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, 3 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
GOAL AND OBJECTIVES
Goals
The goal of this research is to complement the understanding about forest structure and regeneration characteristics of mangrove areas in order to propose some solutions for sustainable protection and development of mangrove forest in Tien Hai district, Thai Binh province.
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
Here is the rewritten paragraph:"The study focuses on the mangrove forests and barren lands along the sea dykes of Tien Hai, spanning from Tra Ly estuary to Ba Lat estuary, within the territories of three coastal communes: Nam Thinh, Nam Hung, and Dong Long These areas were selected due to their status as the largest mangrove areas in Tien Hai, boasting high-density mangrove forests Notably, all mangrove forests in these areas are planted forests, funded by the Japan Red Cross Society in collaboration with the Red Cross of Tien Hai District and Thai Binh province Specifically, the mangroves in Nam Thinh and Nam Hung are designated as special-use forests, while those in Dong Long serve as protective forests."
Figure 3.1 Locations of study areas
Study methods
- References of some documents of study areas about tide-tables, using maps of land use, project, some information supported from Tien Hai Resources and Environment Department and People’s Committee of three communes in study areas
- Carry out field research three coastal communes with total area of 1,571.95ha mangrove forest Since then, select three specific communities of study areas with the representative species and an area of more than 100ha, including 100ha pure plantations of Trang in Nam Thinh commune, 157.3 ha a mixed plantations of Trang – Ban in Dong Long and 449.22ha a mixed plantation of three species Trang – Ban – Su in Nam Hung commune
Each typical plant communities, setting up 3 transects parallel to the coast, in the inward direction from the sea edge to dike footing On each transect, 10 sample plots of 400m 2 (20x20m) were randomly located Due to statistical rule, total number of sample plots that were set up in each survey area is 30 plots a Study the characteristics of canopy layer
- Survey the canopy layer trees as follows: name of mangrove species, diameter at the breast-height (D1.3), tree height (Hvn), canopy diameter (Dt) and tree quality Collected data is recorded in table as follow
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
Quality of canopy trees is divided into three levels in which, Good quality trees (A) have good growth quality, strait form and have no diseased Bad quality trees (C) have poor growth, diseased and broken branches Medium quality trees (B) are the intermediate level of A and C
Here is a rewritten paragraph that captures the essence of the original text, optimized for SEO:"To assess canopy cover in forested areas, researchers employed an estimation method, randomly selecting 50 points within each plot to observe canopy types A scoring system was used, where points with visible main foliage at the top crown received a value of 1.0, those with visible canopy edges and empty space received 0.5 and 0 respectively The canopy cover ratio was then calculated as the mean value of these 50 points, providing a quantitative measure of forest canopy cover."
During field study, some main parameters including name of species, root collar diameter of a tree (Doo),tree height and canopy diameter were identified using normal forest survey methods In which, tree height was classified into four different level including H vn ≤ 0.5m, 0.5 < Hvn ≤ 1m, 1< Hvn 1.5m
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:
Some factors affect to the regenerated trees such as canopy cover, substratum, salinity and other factors as sea weed, marine-fouling organisms and human activities These information were investigated during field survey
- 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
- Growth of the canopy layer: Calculate standard deviation and standard error are two parameters which refer to variation of sample mean in a population mean, meaning the difference levels of sample mean Calculate mean value of density, diameter at breast height, diameter at crown canopy, height of tree in each plot b Characteristics of the regenerated trees
- 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
Here is a rewritten paragraph that maintains the original meaning while complying with SEO rules:"Species composition is a crucial ecological element in assessing biodiversity and the stability of forest ecosystems, encompassing the variety and abundance of plant species within forest communities By analyzing the number of species and their composition, forests can be classified into either pure stands or mixed stands Notably, a survey of mangrove growth revealed significant variations in the rate and quantity of each mangrove species 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 in a good growth and development, high density on silt while a mixed plantation between Trang – Ban in which Trang is dominant species with composition value of 9.17 ÷ 9.55, only grow onshore Ban is planted at the sea edge and
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 mixed plantation of Trang – Ban –Su: Trang is dominant species with composition value of 8.75 ÷ 9.17; Su grows mostly at sea edge and along the canal with composition value of 0.47 ÷ 0.97 Especially, Ban Myanmar has height of 20 meters with the advantages of non-deciduous in winter, broad canopy and high salt tolerance
Picture 4.1 Mangrove community of Trang – Ban – Su
Observations along transect lines revealed the presence of various mangrove tree species at shoals and dike footings, including Ipomoea pescaprae, Portulaca oleracea, Cynodon dactylon, and Casuarina equisetifolia Additionally, Casuarina equisetifolia and Hibiscus tiliaceus were found to thrive on higher ground, unaffected by tidal activity.
