand until it is fully transformed, with pioneer species like Sonneratia caseolaris and Aegiceras corniculatum continuing to migrate seaward As the land builds up towards the dike, terrestrial vegetation begins to establish, signaling the ongoing succession from intertidal to terrestrial ecosystems This process highlights the dynamic nature of coastal land development and the critical role of pioneer species in ecosystem restoration.
Figure 4.7 Primary succession of mangrove vegetation in Dong Long Commune
CONCLUSION AND RECOMMENDATION
Conclusion
The study has identified 51 vacuolar plant species across 49 genera and 13 families, distributed within two major phyla, Polypodiophyta and Magnoliophyta Among these, seven are true mangrove species, 15 are associated mangrove species, and 29 are immigrant local species The primary mangrove species include Sonneratia caseolaris, Aegiceras corniculatum, Kandelia candel, and Acanthus ebracteatus, with Sonneratia caseolaris serving as the dominant species in the ecosystem.
Mangrove vegetation is distributed across five main locations, including the regular intertidal zone (9.8%), irregular intertidal zone (19.6%), sands sludge formation and improvement areas (7.8%), regions with improved sands and less tidal influence as well as coastal shrimp farms (23.5%), and areas along roads and sea dikes (88.2%) These distribution patterns highlight the significance of mangroves in coastal ecosystems, emphasizing their presence in varying habitat types to support biodiversity and coastal protection Understanding the spatial distribution of mangroves is crucial for effective conservation strategies and sustainable coastal management.
The study site comprises three distinct communities: Sonneratia caseolaris - Kandelia candel - Acanthus ebrateatus (Sc-Kc-Ae), Acanthus ebrateatus - Aegiceras corniculatum - Sonneratia caseolaris (Ae-Ac-Sc), and Aegiceras corniculatum - Kandelia candel - Acanthus ebrateatus - Sonneratia caseolaris (Ac-Kc-Ae-Sc) Among these, the Sc-Kc-Ae community is the most prevalent, especially distributed along Line 01.
Mangrove succession in study site is primary succession Sonneratia caseolaris and
Aegiceras corniculatum is a pioneering species that initiates ecological succession As pioneer species establish themselves, the soil becomes more compact and stable, creating favorable conditions for other plants This process leads to increased invasion and competition among various species, prompting some to migrate towards the sea and adapt to their environmental conditions.
Recommendation
Mangrove forests are vital ecosystems that play a crucial role in maintaining the health of estuary zones Therefore, studying mangrove forests is essential for understanding their ecological functions and conservation needs Continued research on species composition and community structure in areas like Dong Long Commune is necessary to enhance our knowledge and develop effective management strategies for these important habitats.
Effective management of forest structure is essential, with a focus on understanding mangrove succession to enable accurate predictions and support conservation efforts Increasing research projects on planting and protecting mangrove forests is crucial for their sustainability Additionally, providing up-to-date research equipment will enhance the efficiency of studies on mangrove ecosystems Raising awareness among local communities about the vital ecological roles of mangroves and implementing strict penalties for illegal destruction are key strategies for safeguarding these vital forests.
1 Dao V.T et al (2005) Structural characteristics of some mangrove forest communities at Dien Chau district, Nghe An province
2 FAO and Wetlands International, 2007 Mangrove Guidebook for Southeast Asia Printed by Dharmasarn Co Ltd
3 Giri, C., Ochieng, E., Tieszen, L., Zhu, Z., Singh, A., Loveland, T., Masek, J., Duke, N.,
2011 Status and distribution of mangrove forests of the world using earth observation satellite data Global Ecol Biogeogr 20(1), 154–159
4 Hoang Chung (1980) Forest tree name of Vietnam Ministry of Agriculture and Rural Development
5 Hoang V.T (2005) Research on mangrove forest structure and the relationship between mangrove plant distribution and frequent tidal mangrove in Ca Mau
6 Hoang.T.O 2008 Research on changing structure of mangrove forest following to substratum forms of brackish water in Xuan Thuy national park, Giao Thuy district, Nam Dinh province Thesis in Vietnam Forestry University
7 Nguyen H.T (1996): Ecological mangrove.Agriculture Publishing House
8 Nguyen H.T 1996 Plants in Mangroves of Vietnam National University, Hanoi
