Importance of arboreta for ex situ conservation of threatened trees

Threats to biodiversity continue to increase worldwide and the conservation of biodiversity through in situ and complementary ex situ measures are more important than ever. Here we studied the presence of introduced tree species in New Zealand considered threatened according to the IUCN Red List of Threatened Species. We conducted desktop assessments of tree collections across New Zealand in conjunction with a field assessment of the identity and status of threatened introduced trees in eight regional tree collections, focussing on endangered (EN), critically endangered (CR), and extinct in the wild taxa. A total of 15 CR and 52 EN gymnosperm taxa were recorded for New Zealand representing approximately 38 and 40 % of the world's CR and EN gymnosperms, and a smaller percentage (1 %) of the world's CR and EN angiosperms. Of particular note are the CR Cupressus chengiana var. jiangensis and Widdringtonia whytei, and several EN gymnosperms, including Cupressus guadalupensis var. guadalupensis, Nageia maxima, and Pinus nelsonii, that are considered priority taxa for ex situ conservation by Botanic Gardens Conservation International. The field assessment confirmed the presence of seven CR and 26 EN tree taxa growing in the Canterbury region. Although many of these were present as one or two individual trees, the combined resources of the collections and the presence of several globally rarer and priority taxa indicate a potentially important role of New Zealand's tree collections in ex situ conservation. To fulfill their potential, their protection and health status as well as propagation and rejuvenation should be given urgent attention.