Floral diversity in the central part of Chattogram city, Bangladesh

Purpose – This study/paper aims to evaluate the floral richness of the central part of Chattogram city, Bangladesh. Chattogram is recognized as the largest port city and the commercial capital of Bangladesh, which confronts faster urbanization and swift infrastructure development. Green spaces in and around Chattogram city are shrinking sharply, which resulted in rapid loss of floral and faunal resources in this area. The present study was carried out from February 2018 to January 2019 to enumerate the vascular plant species of the Sulakbahar ward located in the central part of Chattogram City, Bangladesh. Design/methodology/approach – The study area was categorized into 10 habitats to assess the variation of floral composition. The extensive whole area survey method was applied to record the flora from all sorts of plant habitats of the research area. Findings – The study enumerated 418 vascular plant species under 315 genera and 120 families including natural, planted and cultivated from the study area. The habit form of the recorded plant composition indicated that herbs (35%) constitute the major plant category followed by trees (34%), shrubs (17%), climbers (12%), ferns (1%) and orchids (1%). The study also indicated that exotic species (50.3%) became dominant than native species (49.7%) in Chattogram city because of their scenic beauty, easy propagation and ornamental value to the city planners and inhabitants. Originality/value – It appeared that floral resources of the Chattogram city area are in great threat due to aggressive and unplanned infrastructure development for housing, offices and institutions by replacing the © Shourav Dutta, Trapa Biswas, Md. Akhter Hossain, Md. Rayhanur Rahman, Saddam Hossen and Mohammed Kamal Hossain. Published in Ecofeminism and Climate Change. Published by Emerald Publishing Limited. This article is published under the Creative Commons Attribution (CC BY 4.0) licence. Anyone may reproduce, distribute, translate and create derivative works of this article (for both commercial and non-commercial purposes), subject to full attribution to the original publication and authors. The full terms of this licence maybe seen at http://creativecommons.org/licences/by/4.0/ legalcode The authors cordially acknowledge the Chittagong City Corporation, Bangladesh for providing funding and necessary support to conduct this study. Moreover, the authors are really thankful to the Biodiversity Research Group of Bangladesh for its support in the fieldwork. The authors also acknowledge the Institute of Forestry and Environmental Sciences, University of Chittagong; and BFRI, Bangladesh for extending their supports during the taxonomical activities. Conflict of interest:Authors have declared that no competing interests exist. Contribution of the authors: This research was conducted in collaboration among all authors with simultaneous efforts. Author TB collected, compiled and analyzed the data and wrote the main protocol. Author SD (corresponding author) managed literature searches, performed data compilation, statistical analysis and prepared the first and final draft of the manuscript to finalize it. Authors MRR and SH collected and compiled the species data and managed literature searches. Authors MAH and MKH identified the species, designed the research, delivered the guidelines, did overall supervision, reviewed and evaluated the final draft of the manuscript. Floral diversity Received 31 January 2021 Revised 6March 2021 Accepted 6March 2021 Ecofeminism and Climate Change EmeraldPublishingLimited e-ISSN: p-ISSN: 2633-4062 DOI 10.1108/EFCC-01-2021-0002 The current issue and full text archive of this journal is available on Emerald Insight at: https://www.emerald.com/insight/2633-4062.htm


