www.tropicalplantresearch.com 502 Received: 30 April 2020 Published online: 31 August 2020 https://doi.org/10.22271/tpr.2020.v7.i2.060 7(2): 502–507, 2020 DOI: 10.22271/tpr.2020.v7.i2.060 ISSN (Online): 2349-1183; ISSN (Print): 2349-9265 TROPICAL PLANT RESEARCH The Journal of the Society for Tropical Plant Research Research article Effect of tree canopy opening in the regeneration layer of Terai Sal (Shorea robusta Gaertn.) forest in Western Nepal: A case study Shishir Baral and Pramod Ghimire* Faculty of Forestry, Agriculture and Forestry University, Hetauda, Nepal *Corresponding Author: pghimire@afu.edu.np [Accepted: 18 August 2020] Abstract: A study about the effect of tree canopy opening in the regeneration layer of Sal ( Shorea robusta) forest was investigated in four strata of forest viz. 0–25, 25–50, 50–75 and 75–100 percentage crown cover vegetation in Buddha-Shanti Collaborative Forest Management of Nawalparasi district, Nepal. Systematic sampling was carried out for regeneration survey in two sub-compartment of each 10 hectare, where in one sub-compartment was (C1S2) silviculturally managed where Irregular shelter wood system was adopted with regeneration felling and the other sub-compartment (C1S3) was undisturbed with no regeneration felling. The seedling density of Sal was found higher in the 0–25 and 25–50 percentage crown cover (22,167 ha -1 and 13,667 ha -1 ) respectively than 50–75 and 75–100 percentage crown cover area (11,667 ha -1 and 11,000 ha -1 ) respectively. Likewise, sapling density was also higher in the open canopy than dense or closed canopy. Crown cover percentage was found negatively correlated with regeneration density per hectare (ha) in Sal forest. Hence, the study concluded that open canopy favours regeneration; promotes seedling densit in Sal forests and regeneration layer of Sal is dependent on canopy opening or threshold light intensity for better growth and survival. Keywords: Crown cover - Regeneration felling - Seedling. [Cite as: Baral S & Ghimire P (2020) Effect of tree canopy opening in the regeneration layer of Terai Sal (Shorea robusta Gaertn.) forest in Western Nepal: A case study. Tropical Plant Research 7(2): 502–507] INTRODUCTION Shorea robusta Gaertn. (Commonly known as Sal tree) is a tropical tree species native to Indian subcontinent, ranging south of the Himalaya, from Myanmar in the east to Nepal, India and Bangladesh (Tiwari 1995). One of the most important timber species of Nepal, it is found mostly in the Terai region from east to west, especially in the Siwalik Hills (Churia Range) in the subtropical climatic zone (Jackson 1994, DFRS 2015). In addition, the species is regarded as a climax formation throughout and also capable to colonize new areas with heavy growth of seedlings. However, it prefers the Bhabar region and the alluvium of Terai where water logging does not happen (DFRS 2015). Sal forms extensive forest and gregarious in nature. At the national level, Sal has the highest stem volume 31.76 m 3 ha -1 which is 19.28% of total stem volume of the country (DFRS 2016). Canopy cover describes the proportion of the forest floor covered by the vertical projection of the tree crowns (Avery & Burkart 1994, Cook et al. 1995). Canopy cover affects plant growth and survival; hence determining the nature of the vegetation. It is an important ecological parameter of forest ecosystem for its relationship with natural regeneration and species richness (Ganey & Block 1994, Zollner & Crane 2003). In addition, regeneration status of a forest is very important for its health and vitality as healthy forest ensures good future regeneration. The regenerating and productive character of forest is determined by presence of different age-group of seedling, sapling and tree (Chauhan et al. 2008). Moreover, regeneration is measured to determine whether it meets the objective of forest management, and in particular, whether the productive capacity and biological diversity of forest are maintained (Lutze et al. 2004). The natural regeneration in sal forest is adversely affected by external factors such as heavy grazing, extensive lopping and forest fire. Furthermore, Sal