Relationship of readings from the LI-COR canopy analyzer to total one-sided leaf area index and stand structure in immature Douglas-fir

Estimation of leaf area is important in predicting potential growth. This estimation is often done by means of a photometer, such as the LI-COR plant canopy analyzer, but such instruments generally give biased estimates. Consequently, conversion factors are required to convert output from the photometer to the actual leaf area index (LAI). Foliar biomass was estimated in a 52-year-old Douglas-fir (Pseudotsuga menziesii (Mirb.) France) stand which had been treated with three levels of thinning and three levels of fertilization 28 years previously. The four treatment extremes (no thinning or fertilization up to heavy thinning and heavy fertilization) were sampled for foliage. Projected leaf areas were calculated from these biomass samples using specific leaf areas derived in a previous biomass sampling. Total one-sided leaf area was then computed by dividing the projected leaf areas by 0.9 to allow for lateral leaf curvature. In addition, LAI-2000 readings were taken in the same plots and then factors were derived to convert LAI-2000 readings to total one-sided LAI. These conversion factors were found to vary strongly with quadratic mean diameter, stand density, mean dbh, mean height and stand basal area. The effect of live crown height was minimal. These should allow the prediction of the conversion factor based on two or three of these highly correlated factors. (C) 2000 Elsevier Science B.V. All rights reserved.