Introduction
The largest delta of the world -Bangladesh, lying in the north-eastern part of South Asia, dwelt at the cross borders of the Indo-Himalayan and Indo-Chinese sub-region, is the harbor of a wide variety of flora and fauna (Dutta et al., 2014;Foster-Turley et al., 2016). About 5,000 species of angiosperms alone are residing in Bangladesh of which around 2,260 species are enumerated from the Chattogram zone of Bangladesh (Anon, 1992;CRPARP, 2015;Foster-Turley et al., 2016). The landscapes of the Chattogram region of Bangladesh, categorized by hills, hillocks, flatlands, wetlands, canals, rivers and the Bay of Bengal, etc. reflect a rich ecological heritage of giant animals, insects, birds, fishes, angiosperms, gymnosperms, climbers, vines and plants with medicinal and aesthetic values (Dutta and Hossain, 2020;Hossain, 2001).
Chattogram, the southeastern part of Bangladesh, was established in 1666 with a total area of about 5,282.92 km 2 including the Chittagong Hill Tracts (CHTs) and Cox's Bazar (BBS, 2011). The natural heritage and floristic composition 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). Urban forests of the city area play a vital role to protect tree species diversity, as well as to confirm the environmental sustainability and also the entity of green landscapes of the Chattogram Metropolitan Area (Anon, 2003). However, it is very unfortunate that Chattogram city losses its beauty and biological heritage faster due to the rapid unplanned urbanization and anthropogenic activities, i.e., illegal cutting of trees and hills, unplanned slum and housing, excessive infrastructure development, etc. Uddin and co-researchers reported that hill cutting, urbanization and industrialization tremendously affect biodiversity distribution of several hills and urban forests of Chattogram city (Uddin et al., 2015). Hence, we need to effectively preserve and efficiently manage this rich biological diversity and ascertain the green spaces in Chattogram city of Bangladesh for the betterment of future city dwellers (Hossain, 2004;Uddin et al., 2015).
Both urban biological diversity and ecological sustainability are tremendously threatened due to the rapid progress of urbanization (Elmqvist et al., 2013;Uddin et al., 2015). Urbanization creates a devastating scope for land degradation, separation of urban green cover and tremendous loss of urban biological diversity (Elmqvist et al., 2013). Green parks, domestic gardens, homestead plantations, botanical gardens and recreational parks and remnant forest patches are the major elements of urban green spaces (Jaganmohana et al., 2018). Due to rapid urbanization, a few plant species are seen in the urban landscapes of Chattogram city. Meanwhile, the overall floral composition and vegetation coverage of the Chattogram urban area has been changed due to several anthropogenic disturbances and ongoing encroachments (Uddin et al., 2015). It is necessary to assess the floral composition of Chattogram city for sustainable urban planning and management.
Uddin and co-researchers recorded 65 tree species under 28 families from the hilly areas of Chattogram city and surrounding areas (Uddin et al., 2015). Dutta and co-researchers recorded 332 vascular plants under 266 genera and 93 families from a nearby botanical garden and eco-park of Chattogram city, Bangladesh (Dutta et al., 2014). However, there is EFCC no recent study that covers the complete floral diversity of the Chattogram city area or any part of it.
In that regard, it is important to record the present flora of the Chattogram city to help in developing chronological baseline information and monitoring changes. In this study, an attempt has been made to evaluate the floral richness of the central part of Chattogram city, Bangladesh. Another objective of the present study was to assess the distribution of vascular plant species in different habitats of the Chattogram city, Bangladesh.
2. Materials and methods 2.1 Study site Chittagong (Officially Chattogram), established in 1666, is a large port city on the southeastern coast of Bangladesh. Chattogram resides latitudinally between 21°54'N and 22°59'N; and longitudinally within 91°17'E and 92°13'E (BBS, 2011). The Chattogram city comprises an area of about 171 km 2 with around 6.0 million of population (BBS, 2011). The study was conducted in the Sulakbahar ward [1] comprising almost the central part of the Chattogram City Corporation (CCC). The area has a variety of land uses e.g., industrial, residential, educational, vacant lands, hills, markets, etc. (Figure 1).

Physiographic condition of the study area
Chattogram lies at the straddles of the coastal foothills of CHTs in south-eastern Bangladesh and enjoys a moist tropical climate with 25.7°C mean annual temperature, 2,794 mm of annual precipitation and 78% mean annual humidity (MAH) (Climate data, 2018). The properties of urban soils differ greatly from agricultural lands to the particular area of hills. The soil types in urban areas of Chattogram city are sandy loam, loamy sand and silt loam with 53%-83% sand (Alamgir et al., 2015).

Collection and compilation of data
Prior to the fieldwork, a reconnaissance survey was conducted in the study area to gain a general idea about physiographic and overall conditions of the study site with particular attention to species composition, nature of species occurrence and habitat of the vascular plant species. The identified potential plant habitats were fallow land (plain), fallow land (hill), graveyard, institution, homestead, nursery, roadside and island, water-body, industrial area, roof-top, etc. Most of these habitats were spread across the study areas and interwoven.
As the research approach was to find total diversity in the whole study area, that is why we have included all available units for the floral survey. All types of observed plant species (i.e., herbs, shrubs, timber, non-timber, exotics, native, orchids, ferns, cactus, etc.) occurring in the above-mentioned habitats were identified and recorded in the field by their species names. Plant samples of unknown species were collected to prepare herbarium.
Data about the purpose of planting or site-specific use of the plants was also collected. The assessment of floral composition in the rooftop garden was determined by the interviewees' perception and field observation. The indoor plants including the plants occurring on the balcony of the households were recorded together with roof-top plants.

