Chapter 3
Materials and methods
3.1 Study site
The Tilagarh Eco-park is located at North Sylhet Range-1 in Sylhet Forest Division under tropical evergreen and semi-evergreen biogeographic zone. It is about 6 km from Sylhet city. The Eco- Park is established through Gazette Notification No. PA BA MA / PA RI SHA-1/ Tilagarh Eco-park /4/ 2006 /234. The Tilagarh Eco-park is 45.35 ha (112 acres). Soil ranges from clay loams to pale brown (acidic) clay loams on the hills. Red sandy clay contains granules of magniferous iron ore (Anon, 2006).And soil ph range is 6 to 7.5.Climate conditions are warm and humid. April and May are the warmest, and December and January are the coolest months. The tropical monsoon climate prevails in the area with average maximum temperature of 31.6˚C and average minimum temperature of 19.9˚C. The average annual rainfall is 3937mm, most of which falls between June-September (BBS/UNDP, 2007).
Source: Anon, 2007b
Figure : Map of Tilagarh Eco-park.
3.2 Methods:
The study was conducted through stratified random quadrate method. The area was divided into three slope category into the map and sampling point was selected randomly into the map. Total thirty plots were selected from three different slope i.e. ten plot from each slope. The study was conducted from 1st November to April 20, 2008 .There were taken thirty plots each 10m×10m in size. The optimum quadrate size (10m×10m) for tree species was determined by applying species area curve through Ambasht (1978), Sharma (1979) and Gareth’s (1991) method. Within each plot the number and name of all the trees were counted and recorded. Diameter of all trees was measured at breast height (dbh). The collected data were analyzed to determine number of stems per hectare and basal area per hectare. The data also analyzed for relative density, relative frequency, relative dominance and importance value index through Shukla and Chandal (2000).For this pourpus I use meter tape, dia meter tape and hugalti meter.
3.2.1Quantitative structure of plant communities:
The parameters that commonly used to characterize the structure of plant community are Number of stems ,Basal area Density Relative density Frequency Relative frequency
Abundance Relative abundance Relative dominance and Importance Value Index.
3.2.1.1 Number of stems :
To measure the number of stem, calculate the number of stem in 10m × 10m plot. Finally calculate all the number of stem.
3.2.1.2 Basal area: To determined the basal area I use the formula
Basal area = п r² at the breast height.
= п (d/2)²
= п/4 d²
Here d = Diameter at breast height.
3.2.1.3 Density of a species:
The numerical strength of a species in relation to a definite unit space is called its density. The crude density refers to the number of individuals of a particular species per unit area. Each organism occupies only the area that can adequately meet it requirements. Thus the density of an organism refers to the area available as living space. This would be ecological density. According to Shukla and Chandal (2000), the following formula is used for calculating density of a species:
Density of a species per unit area
3.2.1.4 Relative density of a species:
The proportion of density of a species to that of a stand as a whole is referred to as relative density. According to Shukla and Chandal (2000), the following formula is used for calculating relative density of a species:
Relative density of a species 
× 100
3.2.1.5 Frequency of a species:
In the community, the individuals of all the species are not evenly distributed. Individuals of all the species are widely spaced while those of some other species are found in clumps or mats. The distribution patterns of individuals of different species are indicating their reproductive capacity as well as their adaptability to their environment. Frequency refers to the degree of dispersion in terms of percentage occurrence. According to Shukla and Chandal (2000), the frequency of a species is determined with the help of following formula:
Frequency 
3.2.1.6 Relative frequency:
The dispersion of species in relation to that of all the species is termed as relative frequency of a species. According to Shukla and Chandal (2000), Relative frequency is determined by the following formula:
Relative frequency of a species
3.2.1.7Abundance of a species:
The estimated number of individuals of a species per unit area is referred to as abundance. According to Shukla and Chandal (2000), the abundance is determined by the following formula:
Abundance of a species 
3.2.1.8 Relative abundance of a species : To estimated the relative abundance of a species I use the formula
Relative abundance of a species
× 100
3.2.1.9 Relative dominance:
Relative dominance is the proportion of the basal area of a species to the sum of the basal coverage of all the species in the area. According to Shukla and Chandal (2000), Relative dominance of a species is calculated by the following formula:
Relative dominance of a species 
3.2.1.10 Importance Value index:
The overall picture of ecological importance of a species in relation to the community structure can be obtained by adding the values of relative density, relative dominance and relative frequency. The total value out of 300 species is called importance value index of the species (Shukla and Chandal, 2000). A score of zero in this indicates absence of a species; a score of 300 indicates a single species in the stand.
3.2.2 Diversity index of plant communities
the different formula were commonly used to determine the diversity of plant communities are Shanon-winner diversity index, Species diversity index, Index of dominance, Species evenness index and Species richness index.
3.2.2.1 The Shanon-winner diversity index
The Shanon-winner diversity index was calculated according to Michael (1990) and it is as follows:
H = -∑ PiLnPi
Where, H = Index of species diversity; Pi 
3.2.2.2 Species diversity index
Species diversity index was calculated on the basis of the following formula given by Odum (1971):
SDI 
Where, SDI = Diversity index; S = number of species; N = No. of individuals.
3.2.2.3 Index of dominance
Index of dominance (ID) was measured by Simpson index (Simpson, 1949)
ID =∑ (Pi)
Where, ID = Index of dominance; Pi =
3.2.2.4 Species richness index
Species richness index (R) was estimated employing the following formula given by Margelef (1958).
R 
Where, R = Species richness index; S= total number of species; N = total number of individuals of all the species.
3.2.2.5 Species evenness index
Species evenness index (E), was estimated by following formula given by Pielou (1966).
E 
Where, E = Species evenness index; H = Shanon-winner index of diversity; S = Total
number of species.
