After 5,000 years, British tree changes its sex

After 5,000 years, the Fortingall Yew tree in Scotland finally decided it was time for a change: one of its branches is beginning to exhibit characteristics attributable to female yew trees, while the rest of the tree has remained male.

As a general rule, yew trees are dioecious, which means that they are one sex or the other. This is a biological tactic that enables yews and other dioecious trees to produce larger fruits that contain more seeds.

The Fortingall Yew is estimated to be between 3,000 and 9,000 years old, although its exact age is unknown because parts of the early tree have since decayed. Scientists now estimate its age by comparing its current measurements to what the size of its trunk was in 1769.

The tree has been documented for its entire history as a male tree; male yews have small conical structures that issue clouds of pollen upon reaching maturity. Female yew trees, by contrast, have red berries during the autumn and winter months.

“It was, therefore, quite a surprise to me to find a group of three ripe red berries on the [Fortingall] yew this October when the rest of the tree was clearly male,” Botanist Max Coleman wrote in a post on the blog of the Royal Botanic Garden Edinburgh.

It is not entirely uncommon for trees to switch from one gender to the other, but as Dr. Coleman noted in an interview with Agence France-Presse, "It's a rare [occurrence] ... rare and unusual and not fully understood."

Dr. Coleman and his fellow scientists are theorizing that the sex change could have been prompted by environmental factors, or may be a tactic the tree is using in an attempt to prolong its lifespan.

“It’s a strategy for longevity,” Brian Muelaner, chair of the Ancient Tree Forum, told the Guardian. “The Fortingall yew is fragmented and it may be so compartmentalised that part of it has become sexually ambiguous. We are all continuously learning about ancient trees – the ageing process of trees is a new science.”