INTRODUCTION
Mangrove forests are among the most productive and vital ecosystems, primarily found along coastlines and offshore islands They serve as essential food sources and nurseries for many commercially significant aquatic and terrestrial species, while also stabilizing coastal lines, promoting accretion, and acting as natural barriers against storms, cyclones, and tidal surges For centuries, Vietnamese coastal communities have relied on mangroves for resources like building materials, charcoal, firewood, tannins, food, honey, and traditional medicines, supporting stable livelihoods Although Vietnam's mangrove forests are less diverse than inland tropical rainforests, they provide crucial habitats for species adapted to saline tidal environments, including numerous migratory waterfowl, terrestrial animals, and aquatic organisms such as algae, mollusks, and crustaceans like Brachyura and Decapoda.
Tien Hai district, situated approximately 23 kilometers southeast of Thai Binh province, boasts a diverse and fertile landscape formed by three major estuaries—Ba Lat River of the Red River, Tra Ly River, and Lan River—that flow into the sea These estuaries have contributed to the accretion of over 6,000 hectares of alluvial soil, creating extensive coastal wetlands rich in biodiversity The district is renowned for its vibrant flora and fauna, including the protected Tien Hai Nature Reserve, making it a vital area for ecological preservation and eco-tourism.
Mangrove ecosystems in Tien Hai play a crucial role in coastal protection against tidal waves, wind, water currents, and natural disasters However, these vital forests are increasingly threatened by climate change, human exploitation, and overuse, leading to habitat degradation, changes in species composition, and ecological imbalance Implementing afforestation, reforestation, and habitat rehabilitation strategies—especially those based on natural regeneration—is essential for maintaining ecological integrity and supporting local communities Recognizing their importance, various policies and projects have been launched in Tien Hai's coastal communes to conserve and restore mangroves Therefore, conducting research on the forest structure and regeneration characteristics in Tien Hai district, Thai Binh province, is vital for providing scientific data to guide sustainable mangrove management and rehabilitation efforts.
GOAL AND OBJECTIVES
Goals
This research aims to enhance understanding of the forest structure and regeneration characteristics of mangrove areas in Tien Hai district, Thai Binh province The findings will support the development of effective strategies for the sustainable protection and management of mangrove ecosystems in the region By analyzing these key aspects, the study seeks to propose solutions that promote the conservation and responsible development of mangrove forests Ultimately, the research contributes to ensuring the long-term health and resilience of mangrove ecosystems in Thai Binh.
Specific objectives
Specific objectives of this study are to:
Assess structure and growth characteristics of the canopy layer;
Assess growth of regenerated trees and some factors affected to regeneration;
Propose some solutions in order to rehabilitate and develop mangrove forests in sustainable ways
STUDY AREA AND METHODS
Study area
The study sites include mangrove forests and barren lands along the sea dykes of Tien Hai, spanning from Tra Ly estuary to Ba Lat estuary within the coastal communes of Nam Thinh, Nam Hung, and Dong Long These areas are chosen because they host the largest and most densely packed mangrove forests in Tien Hai, all of which are plantation forests funded through a collaboration between the Japan Red Cross Society, Tien Hai District Red Cross, and Thai Binh Province Notably, the mangroves in Nam Thinh and Nam Hung are designated as special use forests, while those in Dong Long serve as protective forests, highlighting their vital ecological functions.
Figure 3.1 Locations of study areas
Study methods
The study incorporates comprehensive data from tide tables and land use maps to analyze the project's environmental impact It includes references to relevant research documents in the study areas, supported by information from the Tien Hai Resources and Environment Department Additionally, the project benefits from collaboration with the People’s Committees of the three communes within the study regions, ensuring local insights and compliance with regional planning and conservation efforts.
Field research was conducted in three coastal communes covering a total area of 1,571.95 hectares of mangrove forest The study focused on selecting three representative communities, each with areas exceeding 100 hectares, including a 100-hectare pure mangrove plantation in Trang, Nam Thinh commune; a 157.3-hectare mixed plantation of Trang and Ban in Dong Long; and a 449.22-hectare mixed plantation of Trang, Ban, and Su in Nam Hung commune.
In each typical plant community, three transects are established parallel to the coast, extending inland from the sea edge to the dike footing Along each transect, ten randomly located 400m² (20x20m) sample plots are set up, resulting in a total of 30 plots per survey area to ensure statistical validity The study focuses on examining the characteristics of the canopy layer within these plots to gain insights into vegetation structure and diversity.
