Accurate estimates of foliage clumping index (X) are required to improve the retrieval of leaf area index (L) from optical instruments like LAI-2000/2200 Plant Canopy Analyzer (PCA) and digital hemispherical photography (DHP). The logarithm averaging method is often used to approximate L because clumping effects are considered at scales larger than the sensor’s field of view. However, the spatial scaling considered for logarithm averaging typically differs between PCA and DHP, resulting in different estimates of foliage clumping. Based on simulation, we demonstrated that applying restricting azimuth view caps (e.g., 45 or 10) allows reliable estimation of X and more accurate estimation of L from PCA. Simulated X and L values were comparable to those measured using the PCA, DHP and litter traps. Linear averaging of the gap fractions across readings at a plot or site yields a concurrent estimate of effective leaf area index (Le), thus enabling the calculation of Le, L, and X from a single instrument fitted with view caps. Users need to be aware that the method they use for averaging gap fractions determines whether they are measuring Le or L, and PCA users need to be aware that they are applying increasingly large corrections for foliage clumping as they use more restrictive view caps, a fact that they can use to their advantage to improve estimates of L.
|Autori:||Chianucci, F.;Macfarlane, C.;Pisek, J.;Cutini, A.;Casa, R.|
|Data di pubblicazione:||2015|
|Titolo:||Estimation of foliage clumping from the LAI-2000 Plant Canopy Analyzer: effect of view caps|
|Appare nelle tipologie:||1.1 Articolo in rivista|