The Yamagata University Research Forest is located in the Asahi Mountains (38˚ 33' 17'' N; 139˚ 51' 43" E), approximately 35 km south of Tsuruoka city, Yamagata Prefecture . This is an experimental forest, where students and researchers from YU can conduct their studies. This forest is mainly dominated by beech trees (Fagus crenata) in their natural habitat and at present extensively planted by cedar (Cryptomeria japonica) trees at altitudes ranging from 230 to 450 m.a.s.l. We have used UAVs on a 12 ha cedar plot in a steep slope (25.8˚) to first determine the number of trees, their biomass and the effect of the slope on tree growth. Based on canopy height models (CHM) generated from UAVs-acquired images, we determined that tree heights to range between 5 to 50 m high of the 2858 trees present in the plot, which were corroborated by field surveys. At present, we are testing different models that can automatically determine individual tree biomass, from digitally calculated tree height and DBH values. This will highly contribute to cedar forest management since this is the most commonly planted tree in Japan.