Identification of the collected specimens and data analysis
Herbarium was prepared with the fertile materials of plant samples and mounted on a sheet of paper of standard size 29.21 cm Â 41.91 cm (11.5" Â 16.5"). A tag with the information such as local name, scientific name, area of collection, collection time, habit, habitat, family, collector's name was attached with each sheet. The unknown samples were identified with the help of taxonomists of the Forest Botany Division of Bangladesh Forest Research Institute (BFRI). A consultation with published journals and reference books, e.g., Bengal Plants (Prain, 1903); Encyclopedia of Flora and Fauna of Bangladesh (Ahmed et al., 2008(Ahmed et al., , 2009); Trees of Bangladesh (Das and Alam, 2001), etc. was also conducted to identify the plant specimens.
Identified plants were compiled together, and categorized based on their habitat and habit forms. Then, the relative proportion of the number of species in different habit forms, habitats, nature of occurrence (i.e., exotic or native) and taxonomic families, etc. were estimated. Moreover, the plants were categorized based on the purpose of the plantation.
All the collected data and information (qualitative and quantitative) were gathered in an MS Excel sheet and sorted carefully. Then, we rearranged all the data in a systematic way to acquire the intended results from this research. Finally, we analyzed the compiled data using spreadsheets (MS Excel, version: 2010) and demonstrated the findings in the form of figures and tables.

Floral composition
The study enumerated a total of 418 vascular plant species under 315 genera and 120 families from the central urban part (Ward-8: Shulakbahar) of Chattogram city, Bangladesh. Among the 418 vascular plants, herbs formed the major habit (145 species) and occupied around 35% of all the recorded plant species followed by trees (34%), shrubs (17%), climbers (12%), orchids (1%) and ferns (1%). We categorized all the recorded plants based on their habit forms, then classified and demonstrated under genus and family (Table 1).
The present study recorded three gymnosperms, among which Cycas pectinata (Cycas) was the only native gymnosperm whereas, Araucaria cunninghamii (Araucaria) and Pinus oocarpa (Pine) recorded as exotic tree species in the study area. Thuja orientalis (Thuja) was the exotic ornamental shrub commonly found in the nursery and also in the institute premises.
The present study revealed a distinctive variation among the abundance of various vascular plant species belonging to different families. In this study, we found that 15 dominant families contained about 48% of the total plant species and the remaining 52% plant species under the rest of 105 families ( Figure 2). Maximum number of species (24) was contained by Asteraceae family followed by Poaceae (21 species), Euphorbiaceae (18 species), Fabaceae (16 species), Araceae (14 species), Apocynaceae (13 species) and Arecaceae (13 species).

Occurrence of plant species in 10 habitats
The study recorded the highest number of plant species from the home gardens and nurseries in comparison with other habitats. Maximum tree species were found in the nursery (98 species), followed by home garden (94 species), institution (89 species), graveyard (63 species), plain fallow land (62 species) and hilly areas (44 species) ( Table 2). The study recorded 143 plant species occurring in the plain fallow lands followed by 80 plant species in the hilly fallow areas. Our study enumerated a total of 183 plant species belongs to 162 genera and 77 families from the premises/campus of the institutions. However, the minimum number of tree species (19) was recorded from the industrial area Floral diversity and near water bodies (36). In the case of herbs, maximum (57) was recorded from the rooftop gardens followed by the home garden (47) and plain fallow areas (41). On the other hand, the maximum number of shrub species (52) was enumerated from the rooftop gardens followed by institutional areas (43) and home gardens (39).