A comprehensive survey of the canopy layer trees was conducted, focusing on mangrove species identification, diameter at breast height (D1.3), tree height (Hvn), canopy diameter (Dt), and overall tree quality The collected data has been systematically recorded in a table to facilitate detailed analysis This information provides valuable insights into the growth characteristics and health status of mangrove populations, essential for effective conservation and management efforts.
Table 3.1 Field data sheet to survey the canopy layer
No Species 𝑫 𝟏.𝟑 (cm) H vn (m) D t (m) Tree quality
Canopy tree quality is categorized into three levels: Good quality trees (A) exhibit optimal growth, straight forms, and are free from disease Poor quality trees (C) display poor growth, signs of disease, and broken branches Medium quality trees (B) represent an intermediate level, with characteristics falling between those of high and low-quality trees.
In the field, forest canopy cover was estimated by randomly selecting 50 points within each plot to observe canopy types Each point was assigned a value based on visibility: 1.0 if the main foliage of the top crown was visible, 0.5 if only the canopy edge or empty space could be seen, and 0 if there was no canopy visibility The canopy cover ratio was then calculated as the mean value of these 50 points, providing an accurate measure of canopy density.
During field studies, key parameters such as species name, root collar diameter (Doo), tree height, and canopy diameter were systematically measured using standard forest survey methods Tree height was categorized into four levels: Hvn ≤ 0.5 meters, 0.5 < Hvn ≤ 1 meter, 1 < Hvn < 1.5 meters, and Hvn > 1.5 meters, facilitating comprehensive analysis of tree growth patterns.
Collected data was recorded in following table:
Table 3.2 Field data sheet to survey the regenerated trees
… c Survey some factors affect to the regenerated trees:
Several factors influence the regeneration of trees, including canopy cover, substrate quality, salinity levels, and environmental conditions such as seaweed, marine-fouling organisms, and human activities These factors were thoroughly investigated during a comprehensive field survey to understand their impact on tree regeneration in the area.
- Canopy cover was determined by estimation method
- Data of substratum and salinity was collected from Resources and Environment Department of Tien Hai
After collecting data in field work, data is analyzed and calculated by Excel software: a Characteristics of the canopy layer
- Species composition of the canopy layer
Where: K is composition coefficient of species; n is number of specific species; N is total number of species in a plot
Composition coefficient consists of both letters and numbers, in which numbers are
8 arranged and wrote from the highest number to the lowest number, and letters are the abbreviation of name of species and wrote after numbers
- Tree density of the canopy layer: N/ha = 𝑁∗10000
Where: N is total number of trees in one plot; S is plot area
- Quality of trees in the canopy layer plants: (A,B,C) % = ( Ni/N ) / 100
Where: A, B, C are quality of trees; Ni is number of trees; N is total number of trees
The growth of the canopy layer can be assessed by analyzing key parameters such as tree density, diameter at breast height, diameter at crown canopy, and tree height across different plots Calculating the mean values of these parameters provides a comprehensive understanding of forest structure, while the standard deviation and standard error indicate the variability and precision of the sample means within the population Additionally, evaluating the characteristics of regenerated trees helps to gauge forest renewal and succession dynamics, contributing to sustainable forest management strategies.
- Species composition of the regenerated trees:
Where Ki is composition coefficient of the ith species ni is total number of individuals in the ith species m is total number of individual of all species
- Tree density of the regenerated trees: N/ha = ( N * 10000) / S
Where N is total number of individual in a plot; S is plot area
- Height distribution of the regenerated trees: D i = (n i / M) / 100
Where Di is distribution of regenerated trees at height level i n i is the number of regenerated trees at height level i
M is total number of regenerated trees in a plot c Evaluate structure and regeneration of mangroves based on data collection and write report
RESULTS AND DISCUSSIONS
Characteristics of canopy layer
4.1.1 Species composition of canopy layer
Species composition is a key ecological factor used to assess biodiversity and the stability of forest ecosystems, referring to the diversity and presence of plant components within forest communities Based on the number of species and their composition, forests can be classified into pure stands or mixed stands A survey of mangrove growth revealed that the rate and quantity of each mangrove species vary within mangrove communities, as summarized in Table 4.1.
Table 4.1 Species composition of trees in canopy layers Study area Transect number Species composition
The pure plantation of Trang is experiencing strong growth and development, with high-density planting on silt soils A mixed plantation between Trang and Ban is also underway, with Trang as the dominant species, exhibiting a composition value of 9.17 to 9.55, primarily onshore Additionally, Ban is cultivated at the sea edge, contributing to the diverse coastal plantation landscape.
