Rubus humulifolius rescued by narrowest possible margin, conserved ex situ, and reintroduced in the wild

Highlights

• The westernmost population of Eurasian species Rubus humulifolius became extinct in the wild in Finland in 1957.

• Five ramets of R. humulifolius were rescued only hours before their habitat was destroyed.

• R. humulifolius survived decades in ex situ conservation in a private garden.

• R. humulifolius was micropropagated and reintroduced to a new site in 1988.

• This was the first time that micropropagation was used to save an extirpated species.

Abstract

Rubus humulifolius is a Eurasian species that has got wide geographic distribution from western parts of Russia to Manchuria. The westernmost and separate population of R. humulifolius was found in Central Finland in 1917. The population was assumed to be formed via anthropogenic dispersal either in early nineteenth or early eighteenth century. In 20's the population was regarded as viable as it covered an area of a hectare almost as a monoculture in the field layer and it was protected by law in 1933. However, the state of the population started to decline in the same year as the area was ditched. In 1957 there were only fifteen rosettes left and five rosettes of were transplanted from the site to a private cottage garden just before the whole area was turned into a construction area and remaining population destroyed.

The rescued population thrived but attempts to reintroduce plants from it to other sites considered to be suitable for the species were unsuccessful. Therefore, a research project initiated in 1986 for finding a suitable in vitro method for vegetative propagation of the plant. Eventually, the right formula for a substrate was found and 1500 new plants were produced in a couple of months. Now the in vitro propagated descendants of the five rescued ramets grow in several Finnish botanic gardens as part of their living collections and they also have been reintroduced to a natural site close to the original one in Central Finland.

One can assume that a plant population that has gone through two bottlenecks – i.e. establishment of new population by presumably few long-distance dispersed genetic individuals and population decline to near extirpation – has got very narrow genetic diversity. Whether this is the case and whether inbreeding depression could explain e.g. the observed poor seed production in the population remains as a challenge for future research.

Owing to ex situ conservation and in vitro technique applied for the first time to reintroduce an endangered species R. humulifolius is no more in immediate danger of extirpation. However, it is still classified as Critically Endangered (CR) as there is still only one population in the wild and it may be genetically depauperate.