Some rare species whose seeds cannot be stored by conventional means or do not produce seeds (exceptional species; Pence 2014) will need to be maintained as whole plants growing in a group or population on property that can offer long-term security. Field genebanks have been traditionally developed for cultivars of commercially valuable plants that must be maintained as living clones (FAO 2013). Within the CPC network, field genebanks, sometimes called living collections, are grown at our botanical gardens or on properties where landowners have agreed to conserve and maintain living populations of the species for many years. When the field genebank is located near a water source and fenced so that plants are protected from herbivory, it improves the ability to care for the collection and the chances of the collection’s long-term survival. Most CPC field genebanks support long-lived tree species with five to 20 unrelated individual plants per conservation collection. Most require collaborations across institutions, because it is unlikely that a single institution will have enough space available to house the 100 or more individuals needed to capture the desired genetic diversity of a species.
In Hawai’i, special field genebanks have been established and are known as inter situ collections. They are, in a sense, half-way houses between the full care facilities offered at a botanical garden and the “fend for oneself” life in the wild. Often located at mid-elevation between the plant’s wild habitat (which in many cases can no longer support the species) and the practitioner’s botanical garden, these semi-protected settings provide a place where plants can experience some natural climatic variation, while still receiving supplemental care when necessary.
Field genebanks require very long-term planning and commitment by property owners. Plants have the best of both worlds: exposure to some natural climatic conditions and extra help (usually in the form of water, fertilizer or hand-pollination) when necessary. This can help ensure maintenance of adaptive traits; support of mutualists like pollinators, seed dispersers, and soil microorganisms; and easy access to propagules for restoration.
Figure 2.4 – Genetic analysis can help quantify whether a conservation collection holds the majority of genetic diversity of a wild population. Griffith et al. (2015) compared the number of alleles measured in 10 microsatellite markers of the cycad Zamia decumbens to the numbers captured in 205 ex situ plants held in botanical garden collections. A single-accession collection (smallest points) would capture between 27% and 57% of in situ alleles, while the entire ex situ collection (7 accessions, 205 plants) captures 78% of wild population alleles.
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