PLANT COMMUNITY STRUCTURE AND BIODIVERSITY PATTERNS IN CHATTOGRAM METROPOLITAN CITY OF BANGLADESH

The present study aims at investigating the vegetation in different sites of Chattogram metropolitan area following appropriate techniques. In order to enumerate the distribution of species, several diversity indices including Shannon-Winer Index, Pielou’s Evenness and Simpson’s Index were employed. A total of 645 species belonging to 414 genera under 120 families were documented from the studied area for the first time. Of these, 37 species (5.73%) are pteridophytes, 607 species (94.11%) are angiosperms and single representation of gymnosperm (0.16%). Among the recorded species, 384 are medicinal species belonging to 277 genera under 93 families. Bacopa monnieri is a dominant species in the forest area with some co-dominant species like Eichhornia crassipes , Centella asiatica, etc. Moreover, this study provides potential sources to the environmental planners, herbalists, ecologists, taxonomists, ethnobotanists, pharmacists, phytochemists and local administration that would help to plan for future green infrastructure and maintain ecosystem function providing long-term benefits for the city dwellers.


Introduction
Urban ecosystems, which offer many advantages including defenses against pollution and biodiversity preservation, are significantly influenced by plants. Urban ecosystem helps to conserve energy, to reduce urban heat island effect, to improve air and water quality, to conserve biodiversity and to sequestrate carbon level of a metropolitan city (Nowak et al., 2006). In instant, urban forest is principal component of urban ecosystem that provide significant environmental benefits and services to the urban environment 1999). A healthy urban ecosystem also improves the quality of microclimate, which acts as an aid for quick recovery from illness by providing natural recreation services and reducing psychological stress, subsequently reduces health cost (McPherson et al., 1997;Maco and McPherson, 2003). Environmental quality within urban areas is highly influenced by urban forest structure and composition (Jim and Chen, 2003;Zhao et al., 2010). One such city is Chattogram. The Chattogram in Bangladesh is a densely populated city. In contrast, the city comprises of highly urbanized area, semi urbanized area with homestead vegetation, hilly urbanized area with scattered forest, semievergreen hilly forest and coastal vegetation along the coast of the Bay of Bengal. The natural heritage and floristic composition *Corresponding author. E-mail: <omf@cu.ac.bd>, < bokhtear@cu.ac.bd>. 1 Effective Creation on Human Opinion (ECHO), Chattogram, Bangladesh.
of Chattogram city attracted plant explorers and taxonomists from prehistoric times and provided a basis to conduct floristic research in that evergreen city (Anon, 2003;Uddin et al., 2015). However, it is very unfortunate that Chattogram city is losing its beauty and biological heritage faster due to the rapid unplanned urbanization (Uddin et al., 2015). Urbanization, the most concentrated and prompts human-driven factors that peril biodiversity as well as urban ecosystem (Kondratyeva et al., 2019). The ecological balance of such type of city is very significant for nature and human being. Most importantly, plantation in planned way in Chattogram city may protest soil erosion, reduce environmental pollution, reduce ever increasing temperature of a city area, increase rainfall and protest from natural disaster. Besides, such forest has huge aesthetic value, which could be an attraction for tourist from home and abroad. Therefore, this type forest is also source of traditional medicinal plants, which are source of raw materials of pharmaceutical industries in developed country in present era.
Previously, some partial and isolated works have been carried out in Chattogram city to understand floristic characters of the city. In instant, Uddin et al. (2015) conducted research on only tree species and Biswas et al. (2021) carried work on only Sulakbahar Ward of the city. Such research is neither complete nor might describe the entire floral scenario of such a big city. Nevertheless, these works carry significance that Chattogram city consist lots of floral diversity, which are yet to be discovered.
Documentation of traditional uses of the local plants used by local communities is very important to know local status of the plant diversity and medicinal plants along with their taxonomic and ecological status. This study aimed to record all types of plant species present in the Chattogram city since the literature studies are largely bereft on it. Therefore, present study intended to record the whole plant diversity of Chattogram city to know the total number of plant species as well as total number of medicinal plants species. We also aimed to know whether any threatened/rare species are there which are medicinally important to draw attention to the national policy makers for conservation those species. Alongside, we expect to record new species from the study areas, as many areas of the city remain unexplored yet. Overall, this research study intended to explore floral diversity, density, conservation status along with threats on floral diversity of the studied areas, which would be useful to develop long-term management plan. The goal of this study is to present the actual scenario of the plant diversity and to make this data available to the stakeholders to protect and preserve them by sustainable planning and management of the city for the current and future generations.

