ANGIOSPERM DIVERSITY OF LAWACHARA NATIONAL PARK ( BANGLADESH ) : A PRELIMINARY ASSESSMENT

The present article focuses on an inventory of angiosperm diversity of Lawachara National Park. Using traditional taxonomic techniques data have been collected from the Park during January to October 2008. In this preliminary assessment, a total of 374 angiosperm species including cultivated ones have been catalogued under 84 families. Nineteen threatened plant species have also been recognized in the Park.


Introduction
Lawachara National Park under Kamalganj upazila of Maulvi Bazar district is a part of West Bhanugach reserve forest, which was declared reserve in early nineteenth century as per the Forest Act 1878, the Assam Forest Manual 1898 and the Forest Act 1927.The Park is located nearly 160 km northeast of Dhaka and approximately 60 km south of Sylhet city.It lies between 24˚30΄-24˚32΄ N latitude and 91˚37΄-91˚39΄ E longitude.A part of the reserve forest was declared as a National Park in 1996 having a total area of 1250 ha (Green, 1990;Canonizado and Rahman, 1998;Riadh, 2007;Ahsan, 2007).Present forest types of Lawachara are a combination of planted exotic species and mixed forest with a deciduous canopy and an evergreen understory (Ahsan, 2000).The forest originally supported an indigenous vegetation cover of mixed tropical evergreen type (Alam, 1998).
The topography of Lawachara National Park is undulating, with slopes and hillocks that range from 10 to 50 m in elevation (Rizvi, 1970;Riadh, 2007).These hillocks are scattered and interspersed with numerous streams that flow through the forest.The hills are composed of upper tertiary rocks in which sand stone largely predominates (Ahmad, 1970;Stevens, 1986) along with siltstones and mudstones, locally altered to slates and shales.The significant soils in the hills of Maulvi Bazar belong to Ramgarh and Rangamati series on Dupitila formation (Stevens, 1986).Soils of the Park are generally sandy loam and the rest are mostly clayey loam (Ahmad, 1970).The area enjoys a moist tropical climate characterized by a period of high precipitation from April to September and five months of relatively dry period from November to March.
In Bangladesh, assessment of plant diversity of the forests of different protected areas has already been started.Khan et al. (1994), Rahman and Hassan (1995), Uddin et al. (1998), Uddin and Rahman (1999), Khan and Huq (2001) and Uddin and Hassan (2004) have so far published floristic works but no such work was carried out for Lawachara National Park.The values of different aspects of this Park is now realized both by local and international communities.One international organization USAID and Nishorgo Support Project in collaboration with Forest Department have been working in the Park to establish co-management strategy for the conservation of biodiversity and sustainable development.For the sake of management of biodiversity, assessment of plant diversity especially angiosperm diversity as major component of the park, is very essential that will provide baseline information on which action plan can be made.The present study has been undertaken to make an inventory of angiosperm diversity of Lawachara National Park.

Materials and Methods
Six field visits, each lasted for five days have been made to the area during January 2008 to October 2008.Each section of this spectacular National Park was carefully combed to assure all species in the list including those that were scattered or infrequent.Special effort was made to locate the species already listed as threatened or endangered in the country.Botanical specimens were collected and field identifications were confirmed back at Dhaka University Herbarium (presently known as Salar Khan Herbarium).Voucher specimens were preserved in the same Herbarium.Woody flora of Sylhet (Alam, 1988) and flora of Rema-Kalenga wildlife sanctuary (Uddin and Hassan, 2004) were also consulted for the identification of specimens.

Results and Discussion
Based on this study, a preliminary list of angiosperm diversity of the Lawachara National Park was made that includes 374 species under 264 genera and 84 families.For each species scientific name, Bengali name (when available) and family are provided (Table 1).Of 374 species recorded here, herbs are represented by148, shrubs by 71, trees by 90 and climbers by 65 species.Nineteen species listed as threatened in the Red Data Book of Vascular Plants of Bangladesh (Khan et al., 2001) have been located in this Park.These are Ammomum aromaticum, Aquillaria agallocha, Bombax insigne, Calamus guruba, Cymbidium aloifolium, Desmos longiflorus, Globba multiflora, Hedychium coccineum, Hedychium thyrsiforme, Holigarna longifolia, Hydnocarpus kurzii, Mangifera sylvatica, Phrynium imbricatum, Pinanga gracilis, Pterospermum semisagittatum, Rauvolfia serpentina, Steudnera colocasioides, Taxillus thelocarpa and Terminalia citrina.One species of gymnosperm (Gnetum oblongum) and one species of tree fern (Cyathea gigantea) listed as endangered in Bangladesh were also located in the Park during this survey.Based on the field observations and present results it may be concluded that the angiosperm diversity of Lawachara National Park is very rich and the Park is the home for many threatened plant species of Bangladesh.The present result is a preliminary list of angiosperm diversity of the Park.
Currently plant diversity of this Park is in great risk because of many threats as observed during field works.Noteworthy threats are frequent forest fire during dry season, illegal logging, fire wood collections, betel leaf cultivation, oil exploration, development works, uncontrolled visitors and population pressure.Though the plant diversity of the park is under in situ conservation plan, the management plan should be made based on local knowledge of plant diversity.As the Park is the home of many threatened plant species and as well as for wildlife, for the sake of better management option distribution map of threatened plant species should be made on priority basis.Such map will facilitate accurate location and home range of threatened species in the Park so that monitoring activities can be carried out easily.In severe cases, ex situ conservation for particular species may be followed to replicate their population number.Present management system should be strengthened by deploying relevant manpower including plant taxonomists for proper documentation and conservation and sustainable development of Lawachara National Park.