The present study was carried out during the period from May to July 2014 to assess the vegetation pattern and to estimate biomass of the mangroves in Irakkandy Lagoon, Trincomalee. Five belt-transects of 10 m in width were laid perpendicular to the shoreline. Data were collected on tree diameter at breast height (dbh) and tree height from each sub-plot (100 m 2 ) in belt transects using standard methods. Above ground biomass, basal area and relative density of the mangroves were also estimated. Diversity and evenness of each sub-plot was calculated using Shannon-Wiener diversity index and Pielou's evenness index respectively. Results revealed that the study site is composed of 5 true mangrove species and highest density was recorded for Avicennia marina (414 trees/ha, 700 saplings/ha, 2354 seedlings/ha), followed by Lumnitzera racemosa, Excoecaria agallocha, Rhizophora apiculata and Heritiera littoralis. The greatest mangrove diversity (1.28) was observed in subplot 1 of transect 2. The least mangrove diversity (0) was found in transect 5. There is a significant difference among transects concerning the diversity and evenness (P<0.05). The results showed that Avicennia marina was the dominant species with Height (H) and dbh of 3.65±1.43 m and 5.06±1.07 cm respectively, followed by Lumnitzera racemosa (3.36±1.19 m and 5.81±1.06 cm, Excoecaria agallocha (4.92±2.45 m and 5.31±1.93 cm), Rhizophora apiculata (4.56±1.70 m and 4.89±0.96 cm) and Heritiera littoralis (8.80±0.849 m and 26.50±4.95 cm). The above ground biomass of Lumnitzera racemosa was recorded as 8334.89 kg/ha and Avicennia marina was recorded as 1361.13 kg/ha. Species diversity (H') of whole mangrove area studied was 0.86 and evenness (E) was 0.54. It reveals that Irakkandy Lagoon consists of fairly high biological diversity (Diversity index=0.86) of mangroves and extremely valuable for stability of the ecosystem.
The mangrove along Vangalai coastal area associated with numerous marine flora and fauna communities remained rarely studied. The present study was carried out during the period from April to July 2015 to document the status of mangrove distribution of selected sample sites in Vankaalai estuary, Mannar. Seven belt-transects of 10 m in width were laid perpendicular to the shoreline. Data were collected on floristic composition and tree height along the plot of each sites. Mangrove Diversity and evenness were calculated using Shannon-Wiener diversity index and Pielou"s evenness index respectively from each sub-plot (100 m 2) in belt transects. Results revealed that six mangrove species such as Avicennia marina (Avicenniaceae), Rhizophora mucronata (Rhizophoraceae), Bruguiera cylindrica (Rhizophoraceae), Sonneratia alba (Sonneratiaceae), Excoecaria agallocha (Euphorbiaceae) and Pemphis acidula (Lythraceae) were recorded from the mangrove forest in study period. Further, 5 major mangrove associated plants were observed in the study period. The greatest mangrove diversity (1.296) was observed in sub-plot 14 of transect 5 and the lowest mangrove diversity (0.453) was recorded in sub-plot 3 of transect 1. The results showed that A. marina was the dominant species. Species diversity (H") of whole mangrove area studied was 1.155 and evenness (E) was 0.645. It revealed that Vankaalai lagoon should be protected since it consists of high biological diversity of mangroves.
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