Study area
Chattogram is a densely populated city of Bangladesh. The city comprises of highly urbanized area, semi urbanized area with homestead vegetation, hilly urbanized area with scattered forest, semievergreen hilly forest and coastal vegetation along the coast of the Bay of Bengal. Chittagong City Corporation area 160.99 sq km, located in between 22°13' and 22°27' north latitudes and in between 91°40' and 91°53' east longitudes (Fig. 1

Sampling methods
Stratified random sampling method was used for survey of the vascular plants; each site was divided into tree zone based on topography (top, middle and bottom slope). A total of 300 plots were taken from 20 different areas and 5 plots from each zone. All habit types of plant population in each quadrat were recorded. The plot size and identification procedure follow according to methods describe at Rudra et al. (2021)

Identifying medicinal plants with their traditional knowledge and pharmaceutical uses
Identification of medicinal plant was done by consulting with experts, literature survey, online search, market survey and consulting with local herbalists. Pharmaceutical uses and important medicinal plants and their demand in pharmaceutical industries also determine by consulting with expert. Ethnomedicinal information was stored to our existing online database at mpbd.cu.ac.bd.
In dicotyledonous group, Euphorbiaceae appeared to be the largest family comprised of 33 species under 21 genera followed by Asteraceae consisted of 20 species under 18 genera, Rubiaceae with 24 species under 16 genera, Fabaceae with 28 species under 14 genera, Apocynaceae consisting 14 species under 11 genera, Verbenaceae with14 species in 10 genera, Acanthaceae with 11 species under 8 genera, Caesalpiniaceae consisting 17 species under 7 genera, Mimosaceae with 15 species under 7 genera and Lamiaceae with 11 specis under 7 genera.
In monocotyledonous group, Poaceae is the largest family having with 41 species under 27 genera followed by Araceae, Arecaceae, Zingiberaceae and so on (Table 3). Among the all recorded 120 families, the most dominant 10 families are Poaceae, Euphorbiaceae, Asteraceae, Araceae, Rubiaceae, Fabaceae, Arecaceae, Apocynaceae, Verbenaceae, and Acanthaceae respectively (Tabel 2). In Magnoliopsida, Euphorbiaceae appears to be the largest family having 33 species and 21 genera whereas, in Liliopsida, poaceae appears to be the largest family having 41 species and 27 genera. But in the Bangladesh Flora, Poaceae is the 1 st largest family followed by Fabaceae, Orchidaceae, Rubiaceae, Asteraceae, Cyperaceae and Euphorbiaceae. In the Bangladesh Flora, Euphorbiaceae represented by 159 species and 50 genera and Poaceae by 342 species and 132 genera (Pasha and Uddin, 2013). The largest genus of dicotyledons group holding fourteen species found in Ficus followed by Sizygium (nine species) Desmodium (eight species), Senna, Ipomoea and Solanum (seven species from each). On the other hand, in monocotyledons group, the genus Cyperus appeared to be the largest with ten species followed by Digitaria (five species), Colocasia and Calamus (four species from each), Alocasia, Cleome, Musa and Bambusa (three species of each).
In the Study area, Bacopa monnieri having an IVI value of 3.36% is dominant in the forest area, some co-dominant species are Eichhornia crassipes (2.63%), Centella asiatica ( , Tinospora crispa, Tinospora cordifolia and Passiflora foetida are rarely found in study area. This study also recorded some threatened and rare species for example, Tinospora crispa, Diploclisia glaucescens, Tinospora cordifolia and Wrightia arborea are threatened species (Ara et al., 2013) which are popular medicinal plant used by the local people. Santalum album L. is a rare species recorded from study area. Status of occrence have been determined by field observation and quadrat sampling of the area. Status of occurrence has been recorded for proper conservation management and sustainable utilization of the taxa which show 452 (70.08%) to be common, 180 (27.91%) as least concern, 9 (1.40%) as vulnerable, and 4 (0.62%) are found as near threatened in the study area. (Table 2). The survey enumerated only one gymnosperm Cycas pectinata from the Chattogram city area.

