Sains Malaysiana 45(4)(2016): 523–533

Relationships between Crown Size and Aboveground Biomass of Oil Palms: An Evaluation of Allometric Models

(Hubungan antara Saiz Silara Pokok dan Biojisim atas Permukaan Tanah Kelapa Sawit:

Penilaian terhadap Model Alometri)

ALEXIUS KOROM¹*, MUI-HOW PHUA² & TOISHIYA MATSUURA³

¹Universiti Teknologi MARA (UiTM) Cawangan Sabah, Beg Berkunci 71, 88997 Kota Kinabalu

Sabah, Malaysia

²Forestry Complex, Faculty of Science and Natural Resources, Universiti Malaysia Sabah (UMS)

Locked Bag No. 2073, 88999 Kota Kinabalu, Sabah, Malaysia

³Forestry and Forest Products Research Institute, Matsunosato 1, Tsukuba, Ibaraki, 305-8687, Japan

Received: 15 April 2014/Accepted: 23 October 2015

ABSTRACT

Oil palms (OP) in Sabah, Malaysia were studied to explore the relationship between canopy size and aboveground biomass (AGB). Four available allometric equations were used to calculate the dry AGB. Pearson’s correlation analysis was performed between crown diameter (CD) and crown area (CA) towards the variables of AGB, height and dbh. In this analysis, the transformation to natural log of variable resulted in better coefficient compared to the original one. The mean of various variables such as height (stem, total and height difference), biomass (crown, trunk and total), dbh (inner and outer) and number of petiole leaf were calculated based on 32 independent sample plots (N = 222 palms) across various age stages from 2 to 24 years. These variables were regressed against CD and age. AGB versus CD was a nonlinear with R2 ranging from 0.950 to 0.975. Random modelling and cross validation between AGB and CD was applied at the ratio of 70:30. Upon checking, the best estimation was achieved by using the allometric equation based on total height due to the lowest relative RMSE (18.5%) and the least fluctuation between predicted and actual AGB. The other three models had relative root mean square error (RMSE) that ranged between 23.9 and 68.8%. This study shows that AGB can be estimated using CD of OP consistently at all ages.

Keywords: Aboveground biomass; allometric equation; crown diameter; oil palm

ABSTRAK

Kelapa sawit di Sabah, Malaysia telah dikaji untuk menentukan hubungan antara saiz kanopi pokok dan biojisim atas tanah (AGB). Empat persamaan alometri telah digunakan untuk mengira AGB kering. Analisis korelasi Pearson telah dijalankan antara diameter kanopi pokok (CD) dan luas kanopi pokok (CA) terhadap pemboleh ubah AGB, ketinggian dan diameter batang pada paras dada (dbh). Dalam analisis ini, penukaran kepada log asas bagi pemboleh ubah menghasilkan pekali yang lebih baik berbanding pemboleh ubah asal. Purata bagi pelbagai pemboleh ubah seperti ketinggian (tinggi batang, tinggi keseluruhan dan beza tinggi), biojisim (kanopi pokok, batang dan keseluruhan), dbh (dalam dan luar) dan bilangan pangkal daun telah dihitung berdasarkan 32 sampel plot yang tidak bersandar (N = 222 pokok sawit) merangkumi peringkat umur 2 hingga 24 tahun. Pemboleh ubah tersebut diregrasikan terhadap CD dan umur pokok. Perhubungan AGB menentang CD didapati tidak linear dengan R2 terjajar daripada 0.950 hingga 0.975. Pemodelan rawak dan validasi silang antara AGB dan CD telah dilakukan mengikut nisbah 70:30. Setelah diperiksa, penganggaran yang terbaik adalah menggunakan persamaan alometri ketinggian keseluruhan pokok berdasarkan hasil relatif sisihan purata punca kuasa dua (RMSE) (18.5%) yang terendah dan paling kurang sesaran antara AGB sebenar dan ramalan. Tiga model yang lain mempunyai relatif RMSE berjajar di antara 23.9 dan 68.8%. Kajian ini menunjukkan bahawa AGB boleh dianggarkan secara mampan pada semua peringkat umur menggunakan CD kelapa sawit.

Kata kunci: Biojisim atas permukaan tanah; diameter silara pokok; kelapa sawit; persamaan alometri

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*Corresponding author; email: alexi502@sabah.uitm.edu.my