4.1.2 Density of trees in canopy layer
Tree density, measured as the number of individuals per hectare, plays a crucial role in forest formation, influencing the potential growth and competition for survival among trees in a stand, ultimately shaping the forest's structure and ecosystem.
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 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 2 -3 branches growing and developing as an independent tree in the dense plot
Picture 4.2 Division of branches of Trang
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
Here is the rewritten paragraph:"Interestingly, tree density within the same species is influenced not only by the species' growth patterns, but also by the stages of forest growth and development As forests mature, the density of trees naturally decreases, a phenomenon governed by the laws of natural selection, which favor the survival of the fittest and most resilient trees."
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:
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
Here is a rewritten paragraph that captures the essence of the original text, complying with SEO rules:The growth patterns of plant communities in the study areas were evaluated based on diameter at breast-height (D1.3), height (H), and diameter at canopy (Dt) Notably, the growth rates of each community differed significantly However, Trang and Trang-Ban plantations exhibited comparable growth abilities Specifically, the mean growth of mangrove species in pure Trang plantations was 4.3m (D1.3), 2.2m (H), and 1.3m (Dt), whereas mixed plantations of Trang and Trang-Ban showed higher mean growth rates, with Trang-Ban achieving the highest growth at 4.7m (D1.3), 2.8m (H), and 1.6m (Dt).
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
14 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
Here is the rewritten paragraph:"Mangrove forests in the study areas are still in the development stage, with varying densities leading to distinct forest formations Site conditions such as soil texture, sediment thickness, salinity, and tidal fluctuations significantly impact tree growth, resulting in differing forest characteristics In denser forests, trees compete for nutrients and sunlight, driving them to grow taller, whereas in less dense forests, such as those found in Trang-Ban, trees have ample resources to develop in diameter, branch out, and expand their canopy."
Sonneratia caseolaris typically thrives in flooded environments, where it forms a mixed community alongside Trang and Ban trees In these conditions, the trees' roots expand as spongy tissues effectively absorb water from the surrounding pore-water, enabling them to adapt to prolonged inundation.
Characteristics of regeneration
4.2.1 Species composition and density of trees regeneration
Mangrove ecosystems are characterized by tree regeneration through propagules that grow before detaching from parent trees These propagules may lie horizontally on the sediment or remain submerged in water When a seedling falls, it often appears to plant itself in the sediment beneath the parent tree; however, tidal action frequently disperses it further away to prevent overcrowding of young plants The final location where these propagules settle becomes a nurturing ground for the development of regenerated mangrove trees.
Table 4.5 Species composition and mean density of the regenerated trees
A recent survey revealed that regenerated trees across three study areas are primarily in the propagation stage, with notable height differentiation among them The majority of regenerated trees are found under parent trees in the Trang region, particularly along the sea and dike edges However, there is a lack of Ban regeneration within the Trang – Ban – Su plant community, attributed to the dense canopy layer, small seedling sizes, and poor growth conditions during cold weather, as they thrive only in low salt concentrations (5-15 ppt) Additionally, in transect number 02 of the Trang – Ban and Trang – Ban - Su communities, high growth and density levels contribute to the limited regeneration observed.
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 from transect number 03 in the Trang – Ban – Su plant communities indicate that the highest density of tree regeneration is 800 trees per hectare Additionally, across all three study areas, tree regeneration shows a notable increase in density closer to the dike footing.