Habitat diversity
Among the vascular plants herbs represented by 293 (46%) species under 220 genera and 87 family, shrubs 102 (16%) species under 87 genera and 45 family, trees 176 (27%) under 127 genera and 62 family, climbers 59 (9%) under 53 genera and 34 family and epiphytes by 15 (2%) species under 14 genera and 10 family respectively. The habit diversity shows that herbaceous plants are dominating over shrubs, trees and Climbers ( Fig. 2A and B) as also observed by others (Jashimuddin and Inoue, 2012;Uddin et al., 2015;Faruque et al., 2018;Malik et al, 2018;Gumisiriza et al., 2019;Durso et al., 2021)  Exotic plants are deliberated as a great threat to the native biodiversity and ecosystems due to their deleterious influences on the existence and survival of indigenous plants and wildlife (Biswas et al., 2007;Dutta et al., 2015). The present study clearly stated that several exotic plants have aggressive growth, also have negative impacts on the growth and development of native plant species. A number of well-established exotic tree species, i.e., Acacia auriculiformis, Acacia mangium, Albizia richardiana, Dalbergia sisso etc. and some noxious exotic weeds, e.g., Chromolaena odorata, Mimosa pudica, Duranta erecta, Lantana camara etc. were recorded from the plantation sites of different areas.

Medicinal and Non-medicinal
This Study recorded a total of 384 (60%)) medicinal plant species belonging to 277 genera under 93 families from the study area (Fig. 3) while other researchers recorded only 24 nonwoody medicinal plants form Sulakbahar ward of Chattogram metropolitan area ( Biswas et al., 2021).

Diversity indices
The calculated magnitude of Shanon-Wiener index (3.03) of this study was 3.03 indicating indicates the presence of diverse vascular plants in comparable to the magnitudes of other studies conducted in community managed VCFs as well as government managed forests in Bangladesh. The calculated magnitude is lower than the other study in Bangladesh (Nath et al., 2016a ;Chowdhury et al., 2019;Jannat et al., 2020;Rudra et al., 2021) and comparabley higher than other   (Fig. 3). Contrariwise, lower Simpson's index of 0.05 was also on of the key indicator of presence of considerably diverse vegetation in the study areas, which close to the result for other reported VCFs and one government managed forest (Nath et al., 2016b;Rahman et al., 2016;Chowdhury et al., 2019;Jannat et al., 2020;Rudra et al., 2021) (Fig. 4). Species evenness index was computed as 0.45 indicating that all species were almost evenly distributed. These outcomes also identical to Komolchori VCF in Khagrachori and Chunati Wildlife Sanctuary and markedly heterogenous to other two VCFs and BFD managed forest as demonstrated in Fig. 4. Phytosociological attributes and diversity indices showed elevated results compared to other studies reported from the BFD managed forests and community managed forest (Nath et al., 2016b) which indicated that community induced forest management approach is more effective than the government managed forests. This variation in diversity indices among different forest type is attributable to alterations in species biomass, perturbations, and topographical factors. The community works in a collaborative way for the sustainable management of VCF and helps to grow stewardship among the community members. However, the population density in CHTs is very low compared to other parts of the country and this may be why they exist in rich diverse forest patches. On the other hands, population density in metropolitan area is comparatively higher than it's of CHTs. Aforementioned statistical analysis indicates that current research field namely Chattogram metropolitan hilly areas are still occupied with diversified vegetation and trees but yet there has been significant risk of degrading this diversity due to over growing population pressure, urbanization practices advent of modern technology, unplanned forest management practice without involving local peoples, climate change and other factors. To maintain the current plant species variety, the extant plant species diversity richness should be protected by establishing an effective monitoring system and implementing a conservation strategy that is ecologically viable. Moreover, flora holds a pivotal role amongst each geographical area's natural wealth affluence. Thereby, plant biomass of any place delivers a concise illusion of floristic richness, that either may be convenient for formulating sustainable conservation and management strategies of biodiversity. Thus, the forthcoming sustainable protection strategy for the plant resources would be beneficiary to the affordable management and effective protection of the forest ecosystem.

Conclusion
Forests play an important role as a lung of the whole world. Naturally growing forest resources distributed in Chattogram city are actively involved to run ecosystem properly and to keep balancing the abiotic and biotic components in a very organized way. For example, carbon sequestration is a long-term process to store/capture carbon from the atmosphere in plants organs through biological, chemical and physical processes, which play an important role to sustain the atmospheric temperature as well as reducing global warming. Likewise, to reduce landslide in the hilly regions, plantation could be a solution to overcome this issue. Therefore, it is urgently needed to record plant species found in the study area as many anthropogenic activities are actively participated for the deforestation process otherwise, we may lose important or new species forever from the study areas. However, this study provides potential sources to the environmental planners, herbalist, ecologist, taxonomists, ethnobotanists, pharmacists, phytochemists and local administration.