Zao Mountains are located in the border between Yamagata and Miyagi Prefecture. Our research is centered in the area where the Zao ropeway operates (38 ˚ 09’06” N; 140˚ 24’ 39”E). The mountains from an altitude from an approximate altitude of 1350 m.a.s.l. is covered by Mariesi fir (Abies mariesii). The distribution of Mariesi fir in Japan extends from Gifu Prefecture in central Honshu to Aomori Prefecture in the northernmost area of Honshu island, covering an altitudinal range of 1300 to 2800 m.a.s.l. Fir tree structure has the peculiarity to trap large amounts of snow, shaping the figure of the tree to become a 'Snow Monster' as it is known in Japan, with Zao Mountains being the most famous place for tourist to see it. However,   However, bark beetle infestation has caused severe tree mortality in fir forests near the tree line (sites ④ and ⑤ in the west side in the adjacent figure), but not on the east side (site ⑥）in the last decade. The infestation has slowly but steadily moved downward (sites ①－③）, where from 2019, our research group has been collected images of fir tree health condition, following bark beetle infestation.