10 inshore at the lowest composition value of 0.45 ÷ 0.83 In addition, people usually plant
Casuarina equisetifolia near dike footing to reduce salinity in soil
In the mixed plantations of Trang – Ban – Su, Trang is the dominant species with a composition value ranging from 8.75 to 9.17, indicating its prevalence in the area Su primarily grows along the sea edges and canal areas, with composition values between 0.47 and 0.97, highlighting its shoreline adaptability Notably, Ban Myanmar reaches heights of up to 20 meters, offering advantages such as being non-deciduous during winter, possessing a broad canopy, and exhibiting high salt tolerance, making it well-suited for coastal environments.
Picture 4.1 Mangrove community of Trang – Ban – Su
Mangrove presence along transect lines is characterized by species such as Ipomoea pescaprae, Portulaca oleracea, Cynodon dactylon, and Casuarina equisetifolia, which are found at shoals and along dike footings Additionally, planting Casuarina equisetifolia and Hibiscus tiliaceus on elevated, non-tidal grounds helps promote sustainable land use and coastal stability.
4.1.2 Density of trees in canopy layer
Tree density, measured as the number of individual trees per hectare, is a crucial factor influencing forest development It significantly affects the process of forest formation, as well as the potential for growth and competition among trees within a stand Understanding tree density helps in managing forest resources effectively and promotes healthy forest ecosystems.
The survey results of mangroves density in study areas are shown in table
Table 4.2 Mean density of trees in canopy layer at the study area
Tree density Individual/plot Individual/ha
Survey results of the canopy layer's tree density in the study areas indicate that pure plantations in Trang have the highest mean density of 7,650 trees per hectare, with trees predominantly growing in height Field surveys revealed that each tree in Trang, measuring one foot in height, develops 2 to 3 branches that grow independently within dense plots, contributing to the overall high tree density in the area.
Picture 4.2 Division of branches of Trang
The mangrove community in Trang – Ban exhibits the lowest density among studied areas, primarily due to Ban's dominant growth of large-diameter mangrove trees at breast height This extensive growth limits the emergence of other species and monopolizes vital nutrients, thereby influencing the overall biodiversity and density of the mangrove ecosystem.
Tree density within the same species is influenced not only by overall species growth but also by the stages of forest development As forests age, natural selection processes lead to a decrease in tree density, with older forests typically exhibiting fewer trees Understanding these dynamics is essential for forest management and conservation strategies.
Canopy cover is a crucial structural indicator of forest health, representing the extent of forest coverage on the soil surface and influencing seedling regeneration, growth, and development by affecting available light The study revealed that pure Trang plantations have the highest canopy cover at 0.92, indicating dense forest coverage Mixed plantations, such as Trang – Ban with a canopy cover of 0.83 and Trang – Ban – Su with 0.90, show slightly reduced coverage but still maintain significant forest presence These findings highlight the importance of canopy cover in assessing forest status and regeneration potential.
4.1.4 Characteristics of the growth of mangroves
Studying the growth in height and diameter of mangrove species helps identify their growth stages, enabling the selection of appropriate silvicultural measures to optimize mangrove yields Understanding these growth stages also provides insights into the developmental changes within mangrove communities The growth characteristics of mangrove populations in the study areas are detailed in the table, highlighting key metrics essential for effective mangrove forest management and conservation.
Table 4.3 Growth parameter of trees in canopy layer 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
The growth of plant communities in the study areas is characterized by measurements of diameter at breast height (DBH), height, and canopy diameter, with each community exhibiting distinct growth patterns Both Trang and Trang-Ban communities demonstrate equal growth potential In pure Trang plantations, the average growth of mangrove species shows a DBH of 4.3 meters, a height of 2.2 meters, and a canopy diameter of 1.3 meters Mixed plantations of Trang exhibit slightly lower average growth metrics, with a DBH of 4.0 meters, a height of 2.5 meters, and a canopy diameter of 1.3 meters Conversely, the Trang-Ban mixed plantation achieves the highest growth among the studied communities, with a DBH of 4.7 meters, a height of 2.8 meters, and a canopy diameter of 1.6 meters.
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
TrangTrang - BanTrang - Ban - Su
Plant height and canopy development are closely related, with taller plants typically exhibiting increased diameter at breast height (DBH) The Trang-Ban plant community demonstrates the most substantial growth in both height and DBH, indicating vigorous development In contrast, the Trang-Ban-Su community shows the lowest levels of growth in these parameters, reflecting differences in ecological conditions and growth potential among the plant communities.