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
The majority of regenerated trees are found at a height of ≤ 0.5 m, accounting for 70.8% in the mixed plantation of Trang – Ban – Su Trees between 0.5 m and 1 m are the next most common, while those ranging from 1 to 1.5 m are quite rare, with no regenerated trees exceeding 1.5 m This limited growth is attributed to the trees being overshadowed by under-layer plants, resulting in insufficient sunlight and nutrients for taller growth.
4.2.2 Impacts of some factors on regeneration mangrove species a Impacts of canopy layer
The dense canopy layer hinders the growth of regenerated trees by limiting their access to essential nutrients and full sunlight Additionally, propagules often remain attached to tree trunks or roots instead of falling to the ground, which leads to water being swept away, further reducing the number of successful regenerations Furthermore, tidal fluctuations have a significant impact on this process.
A study on tidal characteristics and their impact on mangrove distribution and development in Vietnam highlights that mangroves thrive better in semi-diurnal tidal conditions compared to diurnal ones In the research area, tidal fluctuations range from a high of 3.2m to a low of 0.4m, with a slower rising tide than ebbing These tidal variations significantly influence surface and groundwater salinity, which affects the survival of propagules and the distribution of regenerated trees Additionally, in areas with irregular tidal regimes, intertidal zone plants impact respiration, transpiration, and photosynthesis processes The proximity to shore, where wave action is strong, results in a lower number of regenerated trees.
Tidal amplitude significantly influences the distribution and growth of mangrove trees, with average amplitudes in the study areas ranging from 1.5 to 1.8 meters, peaking at 3.5 meters and dropping to a minimum of 0.25 meters As a result, mangrove forests are found extensively inland, while tree regeneration is primarily concentrated onshore and along canals and creeks Additionally, the characteristics of the substratum play a crucial role in this ecosystem.
Substratum plays a crucial role in the regeneration of mangrove trees, as the growth of propagules is significantly influenced by the type of soil Research indicates that clay and sandy clay substrates promote optimal growth, while a transition to silt occurs from the dike edge to the shore The impacts of different substratum types on mangrove regeneration are summarized in the accompanying table.
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 the shoreline where salinity is high, barnacles hinder tree regeneration, leading to slow development in both growth and stem diameter These fast-growing barnacles can create a hard coating around the stems, leaves, and twigs of the seedlings Additionally, the elevated salinity levels contribute to poor tree growth, while seaweed forms large plaques that cover the seedlings, resulting in their drooping.
Picture 4.4 Barnacles stick on a regenerated tree
Human activities in the study areas primarily revolve around fishing and seafood harvesting, which have led to the uprooting and damage of seedlings due to trampling and the exploitation of clams and Vạng for daily sustenance Additionally, the grazing of ducks and buffaloes contributes to this environmental impact The annual population growth and the conversion of mangrove forests for agricultural purposes further exacerbate the situation, highlighting the urgent need for sustainable practices.
Agricultural activities, particularly rice production and shrimp aquaculture, significantly impact mangrove ecosystems by replacing these vital habitats with ponds Additionally, local residents often engage in uncontrolled practices such as timber cutting and overexploitation, which further hinder the regeneration of mangrove trees.
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 benefits to both the marine environment and human communities, including protection against sea dikes and natural disasters Therefore, it is essential for managers to oversee tree planting efforts, ensure the selection of high-quality mangrove species, and directly supervise afforestation initiatives.
Picture 4.6 (a) Flower of Sonneratiasp , (b) Fruit of Sonneratiasp ;
Forestry scientists should assess local afforestation conditions to develop effective solutions for reducing barnacle infestations on regenerated trees This includes conducting scientific research to create environmentally friendly biological products for barnacle extermination Additionally, it is essential to promote forest protection efforts that align with community interests in afforestation, as well as to educate local populations and schools about forest protection legislation.
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 must focus on research and technology transfer to assist communities in implementing effective production models in agriculture, forestry, and fisheries By integrating sustainable methods, we can enhance human life while alleviating pressures on vulnerable mangrove ecosystems.
