There is a decrease in canopy closure in recent years. In 1960, 78% of the total area of the Sundarbans had a canopy closure of 75 % or more. A survey made in 1985 showed 65% of the forest as having a canopy closure of 70% or more. In 1996, the situation worsened further. Pre-dominant canopy classes are those having only 30% or more closure. In general, the forest is more closed in the east than in the west. The canopy closure in the east is usually more than 70%, in the middle part it is between 30 and more than 70% and the western part has from 30 to less than 70% (Siddiqui 2001).
Vegetation Study
Satkhira rage was selected on the experimental area. This area is strong saline zone. Every sampling spot was divided into-3 sites mainly on the basis of sloping, vegetation, age and soil erosion etc. The selected sites in all the sampling spots were treated as “permanent sample plots”.
Selection of sampling season:
The Sundarbans, mangrove ecosystems is dynamic and complex. Changes of vegetation are continuous. The mangove plant species of the different sample plots were recorded and collected round the three year with every Summer, Monsoon, Post-monsoon and winter seasons from March 2006 to February 2009.
Determination of quadrat size:
Mangrove plants investigation was performed by random quadrat method. In the present investigation quadrat size was determined by a more or less constant presence of plant species and in this regard ‘Species area curve’ (Ambasht 1990) was determined first. 5m×5m size was found to be most convenient quadrat size. Thus 5m×5m quadrat was considered finally for permanent spots for vegetation sampling in all the permanent sampling plots.
Vegetation recording and sampling:
In each permanent sampling plot, at least 20 quadrats were applied randomly. Plants names including local name, habits, life-form; (Raunkaier 1934) and economic uses of individual plant species was recorded. Samples of recorded plants were also collected in a view to build up small herbarium on ‘Mangrove Forest Flora of Satkhira range’. In this way, vegetation recording and sampling were accomplished in “Satkhira Range
Phytodiversity analysis:
The quantitative phytodiversity attributes density, relative density, frequency and relative frequency and importance value percent (IV %) of each attributes were analyzed and computed by following formulae.
Total number of individual s of a species in all the quadrat
i. Density (D) = -----------------------------------------------------------
Total number of quadrat studied.
Total number of invividual s of a species
ii. Relative density (D3) = ---------------------------------------------------- X 100
Total number of individual s of all the species.Number of quadrat in Which species occurred
iii. Frequency (F) = ---------------------------------------------------- X 100
Total number of quadrat studied
Frequency of the species
iv. Relative frequency (F3) = ---------------------------------------- X 100
Total frequency (F) of all the species
v. The importance value percent (IV%) for each species was calculated by adding relative density (D3), relative frequency (F3) and dividing it by 200 and multiplied by 100.
PHYSICO-CHEMICAL CONDITIONS OF WATER
In every water sample were collected from all the permanent sampling sites. Then immediately different parameters of the samples were analyzed using the following standard methods.
PHYSICO-CHEMICAL CONDITIONS OF WATER
In every water sample were collected from all the permanent sampling sites. Then immediately different parameters of the samples were analyzed using the following standard methods.
WATER TEMPERATURE
Centigrade thermometer was used to determine of water temperature.
WATER SALINITY
Water salinity was recorded by using Hand Refractometer. The result was expressed in ppt.
HYDROGEN-ION CONCENTRATION OF WATER (pH)
Water pH was measured by HANNA digital pH meter (Model H198107).
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