Utility of spectral vegetation indices for estimation of light conversion efficiency in coniferous forests in Japan

To clarify the utility of spectral vegetation indices (VIs) for estimating light conversion efficiency (ɛ) in Japanese coniferous forests, we investigated the relationships between six VIs (NDVI, EVI, SAVI, PRI, CI, and CCI) and ɛ in two mature monospecific forests of deciduous conifer (Japanese larch) and evergreen conifer (Japanese cypress) and one young mixed stand of deciduous conifer with evergreen undergrowth (hybrid larch and dwarf bamboo). In each forest canopy, we measured seasonal variations in CO2 flux, radiation environment, and visible–near-infrared spectral reflectance during 1 or 2 growing seasons. We calculated ɛ as gross primary production (GPP) divided by the difference between incoming and reflected photosynthetically active radiation (PAR). VIs and ɛ under clear skies were averaged between 11:00 and 13:00 JST and their relationships were analyzed.