Spatial and Vertical Leaf Area Index of a Deciduous Forest Resolved Using the LAI-2000 Plant Canopy Analyzer

摘要

The LAI-2000 Plant Canopy Analyzer (LI-COR Inc., Lincoln, Nebraska) was used to determine the spatial and vertical canopy structure of a heterogeneous deciduous forest near Chalk River, Ontario. Overstory vegetation area index (VAI) demonstrated the spatial heterogeneity that exists between points at 10 m spacing and also with direction along transects, emphasizing the need for an appropriate sampling strategy. Average (± standard deviation) VAI for the forest was determined to be 3.00 ± 0.70, which lies within 3% of an estimate made by litterfall analysis in 1989 for the same forest location. The average VAI differs from the plant area index (PAI) determined by hemispherical photography by 9%. Owing to the large standard deviation in the estimate of VAI, it was calculated that 84 samples need to be taken to be within 5% of the mean at the 95% confidence level. This number drops to 21 if the accuracy requirement is relaxed to 10%. The large number of samples can be reconciled by the speed of sampling that is possible with the LAI-2000. One-hundred-thirty-two samples were obtained in this forest during a 7 day period. Vertical measurements of VAI were made from five levels on a 25 m scaffold tower in all four cardinal directions. VAI in the top third of the canopy compared well with hemispherical photography values taken along the vertical profile. The estimates in the middle and bottom levels differ from PAI. Directional heterogeneity was shown to increase with height. VAI measured at the lowest canopy level from the tower (3.11 ± 0.34) was not significantly different from the spatial overstory average of 3.00.