The genetic health of the Irish oak remains strong despite a shrinking tree population, according to new research published next month. Dick Ahlstrom reports
How "native" is the native Irish oak? As native as a species can be when only 10,000 years old, according to research to be published next month on the tree's genetic status.
Dr Graham Muir has worked for the past five years with colleagues in Belfast, Edinburgh and Vienna analysing oak DNA in an effort to answer two questions: do our forests contain native or foreign oaks and; is the species under threat due to a shrinking gene pool and loss of variety.
Muir and colleagues Colin Fleming, Claus Vogl and Andy Lowe provide answers to these questions in a research report to be published next month in the journal, Annals of Botany.
Ireland is one of the least wooded countries in Europe, Muir points out. Our current woodland cover is about 10 per cent, but only 0.2 per cent is original ancient woodland. Tree cover stood at about 80 per cent 10,000 years ago after the glaciers had retreated.
The Government supports policies aimed at increasing woodland cover, but it is important to know that you are planting native varieties and not newcomers perhaps less genetically suited to conditions here.
Ireland had virtually no trees when the glaciers finally receded. As the ice moved north, so too did many species of trees and plants that migrated from their refuge on the Iberian Peninsula. This migration continued until the melting ice finally washed away the land bridge 6,000 to 8,000 years ago and Ireland became an island. "Not all continental species made it back before the land bridge ended," says Muir.
The research team decided to check whether today's natives, Quercus petraea and Q robur, share the same variants of DNA present in oaks now growing in Spain and Portugal, a proof that the oaks here were descended from the Iberian originals. They did this by studying elements of DNA associated with the plant's chloroplast.
The team went into the woods and collected leaf samples from 30 trees. "You take a leaf and try to sample evenly throughout the woods so you don't sample families," Muir explains.
"Our research suggests that Irish oaks are indeed closely related to oaks growing on the Iberian Peninsula and so they appear to be native," he said. "We can't discount the chance that they are descendants of seeds planted by humans, but we can say that even if they were planted, the source of seed came from or is closely related to oak material from this peninsula."
The modern Irish oak's gene pool or level of genetic diversity was studied by looking at the degree of variation between similar genes. With so little ancient forest left, the concern is that if the pool shrinks any further the species could drift into extinction, something that has happened in Ireland to the native Scots pine, says Muir.
"The oak is under threat. The numbers here have reduced dramatically," he says. "Just look at the Scots pine to see what can happen."
So far the oaks are holding their own in terms of genetic diversity, as seen in gene variations. "We found that levels of this type of DNA variation were compatible with levels on the Iberian Peninsula." The trees are not yet tending to cross with family members. "Oaks are a highly out-crossing species, but in time they could have problems."
The key threats faced by the oaks are not development, roads or pollution, but rather the depredations of hungry sheep and deer that gobble up oak seedlings.
"One of the problems is the current woodland is unprotected. The simplest thing to do now is to stick up a fence and keep out the sheep and deer," he says.
Muir is now based at the Institute of Animal Breeding and Genetics at the Veterinary University in Wien, Austria, but became involved in Irish oaks at Queen's University Belfast when working under Fleming of the department of applied plant science, who started the project. "It has been going on for five years," he says, with funding from the North's Department of Education, the European Science Foundation, Austrian Science Fund and the Natural Environmental Research Council.