Da. Sampson et Hl. Allen, DIRECT AND INDIRECT ESTIMATES OF LEAF-AREA INDEX (LAI) FOR LODGEPOLE AND LOBLOLLY-PINE STANDS, Trees, 9(3), 1995, pp. 119-122
We compared direct and indirect estimates of leaf area index (LAI) for
lodgepole and loblolly pine stands. Indirect estimates of LAI using r
adiative methods of the LI-COR LAI-2000 Plant Canopy Analyzer (PCA) di
d not correlate with allometric estimates for lodgepole pine, and corr
elated only weakly with litter-trap estimates for loblolly pine. The P
CA consistently under-estimated LAI in lodgepole pine stands with high
LAI, and over-estimated LAI in the loblolly pine stands with low LAI.
We developed a physical model to test the hypothesis that the PCA may
under-estimate LAI in high leaf area stands because of increased foli
age overlap and, therefore, increased self-shading. Radiative estimate
s of LAI using the PCA for the physical model were consistently lower
than allometric measures. Results from the physical model suggested th
at increased foliage overlap decreased the ability of the PCA to accur
ately estimate LAI. The relationship between allometric and radiative
measures suggested an upper asymptote in LAI estimated using the PCA.
The PCA may not accurately estimate LAI in stands of low or high leaf
area index, and the bias or error associated with these estimates prob
ably depends on species and canopy structure. A species specific corre
ction factor will not necessarily correct bias in LAI estimates using
the PCA.