Estimating the needle area from geometric measurements: application of different calculation methods to Norway spruce

Different calculation methods, based on needle geometry, for estimating bot h projected area (PLA) and total surface area (TLA) of foliage in Norway sp ruce [Picea abies (L.) Karst.] were compared. Seventy-eight shoots of four age classes were sampled from both the basal and top thirds of crowns. Thre e dimensions (the length, minor and major diameters) of needles were taken, and the needle shape was approximated to a parallelepiped or ellipsoid. Th ere was a perfect coincidence of the measured and estimated values of PLA c alculated as the width of the needle projection multiplied by needle length , and corrected for needle taper (method III), or when the needle projectio n was treated as a rectangle joined with half-ellipses at both ends (method IV). The most reliable estimations of TLA resulted from treating the needl e sides as faces of the parallelepiped tapering at their ends in the form o f half-ellipses. The ratio of TLA to PLA ranged from 2.2 to 4.0 depending o n the needle morphology. Needle minor diameter (anatomical width; D-1) was found to be a better morphological index of the spruce foliage than needle flatness, i.e. the ratio of major to minor diameter. Expressing the factor for converting PLA to TLA as a function of D-1 considerably improved the pr ecision of the estimates. Close relationships were established between spec ific leaf area, expressed on both a projected area (SLA(P)) and total surfa ce area basis (SLA(T)), needle dry weight (R-2 was 0.799 and 0.852, respect ively) and minor diameter of needles (R-2 was 0.701 and 0.554, respectively ).