1. Academic Member, Soil Conservation and Watershed Management Research Institute, P.O. Box 13445-1136, Tehran, Iran (corresponding author).
2. Associate Professor, Faculty of Forestry, Univ. Putra Malaysia, 43300 UPM, Serdang, Selangor, Malaysia.
3. Associate Professor, Institute for Mathematical Research (INSPEM), Univ. Putra Malaysia, 43300 UPM, Serdang, Selangor, Malaysia.
4. Lecturer, Faculty of Forestry, Univ. Putra Malaysia, 43300 UPM, Serdang, Selangor, Malaysia.