Study site Like the other comanaged PAs in Bangladesh, Kaptai National Park (KNP), a tropical evergreen to semievergreen forest that harbors 412 floral species (Rahman, Roy, Anik, & Fardusi, 2013), was also declared as a PA in September, 1999 with an aim to protect its depleting flora and fauna (BFD, 2016). Prior to the PA declaration, its legal status was a reserved forest. Its conversion from the “reserved” to the “protected” status has shrunk local people’s scopes for their livelihoods from PA resources. As has been observed in the other PAs in the country, the interests of KNP administration and the KNP-dependent people differed to a great extent. Given this similarity, we assumed that, KNP could be a better representative of the typical PAs in Bangladesh in terms of bioresources and the anthropogenic pressure on these resources. Hence, we considered KNP as a case to study the general biodiversity situations of PAs in Bangladesh. Administratively, KNP belongs to Kaptai Forest Range under the management of Rangamati South Forest Division, Bangladesh. It is approximately 57 km away from and to the northeast of Chittagong City. The area located at 22° 29.991´ N and 92° 10.722´ E in the Chittagong Hill Tracts (CHTs) of Bangladesh. It covers an area of 5,464 ha. The level of valley bottoms range from 32 to 90 m above the mean sea level and the maximum elevation is about 500 m (Uddin & Hassan, 2012). It falls under tropical monsoon climate with annual average rainfall of 254 cm (BFD, 2010; Rahman, 2004) to 290 cm (Uddin & Hassan, 2012), average maximum temperature of 25.5°C, and average minimum temperature of 15.6°C. December is the driest month here with almost no rainfall and with an average humidity of 74% (BFD, 2010; Rahman, 2004). Historically, KNP is famous for the reason that the first Tectona grandis plantation in Bangladesh was established here in 1871. As early as 1873, this massive plantation was initiated by local forest management that resulted in much of today’s beautiful growth (Hossain, Alam, & Miah, 2008). Sampling framework Kaptai National Park is divided into two ranges: Kaptai Range and Karnaphuli Range. Kaptai Range consists of Kaptai Sadar Beat, Kamalyachari Beat, Shuknachari Beat, Bangchari Beat, and Rampahar Beat. On the other hand, Karnaphuli Range has Karnaphuli Sadar Beat, Kaptaimukh Beat, Patachari Beat, Chakua Beat, Chitmorom Beat, Fringkhiong Beat, Kalmichara Beat, Brick Field Camp, and Fringkhiong Depot. To examine if the biodiversity health of KNP was different from that in its adjacent areas, we had to collect data from inner part of, on, and from outside the administrative boundary of KNP. Thus, the study site was divided into three strata—namely, INSIDE, ON, and OUTSIDE of the KNP boundary for the measurement of biodiversity attributes and indices. The INSIDE consisted of the villages that were in the core zone of KNP. The villages thus selected were Bangchari, Bot Toli, Kaptai Sadar Beat, and Rampahar Beat. The ON zone consisted of the villages that were situated on the administrative boundary of KNP. The ON zone included the villages—namely, Chowdhury Chara Para, Aara Chara Para, and Chakua Para. The OUTSIDE zone contained the villages around KNP that had entirely private forest ownership while the IN and ON zones contained only public forests. From the OUTSIDE zone, we studied Kodalia Beat, Pomora, and Rassel Ecopark villages. The INSIDE, ON, and OUTSIDE zones were at least 1 km apart from each other. However, the width of the OUTSIDE zone was kept limited to 4 km outward. A total of 66 sample plots, each measuring 20 m × 20 m, were identified for studying the phytosociological attributes and biodiversity indices. Of the 66 plots, 22 plots were from INSIDE, 22 plots from ON, and 22 plots from OUTSIDE zone. The plots were selected at an interval of 500 m from each other. In each of these plots, we counted the number of trees, seedlings, and saplings by species. We also measured diameter at breast height (DBH) and total height of all trees in these plots. Again, a plot of size 2 m × 2 m was inscribed in the center of each of the 20 m × 20 m plots for the study of natural regeneration status. Thus, total number of regeneration plots was also 66. We counted the number of naturally growing seedlings of all available species in each of the regeneration plots.