Table 4.4 presents the quality distribution of trees in the canopy layer across different plantations In pure plantations of Trang, 53% of trees are classified as good quality, 36% as medium, and 11% as bad quality Mixed plantations of Trang – Ban show a decline in good quality trees to 35%, with bad quality trees comprising 17% Conversely, the combined Trang – Ban – Su plantation exhibits the highest proportion of good quality trees at 55%, with bad quality trees at 13%, indicating improved tree quality in mixed plantations with more species.
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
Survey results indicate that mangrove forests in the study areas are still developing Variations in forest density are primarily driven by site-specific conditions such as soil texture, sediment thickness, salinity, and tidal fluctuations, which influence tree growth and forest formation In denser, mature forests, trees compete for nutrients and sunlight, leading to taller growth, while in thinner forests like those in Trang-Ban, trees have ample access to nutrients and light, resulting in broader canopies, increased branching, and greater diameter growth.
Sonneratia caseolaris is commonly found in the region Additionally, a mixed community of Trang, Ban, and Su experiences prolonged flooding, which causes the tree roots to broaden; this adaptation occurs as the spongy tissues absorb water from the pore-water surrounding the roots.
Characteristics of regeneration
4.2.1 Species composition and density of trees regeneration
In mangrove ecosystems, tree regeneration occurs through propagules that develop while still attached to parent trees, either lying horizontally on the sediment or standing upright and submerged during dispersal When propagules drop from the parent tree, they often land beneath the canopy but are frequently dispersed further away by tidal action to prevent overcrowding of young plants The final settlement site of these propagules becomes the ideal location for new mangrove trees to grow and establish themselves, ensuring healthy forest regeneration.
Table 4.5 Species composition and mean density of the regenerated trees
A survey revealed that regenerated trees in the three study areas are primarily in the propagation stage, with clear differentiation in their height levels The number of regenerated trees predominantly results from regeneration beneath parent trees and is mainly distributed along the sea and dike edges In the Trang – Ban plant community, no regeneration was observed due to high canopy density, small seedling sizes, and poor growth during cold weather, with regeneration only occurring in low salinity conditions (5-15‰) On transect 02 within the Trang – Ban and Trang – Ban – Su communities, higher growth and density of mature trees limit the occurrence of regeneration.
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 for Transect 03 in the Trang – Ban – Su plant community indicate it has the highest regeneration density at 800 trees per hectare The data shows that tree regeneration is most concentrated towards the inward side of the dike footing across all three study areas, highlighting this zone as crucial for forest regeneration efforts and ecological recovery.
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
In the mixed plantation of Trang – Ban – Su, the majority of regenerated trees (70.8%) are found at a height of ≤ 0.5 meters, indicating that most regeneration occurs at the lowest height level Regenerated trees are predominantly observed at heights between 0.5 to 1 meter, while very few reach 1 to 1.5 meters, and none are present at heights ≥ 1.5 meters This growth pattern is due to regenerated trees growing beneath the understory plants, which limit sunlight and nutrients, restricting their growth to the smallest height level.
4.2.2 Impacts of some factors on regeneration mangrove species a Impacts of canopy layer
The dense canopy layer restricts sunlight penetration, leading to poor nutrition and limited growth for regenerated trees Additionally, propagules often do not fall directly to the ground but are held on tree trunks or roots, making them vulnerable to being washed away by water As a result, the overall number of successfully regenerated trees remains low Tidal fluctuations further impact regeneration by dispersing seedlings and disrupting their establishment in the habitat.
Studies on tidal characteristics and mangrove development in Vietnam reveal that mangroves thrive better in semi-diurnal tidal zones compared to diurnal tides, as noted by Phan Nguyen Hong (1991) In the study area, tidal heights range from 0.4m to 3.2m, with the tide rising more slowly than it recedes, significantly affecting salinity levels in surface and groundwaters These salinity fluctuations influence the survival of propagules and the growth of regenerated mangrove trees In regions with irregular tidal regimes, intertidal plants are impacted in their respiration, transpiration, and photosynthesis processes Additionally, wave action near the shore reduces the number of regenerated trees, highlighting the importance of tidal patterns and hydrodynamic conditions for mangrove conservation and development.
Tidal amplitude significantly influences the distribution and growth of mangrove trees, with higher tidal ranges promoting wider inland spread In study areas, the average tidal amplitude ranges from 0.25 meters to 1.8 meters, reaching a maximum of 3.5 meters, resulting in mangrove forests being distributed extensively inland The regeneration of mangrove trees is primarily concentrated along onshore areas, canals, and creeks, where tidal influence and substratum conditions favor growth The substratum plays a crucial role in supporting mangrove development, with suitable soil conditions enhancing tree establishment and overall forest health Understanding tidal dynamics and substratum characteristics is essential for effective mangrove conservation and restoration efforts.
