 We examined the use of the green-red vegetation index, GRVI, as a phenological indicator based on multi-year stand-level observations of spectral reflectance and phenology at several representative ecosystems in Japan. Our findings revealed that GRVI equals zero can serve as a reliable site-independent single threshold for detecting the early phase of leaf green up and the middle phase of autumn coloring. Additionally, we observed that GRVI could distinguish between different ecosystem types and responded to subtle disturbances. This article was authored by Takashi Motoka, Kenlo Nishida Nasehara, Satoshi Tsuchida, and others.