To enhance the management and oversight of mangrove ecosystems, it is essential to reinforce the roles of inspection and patrolling forces This approach aims to ensure a comprehensive understanding of mangrove land use in aquaculture, prevent overexploitation, and safeguard natural regeneration processes Timely intervention is crucial to address any negative impacts on mangrove forests, promoting sustainable practices and protecting these vital ecosystems.
CONCLUSION
Characteristics of canopy layer
The composition values of the Trang species in the canopy layers of all three mangrove communities consistently showed the highest values, ranging from 8.75 to 10 In contrast, Su species exhibited values between 0.47 and 0.97, while Ban species had the lowest values, ranging from 0.12 to 0.83 Most mangrove communities demonstrated significant density, with a pure plantation of Trang reaching an impressive 8,850 trees per hectare Additionally, over 50% of the trees in these mangrove communities are of good quality.
The canopy cover of pure Trang plantations is 0.92, while mixed plantations of Trang and Ban have a canopy cover of 0.83 Additionally, mixed plantations of Trang, Ban, and Su exhibit a canopy cover of 0.9.
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 showcases the highest diversity in species composition within each community Regeneration primarily occurs along the sea edge and dike edge, where trees exhibit varying height levels Most regenerated trees are predominantly found at a height of 0.5 meters or less, with a significant concentration along the shore and dike edges.
Mangrove community of Trang – Ban – Su
In summary, transect lines reveal the presence of various mangrove tree species at shoals and along dike footings, including Ipomoea pescaprae, Portulaca oleracea, Cynodon dactylon, and Casuarina equisetifolia Additionally, the planting of Casuarina equisetifolia and Hibiscus tiliaceus on elevated, non-tidal areas is recommended.
4.1.2 Density of trees in canopy layer
Tree density, defined as the number of individual trees per hectare, plays a crucial role in forest formation processes It significantly influences the potential growth and competition for survival among trees within a stand.
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 of Trang exhibit the highest mean tree density at 7,650 trees per hectare, with trees primarily growing in height Fieldwork observations reveal that each foot of a Trang tree typically divides into 2-3 branches, which develop as independent trees within the dense plot.
Division of branches of Trang
The mangrove community in Trang – Ban exhibits the lowest density due to the dominance of Ban species, which have the largest diameter at breast height among mangrove species This dominance restricts the growth of other species and utilizes a significant portion of available nutrients.
In any given species, tree density is influenced by both species growth and the various stages of forest development As forests mature, natural selection tends to reduce tree density, leading to fewer trees in older forests.
Canopy cover is a crucial indicator of forest health, reflecting the extent of forest coverage on the soil surface, which influences seedling regeneration, growth, and development through light availability Research findings indicate that the pure Trang plantation exhibits the highest canopy cover at 0.92, followed by the mixed Trang-Ban plantation at 0.83, and the mixed Trang-Ban-Su plantation at 0.90.
4.1.4 Characteristics of the growth of mangroves
Researching the growth in height and diameter of mangrove species is essential for understanding their growth stages and selecting appropriate silvicultural practices to enhance mangrove tree yields This study also examines the changes in the growth stages of mangroves, with the growth characteristics of mangrove communities detailed in the accompanying table.
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 measured by diameter at breast height, height, and canopy diameter, revealing distinct growth patterns among different communities Both Trang and Trang-Ban exhibit similar growth capabilities In pure Trang plantations, the average growth of mangrove species is recorded at a diameter at breast height (D1.3) of 4.3m, height (Hvn) of 2.2m, and canopy diameter (Dt) of 1.3m Conversely, mixed plantations show an average D1.3 of 4m, Hvn of 2.5m, and Dt of 1.3m Notably, the mixed Trang-Ban plantation demonstrates the highest average growth, with D1.3 at 4.7m, Hvn at 2.8m, and Dt at 1.6m.
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 relationship between canopy height and diameter at breast height shows that as height increases, diameter also expands Among the plant communities studied, Trang – Ban exhibits the highest growth, while the Trang – Ban – Su community demonstrates the least growth.
