The geographic scope of the study was in the Hazarikhil forest areas lying between 22°40' and 22° 46'N latitude and between 91°38' and 91°42'E longitude under the Chittagong North Forest Division of Bangladesh. The specific study area was in the Hazarikhil forest beat. The study conducted its attempts from August 2018 to May 2019. Description of the study area The study area was under the Hazarikhil Wildlife sanctuary (HWS). It includes the entire area of Hazarikhil and Rangapani blocks of the Hazarikhil forest beat and Harowalchari block of the Fatikchari forest beat under Hazarikhil Forest Range. The northern boundary of the sanctuary touches Idilpur Badurkhil Block of Balukhali Beat under Narayanhat Range. The eastern boundary touches the Balukhali Beat under Narayanhat Range and Fatikchari Block of Fatikchari Beat under the Hazarikhil Range and Harualcahri canal (Khal). The southern boundary touches the Baromashia Block of Hazarikhil Range. The western boundary touches the ridge of Reserve Forest of Ramghar, Sitakunda under Mirsharai Upazilla, and Kunderhat Block of Bartakia Beat under Baraiyadhala Range, and also Wahedpur Block of Baraiyadhala Beat and Baraiyadhala Block. The HWS is formerly a part of the reserved forest of the Chittagong North Forest Division. The Ministry of Environment and Forests declared Hazarikhil reserve forests as Hazarikhil Wildlife Sanctuary (2908.50 ha) on 6 April 2010 by the gazette notification no. MoEF/ForSec-02/02 Wildlife Sanctuary/11/2010/211 dated 06/04/ 2010 under the power given under section 23(3) of Bangladesh Wildlife (Preservation) (Amendment) Act 1974 (Hossain, 2015). The forest is under the jurisdiction of the Hazarikhil Forest Range of Chittagong North Forest Division. According to Bangladesh Wildlife (Preservation), (Amendment) Act of 1974, any killing, hunting, or trapping of any wildlife, agricultural activities, living, or entering into the sanctuary of any persons or destruction to the sanctuary habitat are strictly prohibited. The HWS enjoys a tropical monsoon climate, characterized by basically four seasons, e.g., Winter (December-February), summer (March-May), monsoon (June-September), and autumn (October-November). The south-west monsoon provides the majority of the annual rainfall. The average annual rainfall of the area is 3000 mm, with a range of 1,611–3,878 mm. On average, the highest rainfall occurs in July (727 mm), and the lowest rainfall in January (5–6) mm. The temperature range of the area is 12.5°C to 37°C (Hossain, 2015). The low hill ranges cover part of the HWS while the rest is in the Bengal flood plain. The soils are clay to clayey loam on level ground and from sandy loam to coarse sand on hilly land. The clayey and sandy loams are fertile, and the sandy soil is rich in iron resulting in red or yellowish tinge. Soils developed in the hills from unconsolidated rocks are moderately well to excessively well-drained, generally deep, and probably the oldest soils in this region. In contrast, those occurring on hills from consolidated rocks tend to form in weathered sandstone, shale, and siltstones (Hossain, 2015). It identified a total of 478 species belonging to 88 dicot families from the flora of the HWS (Rahman, 2015). Of these, 189 species are trees, 119 shrubs including 26 climbers/twiners and 170 herbs including 46 climbers and two epiphytes. Among the species, about 86 species are rare and endangered, and 14 species are critically endangered. The Hazarikhil Wildlife Sanctuary (WS) and Baraiyadhala National Park (NP) had a total of 85 birds, 27 mammals, 34 reptiles, and 12 amphibians species (Hossain, 2015). Ministry of Environment and Forests established comanagement in the HWS in November 2014 under the project, Climate Resilient Ecosystems and Livelihoods (CREL) project (USAID, 2018). It formed the Comanagement Committee (CMC) which had a critical role in protecting the forests. Data analysis Structure and growing stock of plantation Firstly, the study figured out a richness of the frequently planted tree species in the representative samples. Secondly, it determined the distribution of the diameter (dbh) class and total height class of the trees species wise. The study classified the tree-data into four dbh and four height classes. For this, it used three cut points in all values to make dbh class and height class based on equal percentile with a width of 25%. Hence it made three height classes as ≤7.50, 7.51–9.50, 9.51–12.00, and 12.01 + m, and three dbh classes as ≤8.91, 8.92–12.18, 12.19–16.87, and 16.88+ cm. The gain and loss method estimated the net offset of atmospheric carbon by the plantation forests under the Tier 1 approach of the IPCC (2006). It followed the equation below; ΔC ΔCG ΔCL Where ΔC = Annual carbon stock change in the pool, tones Cyr−1 ΔCG = Annual gain of carbon, tones Cyr−1 ΔCL = Annual loss of carbon, tones Cyr−1 It estimated the carbon stock due to the afforestation/reforestation/using the present growth data of trees planted. It measured the mean annual increment (MAI) using the age of the tree. It then transformed the biomass to carbon using the standard biomasscarbon conversion factor. It used tree diameter (dbh) in the allometric equation of aboveground and belowground biomass. As species-specific allometric equation was not available during the analysis for all the species, it used only a general equation. It estimated the aboveground biomass density (ABD) of trees using the allometric model described by Pearson et al. (2013). Biomass (kg/tree) = exp(−2.289 + 2.649*lndbh0.021*lndbh2 ), where ln is the natural logarithm of tree dbh. The following model, described by Pearson et al. (2013), estimated the belowground biomass density (BBD). BBD, kg/tree = exp (−1.0587 + 0.8836 × ln ABD), here ln is the natural logarithm. After that, it converted biomass, ABD and BBD, into carbon, ACD (Aboveground carbon density), and BCD (Belowground carbon density) using the standard biomass-carbon conversion factor, 0.5 (Pearson et al., 2013).