The Royal Botanic Gardens, Kew is collecting seeds of native British trees to store in its Millennium Seed Bank, a project to gather and preserve examples of British tree flora. The aim is to ensure the survival of the full genetic diversity of the UK’s tree population, an especially important project now that so many pests and diseases threaten Britain’s trees. Here are 10 of the trees that are the highest priority for conservation and which, among others, will have their seeds preserved in the seed bank.
Oak
This is at the top of the list of trees for conservation, not only because it is common but also because of the number of threats it faces. There are two native oaks in the UK: the English and the sessile. The biggest threat comes from acute oak decline, a bacterial disease first observed in the 1980s. Oak jewel beetle may be the agent of this bacteria, which is affecting trees in the southeast and east of England.
Juniper
There are three subspecies of juniper. They are mainly threatened by a fungal disease called Phytophthora austrocedrae, discovered in Argentina and Chile about 50 years ago. It has affected junipers in the UK in Upper Teesdale and Perthshire. It is mainly spread by water so it could be in soil in imported plants or transported in other ways, such as on footwear. Juniper is also threatened by habitat change, over-grazing and burning of moorland, and the way it reproduces.
Scots pine
Abundant in plantations, but native to Scotland, the Scots pine (pictured left) is being affected by Dothistroma septosporum needle blight, a fungal disease, which has severely affected other species of pine and is now affecting Scots pine.
Ash
The advent of ash dieback in the UK, particularly in the east and south of the country, has been widely reported. It is thought to have been introduced here by wind from the continent and through tree imports. It has caused 60 to 90 per cent of ash trees in Denmark to die and threatens to change the British landscape dramatically, since the ash is a very common species. Insect pests are also a problem.
Alder
Alder is threatened by a pathogen called Phytophthora alni, first observed in 1993, which is widespread in southeast England and is transmitted through water. Alder grows along water courses and the pathogen is likely to have an impact on ecosystems along streams and rivers.
Wild cotoneaster
This is a very rare species found in north Wales. Its gene pool is very small and consequently it is less able to deal with environmental changes or threats. It is critically endangered: only six are left in the wild.
Plymouth pear
The Plymouth pear, a wild relative of the domestic pear, is designated as “vulnerable” on the International Union for the Conservation of Nature’s Red List of Threatened Species. It is one of Britain’s rarest trees (it is found in only two locations in the wild, in Devon and Cornwall, although there are others in cultivation.) It can be seen at Wakehurst Place, Kew’s country garden.
Beech
Another abundant native tree, beech is also important for forestry. It has been affected by Phytophthora ramorum, which has had an impact on oak trees in the US, where it is known as “sudden oak death,” as Clive Anderson discusses on p58. In the UK, it has blighted larches in southwest England, where foresters have had to clear hectares of trees to contain the spread of it.
Silver birch
A native tree (pictured right) found across the UK, the silver birch is vulnerable to the Asian longhorn beetle and citrus longhorn beetle. These beetles are capable of affecting all broadleaf trees. Outbreaks of Asian longhorn beetles have been reported in the southeast of England. Trees have had to be felled to stop the spread.
