The survey was conducted in the mangrove forests around the Magyi and Utto Creeks at Shwe-Thaung-Yan coastal areas in Ayeyarwady Delta region, April 2018. Transect lines were laid as lower, middle and upper, and quadrate plots based on Point Center Quarter Method (PCQM) P-DATA PRO were used. A total of 15 species of true mangrove was recorded. Rhizophora apiculata and Bruguiera gymnorhiza are the most dominant and distributed species in the study area. Followed by Bruguiera sexangulata, Cerop tagal and Rhizophora mucronata then remaining species. Zonation pattern of mangroves species as lower, middle, upper was also examined in study areas. Among than 1 species in Near Threaten (NT), 1 species in Critically Endangered (CR), 1 species in Endangered (EN) and remaining species are Least Concern (LC) had been considered according with IUCN red list. The environmental parameters such as water salinity and temperature, soil salinity, soil temperature and soil pH of study area were also recorded.

Keyword: ayeyarwady region, environmental parameters, lowers, magyi and utto creek, middle, mangrove forest, shwe-thaung-yan coastal, transect lines, upper, zonal pattern.

Myanmar has along coastline which is 2832km and can be divided into three coastal areas. The Rakhine Coastal Region (from the mouth of Naaf River to Maw Tin Point, about 740km length), the Ayeyarwady Delta and the Gulf of Mottama Coastal Region (Maw Tin Point to the Gulf of Mottama, about 460km in length) and Tanninthayi Coastal Region (from the Gulf of Mottama to the mouth of Pakchan River, about1200km length), extending along the Bay of Bengal and Andaman Sea. There are estuaries with deltaic systems, and numerous offshore islands along with a considerable diversity of coastal habitats, including mangroves, seagrass meadows, Coral reefs, sandy beaches and mudflats along the three Coastal Regions of Myanmar.

Myanmar has the fourth largest expense of mangrove area in Southeast Asia after Malaysia, Bangladesh and Papua New Guinea. Myanmar possesses 4% of world mangroves, and 8.8% of Southeast Asia mangroves. In these mangroves, 46% are including in Ayeyarwady, 37% in Taninthayi and 17% in Rakhine. So mangrove forest area greatest in Ayeyarwady Delta.

Mangroves of Shwe-Thaung-Yan coastal zone dominant along the deltaic areas of the Magyi and Utto tidal creeks. The distance of Magyi tidal creek and Utto creek has nine miles and seven miles respectively. Today, mangrove forests in Shwe-Thaung-Yan coastal areas are being degraded and destroyed on a larger scale through the natural disturbance and anthropogenic activities such as transforming to agriculture land, aquaculture ponds, salt pond/land etc, which are major causes of their degradation land loss of mangrove ecosystem.

The objective of this study is to know vegetative structure and zonal distribution of true mangrove species in Shwe-Thaung-Yan coastal areas.

The present study was conducted in the mangrove forest around Magyi tidal creek (Lat12.34º 15'72" N, Long 94.29º 46'27"E) in April 2018(Figure 1). A total of six random transects were set up based on the different forest conditions such as upper, middle, lower at Magyi and Utto tidal creeks, Shwe-Thaung-Yan coastal areas. The transect lines were measured by using diameter tape in meter. The distances and intervals of each transect were shown in Table 1.Totally, 15 sampling plots were set up in each transect. The measurement of plot is 10m², respectively. Each plot subdivided into four quadrants. Only one of nearest tree was recorded in each quadrant. The data of vegetation was recorded by using Point Center Quarter Method (PCQM) according to Dahdouh-Guebas, F and Koedan.¹ Then, the variable parameters such as the stem density (De), basal area (Ba) for each species and for entire mangrove stand, the complexity index (C.I), the relative density (De_r), the relative dominance (Do_r), the relative frequency (F_r) and the importance value (I.V) for each species were calculated by using Microsoft Excel-base Workbook P-DATA-PRO_1000 (Version 5.01) software. For all recorded mangrove species: flower, fruit, bud, leave, root and stem were recorded by using digital camera. The location of study areas were marked by using GPS for each transects line in the study areas. The environmental parameters such as soil temperature, soil salinity, water salinity, and water temperature and soil pH were measured at the field immediately. (Figure 2-5).

Figure 1 Map showing the location of study area: Magyi and Utto tidal creek, Shwe-Thaung-Yan Area.

