Leaf area index measurements at Fluxnet-Canada forest sites

Leaf area index (LAI) measurements made at 17 forest sites of the Fluxnet Canada Research Network are reported here. In addition to LAI, we also report other major structural parameters including the effective LAI, element clumping index, needle-to-shoot area ratio, and woody-to-total area ratio. Values of the fraction of photosynthetically active radiation (FPAR) absorbed by green leaves in these stands at noon of 15 August are also provided, and a procedure is suggested for using the effective LAI for estimating FPAR at various times of the day and year. Labour-intensive laboratory measurements of the needle-to-shoot area ratio were made for five conifer sites. For each site, 45 shoot samples were measured at three heights from three trees. LAI-2000, TRAC and digital hemispherical photography (DHP) were used in the field, and good agreements between these techniques were obtained. In particular, the low cost DHP technique agreed within 21% of LAI-2000 in terms of effective LAI measurements and 12% of TRAC in terms of element clumping index measurements, suggesting a possibility of using DHP alone for indirect LAI measurements. However, LAI-2000 and TRAC are still found to be more reliable than DHP because of some remaining technical issues with DHP. We confirm the correct method for determining the photographic exposure proposed in previous studies and suggest optimum zenith angle ranges in photograph processing to estimate the effective LAI and the clumping index.