Comparison of direct and indirect estimation of leaf area index in mature Norway spruce stands of eastern Germany

IIn three mature Norway spruce (Picea abies (L.) Karst.) stands of the Erzgebirge (Ore Mountains) in eastern Germany, the performance of the LAI-2000 plant canopy analyzer (LI-COR instruments) was tested for indirect estimation of leaf area index (LAI). The LAI-2000 calculates effective leaf area index (LAIe, m2/m2) resulting from radiation measurements and subsequent model calculations. LAIe underestimated directly estimated half the total leaf area index (LAI0.5t, m2/m2) by 37-82% as determined from allometric relationships derived from subsample harvesting. The degree of underestimation was dependent upon stand density in two of three spruce stands examined; it was the highest in sparsely stocked plots. The relationship of LAIe to allometrically determined LAI0.5t for one of the three stands differed significantly from the other two spruce stands and the underestimation of LAI0.5t was less distinct. This was explained by stand structure, i.e., higher amounts of nonassimilating surfaces relative to LAI0.5t. These results indicate that the LAI-2000 is not generally applicable for estimation of LAI in mature spruce stands of the Erzgebirge because of effects of stand structure on LAIe-LAI0.5t relationships, which are stand specific.