Figure 2 The location, distance of transects, and plot interval of each transect around the Magyi and Utto tidal creeks mangrove, Shwe-Thaung-Yan coastal Area.

Figure 3 Species composition of mangrove in the Magyi and Utto creek,Shwe-Thaung-Yan coastal areas.

Figure 4 Zonal distribution of number of mangroves species in the study sites.

Figure 5 Forest parameter of different mangrove species at study sites.
IV, Important Value; RF, Relative Dominance; Rd, Relative dominance; RD, Relative Density; BA, Basal Area

In the present study area, a total of 15 species belong to 9 genera from 7 families of true woody mangrove plants in the Magyi and Utto tidal creeks, Shwe-Thaung-Yan coastal areas were recorded .They are 7 species from family Rhizophoraceae, 3 species in family Avicenniaceae, one species were recorded in families Sonneratiaceae, Meliaceae and Steruliaceae, Arecaceae and Combretaceae at Magyi and Utto creeks, Shwe-Thaung-Yan coastal areas. The Systematic positions of classification of recorded species were described in Table 2.

The mangrove ecosystem in the tropical regions, along coastal shorelines and associated is important for many flora and fauna. The present study was conducted at two stations which represented different mangrove types in upper, middle and lower zones. The present study deals with the occurrence, composition and vegetative structure of true mangrove in Magyi and Utto Creeks, Shwe-Thaung-Yan coastal area.

 There are many previous studies in Myeik and Ayeyarwady delta Area. Among them, a total of about 50 species of mangrove,² the zonation of true and associate mangrove species distribution,³ botanical study of importance of mangrove ecosystem for conservation and Management purpose,⁴ 44 species of mangrove including true and associate species of mangroves⁵ and 30 species including true mangrove and mangrove associates⁶ were recorded in Myeik Coastal area. Moreover, the zonation pattern of mangrove in Magyi Tidal Creek by using transect lines method⁷, species composition and zonation pattern of mangrove of kandon-kani, Amherst and Setse areas,⁸ the mangrove reforestation from the Ayeyarwady Delta.⁹ The species composition, zonation and succession of mangrove community along the Magyi coastal area.¹⁰

In some cases, zonation may be very irregular or restricted to a particular part of the tidal gradient.¹¹ Similarly, the zone of study sites termed as upper, middle and lower zone. A total of 15 species of true mangrove were observed in the .present study in Shwe-Thaung-Yan coastal area were distributed, Transet 1, 3 and 5 were measured at Magyi creek and Transects 2,4 and 6 were measured at Utto tidal creek. According to the zonal species distribution, the same zonal species distribution in Magyi, but the highest species were found in middle and lowest species in lower zone in Utto tidal creek. Two species of Bruguiera mucronata and Rhizophora apiculata were distributed all the study sites. And then followed Bruguiera sexangular,Cerop tagal and Rhizophora mucronata were zonal distributed. Avicennia alba, Cerops dencandra,Lumnizera littorea, Sonneratia alba and Xylocarpus granatum were upper zonal distributed while ,Bruguiera cylindrical, Cerops dencandra,Nypa frutican,Heritiera forms and Xylocarpus granatum were also lower zonal distribution and then Avicennia alba, A.marina , A.officinalis were distributed only at the middle zone.

The structure and composition, called mangrove vegetation structure dynamics, are rarely studied worldwide. The result of present study recognized the various types of dynamics. As the calculated result, mean basal area was variable ranging from (0.01 to 0.6), mean relative density was variable ranging from(1.7 to 53.5),mean relative dominance was variable ranging from(0.5 to 51.6), mean relative frequency was variable ranging from(3.7 to 42.9) and then mean important value was variable ranging from(6.1 to 148.12 ) at study sites.