Indigenous and exotic trees with their distribution
In the present research, a comparative study between native and exotic plant species revealed that exotic species (50.3% of all 418 species) became more common than native (49.7%) species due to their aesthetic value and low space occupancies in the indoor, rooftop and premises. This study recorded 210 exotic plant species under 112 families and 208 native species under 99 families. This is maybe because of wider adaptability in the Maximum number of species was recorded from the rooftop gardens (25 natives and 88 exotic species) followed by nursery (32 natives and 75 exotic species), home garden (44 native and 59 exotics) and graveyard (53 native and 48 exotic species) (Table 3).
Highest percentage (75%) of exotic species was recorded from the roof-top gardens and lowest (31%) was recorded from the plain fallow lands. Maximum percentage (68%) of native species was found from the plain fallow lands, whereas the lowest (21%) was revealed from the roof-top gardens (Figure 3).
The comparative study on the occurrence of indigenous and exotic species in different habitat revealed that the proportion of exotic species was increasing in comparison to indigenous species in several habitats because of their faster growth and low mortality rate. In some plantations, exotic species were found where native species were very low in number. These results indicated that people are willing to establish the plantation of exotic species rather than indigenous plant species.

Roof-top gardens of ornamental, native and introduced plants
Hobby and environmental considerations are the main purposes of rooftop gardening in most cases as revealed by the present survey. Beautification, recreation, etc. are also some common reasons for rooftop gardening in the study area. Some people opined it as a good means of passing ones' leisure time. During the field survey, it was observed that rooftop  Floral diversity gardens were managed by the local communities for fruit and vegetable productions. In some cases, people mentioned that they managed roof-top gardens for biodiversity and environmental conservation. This study also revealed that women are engaged more (60%) in roof-top gardening than that of the males (40%).
Seedlings and graftings were popular as the planting materials used by the gardeners for raising roof-top gardens. Around 70% of the interviewees opined that they collect the planting materials from the nearby nursery, hawker, exhibition and relatives' gardens among which nursery is the very feasible source.

Threats posed by the exotic plants
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, and also have negative impacts on the growth and development of native tree species. A number of well-established exotic tree species, i.e., Acacia auriculiformis, Albizia richardiana, Araucaria cunninghamii, Dalbergia sisso, Eucalyptus camaldulensis, etc. and some noxious exotic weeds, e.g., Chromolaena odorata, Duranta erecta, Lantana camara, Mimosa pudica, etc. were recorded from the plantation sites of different habitat.

Non-woody medicinal plant resources
In the present study, 24 non-woody medicinal plant species (belonging to 21 genera and 14 families) were enumerated from the study area including cultivated and planted. Of the 24 non-woody medicinal plant species, 13 species were herbs, 9 species were shrubs and only 2 species were climbers (Figure 4).
Aloe vera, Centella asiatica, Coriandrum sativum, Scoparia dulcis, etc. were the common herbs recorded from the home gardens. Abelmoschus esculentus, Capsicum annuum, Citrus aurantifolia, etc. were the common plantation shrub species recorded from the graveyards, home gardens and hilly areas. Calotropis gigantea and Urena lobata were the only two medicinal shrub species naturally grown in the study area.
The abundance of non-woody medicinal plant species in different families showed a comprehensive variation. Among them, 71% of species were represented by seven dominant families, whereas 29% of species by others. The most dominant seven families were Apiaceae (three), Araceae (three), Solanaceae (three), Apocynaceae (two), Malvaceae (two), Rutaceae (two) and Zingiberaceae (two) ( Figure 5).

