Invasives Blog

Wild gingers, Hedychium spp., belong to the same family as edible ginger (Zingiber officinale), but they have no culinary value. Native to moist tropical forests of Central and Southeastern Asia, they are cultivated the world over as ornamentals. Their large, glossy leaves flare out around their tall reedy stems and their orchid-like, showy blossoms come in a breathtaking array of colours, exuding a heady perfume.  Such is their aesthetic appeal, that they are showcased in the finest Hawaiian leis (floral and leaf garlands). Their scientific name, Hedychium (pronounced “heh-DIK-ee-um”), is derived from the greek “hedys” meaning sweet and “chion” meaning snow and is based on the type species for the genus Hedychium coronarium (white ginger), the sweetly fragrant and best known ornamental ginger, which Cuba adopted as their official national flower in the 19th Century as a symbol of purity, rebelliousness and independence.

But in parts of its introduced range, such as Hawaii, New Zealand, Australia, South Africa, La Réunion and the Macaronesian Archipelagos, beauty has turned to beast; the very characteristics which gained them favour in gardens, such as hardiness and capacity for rapid, vegetative growth, have allowed them to naturalise in the wild and smother many unique and specialised communities, threatening delicate ecosystems, especially forest ground flora and associated fauna.  In particular, Kahili ginger, Hedychium gardnerianum has earned a place as one of the world’s 100 worst invasive alien species and biological control is considered the only practical and sustainable approach for the long-term management of large infestations in native forests.

To this end, the first phase (scoping study) of a biological control programme was initiated by CABI in 2008, funded by a consortium of sponsors from New Zealand and Hawaii (Landcare Research, New Zealand, The Nature Conservancy, Hawaii and the United States Geological Survey – Pacific Island Ecosystems Research Center). As with every new biocontrol initiative, a thorough review of the scientific and botanical literature, as well as records of the target species from UK and subsequently Indian herbaria, gave the expedition geographical focus. A short exploratory survey in collaboration from KFRI confirmed Sikkim state in India to be a hot spot for Hedychium biodiversity, including Kahili ginger. A large number of natural enemies is known from economic crops such as edible ginger, turmeric and cardamom which are all in the same family as wild gingers (Zingiberaceae) however very little information was available on the fauna and mycobiota associated with Hedychium spp. Repeat surveys in 2009 and 2010 have continued to reveal a large number of natural enemies associated with the invasive Hedychium species and in 2011, with the export of natural enemies recently endorsed by the Indian government and renewed collaboration at national level with NBPGR , the project is poised to carry out further surveys and begin host range testing in the UK of the most promising species for Hawaii and New Zealand.

The wild ginger complex should lend itself well to a biological control initiative as there are no other native, representative Zingiberaceae present in Hawaii or New Zealand. However, the economic, ornamental and cultural appeal of Hedychium species in their introduced range (especially in  Hawaii) cannot be underestimated, no matter how damaging the plant is to native forests; early engagement with the Hawaiian community and horticultural stakeholders will be paramount and planning of educational and outreach programmes to address concerns and potential challenges  can only be of benefit if biological control is found to be a viable option and is to be accepted as an essential part of the wild ginger management strategy for biodiversity conservation.

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