Accurate estimation of leaf area index (LAI) of forest is crucial for studies of ecosystem functions. In this study, to evaluate different methods for monitoring seasonal change and the seasonal maximum value of LAI in a deciduous broadleaf forest, we applied four methods: (1) Monsi-Saeki theory, (2) hemispherical photography, (3) litter-fall, and (4) MOD15 product of Terra/MODIS.

Methods 1 and 2 showed typical seasonal change of LAI of the forest: increasing in May-June and decreasing in September-October. Method 3 enabled us to quantify the seasonal maximum LAI of each year, with a spacial variation in a research plot. Method 4 was confirmed to include atmospheric noise, which disturbs monitoring seasonal change of LAI.

In summary, in situ methods provide both accurate estimate of seasonality and maximum level of LAI and combined estimation is essential. They commit to validate the remote sensing data.