Substratum plays a crucial role in the regeneration of mangrove trees, with propagules successfully growing on clay and sandy clay substrates Surveys indicate that the substratum gradually shifts from clay and sandy clay near the dike edge to silt closer to the shore, influencing mangrove growth patterns The impact of substratum variation on mangrove regeneration is summarized in the accompanying table, highlighting how different soil types affect propagation success and forest development.
Table 4.7 Number of regenerated trees on substratum
Study areas Transect Substratum Trees/plot
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
20 pressure causes of collapsed trees, broken branches, buried under sand, washed seedlings away or dead trees due to bad weather
Seaweed and marine-fouling organisms, particularly barnacles, significantly impact the survival and growth of mangrove seedlings Barnacles rapidly grow and develop hard coatings around stems, leaves, and twigs, which can hinder healthy development At coastal areas with high salinity, these barnacle infestations lead to slower growth rates and reduced stem diameter in regenerating mangroves Additionally, dense seaweed plaques cover seedlings, causing them to droop and further impair their growth in saline environments.
Picture 4.4 Barnacles stick on a regenerated tree
The primary human activities in these study areas include fishing and seafood harvesting, which involve frequent trampling and exploitation that cause uprooting, damage, and breakage of seedlings Local residents also rely on clam and Vạng harvesting daily for their livelihoods and practice grazing of ducks and buffaloes Additionally, annual population growth and the conversion of mangrove forests for agricultural development have contributed to significant habitat degradation and environmental change in the region.
Agricultural activities, including rice production and expanding shrimp aquaculture, significantly impact mangrove ecosystems by replacing natural mangroves with ponds, leading to habitat loss Increased shrimp farming has dramatically affected mangrove health and coverage, contributing to deforestation Additionally, local communities often unintentionally harm mangroves through unsustainable practices such as illegal timber cutting and overexploitation, which hinder the natural regeneration of mangrove trees Effective management and sustainable practices are essential to protect and preserve these vital coastal ecosystems.
Some solutions for sustainable development of mangroves in Tien Hai district, Thai
- 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
Mangrove forests are highly productive ecosystems that offer vital services to both the marine environment and local communities, including coastal protection, natural disaster prevention, and habitat preservation To maximize these benefits, mangrove management efforts should focus on guiding proper planting practices, selecting high-quality mangrove species, and implementing strict supervision during afforestation projects.
Picture 4.6 (a) Flower of Sonneratiasp , (b) Fruit of Sonneratiasp ;
Forestry scientists should develop tailored solutions to reduce barnacle infestation in regenerated trees based on the local afforestation conditions Conducting scientific research to create environmentally friendly biological products for barnacle eradication is essential Additionally, promoting forest protection through community engagement, raising awareness about forest protection laws in local communities and schools, can help ensure sustainable afforestation efforts.
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 focus on research and technology transfer to enable local communities to adopt effective, sustainable models in agriculture, forestry, and fisheries By combining innovative techniques with eco-friendly practices, these efforts can improve human livelihoods while reducing pressure on mangrove ecosystems Promoting sustainable development in these sectors is crucial for environmental conservation and the well-being of communities dependent on natural resources.
Strengthening management, inspection, and patrol forces is essential to gaining a comprehensive understanding of mangrove land use within aquaculture areas This proactive approach helps prevent overexploitation, ensuring the natural regeneration of mangrove forests is maintained Prompt action to halt any adverse impacts on mangrove ecosystems is crucial for their sustainable preservation and ecological health.
CONCLUSION
Characteristics of canopy layer
The composition values of Trang species in the canopy layers across all three mangrove communities consistently showed the highest range, between 8.75 and 10, indicating its dominance Su species exhibited moderate values ranging from 0.47 to 0.97, while Ban species had the lowest composition values, between 0.12 and 0.83 Most mangrove communities demonstrate high density, with the pure Trang plantation reaching approximately 8,850 trees per hectare Additionally, over 50% of the mangrove trees are classified as good quality, reflecting healthy and vigorous growth within these ecosystems.
The pure plantation in Trang has a canopy cover of 0.92, indicating dense forest coverage In comparison, the mixed plantation of Trang and Ban exhibits a slightly lower canopy cover of 0.83, reflecting moderate forest density The combined Trang – Ban – Su plantation demonstrates a canopy cover of 0.9, suggesting a healthy and extensive forested area, which is important for biodiversity conservation and ecological balance.
In addition, a mixed plantation of Trang – Ban grows the largest diameter at breast-height and height of mangrove trees.
