A method for estimating sago palm (Metroxylon sagu Rottb.) leaf area after trunk formation

It is important to measure the individual leaf area and leaf area index (LAI) of sago palm (Metroxylon sagu Rottb.) to determine the appropriate planting density and maintain populations that are highly productive with regard to starch production. However, the accurate estimation of sago leaf area from the entire leaf profile or the projecting area of the plant is not possible. Thus, we developed a method for estimating leaf area of sago palm after trunk formation by integrating the leaflet areas. All leaflets were diagrammatically converted to rectangles, each having the same area as that of the corresponding leaflet,and these rectangles were arranged on the rachis to initiate the shape of a leaf without overlapping leaflets and gaps between their bases and between their tips. The leaf shape thus produced by the arrangement of these rectangles was represented as ellipsoidal in the apical half and as trapezoidal in the basal half. The ratios of the estimated to the actually measured area of the apical and the basal half of the leaf were 99-107% and 94-108%, respectively. The ratio of the estimated area of the whole leaf to the measured area was 98-104%. From these results, the method for estimating the whole leaf area by converting the leaflets diagrammatically to rectangles, and calculating the area as the sum of the ellipsoidal apical half and trapezoidal basal half, is considered to be accurate and simple.