Can Botanists Save One Of The Rarest Trees In The World?

A graceful birch native to Japan is one of the rarest trees in the world. Two decades ago, botanists counted just 21 remaining in the wild, all confined to a single stand in the remote, rugged forest of the Chichibu Mountains — likely far too few for the species, Betula chichibuensis, to sustain itself.

Arboretums scrambled to cultivate the tree, with some success. But now the species may have gained a second chance at survival: Botanists in Britain have collected and germinated seeds from these wild birches for the first time in nearly 30 years.

The new seedlings may help restore genetic diversity to the small population of cultivated trees and fuel efforts to reintroduce them in the wild. “Definitely, it’s a great coup for a very rare species,” said Michael Dosmann, a curator at the Arnold Arboretum of Harvard University, who was not involved in the project.

The mission to save B. chichibuensis is part of a broader undertaking by British and Japanese scientists to survey and collect seeds from all of Japan’s native plants, many of which are found nowhere else in the world.

No one knows why B. chichibuensis grew so scarce. Experts now believe that there are more than two dozen in the wild; in recent years, Toshihide Hirao, a forest ecologist at the University of Tokyo Chichibu Forest, has discovered eight other small stands in the mountains. Still, “there is no doubt that this species is very rare and endangered,” he said.

Dr. Hirao and his colleague Satoshi Suzuki led British researchers last year to one of the more accessible patches. The team set out around sunrise on a gloomy October morning, toting plant presses, pruners and GPS units. It was not an easy trek. As they moved deeper into the mountains, the trail became narrow and unruly, often nearly disappearing, said Ben Jones, curator of the University of Oxford Harcourt Arboretum. A drenching rain began to fall as the researchers traipsed over slick limestone outcrops and scrambled over steep hillsides.

Six hours after setting out, the scientists reached the birches. Nestled among conifers, the birch leaves had already changed from bright green to a buttery, autumnal yellow. “Obviously, we were really tired and exhausted and very wet and very hungry, but we were just buzzing,” Mr. Jones said.

“It was like finally meeting a particular celebrity you’re really obsessed with. There’s nothing like seeing these plants in their native range and habitat.”

A closer inspection of the trees brought another thrilling surprise: The branches were loaded with seeds. The team carefully collected 2,000 from seven trees before turning back for home.

Back in the laboratory, X-rays of the seeds raised hopes that at least some were viable. After making the journey to Britain, about half were sent to Millennium Seed Bank in Kew, England, for storage, the remainder to Dan Luscombe, a botanist at the Bedgebury National Pinetum in Kent.

Mr. Luscombe planted the seeds in compost, and to his delight, around 100 sprouted. “I walked by one day and was like: ‘Bloody hell, they’re coming out! The seedlings are germinating!’ ” he said. “I wasn’t really expecting them to do a lot, but they literally came romping up within a matter of a couple weeks.”

Since November, the seedlings have grown about 10 inches high. Eventually, they will be distributed to botanic gardens around Britain, and some may be returned to Japan. The seedlings may prove an enormous help in salvaging the species, and not just because of their numbers.

“B. chichibuensis has never been grown systematically in arboretums, so the success of the U.K. team in germinating seeds of this species may be the first step toward conserving the gene pool,” Dr. Hirao said.

In 1987, Hugh McAllister, then a botanist at the University of Liverpool’s Ness Botanic Gardens, received several hundred B. chichibuensis seeds from a colleague in Japan. Just eight germinated. Dr. McAllister took clippings and created clones from which all captive plants are derived.

Ness Botanic Gardens has distributed seeds to 36 gardens since 2009, and at least 28 facilities have cultivated relatives of Dr. McAllister’s original eight clones, according to PlantSearch, a database of global botanical collections. But saving the species means continually collecting seeds from wild populations, Dr. Dosmann, of the Harvard arboretum, said.

The birches that produced viable offspring 30 years ago may not be the ones doing so today, and field data, lacking for the original 1987 batch, is important for research and restoration. Mostly, though, the new seedlings may play a vital role in widening the genetic diversity of the cultivated specimens.

“It’s important for gardens to have these trees as backups, but we want to be wary of everyone cultivating exactly the same sliver of genetic diversity because we have no way of knowing if it’s representative of the average or not,” Dr. Dosmann said.

“Imagine if an alien came down and kidnapped just three people, but they happened to be your three least favorite celebrities. Do you really want the human race characterized only by those individuals?”

The researchers plan to return to the field next year — this time equipped with camping and climbing gear — to spend more time surveying the birches. Dr. Hirao and his colleagues, meanwhile, are analyzing genetic diversity and gene flow in the wild trees.

In addition to helping revive the species’ prospects, Mr. Jones also hopes that the renewed interest in B. chichibuensis will raise awareness about the plight of rare plants in general.

“That one in five plant species are threatened with extinction probably eludes a lot of people,” he