References and summaries for literature on leaf area index (reviews, methodology, etc.)

Barclay, H. J. (1998) Conversion of total leaf area to projcted leaf area in lodgepole pine and Douglas-fir. Tree PHysiology 18, 185-193.

Summary

It is noted that three distinct definitions of leaf area index (LAI) in the literature have no predictable relationship with each other. Conversion factors were derived, from total LAI to projected LAI of horizontal leaves and to projected LAI for inclined leaves of lodgepole pine and coastal Douglas-fir, enabling comparison of results from different studies. An algorithm was derived to allow determination of these factors based on twig angles and the angles that the foliage subtends with the twig. The conversion factor was more sensitive to differences in vertical angles of the twigs than to twig rotation or foliar arrangement on the twig.

Chen, J. M., P. M. Rich, S. T. Gower, J. M. Norman, and S. Plummer. 1997. Leaf area index of boreal forests: theory, techniques, and measurements. Journal of Geophysical Research-Atmospheres 102, 29429-29443.

Summary

We evaluated LAI values obtained by several research teams using different methods for a broad spectrum of boreal forest types in support of the international Boreal Ecosystem-Atmosphere Study (BOREAS). Methods included destructive sampling and four kinds of optical instruments: the tracing radiation and architecture of canopies (TRAC), the LAI-2000 plant canopy analyzer, hemispherical photography, and the Sunfleck Ceptometer. Apart from the TRAC, the optical methods estimate LAI from measured radiation transmittance (gap fraction) using inversion models that assume a random spatial distribution of leaves. We found that these instruments underestimate LAI of boreal forest stands where the foliage is clumped. The TRAC quantifies the clumping effect by measuring the canopy gap size distribution. For deciduous stands the clumping index measured from TRAC includes the clumping effect at all scales, but for conifer stands it only resolves the clumping effect at scales larger than the shoot (the basic collection of needles). We used a video camera and rotational light table system to determine foliage clumping within conifer shoots. LAI typically fell in the range 1-4 for jack pine and aspen forests and 1-6 for black spruce. These comparative studies provide the most comprehensive set of LAI estimates available for boreal forests. Furthermore they demonstrate that quick and accurate LAI measurements may be obtained using optical techniques combined with limited direct foliage sampling.

Chen, J. M., and T. A. Black. 1992. Defining leaf-area index for non-flat leaves. Plant Cell And Environment 15, 421-429.

Summary

There is confusion in the definition of leaf area index (L) for non-flat leaves. To address this problem, the projection coefficients of several objects including spheres, cylinders, hemicircular cylinders, and triangular and square bars were investigated through mathematical derivation and numerical calculation for a range of ellipsoidal angular distributions. The projection coefficient calculated based on half the total intercepting area was shown to be close to a constant of 0.5 when the inclination angle of the objects is randomly (spherically) distributed. However, the calculated results based on the object's largest projected area was strongly dependent on the shape of the object. We propose that the leaf area index of non-flat leaves should be defined as half the total intercepting area per unit ground surface area, and that the definition of L based on the projected leaf area should be abandoned.