Japan’s Zao mountain ‘snow monsters’ thinning rapidly due to insect, snow damage
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YAMAGATA – The ice formations on trees that create spectacular winter views in the Zao mountain range spanning Yamagata and Miyagi prefectures have been thinning rapidly since 2019, according to research by Yamagata University Emeritus Professor Fumitaka Yanagisawa and others.
The thinning is attributed to the death of many Maries’ fir trees because of pest damage.
The conifer trees, on which ice formations, also known as snow monsters, develop, experience broken branches under the weight of the snow because of the damage.
The Yamagata prefectural government and other groups are planting trees to revitalise this important tourist resource.
Maries’ firs naturally grow in the Zao mountain range at altitudes between 1,300m and 1,700m above sea level; snow monsters form on those situated at heights at and above 1,500m.
They are created when snow and moisture in the air are blown onto these trees.
According to the company that operates the Zao Ropeway, 140,000 people visited to see the ice trees during the season from December 2024 to March 2025.
The Ice Tree Association, a society of researchers of which Prof Yanagisawa is a member, analysed thousands of old photographs of ice tree formations that developed around the ropeway’s Jizo Sancho Station, at an altitude of 1,661m, to compare their sizes over time.
The research found that formations with diameters of 5m to 6m were common in the 1930s to 1950s.
Even after that, ones with diameters of 2m to 3m were seen until the 2010s.
In recent years, however, the majority have measured only about 0.2m to 1m in diameter.
Massive outbreaks of moth larvae and other pests from around 2013 to 2016 caused the deaths of about 23,000 Maries’ firs across an area of 16ha around the station.
These accounted for nearly 20 per cent of the roughly 126,000 trees then growing in clusters on the Yamagata side of the mountain range.
Prof Yanagisawa said the rapid thinning of the ice trees began around 2019, when more and more starved or weakened branches started breaking under the weight of accumulated snow.
Trees with few branches or leaves cannot support large volumes of snow and ice.
Even during 2025’s heavy snowfall, most ice trees in areas above 1,600m above sea level remained only about 0.5m to 1m thick.
“We have seen many trees topple over under the weight of the snow,” Prof Yanagisawa said. “We are afraid that the number of ice trees may decrease.”
The prefecture’s division in charge of nature conservation said the Forestry Agency began planting trees in 2019 and has planted 330 saplings around the station to date.
In 2023, the agency, the prefecture, tourism groups and experts formed the Prefectural Council for the Restoration of Ice Trees in hopes of restoring Zao’s unusual natural landscape. THE JAPAN NEWS/ASIA NEWS NETWORK