Characteristics of regeneration
The regeneration of Trang exhibits the highest species diversity across different communities Regeneration primarily occurs at the sea edge and dike edge, with a notable variation in tree heights within the regeneration layer Most newly grown trees are small, reaching heights of ≤ 0.5 meters, and are predominantly concentrated along the shoreline and dike edges.
Mangrove community of Trang – Ban – Su
Mangrove trees such as Ipomoea pescaprae, Portulaca oleracea, Cynodon dactylon, and Casuarina equisetifolia are commonly observed along transect lines at shoals and dike footings Additionally, planting Casuarina equisetifolia and Hibiscus tiliaceus on elevated, non-tidal grounds helps enhance coastal stabilization.
4.1.2 Density of trees in canopy layer
Tree density, defined as the number of individual trees per hectare, is a crucial factor influencing forest formation and development Higher tree densities can enhance stand growth potential but may also increase competition for resources, affecting individual survival rates Understanding tree density helps manage forests effectively by promoting optimal growth conditions and sustainable forest management practices.
The survey results of mangroves density in study areas are shown in table
Table 4.2 Mean density of trees in canopy layer at the study area
Tree density Individual/plot Individual/ha
Survey results indicate that pure plantations in Trang exhibit the highest canopy layer tree density, averaging 7,650 trees per hectare These trees are predominantly tall, with each tree featuring 2-3 branches that develop independently within dense plots Field surveys confirm that as trees grow, they branch out to form dense, multi-branched canopies, contributing to the high overall tree density in Trang's plantations.
Division of branches of Trang
The mangrove community in Trang – Ban has the lowest density, primarily due to Ban's tendency to produce larger diameter at breast height in most mangrove species This growth pattern limits the development of other species and results in the occupation of a significant portion of available nutrients.
Forest density within a species is influenced by both the growth stages and overall development of the forest As forests mature, natural selection causes a reduction in tree density, leading to less densely populated stands in older forests.
Canopy cover is a vital structural indicator of forest health, representing the extent of forest coverage over the soil surface and influencing seedling regeneration, growth, and development through light availability Our study revealed that pure Trang plantations have the highest canopy cover at 0.92, indicating dense forest coverage, while mixed plantations show slightly lower coverage—with Trang-Ban mixed plantations at 0.83 and Trang-Ban-Su mixed plantations at 0.90—highlighting variations in forest structure that impact overall forest vitality.
4.1.4 Characteristics of the growth of mangroves
Studying the growth in height and diameter of mangrove species is essential to understanding their developmental stages, enabling the selection of appropriate silvicultural measures to enhance mangrove yields Monitoring these growth stages also provides insights into the transformation and progression of mangrove communities over time In the study areas, the growth characteristics of mangrove populations are detailed in a comprehensive table, highlighting key indicators such as height, diameter, and growth patterns crucial for effective mangrove forest management.
Table 4.3 Growth parameter of trees in canopy layer 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
The growth of plant communities in the study areas is assessed based on diameter at breast-height (DBH), height, and canopy diameter, with each community exhibiting distinct growth patterns Both Trang and Trang-Ban communities demonstrate equal growth potential In pure plantations of Trang, the average growth of mangrove species is 4.3 meters in DBH, 2.2 meters in height, and 1.3 meters in canopy diameter Mixed plantations of Trang show slightly lower average growth with a DBH of 4 meters, height of 2.5 meters, and a canopy diameter of 1.3 meters, while the mixed Trang-Ban plantation achieves the highest growth metrics, with a DBH of 4.7 meters, height of 2.8 meters, and canopy diameter of 1.6 meters.
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
TrangTrang - BanTrang - Ban - Su
The height and canopy size of plants are closely linked, with increased vertical growth leading to a corresponding increase in diameter at breast height Among the studied plant communities, Trang – Ban exhibits the highest growth in both height and canopy development, indicating vigorous biomass accumulation Conversely, the Trang – Ban – Su community shows the lowest growth in these parameters, reflecting a more limited development pattern This relationship highlights the significance of vertical growth as an indicator of overall plant community health and productivity.
Table 4.4 illustrates the quality of canopy layer trees, highlighting variations across different plantations In pure plantations of Trang, 53% of trees are classified as good quality, 11% as poor quality, and 36% as medium quality Mixed plantations of Trang and Ban show a decline in good quality trees to 35%, with bad quality trees making up 17% Conversely, the combined Trang – Ban – Su plantation achieves the highest quality, with 55% of trees categorized as good quality and only 13% as bad quality These findings emphasize the impact of plantation composition on tree quality in the canopy layer, essential for forest management and conservation strategies.
