Spatial variability of canopy foliage in an oak forest estimated with fisheye sensors
1992
Wang, Y.S. | Miller, D.R. | Welles, J.M. | Heisler, G.M.
The vertical distribution of forest canopy elements is an important factor in canopy-atmosphere exchange processes and knowledge of the shape of the average vertical profile of leaf area density is a critical input to models of these processes. This study was conducted to determine the spatial variability of Leaf Area Index (LAI) in an oak forest when estimated with indirect fisheye techniques. A 35 mm camera with a 180 degree hemispherical lens and a LI-COR LAI-2000 Plant Canopy Analyzer (wavelengths < 490 nm) were used simultaneously to estimate vertical leaf area profiles and the horizontal variability in an oak forest in central Pennsylvania. Measurements were made at eight different heights in the canopy and repeated at nine different locations. The two sensors were in reasonable agreement. The photographic technique estimated the total leaf area index (LAI) to be 3.58, and the light sensor estimates resulted in an estimate of 3.40. The average precision was 8% for the LAI-2000 and 17% for the photographic technique. The point-to-point spatial variability of the LAI estimates was low when the whole canopy was measured from the ground and quite high when measuring the upper canopy. Ground level estimates of LAI using these fisheye techniques spatially average the canopy to the point where only four replications were necessary to sample the total LAI with 90% confidence.
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