Estimating aboveground biomass of oil palm: Allometric equations for estimating frond biomass

Allometric equations were developed to estimate the biomass of oil palm frond with nontree-lethal methods. The study was conducted in oil palm plantations belonging to the Oil Palm Research Center of the Institut National de Recherches Agricoles du Bénin (INRAB) and to neighboring smallholders oil palm plantations. Complete measurements of individual fronds biomass and measurements of predictor variables were made by two methods: (1) a tree-lethal (destructive) method and (2) a nontree-lethal method. Measurements were done on 25 palm trees of several ages and from different genetic origins. Frond variables measured were: length (L) and dry weight (DW) of the petiole and rachis, dry weight of leaflets, dry weight of a fragment (length = 0.30 m) taken from mid way along the rachis, thickness and width of the petiole cross section (junction of petiole and rachis). Linear regressions were established with biomass data obtained for different parts of the palm frond by the two methods. The results showed that up to rank 9, frond biomass increased with frond position in the crown. From rank 10, fronds were mature and their biomass showed a nearly constant value independently of rank. These results led to the establishment of a simple equation to estimate frond biomass based on rachis dry weight: DWfrond = 1.147 + 2.135 _ DWrachis (R2 = 0.62). This relationship is closer than Corley's one based on the cross section of the petiole (R2 = 0.22). Rachis dry weight can easily be estimated (R2 = 0.94) using rachis length and linear density (or mass per length) of a fragment of 0.30 m taken from mid way along the rachis. The equation is: DWrachis ¼ 1:133_L_rachisDWfragment=0:30. The study also showed that one of the applications of our allometric equations is the determination of the average dry weight of mature fronds from at least three mature fronds (rank > 10). This could allow an estimate of the annual production of oil palm fronds biomass, and then the estimate of fronds carbon stock. The latter could contribute to the assessment of environmental impact of forest conversion into oil palm plantations. (Résumé d'auteur