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
Survey results indicate that mangrove forests in the study areas are still developing; however, variations in density significantly influence forest formation Differences in site conditions such as soil texture, sediment thickness, salinity, and tidal fluctuations affect tree growth characteristics and result in distinct density patterns In dense forests, trees compete for nutrients and sunlight, causing them to grow taller, while in thinner forests like the Trang-Ban community, trees receive ample nutrition and light, promoting broader canopies, thicker trunks, and more branches, facilitating diverse forest development.
Sonneratia caseolaris is the dominant species in the area Additionally, a mixed mangrove community comprising Trang, Ban, and Su species remains waterlogged for extended periods The roots of these trees expand and adapt by absorbing water through their spongy tissues, which enhances their survival in flooded conditions.
4.2.1 Species composition and density of trees regeneration
Mangrove ecosystems rely on a natural tree regeneration process where propagules develop before dropping from parent trees, either lying horizontally on sediment or standing upright submerged in water After falling, propagules may settle beneath the parent tree or be dispersed further by tidal action to prevent overcrowding, promoting healthy growth Ultimately, the location where propagules become stranded serves as the site for new mangrove trees to establish and thrive.
Table 4.5 Species composition and mean density of the regenerated trees
A survey revealed that regenerated trees across three study areas are predominantly in the propagation stage, with height differences clearly observable at varying levels The majority of regenerated trees in Trang grow beneath parent trees and are distributed along sea and dike edges Conversely, no regeneration occurs in the Ban community within the Trang – Ban – Su area due to high canopy density, small seedling sizes, and poor growth during cold weather, although some regeneration occurs in low salt concentration zones (5-15‰) In transect 02 of the Trang – Ban and Trang – Ban – Su communities, higher growth and density levels lead to reduced regeneration rates.
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 of transect number 03 in the plant communities of Trang – Ban – Su reveals the highest regeneration density, reaching 800 trees per hectare The study indicates that tree regeneration is most concentrated inward from the dike footing across all three study areas, highlighting areas of significant ecological recovery and growth.
Regeneration of Trang in plant communities of Trang-Ban-Su
Table 4.6 Distribution of regenerated trees at four height levels
In the mixed plantation of Trang – Ban – Su, the majority of regenerated trees are found at height levels of ≤ 0.5 meters, accounting for 70.8% of all regenerated trees Fewer regenerated trees are observed at heights between 0.5 meters and 1 meter, while those at 1 to 1.5 meters are very scarce Notably, there are no regenerated trees at height levels of 1.5 meters or higher This pattern is primarily due to the growth environment beneath layer plants, where limited sunlight and nutrients restrict regeneration to the smallest height level (≤ 0.5 m).
4.2.2 Impacts of some factors on regeneration mangrove species a Impacts of canopy layer
The dense canopy layer limits sunlight penetration and results in poor nutrition for regenerated trees, causing low growth success Propagules often do not fall directly to the ground but are instead held on tree trunks or roots, where water movement can sweep them away, further reducing regeneration rates Additionally, tidal fluctuations negatively impact seedling establishment by disrupting the availability of suitable growing conditions and dispersal processes.
Research by Phan Nguyen Hong (1991) highlights that mangroves tend to thrive better in semi-diurnal tidal zones compared to diurnal tides, given consistent climate and soil conditions In the studied area, tidal levels range from 0.4m to 3.2m, with the tide rising more slowly than it recedes, influencing surface and ground salinity These salinity fluctuations significantly impact the survival of propagules and the growth of regenerated mangrove trees Additionally, irregular tidal regimes in intertidal zones affect key physiological processes such as respiration, transpiration, and photosynthesis in mangrove plants Wave action near the shore also plays a crucial role, leading to fewer regenerated trees in these areas.
Tidal amplitude significantly influences the distribution and growth of mangrove trees, with an average tidal range of 1.5 to 1.8 meters in study areas The maximum tidal amplitude reaches 3.5 meters, while the minimum is 0.25 meters, contributing to the widespread inland distribution of mangrove forests Additionally, mangrove regeneration primarily occurs alongshore and along canals and creeks, highlighting the importance of tidal dynamics in shaping mangrove ecosystems.
Substratum plays a crucial role in the regeneration of mangrove trees, with propagules thriving better on clay and sandy clay soils Surveys indicate that the substratum transitions from clay and sandy clay near the dike edge to silt closer to the shore, influencing mangrove growth patterns The impact of substratum type on mangrove regeneration is summarized in the following table, highlighting how soil composition affects propagule establishment and growth.
