There are at least two subspecies of juniper (Juniperus communis). The best known, J. communis communis, whose bushes vary between a metre and 10 metres tall, can form tall, conical spires and often appear to have been trimmed into exotic shapes. The evergreen leaves are dark green and the stems are fiercely prickly. The dark purple berries are famous for being used as flavouring for gin. The other subspecies of the plant, J. communis nana, is a matted shrub that grows close to the ground. There might also be a third subspecies, J. communis hemisphaerica, found on sea cliffs in Cornwall and Pembrokeshire.
Juniper has been part of human life for centuries. The spiny branches were used as an early form of barbed wire and the berries, as well as flavouring, were used in ancient medicines for horses as well as humans.
Juniper is a slow-growing tree which may live for up to 200 years. It is dioecious, meaning the male and female flowers are on separate plants. Pollen is dispersed by the wind and the fertilised female flowers eventually produce a hard, green berry. These finally ripen to the well-known blue-black fruit, popular with the birds that are largely responsible for the spread of the tree.
Junipers are found across most of the UK and are one of three native conifers, the other two being Scots pine (Pinus sylvestris) and yew (Taxus baccata). However, it is extremely irregular in its distribution. The subspeciesJuniperus communis communis is found in two main populations, one in the Scottish Highlands and the other on the southern English chalk. It is also abundant on parts of the Chilterns, the North Downs and especially Salisbury Plain. Juniperus communis nana is chiefly restricted to north-west Scotland's mountainous regions. Elsewhere, juniper is a widespread tree, found across both temperate and sub-arctic zones.
Juniper is found on well-drained rocks and soils and tolerates extremes of climate and pH. In Scotland, it occurs on cold, wet acid sites and grows amongst heather and whinberries. In the south of England it is found on hot, dry chalky hillsides. The largest southern population of juniper in England is inside the Ministry of Defence's Establishment at Porton Down in Wiltshire. Here there are estimated to be over 14,000 bushes. It is thought that many of these date from the introduction of myxomatosis and the reduction of the rabbit population, which led to reduced grazing of the seedlings.
Juniper is believed to have declined by up to 60 percent of its pre-1960 population, although with adult bushes being long-lived, it is possible for moribund populations with no regeneration to affect the true status of the species. The biggest threat to the plant is over-grazing, which prevents the regeneration of young bushes. However, too little grazing also affects the spread of juniper by allowing larger trees to shade out the adult bushes. In the uplands, juniper is also threatened by moorland burning for game shooting, which prevents the plants regenerating or leads to a fragmented cover. However, the threat to the species is greater in England than it is in Scotland.
Juniper is listed under the UK Biodiversity Action Plans and included in English Nature's Species Recovery Programme. It is also part of Plantlife's 'Back from the Brink' project. Many juniper populations are within Sites of Special Scientific Interest (SSSIs), and there are grants available to landowners to encourage proper management of the plant. The Forestry Commission Woodland Grant Scheme is also being used to maintain populations where these occur within a woodland context. Juniper is a component of several important habitats, particularly upland scrub woodland, and the loss of this species within this habitat removes a vital element of its biodiversity. It is also planned to carry out a series of regional surveys to assess the age range and reproductive potential of native juniper populations. This information will enable new populations to be established in areas where trees have been lost in order to restore the associated habitats.
The UK Biodiversity Action Plan for this species is available at UK BAP.
Embed this ARKive thumbnail link ("portlet") by copying and pasting the code below.