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Species Diversity, Change in Forest Cover and Area of the Sundarbans, Bangladesh

Asfaque Ahmed
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Md. Ataullah
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Parveen Rashid
Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh

Ashit Ranjan Paul
Deputy Chief Conservator of Forest
Bangladesh Forest Department, Agargaon, Dhaka-1207, Bangladesh

Sukumar Dutta
Bangladesh Space Research and Remote Sensing Organization (SPARRSO), Agargaon, Dhaka-1207, Bangladesh

Md. Shahjahan Ali
Bangladesh Space Research and Remote Sensing Organization (SPARRSO), Agargaon, Dhaka-1207, Bangladesh

Abstract/ Executive Summary:

The phytosociological analysis, species diversity and types, fidelity, presence, constancy, Sørensen similarity index and changes in forest cover, land and water areas since 1972 were analyzed. Forty six species were recorded both in quadrates and growing outside which belong to 26 families and 41 genera, 19 were distinguished as true mangrove species and the rest were mangrove associates. Leguminosae and Rhizophoraceae were the dominant families represented by 5 spp. each. Three species were found to be invasive, namely Blumea lacera (Burm. F.) DC., Catharanthus roseus (L.) G. Don., Wedelia chinensis (Osbeck) Merr. The maximum importance value index was found in Heritiera fomes Buch.-Ham (48.08). The overall species diversity (H) of SMF was found 3.81, species richness (d) was 9.10 and evenness (e) was 0.47. The forest area was 385,237 ha in 2015. The satellite images showed that the forest and water area of SMF decreased gradually till 2015 in comparison to 1972. The bare land of Sundarbans showed a significantly increasing trend till 2015 since 1972.

Keywords: Species diversity, Invasive species, Forest cover, Forest area, Satellite images

Location: Chandpai, Sarankhola, Satkhira and Khulna Ranges, Bangladesh

Start Date: 06-04-2015

End Date: 10-04-2015

Program Area: Conservation and Biodiversity

Commodity: Mangrove

Objectives:

To analyse the current state of the structure, composition, pattern of distribution and the diversity of the mangrove species in the three ecological zones of all four Ranges of SMF and to estimate the changes in forest covers and land area by using satellite images.

Methodology:

Ecological exploration to the SMF of Bangladesh was carried out from 6 to 10 April, 2015. The study was conducted in Chandpai, Sarankhola, Satkhira and Khulna Ranges. Fourteen quadrats were taken in the three ecological zones namely, oligohaline, mesohaline and polyhaline of the SMF (Nazrul-Islam 2003). To find out the total number of different plant species of overall SMF, the plant species situated outside the studied quadrats were also recorded. A 15 × 15 m plot (quadrat) was established in each location at about 15 - 20 m inland from shore to avoid effects of the nearby flowing rivers (Chen and Twilley 1999) for phytosociological survey. Sampling was done in all the strata i.e. trees, shrubs, herbs and climbers. Plants with dbh ≥ 10 cm with height at least 8 - 10 feet and good growing conditions were considered as tree. Among the 14 quadrates, 8 were established in oligohaline zone and 3 each in mesohaline and polyhaline zones of the forest. The chief synthetic character such as important value index (IVI) was measured according to Curtis (Curtis 1959); the types of species (Tomlinson 1986), fidelity, presence and constancy were measured according to Braun-Blanquet (1932). Species diversity (H) of each site was determined by using Shannon-Weaver Index (Shannon and Weaver 1949), species richness index (d) was calculated according to Margalef (1951), and evenness (e) was calculated according to Pielou (1966). Floristic similarities were measured according to Sørensen (1948) similarities index. Remote sensing and geographical information system have been applied to assess the changes in the forest cover, water bodies and bare areas. Satellite TM data of 1972, 1989, 2001, 2010 and 2015 were downloaded from GLOVIS, USA. Satellite data were geo-referenced using ERDAS IMAGINE/ ARC-GIS software. Then mosaic was done to the necessary frame and sub-set of Sundarbans forest area for the research work. Fifteen classes were made by unsupervised classification tools of ERDAS IMAGINE software. Finally three classes of areas like forest cover, water bodies and bare land were calculated through the software.

Source of Information: Bangladesh J. Bot. 47(3): 351-360, 2018 (September)

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The present study provides an update of the state of plant diversity and changes in forest cover and area and is likely to contribute in assessing the different anthropogenic impacts. Therefore, the SMF being World Heritage deserves special attention particularly from the Government of the People's Republics of Bangladesh for its conservation. The maximum importance value index was found in Heritiera fomes Buch.-Ham (48.08). The overall species diversity (H) of SMF was found 3.81, species richness (d) was 9.10 and evenness (e) was 0.47. The forest area was 385,237 ha in 2015. The satellite images showed that the forest and water area of SMF decreased gradually till 2015 in comparison to 1972. The bare land of Sundarbans showed a significantly increasing trend till 2015 since 1972.

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