Juniper

Durham Priority Species
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Juniper Action Plan

Priority Species: Juniper

Priorities
1. Maintain and enhance the present range and population size of Juniper.
2. Encourage natural regeneration of Juniper at existing sites
3. Raise awareness of the species and its conservation requirements

Targets
Vision StatementFor juniper stands of varying ages and age structures to exist in a landscape matrix, with management conditions in place for natural regeneration to occur

Target Type Unit Value
1. To extend the range of juniper in the Durham BAP area from the 1992 baseline. expand ha 50

Juniper Juniperus communis ssp communis is a native coniferous shrub of the British Isles.

Although its centre of distribution lies within the Highlands of central and eastern Scotland, juniper also occurs at scattered localities in southern and northern England and Wales. It forms a component of a number of British plant communities as it is able to thrive on both acid and calcareous freely drained (but moist) soils at a wide range of altitudes, ranging from sea level to montane environments where it occurs on a prostrate form as ssp nana.

In northern Britain juniper is often found within the field layer of open birch and pinewoods and on upland heaths and acid grasslands. Where juniper is the most dominant woody species, it can form a unique woodland vegetation type, W19 Juniperus communis-Oxalis acetosella woodland community (National Vegetation Classification, Rodwell 1991). This northern juniper is particularly important in terms of nature conservation, and stands in Durham represent southern examples of this community.

The ground layer of these woods can be species rich, including a typical woodland ground flora with wood anemone Anemone nemorosa , wood sorrel Oxalis acetosella, and moschatel Adoxa Moschatellina. Juniper also supports a comparatively small, yet characteristic, native invertebrate fauna, including many species with specialised habitat requirements and restricted distribution in the UK. Juniper stands in northern England often support a mix of both northern and southern species on the edge of their range such as the Juniper Carpet Thera juniperata and Juniper Pug Eupithecia pusillata.

Stands of juniper can also diversify upland bird communities, as bushes are an important food source for frugiforous birds such as fieldfares, song thrushes and ring ouzel. In the absence of other native tree cover, juniper stands also provide valuable winter shelter for black grouse.

Nationally, juniper is not a scarce plant. In England, however, there is concern that juniper is becoming increasingly scarce as a semi-natural vegetation type. In southern England juniper is

in a critical state of decline with evidence of habitat fragmentation and contraction in range through extinctions. The poor regenerative status of British juniper stands is widely considered to be the greatest long term threat to this habitat type. In northern England juniper is also a restricted habitat type but it has been part of the local flora since the Ice Age. Again lack of regeneration has been noted.

Local status

Although juniper is locally abundant in parts of Cumbria it is more localised in Durham and Northumberland. The majority of juniper in Durham occurs in or adjacent to the North Pennines Natural Area on unimproved pasture or moorland in isolated stands. The total area of this habitat is approximately 115ha, split between 26 colonies. Around 100ha of this is in the Upper Teesdale NNR (counted as one site).

A notable exception to this westerly distribution in Durham is a site on the Durham Coast at Blackhall Rocks.

Surveys in 1973 and 1994 highlighted the local decline in juniper. Twelve sites and 36% of bushes were lost in this period. Juniper stands are  dominated by old bushes (over 50 years) and natural regeneration is rare.

Threats

Grazing and management

  • The decline in juniper is partly due to intensive grazing, principally by sheep but also cattle and by increasing populations of rabbits and other small mammals. Young juniper plants are very palatable to animals, unlike the older spiny plants.
  • Heavy grazing opens up dense stands of juniper, gradually fragmenting colonies into an open community of scattered individuals.
  • It is also thought that traditional management which included the periodic harvesting of juniper scrub for fuel and haystack bases and so on, combined with variable but lighter grazing regimes might have provided ideal conditions for seed germination.

Regeneration and seed viability

  • Age has been found to affect reproductive output as the capacity of bushes to fruit diminishes as bushes grow older. Seed viability also decreases with age, falling from 80% in young plants to 5% in older populations.
  • These factors, along with the dioecious nature of juniper (presence of male and female flowers on separate plants), mean that older, even aged stands of juniper which are increasingly  fragmented become less and less likely to regenerate.

Burning

  • Rotational burning of heather has affected a number of isolated communities in the past.

Natural succession

  • Juniper which exists in open woodland will eventually be shaded out if the canopy closes. Unless regeneration occurs on the developing open fringes of this woodland, the population will be lost.  This has happened on a number of sites in Durham.
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