Regular Article J F E S Journal of Forest and Environmental Science pISSN: 2288-9744, eISSN: 2288-9752 Journal of Forest and Environmental Science Vol. 33, No. 1, pp. 22-32, February, 2017 https://doi.org/10.7747/JFES.2017.33.1.22 22 Journal of Forest and Environmental Science http://jofs.or.kr Effects of Mixed Plantation on Growth and Biomass Yield of Two Common Plantation Trees of Bangladesh Shourav Dutta * and Mohammed Kamal Hossain Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong-4331, Bangladesh Abstract An experiment was set to assess the effect of mixed plantings on initial growth and biomass yield of two common plantation tree species of Bangladesh namely Acacia auriculiformis (A) and Gmelina arborea (G). Study was carried out in the nursery bed of the Seed Research Laboratory and Nursery of Institute of Forestry and Environmental Sciences, Chittagong University (IFESCU), Bangladesh during February to November, 2015. The treatments consisted of two pure planting plots (100% A and 100% G) and five mixed planting plots (50%A: 50%G, 35%A: 65%G, 25%A: 75%G, 65%A: 35%G and 75%A: 25%G) of these two species. In nursery, seedlings were raised in a randomized blocks with four replicates of seven treatment plots. Periodic increments on height (cm), collar diameter (cm) and leaf/phyllode number of the seedlings was taken in every month and continued up to 10 months. The growth and biomass yield of seedlings were measured 10 months after the first seed was emerged. The effects of mixed plantation on growth and biomass were compared to that of seedlings grown in pure plantation. At the age of 10 months it was found that G. arborea seedlings were significantly tallest (240.13 cm) when planted with A. auriculiformis in a proportion of 25%A: 75%G, whereas A. auriculiformis were tallest in the pure 100% A plot, with an average mean height of 135.36 cm. Maximum collar diameter (1.38 cm) was recorded for G. arborea in the mixed plots 75%A: 25%G. Fresh and dry weight of shoots and roots of the seedlings were found significantly (p＜0.05) highest in 50%A: 50%G plot for G. arborea. G. arborea also showed highest quality index when mixed with A. auriculiformis in a proportion of 50:50, with an average value of 8.96. The results revealed a positive correlation between seedling growth and various planting patterns. Key Words: biomass yield, growth performance, mixed plantation, nitrogen fixation, quality index Received: June 4, 2016. Revised: August 8, 2016. Accepted: August 8, 2016. Corresponding author: Shourav Dutta Institute of Forestry and Environmental Sciences, University of Chittagong, Chittagong-4331, Bangladesh Tel: 88-0312558010, Fax: 88-01710384867, E-mail: shourav.forestry@gmail.com Introduction Bangladesh, the world’s largest deltaic region, lying in the north eastern part of South Asia with a geographical coverage of 14.76 m ha, is exceptionally endowed with a large variety of flora (Nishat et al. 2002; Dutta et al. 2014). But, the natural forests of Bangladesh have been facing a serious onslaught that a large portion of it has already been lost during the last four decades due to population pressure and unscientific management (Hossain et al. 2008; Dutta et al. 2014). Besides this, the management of these low yield- ing forests was very complicated and that’s why the main objective was to replace these heterogeneous natural forests by the planting of valuable timber species (Hossain 2008). In Bangladesh, massive failures of established planta- tions and land degradation have resulted in continuous de- pletion of forest resources (Aryal et al. 1999). In addition, intensive harvesting of forest resource decreases the nitrogen,