The rapid disappearance of a once common plant from UK hillsides has been blamed on infertile females.
Juniper is an important part of the UK's culture and landscape
A study of the aromatic shrub juniper by charity Plantlife found that many are now too old to reproduce.
In the past, the tree was highly valued for firewood and for making gin, ensuring a constant turnover of plants.
But around the turn of the last century, interest in the plant started to wane and land was no longer managed in a way that encouraged its growth.
"A lot of our juniper is now between 100 and 200 years old," said Dr Deborah Long, conservation officer at Plantlife Scotland.
"And like humans they become less reproductive, the older they get."
Juniper, Juniperis communis, is widespread across the world. It is one of only three native conifers in the UK; the others are the yew and Scots pine.
Until recently, it was commonly found in upland areas across Cumbria, Wales, Northumberland and Scotland.
But estimates suggest that up to 46% of juniper plants may have disappeared across England since the 1970s. At the same time, Ireland has seen a 35% decline, whilst Scotland has lost 30% of its plants, and Wales a further 18%.
Its loss has made it the subject of a conservation plan by the government.
More than 40,000 plants were surveyed by Plantlife volunteers
The Plantlife study, conducted between October 2004 and October 2005, examined 44,000 Juniper bushes across Scotland and was carried out by 250 volunteers.
The results, which have taken until now to compile, show that the surviving population lacks a sufficient number of productive female plants.
This is important because the shrub is dioecious, meaning there are both male and female plants. Unlike normal trees where the different sexes occur on the same plant, male and female junipers may be widely dispersed.
"Male bushes produce a lot of pollen, so only a few of them are required for berry production," said Dr Long.
But if there are few viable females to be pollinated and produce berries, reproduction rates fall and eventually populations drop.
The picture is complicated, because any seedlings that are produced are at risk from grazing and fires.
This decline means that a valuable part of the UK's heritage is at risk.
"Juniper is an important part of our ancient landscape and culture," said Dr Long.
The evergreen plants provide a valuable habitat for wildlife including more than 40 types of invertebrate such as the Juniper Pug moth.
It is also home to specialised lichen and fungi, whilst the dense prickly foliage is used as a nesting site for birds.
Humans have also found uses for the versatile shrub. Although they are slightly poisonous, the black berries are used to make gin and to flavour game dishes.
The fragrant wood was also used to cleanse houses and ward off spirits. In Scotland, it was the fuel of choice for illegal whisky stills, as it is said to burn with less smoke than other woods.