A third of critically endangered plants cannot be saved in seed banks: study

More than a third of critically endangered plant species cannot be preserved in seed banks to save them from extinction, researchers have warned.

Efforts to conserve plants, trees and wild relatives of crops outside their natural habitat mostly focus on storing seeds using a process of drying and then deep freezing them at minus 20C in seed banks.

A global strategy for plant conservation has set a target to conserve 75% of  threatened species outside their natural habitat – or “ex-situ” – by 2020, in places such as Kew’s Millennium Seed Bank at Wakehurst Place, West Sussex.

But for many of the at-risk plants, conventional “seed banking” will not work, prompting a need for urgent investment and research into alternatives to preserve some of the world’s most threatened plants, the researchers said.

A study last year by researchers from the Royal Botanic Gardens, Kew,  estimated that about 8% of all the world’s plants produce seeds which cannot be banked, including important UK tree species such as oak, horse and sweet chestnuts, and global foods including avocado and cocoa.

Now new research from the team at Kew suggests the problem may be worse for species that are at risk of extinction.

Researchers used four major plant lists and looked at various categories of threatened plants to see how many species are likely to be “bankable”.

They estimate 36% of the most at risk of extinction, or critically endangered species, produce “recalcitrant seeds”.

This means they do not survive the drying process and cannot be frozen, making them “unbankable”, the study published in the journal Nature Plants said.

More than a quarter (27%) of endangered species produce seeds that cannot be banked, along with 35% of plants considered to be “vulnerable” to extinction.

It is a particular problem for trees, with 33% of all the world’s tree species producing seeds that do not survive the drying process, the study suggests.

In tropical moist forests, such as rainforests or cloud forests, as many as half the species of trees which create the canopy can be unsuitable for preserving in seed banks.

An alternative to conventional storage in seed banks, which can also be unsuitable for seeds which survive the drying and freezing process but still do not last for more than a few years, could be “cryopreservation”.

The preservation technique, which involves removing the embryo from the seed and using liquid nitrogen to freeze it at much colder temperatures of minus 196C, could allow unbankable seeds to be preserved.

John Dickie, from Kew’s Millennium Seed Bank and one of the authors of the paper, said:  “Ex-situ conservation of plants is more critical than ever, with many threats to plant populations including climate change, habitat conversion and plant pathogens, we need to make sure we’re doing all we can to conserve the most important and threatened species.

“As successful as seed banking is for some species, it is not suitable for all seed plants and we need to invest in other ways to safeguard recalcitrant seeds.

“This paper shows that we need greater international effort to understand and apply alternative techniques like cryopreservation which have the potential to conserve many more species from extinction.”

Conventional wild species seed banks should play to their strengths, meanwhile, redoubling efforts to conserve species such as medicinal plants and crop wild relatives which can be banked.

The researchers also warn it may be “somewhat naive and dangerous” to assume conservation outside of habitats is a valid way to protect a high proportion of tropical moist forest trees from extinction – and conserving the forest may be the only feasible tool for many plants.