Wasis, Basuki. 2012. “Soil Properties in Natural Forest Destruction and Conversion to Agricultural Land,in Gunung Leuser National Park, North Sumatera Province”. Jurnal Manajemen Hutan Tropika 18 (3). Bogor, INA, 206-12. https://doi.org/10.7226/jtfm.18.3.206-212.