Don’t bank on seed banks to save New Zealand’s trees

Don’t bank on seed banks to save New Zealand’s trees

New Zealand can’t rely on seed banking to save many of its iconic trees, such as kauri, from disease, a new international study shows.

The study by scientists from the Royal Botanic Gardens, Kew, will soon be published in the international journal Nature Plants (published on November 3). Lead author Dr Sarah Wyse now works with New Zealand’s Bio-Protection Research Centre.

The scientists analysed whether seed banking could achieve the international goal of conserving 75% of the world’s threatened species ex situ – meaning away from their natural habitat. Ex situ conservation offers a type of insurance policy, in case localised disruption or disaster threaten a species.

However, the scientists concluded seed banking could not achieve this goal, because many seeds don’t survive the storage process.

Twenty-one percent of New Zealand’s trees and shrubs, including iconic species such as totara, rimu, and tawa, fit into this group of plants with “recalcitrant” seeds, says Dr Wyse. Swamp maire, which is threatened by myrtle rust, also has recalcitrant seeds.

And while kauri seeds are not recalcitrant, they are viable for less than 10 years after seed banking, so they also cannot be stored this way.

“Most of the plants with recalcitrant seeds are from canopy trees from tropical rain forests,” says Dr Wyse. “New Zealand has quite a high number of plants with recalcitrant seeds because many of our North Island trees are closely related to tropical species.”

Seed banking remained a good way to conserve crop and medicinal plants, and also worked for most New Zealand trees and shrubs, including, for example, pohutukawa and southern rata, Dr Wyse said. But with the other authors she said it was vital to develop alternative conservation methods, such as cryopreservation, for many plants.

For seed banking, seeds are dried and then frozen at -20°C. Once thawed and planted in soil they grow just like fresh seeds. However, cryopreservation involves removing the embryo from the seed then using liquid nitrogen to freeze it at an extremely cold temperature (-196°C). Once thawed, the embryo then has to be grown in a culture in the laboratory.

“It is a much more complex process than seed banking, and requires many more resources,” says Dr Wyse.

In the paper, the scientists say “intensifying research efforts into cryopreservation as a conservation tool” is vital to improve the chances of conserving many of the world’s tree and shrub species ex situ.

However, they say, “it may even be naïve and dangerous to assume that ex situ conservation is a valid means of safeguarding a high proportion of threatened tropical moist forest trees from extinction”.

The same is true of many of New Zealand’s endangered endemic species, says Dr Wyse. “If we are serious about wanting to save our unique trees, we need to do everything we can to save them in their natural environment, because other methods may simply not work.”

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