A comparison of direct and indirect methods for estimating forest canopy leaf area

摘要: Abstract Two indirect gap fraction methods for estimating leaf area index (LAI) are compared with estimates from litterfall collections in a mixed-age oak-hickory forest. One method uses averaged, direct beam penetration data obtained moving tram. The second portable light sensor system that measures diffuse five sky sectors between zenith angles 0 and 75°. Data were collected September 1989 to January 1990. Poisson model the negative binomial of frequency applied estimate LAI observed transmittances. With model, an assumption random spatial distribution contributes underestimation by as much 45%; this is because leaves at site actually clumped both large small scales. binomial, which requires determination clumping parameter, produces comparable those method. Both techniques accurately describe temporal changes using either or model. also allows easy estimation variation within sites, it can be used obtain vertical profile area.