9 Nguyen N.T et al (2011) Species component and characteristics of vegetation of ecological mangrove in Phu Quoc National Park Scientific journal Can Tho university
10 Nguyen.T.T.H 2006 The characteristic of some mangrove forest communities in Giao Thuy distric, Nam dinh province Thesis in Vietnam Forestry University
11 Nguyen.V.C 2014 Research on characteristic of structure and natural regeneration of some plant community’s mangrove forest in Xuan Thuy national park, Giao Thuy district, Nam Dinh province Master’s thesis at Vietnam Forestry University
12 Pham, H.H 1999 An Illustrated Flora of Vietnam Youth Publishing House, HCM Vol I: 230-242
13 Phan B Let al (1998) Some documents about plant in wetland nature reserve at Xuan Thuy, Nam Dinh
14 Phan N.H (1999) Mangrove forest in Vietnam Agriculture Publishing House, Hanoi
15 Research on Mangrove Ecosystem Center, 2001 Biodiversity, Socioeconomic and Educational Propaganda at Coastal zones have recoverable mangrove forest in Thai Binh and Nam Dinh Hanoi
16 Thai, V.T 2000 The Ecological Tropical Forests in Viet Nam: Research on case area- Plants forest of Viet Nam Vietnam Science & Engineering Publishing House
17 UNEP, 2012 Proyecto Manglares United Nations Environment Programme http://www.pnuma.org/manglares/ (accessed 16.08.13)
18 Vien N.N (2002) Research on biomass and primary productivity of natural Avicennia albacommunities at Can Gio, Ho Chi Minh
19 Vu D.T (2003) Assessing the quality of plantation forest at Giao Lac commune, Giao Thuy, Nam Dịnh through structure and forest cover
20 Vu, T.T 2000 The Fundamental Ecology Education Publishing House
21 Vu, V D 1996 Vietnam Forest Trees Agricultural Publishing House, Hanoi
Table 01: List of vascular plants in Dong Long commune
No Vietnamese name Scientific name
1 Acrostichum aureum Ráng dại Herb 1 4,5 M
2 Acanthus ebrateatus Ô rô biển Shrub 1 1,2,3 M
3 Wedelia biflora Cúc hai hoa Herb 3 5 M
4 Eclipta alba Hassk Nhọ nồi Herb 3 5 M
5 Bidens pilosa Xuyến chi Herb 3 5 M
6 Pluchea pteropoda Sài hồ Herb 3 5 M
7 Erigeron crispus Cúc hôi Herb 3 5 M
8 Artemesa vulgaris Ngải cứu Herb 3 5 M
9 Ageratum connyzoides Cứt lợn Herb 3 5 M
10 Lactuca India L Diếp dại Herb 3 5 M
11 Pandanus odoratissimus Dứa dại biển Shrub 2 4,5 M,D,F
12 Sonneratia caseolaris Bần chua Wood 1 1,2,3 W,F
13 Terminalia catappa L Bàng biển Wood 2 4,5 B,A,W
Cà dại hoa trắng Shrub 3 5 M
15 Datura metel L Cà độc dược Shrub 3 5 M,T
16 Rubus alceaefolius Mâm xôi Shrub 3 5 M, F
17 Eleusine indica Cỏ mầm trầu Herb 2 5 M
19 Rhizophora stylosa Đước vòi Wood 1 1 W,A,M
20 Clerodendrum inerme Vạng hôi Shrub 2 4,5 F,M,D
21 Phyla nodiflora L Cở lức Herb 3 5 M
Stachytarphera jamaicensis Cỏ đuôi chuột Shrub 3 5 M,B
Clerodendrum kaempferi Mò đỏ Shrub 3 5 M
24 Premna integriflolia L Vọng cách Wood 3 5 M,W,F
25 Canavalia lineata Đậu đao biển Lianas 2 4,5 M
26 Sesbania taccada Điền thanh Shrub 3 5 M
27 Cynodon dactylon (L.) Cỏ gà Herb 2 2,4,5 M
28 Anona glabra L Na biển Wood 2 5 B,F
29 Achyranthes aspera L Cỏ xước Shrub 3 5 B,M
30 Amaranthus virdis L Rau dền cơm Herb 3 5 M,F
31 Alternanthera sessilis Rau dệu Herb 3 5 M
32 Ricinus communis L Thầu dầu tía Shrub 3 5 M,B,A
33 Phyllanthus reticulates Phèn đen Shrub 3 5 M
35 Cyperus stoloniferus Cỏ gấu biển Herb 2 2,5 M
36 Cyperus rotundus L Cỏ gấu Herb 3 2,5 M
37 Crinum asiaticum L Cây lá náng Herb 3 2,5 M
Cỏ quăn phân đôi Herb 3 2,5 M
39 Cyperus malaccenses Cói chiếu Herb 2 2 M,D
40 Ipomaea pes carpae Muống biển Lianas 2 4,5 M, F
41 Casuarina esquisetifolia Phi lao Wood 2 4,5 W,B,M
Sersuvium portulacastrum Sam biển Herb 2 4,5 M
44 Ziziphus oenoplia Táo dại Shrub 2 5 M
45 Hibiscus tilliaceus L Tra làm chiếu Wood 2 4,5 M,W,B,D
47 Portulaca oleracea L Rau sam Herb 2 4,5 F,M
49 Wikstroemia indiaca L Niệt gió Shrub 3 5 M,D,T
50 Lantana camara L Ngũ sắc Shrub 3 5 M,B
51 Centella asiatica L Rau má Herb 3 4,5 M,F
Note: Group of plant: 1- True mangrove species; 2- Mangrove associated species; 3-
Distribution: 1- Regular intertidal zone; 2- Irregular intertidal zone; 3- sands sludge formation and improvements; 4- improvement sand area less tidal and coastal shrimp farms; 5- road and sea dike
Valuable uses: M- Medicial; W- Wood; B- Bonsai; F- Food; A- Attar; T- Toxic; D-
Table 02 Species composition in line 1
Table 03 Species composition in line 2
Table 04 Species composition in line 3
Table 05 Growth index of mangrove in strip 1 belongs to line 1
No Species Direction Tree height
Table 05 Growth index of mangrove in strip 2 belongs to line 2
Table 06 Growth index of mangrove in strip 3 belongs to line 3
Note: H is tree height and h is trunk height
Acanthus ebrateatus and Aegiceras corniculatum belong to shrub, do not measure diameter of them and do not measure h of Acanthus ebrateatus.
Plate 1: Four dominant species images of mangrove in Dong Long