Bamboo, rattan and cactus species
The survey recorded five bamboo species of which Bambusa vulgaris and Melocanna baccifera were common in plantations. One rattan (Calamus guruba) and one cactus species (Echinopsis pachanoi) were found as plantations. In this survey, Chhan (Imperata cylindrica) infested areas also revealed that indicates degraded soils with low fertility. This study recorded about 418 vascular plants from the central urban part of Chattogram city, which was lower than that is of Rahman (2013); where the researcher recorded 425 angiosperms (under 321 genera and 108 families) containing 113 trees, 74 shrubs, 186 herbs and 52 climbers from the Rajshahi district of Bangladesh (Rahman, 2013). A comparison of floral richness among the three major cities of Bangladesh is shown in Figure 6.
The study recorded only 24 medicinal non-woody plant species (9 shrubs, 13 herbs and 2 climbers) from the study area, which was lower than the medicinal plants mentioned by Akber and co-researchers; where the researchers recorded about 67 medicinal plant species from the Khulna city of Bangladesh (Akber et al., 2011).
The survey enumerated only three gymnosperms from the Chattogram city area, which was comparatively lower than the Chunati Wildlife Sanctuary (CWS), Chattogram by Hossain and Hossain (2014) and Sitakunda Botanical Garden and Eco-park (SBGE), Chattogram by Dutta et al. (2014). Hossain and Hossain (2014) enumerated only four and Dutta et al. (2014) recorded eight gymnosperms from the CWS and SBGE, respectively.
The result of the study indicated the availability of some common plantation tree species (Acacia auriculifurmis, Gmelina arborea, Swietenia macrophylla, Tectona grandis, etc.) in the study area, which supports the findings of similar research (Dutta et al., 2015;Uddin et al., 2015) conducted in Chattogram, Bangladesh. The study also revealed the occurrence of Chhan (Imperata cylindrica) at different habitats in the study area, which implies the Floral diversity presence of low fertile soils with less soil moisture in the Chattaogram city area according to the report of Dutta and Hossain (2016).
Based on fieldwork, a strengths, weaknesses, opportunities and threats (SWOT) analysis was performed to assess the opportunities and available strengths to conserve the native plant species of Chattogram city (Table 4). SWOT analysis was conducted through an extensive field survey and using the key findings of the study prescribed by Dutta and Hossain (2020). The main strength is that vegetation coverage in the graveyards and some other habitats (institutions, nurseries, etc.) is quite dense due to sacredness, proper management and less accessibility. Such areas are mostly protected as a source of biodiversity hotspot, storing carbon and minimizing pollution. Sacredness and spiritual values are really helpful to protect the native trees in the Chattogram city area.
The major weakness identified in this study is that the management of plantations and plant resources is not locally conducted in a scientific approach. Local communities could be aware and skilled enough regarding the preservation, protection and conservation of the existing flora through an urban-forestry scientific approach. Promoting green approaches; raising awareness among city dwellers about urban forestry should be developed by government or non-governmental organizations (NGOs) in a convenient way.
This study recorded the existence of several native plant species from the plain and hilly fallow areas. Such opportunities indicated that both plain and hilly fallow sites have the last hope to build green spaces. Support from the authority for monitoring the plant composition is another opportunity to conserve the existing flora. However, roof-top gardening has seemed to a prominent sector for urban greening as it is getting popularity for ornamentation, as well as growing fruits and vegetables.  The findings of the study clearly showed that unplanned urbanization has caused serious ecological imbalances in Chattogram city. Furthermore, land-cover changes and conversion of natural patches to housing threaten the habitats of plant species day by day. In this regard, the sustainable urban forestry approach should be an effective pathway for improving the current status of plant diversity and the green spaces in the study area.

Recommendations
The following recommendations were made after reviewing the major findings of this study: Urban forestry should be increased in urban communities to conserve the rare native plant species in different habitats.
Institutional premises (such as school, college, university and hospital) and industrial areas should be brought under plantation programs, and those have vegetation coverage should maintain properly.
Policymakers should think about several habitats to introduce the afforestation programs by negotiating discussion with the landowners. Policy about green coverage should formulate and develop to manage the roof-top gardens in a sustainable way.
The present study also highly recommended that green NGOs could develop partnerships and synergies with different stakeholders to ensure the rich floral diversity in the Chattogram city area of Bangladesh.

Conclusion
Chattogram city of Bangladesh is facing extreme unplanned urbanization problems due to the high population, unplanned housing, illegal cutting of trees and hills, encroachments in fallow lands, excessive infrastructure development, etc. Some major challenges for conserving the floral diversity in the Chattogram city are minimizing faster urbanization, eradicating ecological deterioration, restoring natural resources and mitigating climate change. Meanwhile, sustainable management of plant communities in the Chattogram city area is very important for assuring the ecological amelioration, environmental development and socio-economic upliftment of the city inhabitants. The present study focuses on an inventory of vascular plant composition of the central part (Shulakbahar ward) of Chattogram city, Bangladesh. The findings of 418 vascular plants (under 315 genera and 120 families) at different habit forms in the Chattogram city area need immediate conservation plan. The findings of the study provide only baseline information; further study needs to be carried out to evaluate the ecological and environmental effects of existing flora on urban ecosystems of Chattogram city, Bangladesh.