Study area: The study area of the Sitakund Botanical Garden and Eco-park (SBGE) is situated on the southeast part of Bangladesh which is at the northwestern part of Chittagong district, between 22°36' and 22° 39' N latitude and 91°40' and 91°42' E longitude. The total area of the park is 1996 acres (808.1 ha), of which 1000 acres (404.86 ha) is designated as Botanical garden and 996 acres (403.24 ha) as an eco-park. The area is under the Southern “Sitakunda Reserved Forest” of Chittagong Forest Division. The area is covered with natural evergreen forest and possesses high diversity in plant and animal composition. The study area is composed of a number of low and high hills with peak slopes and streams covered with thorny bush, climbers and coppice and root suckers that occur in a scattered manner. These hills are made of Sandstones and shales. The heights of the lower hills are 15.24 m to 76.2 m (50 - 250 ft), the range of medium high hills is between 76.2 m and 152.4 m (250 - 500 ft) and for the high hills between 152.4 m and 365.76 m.
1.2 Vegetation sampling and species diversity analysis A series of field surveys were conducted to collect relevant information regarding species composition, anthropogenic influence. Based on this, the SBGE was classified into two zones on the basis of anthropogenic disturbances: (1) a disturbed zone which is very close to the road, comprising of exotic tree species and agricultural cultivation, mainly in the southeastern part of the area; (2) a less disturbed zone which is mostly inaccessible and has no tourist paths consisting of naturally originated species, mainly in the north portion of the area. In total, 50 circular plots with an area of 314 m2 have been established in the disturbed zone and less disturbed zone. All plots were taken along a transect, whereas the start of the transect was chosen randomly. On each circular plot (10 m radius of each), square plots (1 m × 1 m , 2 m × 2 m and 4 m × 4 m) at 4 m distance from the center of the plot on both sides were demarcated (Figure 2). The distance between the centers of the two circular plots was 100 m. Within each plot, regeneration data were sampled on smaller plots fixed in the field on the basis of abundance. On the small plots (1 m × 1 m) regeneration of trees and shrubs from height range (0 – 0.5 m) was sampled, on plots with a size of 2 m × 2 m regeneration data was sampled from height range (0.5 m - 2 m) and for plots with a size of 4 m × 4 m, regeneration within a height range (h > 2 m, dbh< 6 cm) was recorded. On the whole sample plot (314 m2) trees (dbh > 6 cm) were recorded including diameter measurement. Data for herb coverage percentage was taken from the 4 m × 4 m plots on both sides. The tree and shrub species were identified directly in the field. Local people working in the field and forest officials helped in identifying some species. A minority of species could not be referred to a given scientific name they had been identified by their local name only. In case of herb, the species were not identified, only the percentage of coverage was taken. The Shannon-Wiener index (Nath et al. 2000), Evenness index (Magurran 1988) and Simpson’s index (Simpson 1949) were used as diversity indices.
1.3 Disturbance and statistical data analysis A disturbance index was calculated on the basis of a qualitative assessment of the intensity of different disturbance elements observed in the field by following the approach of Rahman et al. (2009). Disturbances like logging, cutting of regenerated plants, cutting of non-wood products, bark peeling, litter collection, agro forestation, firing and tourism were assessed as present disturbances. For these disturbances different weights were considered like logging (12), cutting of regeneration (10), cutting of non wood products (8), bark peeling (6), litter collection (5), agro forestation (4), firing (3), and tourism (2). The intensity of the anthropogenic measures was assessed qualitatively according to a scale from very high (100), high (80), medium (60), low (40), very low (20) to present (10) and absent (0). Agro-forestation was considered as present or absent only.