Floristic composition and phytodiversity status of Sitakunda Ecopark , Chittagong , Bangladesh

The present study dealt with the exploration and documentation of the floristic composition and phyto-diversity of Sitakunda Eco-park, Chittagong, Bangladesh. A total of 412 vascular plant species under 315 genera belonging to 94 plant families have been recorded from the study area during February, 2013 to April, 2015. Out of these recorded taxa, 330 were dicotyledons, 62 were monocotyledons, 5 were gymnosperms and 15 were pteridophytes. Among those, the maximum 144 species belonged to herbs followed by 138, 75 and 55 species as trees, shrubs and climbers, respectively. The species composition among the plant families varied in plant groups. In dicotyledonous group, Euphorbiaceae appeared to be the largest family with 35 species, whereas Poaceae showed the largest family containing 30 species among monocotyledonous group. The highest values of both Shannon-Weiner and Simpson diversity indices have been observed as 3.82 and 0.98, respectively to site D during monsoon season, whereas the lowest values 3.19 and 0.95, respectively of these indices were recorded in site A during summer season.


INTRODUCTION
Bangladesh is located between 2025 to 2638 North latitude and 8801 to 9242 East longitude with an area of about 14.4 million hectares (BBS, 1997).The majority of country's land is formed by alluvium soil, which consists mostly of flood plains exceptionally occurring some hilly areas and uplifted land blocks with a sub-tropical monsoon climate (Islam, 2003 andRashid, 1991).Geographically, Bangladesh is situated near the Indo-Burma region-one of the prime hotspot areas of the world biodiversity (Mittermeier et al., 1998).Due to its unique geo-physical location Bangladesh is exceptionally characterized by a rich biological diversity (Nishat et al., 2002;Hossain, 2001;Barua et al., 2001;Chowdhury, 2001) which harbored approximately 5,000 species of angiosperms (Khan, 1977).
The rich country's biodiversity is increasingly being depleted day by day due to overextraction and destruction of natural ecosystems owing to multifarious anthropogenic activities as well as natural calamities.Lack of proper management practices in some of the natural ecosystems is also one of the remarkable reasons for this degradation.For the conservation of natural habitat and its biological diversity, Bangladesh government has declared several categories of protected areas including national parks, ecoparks and botanical gardens, safari parks, wildlife sanctuaries, game reserves, world heritage site etc. following IUCN management criteria.
The Sitakunda ecopark is very important due to its unique habitat and rich biodiversity as well as religious and ecotourism point of view.Naturally growing habitat of a threatened gymnosperm species-the Cycas pectinata is harbored in different locations of Sitakunda ecopark.A number of water falls in this hilly region is the special attraction to the tourists and casual visitors.Few research works on the Sitakunda area were conducted (Alam, 2001;Rahman & Uddin, 1997;Misbahuzzaman & Alam, 2006;Shamsuddoha & Nasir, 2005 etc.).Most of these works covered in the fields of taxonomy, forestry, tourism and management aspects.But the detail ecological research work especially, the floristic composition with their diversity status is still uncompleted.Therefore, the present research on floristic composition and phyto-diversity status of Sitakunda ecopark has been conducted with a view to prepare a comprehensive checklist of vascular plants with their distribution and seasonal fluctuation as well as to assess phyto-diversity status which will help to prepare a plan for sustainable management and eco-friendly conservation of the Sitakunda ecopark.

MATERIALS AND METHODS
Description of the study site: Present research work was conducted in Sitakuunda Ecpark and adjacent Botanical garden.The ecopark is situated between 2236 to 2239 North latitude and 9140 to 9142 East longitude and about 15 to 65m above mean sea level.The northern side of the park is Mirsarai upazilla and Pahartali is in the south, Sandwip channel and the Bay of Bengal is in the west and Fatikchari is in the east.Sitakunda ecopark and botanical garden is located along the Dhaka-Chittagong highway in Sitakunda upazilla of Chittagong district.Four main sites were selected covering the whole ecopark area on the bases of gradual hill altitude and geo-spatial location, which were-site-A (Ecopark's office region with an average 220 feet high from the mean sea level), site-B (Suptodhara region with an average 600 feet high from the mean sea level), site-C (Sohosrodhara region with an average 1100 feet high from the mean sea level) and site-D (Chandranath temple region with an average 1400 feet high from the mean sea level).Each site was again divided into three sample area as sub-sites, namely sub-site 1 (upper-slope at the hill top), sub-site 2 (mid-slope of the hill) and sub-site 3 (lower-slope at the hill foot) according to the gradual hill slope.So, a total of 12 sub-sites were selected for the present research investigation.

