The attractions of Japan’s Southern Alps include dense evergreen coniferous forests and alpine meadows full of blooming globeflowers (or Trollius japonicus). These areas have been likened to an earthly paradise. In recent years however, sika deer have moved into this alpine zone. With them grazing on the rare plant community there is a danger that these alpine meadows, a symbol of the rich mountain environment, will disappear.
A questionnaire survey conducted in 1984 found that there were virtually no sika deer breeding in the northern part of the Southern Alps. Then, in the 1990s the sika deer quietly began to use the evergreen coniferous forests of Veitch’s silver fir and Maries fir in the subalpine zone, as well as the Erman’s birch forests and herbaceous communities. By the early 2000s the sika deer had encroached further into the subalpine zone and settled there, and within around ten years the colourful alpine meadows had disappeared.
Previously, it was generally considered that the alpine environment, with its many steep slopes, was too harsh an environment for the sika deer to breed in. However, the hooves of sika deer living on these steep slopes have worn down, and are now like the hooves of the goat-like Serow that perch on cliffs. So why have the sika deer encroached into the alpine zone?
To learn more about their movements, sika deer were tracked using GPS collars. Movement from their winter habitat (at elevations below 1,800 meters) up to their summer habitat was observed taking place in June. This occurred over a long period of time, and was significant in terms of both difference in elevation and distance. It was observed alongside the rise in the foliage front, when plants start to grow and green shoots extend from the lower elevations towards the higher elevations.
In summer, from early June until early October, the sika deer made use of the alpine environment, such as the alpine meadows, from the upper subalpine zone to the alpine zone. During this time, it was found from the positions of individual tracks and from vegetation in the Mount Senjogatake region that the locations where the sika deer grazed most excessively were Erman’s birch forests and on herbaceous species of altherbosa in the upper subalpine zone.
Severe grazing pressure
Protective fencing installed on Mount Senjogatake damaged during winter was repaired in early June. Before the repair, sika deer had already reached the surrounding area and were able to access areas inside and outside the fence. Following the repair, deer were no longer able to access the protected area. After only two weeks, flowers began to bloom inside the protective fence, while outside none could be seen. This demonstrates the effectiveness of protective fences, and the severe impact of sika deer grazing pressure.
It is considered that this expansion in sika deer distribution is the result of movement from regions where the breeding density is high and the grazing conditions have become poor to regions where the breeding density is low and the grazing conditions more favorable. In seeking locations with good grazing conditions – favorable to birth and raising young in the case of females, and to the development of physical size in the case of males – sika deer have encroached into the upper parts of the subalpine zone.
Sika deer are tough creatures that have survived disturbances caused by human activity, and we must continue to live alongside these sturdy neighbors. They are now heading towards the alpine zone of the Northern Alps – towards Mount Shiroumadake and other places with a rich diversity of flowers. We must therefore utilize the past experience of damage in the Southern Alps to make sure it is not repeated in future.
Written by Shigeyuki Izumiyama, Professor at the Institute of Mountain Science (IMS) at Shinshu University in Nagano, Japan. A longer version of this post was first published on the IMS website back in 2015.