Nasution, Ade Parlaungan, et al. “Urgensity of Environmental Management System Implementation on Oil Palm Plantation Management Policies in North Sumatera”. Journal of Social Transformation and Regional Development, vol. 3, no. 1, May 2021, pp. 1-6, https://publisher.uthm.edu.my/ojs/index.php/jstard/article/view/8872.