The quality of trees in the canopy layer varies across different plantation types in Trang In pure plantations, 53% of trees are classified as good quality, while 11% are deemed bad quality, and 36% are medium quality In contrast, a mixed plantation of Trang – Ban shows a lower good quality percentage at 35%, with bad quality trees comprising 17% However, the mixed plantation of Trang – Ban – Su boasts the highest proportion of good quality trees at 55%, alongside 13% categorized as bad quality.
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 are still developing in the study areas, but variations in density significantly impact forest formation These differences arise from site conditions such as soil texture, sediment thickness, salinity, and tidal fluctuations, which influence tree growth characteristics In dense forests, trees compete for nutrients and sunlight, leading to taller growth compared to thinner forests Conversely, in the thin forest community of Trang - Ban, trees receive adequate nutrition and light, allowing them to develop broader canopies and more branches.
Sonneratia caseolaris typically thrives in mixed communities like Trang – Ban – Su, where prolonged flooding causes tree roots to expand This adaptation occurs as spongy tissues in the roots absorb water from the surrounding pore-water, enhancing the trees' resilience in flooded environments.
4.2.1 Species composition and density of trees regeneration
Mangrove ecosystems thrive through a unique tree regeneration process where propagules grow before detaching from parent trees These propagules may either lie horizontally on the sediment or remain submerged in water Once a seedling falls, it often appears to root itself in the sediment beneath the parent tree; however, tidal action frequently disperses it further to prevent overcrowding among young plants Ultimately, the location where these propagules settle becomes a nurturing ground for the development of new mangrove trees.
Table 4.5 Species composition and mean density of the regenerated trees
A survey revealed that regenerated trees in three study areas are predominantly in the propagation stage, with noticeable height differentiation among them The number of regenerated trees is primarily concentrated in the Trang area, particularly under parent trees along the sea and dike edges In contrast, there is a lack of Ban regeneration within the Trang – Ban – Su plant community, attributed to the dense canopy layer, small seedling sizes, and poor growth conditions in cold weather, with regeneration only occurring in low salt concentrations (5-15 ppt) Additionally, in transect number 02 of the Trang – Ban and Trang – Ban - Su communities, high growth and density contribute 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 results from transect number 03 of the Trang – Ban – Su plant communities indicate the highest regeneration density at 800 trees per hectare, with tree regeneration showing a notable increase toward the inner dike footing across all three study areas.
Regeneration of Trang in plant communities of Trang-Ban-Su
Table 4.6 Distribution of regenerated trees at four height levels
The majority of regenerated trees in the mixed plantation of Trang – Ban – Su are found at a height level of ≤ 0.5 m, comprising 70.8% of the total Trees between 0.5 m and 1 m are present in moderate numbers, while those ranging from 1 m to 1.5 m are scarce, with no regenerated trees exceeding 1.5 m in height This limited growth is attributed to the shading and nutrient competition from under-layer plants, which restricts sunlight access and resources for the younger trees.
4.2.2 Impacts of some factors on regeneration mangrove species a Impacts of canopy layer
The dense canopy layer limits sunlight and nutrition for regenerated trees, causing them to struggle for growth Instead of falling to the ground, propagules often cling to tree trunks or roots, resulting in water displacement that further hinders their establishment Consequently, the regeneration of trees is significantly diminished, particularly in areas affected by tidal fluctuations.
A study on the tidal characteristics related to the distribution and development of mangroves in Vietnam highlights that mangroves thrive better in semi-diurnal tidal conditions compared to diurnal ones In the study area, tidal heights range from a maximum of 3.2 meters to a minimum of 0.4 meters, with the tide rising more slowly than it ebbs Tidal fluctuations significantly impact the salinity of both surface and groundwater, which affects the survival of propagules and the distribution of regenerated mangrove trees Additionally, in areas with irregular tidal regimes, intertidal zone vegetation influences respiration, transpiration, and photosynthesis processes Wave action also plays a crucial role, resulting in fewer regenerated trees near the shore.
Tidal amplitude significantly influences the distribution and growth of mangrove trees, with average levels ranging from 1.5 to 1.8 meters and peaks reaching 3.5 meters, while the lowest recorded is 0.25 meters This variation leads to a widespread inland distribution of mangrove forests, with tree regeneration primarily concentrated onshore and along canals and creeks Additionally, the characteristics of the substratum further impact mangrove health and distribution.