The high importance value in the Magyi forest of Phizophora apiculata indicates that the forest is ecologically dominated. From the calculation, mean high of tree was 2.2-2.5 at Utto while 1.9-2.6 at Magyi tidal creek, therefore the trees at Magyi were higher than Utto creek. The total forest densities for trees were 0.24-0.35at Utto while 0.21-0.34 at Magyi creek tree par meter square. Regular distribution was rarely found; this is probably due to intraspecific competition at a local scale. However, Fangliang et al., 1997 mentioned that there is a negative correlation between per capital death rate and population density. Kairo et al., 2002¹² also showed that the sapling density varied greatly between localities but was on average very high, which implies adequate recruitment inmost localities. The circumference of this species is large as well as the height is low. Basal area is related to the circumference of trees. At Utto, the number of complexity index (mean) was highest (2.5-7.7) while (3.7-5.8) at Magyi. The mean number of multiple stem tree were2-2.3 at Utto creek while 2.3 at Magyi. In the present study, total frequency range of Magyi was140-180% while Utoe was140-173.3%.Total basal area range of Utto 0.743-1.4566m²/0.1ha while Magyi was1.049-1.492m²/0.1ha because Rhizophoea apiculata is more prevalent in Magyi. According to the results, Phizophora apiculatas howed the highest mean basal area, mean relative density, mean relative dominance, mean relative frequency and mean importance value of forest parameters at all stations while Heritiera forms and Sonneratia alba were lowest. At the Magyi and Utto, the species of , Phizophora apiculata in T-1,T-2,T-3,T-4 and T-5 were the most abundance species but Bruguiera sexangular and Bruguiera gymnorhiza in T-1, Bruguiera cylindrical T-2, Cerop dencandra T-5 and Sonneratia alba T-4 were least abundance species in the transect according to their rank (Rank-7).

Regarding the environmental parameter measurements, water salinity (35.8‰), highest at T-6, followed by (35.2‰) at T-4,(35‰) at T-1and T-5 , (32‰) at T-2 and T-3. Transect 6 is the highest water salinity while transect 2 and 3 are lowest. Soil salinity was highest 55‰ at transect 1 while lowest 30‰ at Transect 2. The value of soil pH was highest 6.4 in transect 5, followed by 6.2 in Transects 1 and 6, 6.0 in Transect4 , 5.9 in Transect 3 and then5.8 in transect 2 in studying the period at Magyi.

Mangroves and adjacent mudflats are found in all coastal provinces and are widely distributed across the entire coastline. Cunha-Lignon et al pointed regarding individual mangrove species rarely occupy entire estuaries from sea mouth to the tidal limit upstream. Also, Duke¹³ mentioned that each of the mangrove species has a preferred up river estuarine location based on its salinity tolerance range. Likewise, the present study revealed that the various salinity ranges controlled significantly upon the distribution of species of mangroves growing in the study sites from the mouth to the head of the Magyi creek.

Regarding the soil type, Malar³ demonstrated that Avicennia alba, Sonneratia alba, and Rhizophora mucronata plants could grow well on all substrate conditions such as muddy, very soft muddy and sandy mud area. This implies that the substrate types have no restrictions on their distribution along the Magyi tidal creek. The present study showed the same conditions similar with her results on the distribution of mangroves. In addition, the outcomes of this study displayed similar to that of Nan Htwe Htwe Maung⁷ who studied the distribution of mangrove species subjected to varying conditions of salinity concentrations, nutrient levels, substrate structures and tidal movement in Magyi tidal creek.

Mangrove seedlings are apparently adapted to shaded undestroyed environment while mature trees respond better in the sunlight canopy ⁴ but shade tolerance differ among mangrove species.¹⁵ The mean high trees variable ranging (from1.9 to 2.6m), total forest density variable ranging (from210.7to 349.7), and Complexity index variable ranging (from2.5 to 7.7)

The present study has been carried out in the Magyi and Utto creeks, Shwe-Thaung- Yan coastal Area. The method used in the present study the first attempt in Myanmar. The study site was selected and measured the vegetative structure and recorded the species composition so as to estimate the forest value. Almost all of the forests in Utto and Magyi creeks showed not good condition because of several human impacts and activities. Today, mangrove forests are being degraded and destroyed on a larger scale globally through the natural disturbance and anthropogenic activities such as transforming to agriculture land, aquaculture ponds, etc., which are major causes of their degradation and loss of mangroves ecosystem. However, this station may be recovered in the next few years because many juveniles of mangrove species were influent seriously. There should be emphasis on the implementation of reforestation and raising awareness and knowledge of local people on the value of mangrove community in those stations (Table 3-7).

We are greatly indebted to Dr San Tha Tun, Professor and Head, Department of Marine Science, Mawlamyine University, for his encouragement throughout the study period. We would like to acknowledge to Dr Htay Aung (Professor Retire) for reading this manuscript. We sincerely thank the local villagers for their helpful assistance in field works. The first author, Soe Win, would like to thank he beloved family for their physical, moral and financial supports throughout this study.

None.

The author declares that there is no conflicts of interest.

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