Publication
 

Evaluating design unbiasedness of the pre-felling inventory in Peninsular Malaysia

The forests in Peninsular Malaysia are sustainably managed under the Selective Management System, which requires completing a pre-felling (Pre-F) inventory prior to harvest. The goal of this study was to investigate design unbiasedness of the Pre-F inventory using theory and simulation models. Simulations were carried out with an artificial and an actual forest, the former representing a cyclic forest of mature and young trees and the latter being the 50-ha Pasoh census plot. Theoretically, the Pre-F inventory is biased in mean estimates because it consistently undersamples portions of a population. Simulation with the cyclic forest showed that the Pre-F inventory was biased in estimating mean stand density, basal area and volume when the inventory was set up aligned with the cyclic pattern. Results from the Pasoh plot showed that the Pre-F inventory was unbiased in mean stand variables. The contrast was likely due to seemingly random tree distribution in Pasoh. However, using a design unbiased sampling method is more desirable because underlying tree distribution pattern in a forest is normally unknown. We recommend the Random Point Start method, which is unbiased in all simulation trials in addition to retaining all the advantages of the current Pre-F protocol.

Hutan di Semenanjung Malaysia diurus dengan mampan di bawah sistem pengurusan memilih yang memerlukan inventori sebelum tebangan dijalankan sebelum penebangan pokok dilaksanakan. Tujuan kajian adalah untuk menentukan ketidakpincangan reka bentuk inventori sebelum tebangan menggunakan teori dan model simulasi. Simulasi dijalankan ke atas hutan tiruan dan hutan sebenar. Hutan tiruan mewakili pusingan hutan yang terdiri daripada pokok matang dan muda. Hutan sebenar pula terdiri daripada pokok di plot 50 hektar di Pasoh. Secara teori, inventori sebelum tebangan pincang dalam penganggaran purata kerana secara konsisten persampelan sebahagian daripada populasinya rendah. Simulasi hutan tiruan menggambarkan kepincangan dalam penganggaran purata kepadatan dirian, luas pangkal serta isi padu apabila inventori dilaksanakan bersesuaian dengan hutan pusingan. Simulasi plot di Pasoh menunjukkan yang inventori sebelum tebangan tidak pincang dalam purata pemboleh ubah dirian. Perbezaan ini mungkin disebabkan oleh taburan pokok secara rawak di Pasoh. Namun, kaedah persampelan tak pincang memberi keputusan yang lebih baik kerana taburan pokok di dalam hutan biasanya tidak diketahui. Kami mencadangkan agar penggunaan kaedah titik mula rawak yang tidak pincang dalam semua simulasi di samping dapat mengekalkan kesemua kelebihan penggunaan inventori sebelum tebangan.

Abstract in English and Malay; article in English only.

Authors: 
TY Lam, K Abdul Rahman, I Shamsudin, & MD Potts
Journal: 
Journal of Tropical Forest Science
Year: 
2013
Volume: 
25
Issue: 
4
Pages: 
516-527
Site: 
Pasoh