Plant 291

Betula chichibuensis H.Hara (Betulaceae)

Chichibu birch

Betula chichibuensis, one of 117 birch species, is endemic to the Chichibu region on the Japanese island of Honshu. Famously, it is one of the world's rarest birches, living exclusively on Mount Kamo-san where its global range is less than ten square kilometres.

The Chichibu birch is a multi-stemmed, occasionally single-stemmed, tree that can reach 10 metres in height. The bark is brown and flaky when young but later shows conspicuous, and raised, horizontal lenticels. It has papery, deeply veined, oval-shaped leaves that are glabrous and green on the upper surface, and with white hairs on the lower surface. The Chichibu birch is monecious with separate cream-yellow male, and red female, catkins on the same plant. Individuals are self-incompatible, therefore, two separate trees, close by, are needed for cross pollination.

The IUCN's Red List categorises the Chichibu birch as Critically Endangered. In 1993, only 21 mature individuals were identified. In the case of the Chichibu birch, several factors can be attributed to its classification as Critically Endangered. Habitat degradation and deforestation are evident in the Chichibu District. The tree's small population number and size, both of which make it susceptible to disease and natural disasters, are augmented by self-incompatibility and low seed viability.

In more recent years, the Chichibu birch has been the focus of collaborative Anglo-Japanese conservation efforts, with the use of seed banking, and ex situ and in situ conservation. This work, led by the Oxford Botanic Garden and Arboretum (OBGA), involves collaboration with the Bedgebury National Pinetum and the University of Tokyo Forest Chichibu.

The work carried out to date has included Rapid Botanical Surveys (a method developed in the University's Department of Plant Sciences) and the collection of plant samples, both seed and herbarium vouchers. The material from this ongoing project has been shared with partners. In particular, the Bedgebury National Pinetum has developed a germination protocol which has meant more than 100 individual plants have been grown to date. These have been widely shared amongst botanic gardens and arboreta, and are the backbone of the ex situ conservation programme.

The specimens growing at the OBGA also play a vital role in education in terms of plant conservation. At the arboretum, Betula chichibuensis currently features on a trail of threatened trees. To make these threats these trees are under more understandable, their conservation statuses are compared with those of familiar animals in the same IUCN category.

Further reading

Shaw K et al. 2014. Betula chichibuensis. The IUCN Red List of Threatened Species 2014: e.T194282A2309490.

Luke Rowland