Stocking up for the end of days

In a modest building with stuccoed walls made from bales of hay, scientists are working on an ambitious conservation project. They seek to create a "backup of this area's — and the world's — wild plants.

Handful by sweaty handful, they collect seeds from plants in the hills around this city in southern California. Once cleaned and dried, the seeds are put into silver-coloured, insulated envelopes. Half of the envelopes remain here at San Diego Zoo's Conservation and Research for Endangered Species (CRES) and the other half crosses the Atlantic to the Millennium Seed Bank Project (MSBP) in Britain, the acting repository for all the world's wild plant seeds.

Unlike animals, which can theoretically move to more suitable climes, plants can only move as fast as their seeds disperse. But in today's human-dominated landscape, such obstacles as cities, agricultural fields and highways could stop plant migration.

Scientists worry that many plant species won't be able to adjust and will simply disappear. A quarter of Earth's species — plants included — may vanish by the century's end, says the latest report by the Inter-governmental Panel on Climate Change.

Hope for future

So, as American lawmakers haggle over how to handle carbon emissions and avoid what is widely considered a climate catastrophe in the making, seed-banking projects such as the MSBP have moved ahead with a "hope for the best, prepare for the worst" approach.

The worry — and the hurry — is that species may disappear tomorrow.

"We don't know what benefits these plants will provide — sources of medicine, important food crops," says Kayri Havens, director of the Institute for Plant Biology and Conservation at the Chicago Botanic Garden, a contributor to MSBP. "If we lose them, we lose all of those options."

On the other hand, scientists hope that once the proverbial dust settles, reintroducing species to the wild will be possible.

"Seed banking represents a great deal of optimism and hope for the future," writes Flo Oxley, programme co-ordinator at the Lady Bird Johnson Wildflower Centre at the University of Texas at Austin, a contributor to MSBP, in an e-mail.

"Why save a resource if there is no future for it?"

On May 22 — Biodiversity Day — MSBP vaulted its one-billionth seed, a sub-Saharan bamboo in danger of disappearing from its native range.

Working with more than 100 partners worldwide, MSBP has so far banked about 18,000 species from 126 countries. On track to meeting its goal of banking 10 per cent of the world's flora by 2010, it hopes to bank another 45,000 by 2020. That would represent one-quarter of Earth's known flora.

Something about the 21st century has triggered a flurry of seed-banking efforts. In 2001, the US bureau of land management inaugurated its "seeds of success" programme, an effort to bank native US plants for restoration projects and a contributor to MSBP.

More recently, Norway announced the Svalbard Global Seed Vault on the Svalbard archipelago above the Arctic Circle. Buried in permafrost, the bank endeavours to keep seeds from humanity's 21 food crops safe from various possible catastrophes — war, blight, climate change and an asteroid strike among them. The MSBP differs from the Norway effort in one crucial aspect: It seeks to preserve wild species with no immediate economic value. And it seeks to do so by preserving their genetic diversity.

Natural selection "selects" for the individuals within a species that do best in the present circumstances. If hot and dry weather prevails in a field of daisies, for example, then the individual plants that prefer hot and dry conditions will thrive and set seed. If cool wet conditions prevail, cold-loving individuals will prosper. Scientists think that the best way to preserve a species is to preserve its genetic variation — to ensure that any single species contains both heat and cold lovers, so to speak — and to give natural selection a greate number of options to "select" from.

"If we're looking at evolutionary processes with a changing environment, the greatest amount of diversity provides us the greatest number of genes to ensure filling niches," says Jonathan Dunn, the botanical conservation co-ordinator at CRES. So "the best way we can facilitate [plants'] ability to change is to maintain diversity".

On these grounds, scientists involved in MSBP roundly reject comparisons to Noah's Ark: only two members of each species wouldn't preserve nearly enough genetic information to create a viable population. "Noah's fridge" is slightly more palatable, says Michael Way, the Americas co-ordinator in the seed conservation department of the Kew Royal Botanical Gardens near London, which houses MSBP. But even this designation falls short.

MSBP's seeds aren't hoarded and stored away for when the metaphorical floodwaters subside. "There is an active exchange taking place so that our partners are benefiting," says Way.

"They're able to do their job in-country better."

Here is an example: Dalea azurea, a flowering shrub that grows in only one Chilean valley, nearly ceased to exist in the wild, mostly due to habitat loss. By 2003, seeds were so hard to find that even banking prospects for future re-introduction looked dim. But, working with Chilean conservationists, the MSBP grew Dalea in greenhouses. In the end, they succeeded in increasing their seed store, ensuring the possibility of the plant's future restoration in Chile.

Maintaining diversity

But ultimately, seed from banks such as MSBP might be used in much larger-scale — and more controversial — restoration projects. Plants that define an ecosystem, what scientists call "keystone species", may need help migrating as the global climate changes.

If the plains of Illinois are predicted to have the climate of Texas in 100 years, for example, prairie grasses growing there will have to withstand the conditions of present-day Texas, says Pati Vitt, manager of conservation programmes at the Chicago Botanical Garden.

But with both natural and unnatural obstacles between two regions and the rate of change so rapid, scientists worry that species migration won't happen on its own. So some propose "assisted migration" — aiding vegetation shifts by planting southern species in the north ahead of predicted climatic shifts.

An even more controversial approach involves hybridising northern species with southern ones to make plants that will be more tolerant of the future climate. Such proposals raise a host of questions: What should an ecosystem that never existed in a particular place look like? What happens if "assisted" species hurt the plants already there? Whatever the resolutions to these and other questions, without seed banking efforts now, such tactics won't be possible in the future, Dr Vitt says.

Ins and outs of seedbanking

"We maybe have a very narrow window of time where we still have a level of geographic range and diversity and plants that are producing seeds," she says, from a field site near a highway in Illinois. "I can't tell you how narrow that window is. I don't know. But we do have a sense of urgency." Careful drying and storing can reliably hold seeds in suspended animation for at least two centuries. The real challenge is ensuring genetic diversity. Without it, scientists will have a harder time re-establishing viable plant populations in the wild.

At San Diego Zoo's conservation and research for endangered species, scientists typically collect seeds from at least 100 individual plants of the same species. That is enough, they estimate, to preserve 98 per cent of a species' genetic diversity.

Most comprehensive collections include seeds from different years. By gathering seeds from different seasons, scientists know that their seed collections contain any variations that might lead a variety of plant to prefer hot over cold, wet over dry, and vice versa.

While in the field collecting, scientists jot down information on the surroundings. Was the plant in the shade, on a hill, near a stream? Once in the lab, scientists expose some seeds to various combinations of moisture, daylight and temperature to determine their ideal germinating conditions. All this information goes into a database to help guide future restoration efforts.

The remaining seeds are dried for up to several months. Once desiccated, the seeds go into insulated silver pouches and eventually, refrigerators where they'll be kept at minus 20C. In these conditions, seeds can last up to 500 years.

In all, "securing a species" costs some £2,000, says Michael Way, the Americas co-ordinator in the seed conservation department of the Kew Royal Botanical Gardens, which houses Britain's MSBP.

Collections at the MSBP, which can reach more than 15,000 seeds per species, average about 3,500 seeds. But if the number of seeds dwindles for any reason, the seed bank may replenish it by growing plants in greenhouses. However, scientists prefer not to.

Greenhouse conditions could generate plants that thrive in "unnatural" conditions, traits that might work against the species in the wild.