Substratum plays a crucial role in the regeneration of mangrove trees, as propagules thrive in clay and sandy clay environments Surveys indicate that the substratum transitions from clay and sandy clay to silt from the dike edge to the shore, significantly impacting mangrove regeneration The effects of substratum on mangrove growth are detailed in the accompanying table.
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 the saline edge of the sea, barnacles hinder the development of regenerated trees by slowing growth and stem diameter These fast-growing barnacles can create a hard coating around the stems, leaves, and twigs, further complicating growth Additionally, the high salinity of seawater contributes to the poor growth of the trees, while seaweed forms large plaques that cover the seedlings, leading to drooping.
Barnacles stick on a regenerated tree
Human activities in these study areas primarily involve fishing and seafood harvesting, which often leads to the uprooting and destruction of seedlings due to trampling and the exploitation of clams and Vạng Additionally, the grazing of ducks and buffaloes contributes to this environmental impact The annual population growth and the conversion of mangrove forests for agricultural purposes further exacerbate the situation, highlighting the need for sustainable practices.
Agricultural activities significantly impact mangrove ecosystems, particularly through rice production and the expansion of shrimp aquaculture, which often leads to the conversion of mangrove areas into ponds Additionally, local communities frequently engage in uncontrolled practices such as timber cutting and overexploitation, further hindering the regeneration of mangrove trees.
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 vital services to both the marine environment and local communities, including protection against sea dikes and natural disasters Therefore, it is essential for managers to oversee tree planting initiatives, ensure the selection of high-quality mangrove species, and directly supervise afforestation efforts.
Picture 4.6 (a) Flower of Sonneratiasp , (b) Fruit of Sonneratiasp ;
To address barnacle infestation in regenerated trees, forestry scientists must propose effective solutions based on local afforestation conditions This includes conducting scientific research to develop environmentally friendly biological products for barnacle extermination Additionally, it is essential to integrate forest protection efforts with community interests in afforestation, while promoting awareness of forest protection legislation among local populations and in schools.
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 must focus on research and technology transfer to empower communities in effectively utilizing sustainable production models in agriculture, forestry, and fisheries This approach aims to enhance human life while alleviating pressures on vital mangrove ecosystems.
To enhance the management and oversight of mangrove ecosystems, it is crucial to strengthen the roles of inspection and patrolling forces This approach will ensure a comprehensive understanding of mangrove land use in aquaculture, prevent overexploitation, and safeguard natural regeneration Timely intervention is essential to address and halt any detrimental impacts on mangrove forests.
V CONCLUSION 5.1 Characteristics of canopy layer
In all three mangrove communities, the Trang species consistently exhibited the highest composition values, ranging from 8.75 to 10, followed by Su with values between 0.47 and 0.97, and Ban, which had the lowest values of 0.12 to 0.83 Notably, the density of the pure Trang plantation reached an impressive 8,850 trees per hectare, with over 50% of the mangrove communities comprising high-quality trees.
The canopy cover of pure plantations in Trang is 0.92, while mixed plantations of Trang and Ban have a canopy cover of 0.83 Additionally, the canopy cover for mixed plantations of Trang, Ban, and Su is recorded at 0.9.
In addition, a mixed plantation of Trang – Ban grows the largest diameter at breast-height and height of mangrove trees
The regeneration of Trang exhibits the highest species diversity within each community, primarily occurring along the sea and dike edges The regeneration layer reveals significant variations in tree heights, with the majority of regenerated trees measuring 0.5 meters or less, predominantly concentrated along the shore and dike edges.
5.3 Some ecological factors affect to regeneration
The distribution and regeneration ability of mangrove trees are influenced by several key factors, including the presence of canopy layer trees, tidal fluctuations, and the quality of the substratum Additionally, elements such as climate, seaweed, marine-fouling organisms, and human activities also play significant roles in shaping these ecosystems.
According to the research results, propose some solutions to sustainable management such as afforestation, forest protection and policies in management and protection.