Study area KNP was selected for the study because of its unique geo-physical features and richness in biological diversity. KNP is located at North Sylhet Range-1 (subdivision) under Sylhet Forest Division under tropical evergreen and semi-evergreen bio-geographic zone. Formerly known as Khadimnagar Reserve Forest, it was declared a National Park in 2006. The total area of the site is 679 ha, surrounded by three tea gardens and is submerged with several watersheds locally known as ‘chara’ (Office information ... 2009). The hills are dissected by numerous valleys, separated by ridges rising some 50 m above them. The hills are generally low and gently sloping. Soil ranges from clay loams to pale brown (acidic) clay loams on the hills (FMP 1998). Geographically, KNP lies between 240 56' –240 58' N and 910 55' –910 59' E. Climate is 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 30.70C and average minimum temperature of 18.90C. The average annual rainfall is 3931 mm, most of which falls between June and September (BBS/UNDP 2005). The forest is a semi-deciduous tropical forest, where tall trees are deciduous and the under storey is evergreen. The forest operates on the principle of production forestry, for example, the forest was periodically clear felled and subsequently planted with valuable short and long rotations timber trees, cane and bamboo species (International Resources Group 2009; Office information ... 2009).
Research methods The present study was conducted in two phases, namely respondent survey and plot survey, from different topographical stratas in the study areas. Respondent survey was carried out in the first phase and the plot survey in the second phase. The structure of any plant community cannot be studied by observing each and every individual plant of that species growing in a habitat. Therefore, rough estimates of species content in a habitat can be made by observing the plant species at different places or sample areas in the habitat (Shukla and Chandel 2000). Therefore, sample plots in the study areas were selected from three topographical strata, namely plain lands or low lands, middle of the hill, and top of the hill.
Data collection from respondents Interviews were conducted targeting primarily older or experienced persons (predominantly males (69%) and usually aged between 40 and 90 years with an average age of 55 years). In total, 70 respondents were selected for interview. At the family level, informal meetings were held at the interviewee’s home using the native language (Bangla), sometimes with the participation of more than one respondent together, everyone being selected randomly. Our main purpose was to obtain information about medicinal plants used and/or known by the respondents and document the knowledge about their application. The selection of respondents was purposive; we considered those who have medicinal knowledge and practices. A semi-structured questionnaire was used to collect data on status, uses, and sources of medicinal plant species. Respondents were also asked which plant parts were mostly used for which ailments and how do they prepare medicine. Detailed information was taken during interviews and information gaps were checked through additional visits and cross-checking. Data collected from the respondents were cross-checked through interviewing two local herbal medical practitioners locally known as Kabiraj or Hakime, living and working in the study area.
Data collection from sample plot survey A stratified random quadrate method was used to determine the medicinal plants’ status in KNP, Bangladesh. A total of 40 circular plots of 10 m radius were used as sample plots for tree species and plots of 2 m radius were used for herbs, shrubs, climbers, and grass. Circular plots were used as they minimize the edge effect. Total number of species and their individual names were collected for trees, shrubs, herbs, climbers, and grass. Bangla names have been well documented by Dey (2006) together with various local names. The collected specimens were then dried and identified using standard literatures.
Data analysis Quantitative analysis of different characteristics of forests was done for a better understanding of the forests of the area. The characteristics considered were species count and species density, relative density (RD), frequency, relative frequency (RF), abundance, relative abundance (RA), and importance value. The formulae used for calculating these characteristics are indicated here. Density, frequency, and abundance were calculated through Shukla and Chandel (2000); relative density, relative frequency, and relative abundance were calculated through Misra (1968); and the total value (i.e., the added value of RD, RF, and RA) out of a possible maximum of 300 is called the importance value index (IVI). Importance value (IV) is the average of these three entities calculated as IV = (RD + RF + RA)/3 and was calculated through Shukla and Chandel (2000). In the present study, three diversity indices were analyzed to get a clear picture of medicinal plants’ diversity in the study area.