Field survey, sample collection and identification:
A total of nine field trips with seven days duration of each were conducted during three prominent sampling seasons of the year (viz., Rainy, Summer and Winter) from 2013 to 2015.Vascular plants were collected following standard quadrat method (Braun-Blanquet, 1932;Raunkiaer, 1934).The quadrat size, like 2m2m for herbs and grasses, 5m5m for shrubs and 10m10m for trees were standardized on the basis of species-area-curve method (Cain, 1938).In each sub-site, ten plots with 10m10m sized-quadrat were selected and other smaller sizedquadrats were placed within the big one for collecting the respective plants group.Collected plant specimens were properly processed using standard herbarium techniques (Hyland, 1972;Jain andRaw, 1977 andAlexiades, 1996) for voucher specimens, which have been preserved in Plant Ecology and Environment Laboratory, Jahangirnagar University.All plant specimens collected from the study area were identified through consulting the experts and matching with relevant voucher specimens preserved at Jahangirnagar University Herbarium (JUH) and Bangladesh National Herbarium (DACB), taxonomic descriptions and keys available in the relevant literatures (Prain, 1903b;Hooker, 1973;Wu et al., 2003;Siddiqui, 2007a, b;Ahmed, 2008a, b, c, d;Ahmed, 2009a, b; and type images available in the websites of different international herbaria).Updated nomenclatural information was incorporated through data bases including IPNI (2008) andTROPICOS (2010).Scientific name with original citation, family name, local name, major plant group, habit, and one representative specimen number have been provided.The genera under each family and the species under each genus are arranged alphabetically.
Vegetation analysis: Simpson's and Shannon-Weiner diversity indices were calculated by the following formulae-Simpson's diversity index (Simpson, 1949) was calculated by the following formulae described by Kent and Coker (1992 N(N-1) where, n is the total no. of individuals of each species, N is the total no. of organisms of all species.
The Shannon-Wiener diversity index (Shannon and Wiener, 1963) was calculated by the following formulae described by Kent and Coker (1992)-Shannon-Weiner Diversity Index: H= - pi ln pi where, pi is the proportion of individuals or the abundance of the ith species expressed as a proportion of total cover, ln is Log base n .
Statistical Analysis: Data were statistically analyzed using SPSS software (version 16.0).One way ANOVA (DMRT) was used to test for significant differences (P<0.05) for marginal means of variables.

RESULTS AND DISCUSSION
A total of 412 vascular plant species under 315 genera belonging to 94 plant families have been documented from the study area (Table 1).Among the enumerated species, 392 are angiosperms, 5 are gymnosperms and rests of 15 are pteridophytes.Out of the recorded angiospermic flora, the dicotyledons (magnoliopsida) group is represented by 330 species belonging to 252 genera under 67 plant families, whereas the monocotyledons (liliopsida) group occupied 62 species under 49 genera and 14 families.In this study, the gymnosperms consisted of 5 species belonging to 4 genera under 4 families whereas the pteridopytic flora revealed the occurrence of 15 species under 10 genera and 9 families.Among the total species, 144, 138, 75 and 55 species respectively represented as herbs, trees, shrubs and climbers.The number of species in plant families varried from 1 to 35, where 20 families are monospecific representing single species.The most 10 dominant families containing maximum number of plant species of the study area are Euphorbiaceae, Poaceae, Rubiaceae, Fabaceae, Caesalpiaceae, Verbenaceae, Asteraceae, Mimosaceae, Araceae and Arecaceae (Fig. 1).).The highest number of species (324) was recorded during monsoon season followed by 256 and 183 species during winter and summer seasons respectively (Fig. 3).Uddin and Rahman (1997) surveyed the angiospermic flora of Sitakunda in Chittagong, Bangladesh.They reported 203 dicotyledones in the area.But no such work has been carried out so far for Sitakunda Eco-park.Uddin and Hassan (2010) recorded 374 species at Lawachara National Park, Arefin et al. (2011) recorded 186 species at Satchhari National Forest.Hadi and Rahman (2013) recorded 203 species at Tilagarh Ecopark, Sylhet.The present findings indicated that the average values of both Simpson's and Shannon-Weiner diversity indices within the selected sites and sub-sites did not show significant difference, whereas these variation among the seasons showed significant difference at 5% (α = 0.05) level after DMRT (Table 2).Here, the average values of both the indices during summer season showed the lowest and found significant difference from the average values that observed during winter and rainy reasons.But these values in winter and rainy seasons did not show significant variation at 5% level by DMRT.
Sitakunda is the first eco-park of Bangladesh.will be helpful for the sustainable management and conservation of phytodiversity resources of Sitakunda ecopakr of Bangladesh.
), Lindernia (6 sp.), Senna (5 sp.), Syzygium (5 sp.), Crotalaria (4 sp.), Terminalia (4 sp.) and Zyzyphus (4 sp.); while in monocotyledons important genera are-Calamuus (4 species), Cyperus (4 sp.), Setaria (3 sp.), Themenda (3 sp.), and Sporobolus (2 sp. It is highly rich in plant diversity.Floristic composition of Sitakunda ecopark was studied to know the present phytodiversity status in this important natural forest ecosystem.Significant difference of diversity of plants was observed in different seasons.Highest number of species was recorded during rainy season because of growing various types of undergrowth in that season, many of which were not found to grow during winter and summer season.The highest diversity index (DI) observed in site D during Rainy season.The lowest diversity index was observed in site A during summer season.Research findings obtained through this piece of research

Table 2 . DMRT analysis of diversity indices of selected sites, sub-sites and seasons Sites/Subsites/Seasons Diversity index value Shannon-Weiner Simpson's
C=Climber, CH=Climbing Herb, CS=Climbing Shrub, D=Dicot, F=Fern, FH=Fern Herb,  G=Gymnosperm, M=Monocot, SS=Scandens Shrub, ST=Small Tree, T=Tree.  1 Note:Values in the same column that do not share common letters are significantly different at 5% (α = 0.05) level among the sites and seasons after DMRT.Table 1.Comprehensive checklist of plant species recorded from Sitakunda ecopark of Bangladesh S.N .Scientific name Local name Family Type Habit Acc.No. 1 Abroma augusta (L.) L. f.