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Undergrowth Species Diversity of Sundarban Mangrove Forest (bangladesh) in Relation to Salinity

S. Harun Rashid
Department of Biology, Lakehead University, Thunder Bay, Ontario, P7B 5E1, Canada,

Reinhard Böcker
Department of Vegetation Science, Institute of Landscape and Plant Ecology-320, University of Hohenheim, 70593-Stuttgart, Germany.

Abstract/ Executive Summary:

Undergrowth species diversity was investigated by random quadrat method. Ordination and Shannon-Wiener diversity index were produced by the CANOCO program and Cluster analysis was done by the SAS (Statistical Analylitical System, sixth version) program. 48 undergrowth species were recorded in the Sundarban mangrove forest belonging to the dominant families such as Fabaceae (Cynometra ramiflora, Dalbergia spinosa, Derris trifoliata), Poaceae (Myriostachya wightiana, Porteresia coarctata), Palmae (Nypa fruticans, Phoenix paludosa), Acanthaceae (Acanthus ilicifolius), Pteridaceae (Acrostichum aureum), Myrsinaceae (Aegiceras corniculatum), Rhizophoraceae (Rhizophora mucronata, Bruguiera gymnorrhiza). On the basis of frequency distribution of undergrowth vegetation data sets six undergrowth species were found to be dominant and widely adapted to the various salinity conditions in different zones of Sundarban mangrove forest, which were frequently occurring in most of the sites and quadrats such as Acanthus ilicifolius, Acrostichum aureum, Derris trifoliata, Vitis trifoliata, Sarcolobus globosus and Phoenix paludosa. The ordination of undergrowth species was assessed between environmental variables (salinity and pH) and undergrowth species. The ordination of undergrowth species revealed that some species are more saline tolerant, closely associated and widely distributed in the Sundarban mangrove forest like Derris trifoliata, Acanthus ilicifolius, Nypa fruticans, Sarcolobus globosus, Dalbergia spinosa, Flueggia virosa, Pandanus foetidus and Phoenix paludosa. It is interesting to note that salinity is a vital factor for the development of undergrowth species. It can also be concluded that the rich diversity of under growths of healthy individuals might be indicative of the healthy mangrove forest of the low saline zone area and poor diversity of under growths, as well as their stunted growth might be indicative of the ill mangrove forest of high saline zone area.

Keywords: Undergrowth flora, Salinity, pH, Ordination, Sundarban.

Location: Sundarban mangrove forest (Bangladesh)

Start Date:

End Date:

Program Area: Conservation and Biodiversity

Commodity: Plant

Objectives:

The present paper is concentrates on the undergrowth species composition and diversity, dominant categories and zonation patterns of SMF, those are responding in various levels of salinity.

Methodology:

Sundarban The Sundarban was declared as a Reserve Forest (SRF) in 1879, since then it has been directly administered and managed by the Forest Department. Sundarban mangrove forests lying between the longitudes 89° 00' and 89° 55' east and latitudes 21° 30' and 22° 30' north covering an area of 5.770 km² , of which 4.016 km² are covered by the forests and the remaining 1.756 km² are in the form of rivers, canals and creeks, varying from a few meters to several miles. The SRF is an important natural resource provider of a large number of products such as timber, pulpwood, fuelwood, fish, thatching materials, honey, bee wax. In addition, it also supports a very rich and diverse flora and fauna. The only natural habitat of the endangered flagship species, the Royal Bengal Tiger lies in Sundarban. Sundarban biodiversity is noticeably rich in terms of plant and animal diversity. The number of species found in the Indian mangal swamps is nearly as many as those reported for Malaysia and Indonesia (CHAPMAN, 1976). PATIL (1962) reported that half of the total number of mangrove species found in the world occur in the Indian Sundarbans (present in Bangladesh and Indian Sundarbans). 2.2 Study sites The study area included 29 key sites from the SMF in order to represent the various existing identifiable ecological habitats of the mangrove landscape (Fig. 1). Plant specimens recorded represented a wide section of the previously recognized three zones, (CURTIS, 1933; KARIM, 1994; SIDDIQI, 2001) namely oligohaline, mesohaline and poloyhaline zones. 2.3 Methods of plant collection and identification Plant samples were collected by standard quadrat method (BRAUN-BLANQUET, 1964; RAUNKIAER, 1934). The quadrat size (5m x 5m) was determined on the basis of a species area curve (BRAUN-BLANQUET, 1964). During the study period (2002 to 2004) two times was visited in each sites. The quantitative data on undergrowth species, collected from at least ten randomly taken quadrats on its representative part of 29 sites. All undergrowth species were identified at the Bangladesh National Herbarium (BNH). The major floristic works consulted were HOOKER (1872-1897), PRAIN (1903, 1903a), BOR (1960) and HUQ (1988) and the Flora of Bangladesh (Nos. 1-55). 2.4. Methods of Ordination The undergrowth species were analyzed by the ordination method. The collected vegetation data were transformed in a frequency table and analyzed with the ordination method by the application of CANOCO software program (BRAAK & SMILAUER, 2002). Shannon-Wiener diversity index (KENT & COOKER, 1992) and N2 diversity (according to HILL, 1973) were produced by the CANOCO program. The Cluster analysis was done by the SAS (Statistical Analylitical System, sixth version) program. 2.5 Water salinity and pH Water pH and salinity of water were estimated by pH meter and conductivity meter respectively.

Source of Information: Ber. Inst. Landschafts- Pflanzenökologie Univ. Hohenheim Heft 17, 2007, S. 41-56, Stuttgart 2008

Article Link (Online Journal):

Funding Source:

Budget:

Total Budget (Tk.) :

Achievement/Findings:

The undergrowth species are growing in a suitable environment and related to salinity. Influencing factors are soil and water salinity, tidal flooding, sedimentation load and nutrient availability etc. It is indicated that most of the undergrowths species were found growing in the oligohaline to mesohaline zones, because of lower salinity levels. Naturally undergrowth species can not tolerate frequent tidal flooding and strong salinity except some species like Acanthus ilicifolius, Porteresia coarctata. It is interesting to note that the salinity is playing key role for the growing of the undergrowth species. Therefore, the values of salinity are really influencing the undergrowth vegetation as positively or negatively as well as high or poor diversity. It can also be concluded that the rich diversity of undergrowths of healthy individuals might be indicative of the healthy mangrove forest of the low saline zone and poor diversity of undergrowths, as well as their stunted growth might be indicative of the ill mangrove forest of the high saline zone.

Knowledge Management: Report/Proceedings