Table 4.7 Number of regenerated trees on substratum
Study areas Transect Substratum Trees/plot
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
20 pressure causes of collapsed trees, broken branches, buried under sand, washed seedlings away or dead trees due to bad weather
Seaweed and marine-fouling organisms, particularly barnacles, significantly impact the survival and growth of mangrove seedlings At high salinity sea edges, barnacle infestations slow down seedling development and stem diameter growth by forming a hard coating around stems, leaves, and twigs Rapid barnacle growth can impede the seedling’s ability to thrive, while the high salinity environment inherently restricts overall tree growth Additionally, large seaweed plaques covering seedlings cause drooping and hinder healthy development, further threatening mangrove regeneration.
Barnacles stick on a regenerated tree
Many local residents in these study areas rely on catching fish and seafood, which has led to the uprooting, trampling, and breakage of seedlings Their daily activities also include clam and Vạng harvesting, as well as grazing ducks and buffaloes Additionally, the increasing annual population growth and the conversion of mangrove forests for agriculture have further contributed to environmental changes in the region.
Agricultural activities, including rice production, significantly impact mangrove ecosystems The expansion of shrimp aquaculture has led to the replacement of mangroves with ponds, causing substantial environmental degradation Additionally, local communities often harm mangroves through unsustainable practices such as timber cutting, overexploitation, and indiscriminate harvesting, which hinder the natural regeneration of mangrove forests.
Dwellers in Nam Thinh digged oysters in mangrove forest
- 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
Mangrove forests are highly productive ecosystems that offer essential benefits to both the marine environment and local communities, including shoreline protection and natural disaster prevention To preserve these vital ecosystems, managers should guide the planting of mangroves, carefully select high-quality mangrove species, and oversee afforestation efforts to ensure successful and sustainable growth.
Picture 4.6 (a) Flower of Sonneratiasp , (b) Fruit of Sonneratiasp ;
Forestry scientists should propose targeted solutions to reduce barnacle infestation in regenerated trees based on local conditions, including scientific research to develop environmentally safe biological control agents Integrated forest protection strategies must balance ecological conservation with community interests in afforestation efforts, complemented by public awareness campaigns and education on forest protection legislation to promote sustainable practices among local residents and students.
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 play a vital role in researching and facilitating technology transfer to enable local communities to adopt sustainable models in agriculture, forestry, and fisheries Implementing these integrated practices can significantly enhance human well-being while reducing pressures on mangrove ecosystems Promoting sustainable methods through scientific innovation and knowledge sharing is essential for balancing economic development with environmental conservation.
Strengthening management, inspection, and patrol efforts is essential to gaining a comprehensive understanding of mangrove land use in aquaculture areas This proactive approach helps prevent overexploitation that could hinder natural regeneration and allows for the prompt cessation of activities causing adverse impacts on mangrove forests, ensuring their sustainable development.
V CONCLUSION 5.1 Characteristics of canopy layer
The composition values of Trang species in canopy layers across all three mangrove communities consistently exhibit the highest range, between 8.75 and 10, indicating their dominant presence Su species show moderate values ranging from 0.47 to 0.97, while Ban species have the lowest values, between 0.12 and 0.83, reflecting their lesser abundance Most mangrove communities demonstrate high density, with the pure Trang plantation reaching up to 8,850 trees per hectare Additionally, over 50% of the mangrove trees are classified as good-quality, highlighting the overall health and vitality of these ecosystems.
The canopy cover of pure plantations in Trang is 0.92, indicating a dense forest canopy In comparison, mixed plantations in Trang-Ban have a slightly lower canopy cover of 0.83, suggesting a less dense but still substantial forest cover The Trang-Ban-Su mixed plantation exhibits a canopy cover of 0.9, reflecting a high level of forest density comparable to pure plantations These variations in canopy cover highlight differences in forest density among pure and mixed plantation types in the region.
In addition, a mixed plantation of Trang – Ban grows the largest diameter at breast-height and height of mangrove trees
The regeneration of Trang stands out as the most diverse in species composition across local communities Regeneration predominantly occurs along the sea and dike edges, with young trees mainly reaching heights of 0.5 meters or less These juvenile trees are chiefly concentrated along the shoreline and dike areas, highlighting key zones for forest regeneration and growth within the region.
5.3 Some ecological factors affect to regeneration
Our analysis identified key factors influencing mangrove distribution and regeneration capacity, including canopy layer trees, tidal fluctuations, and substrate type Additionally, climate conditions, the presence of seaweed, marine fouling organisms, and human activities significantly impact mangrove health and growth Understanding these factors is essential for effective conservation and restoration efforts.
According to the research results, propose some solutions to sustainable management such as afforestation, forest protection and policies in management and protection.