BSBI Species Accounts ArchiveJuniperus communis
Tue, 08/31/2010 - 11:25 | 
markd
At the species level, Common Juniper, Juniperus communis L., is uncontroversial (Stace 1997). But it is a very variable species, and numerous forms have been described. These have a genetic basis, but whether they should be considered subspecies or merely varieties is debatable (Thomas, El-Bargathi & Polwart 2007). If you get two very different forms growing in one area, it may seem obvious which is which, but in other places there are intermediate forms that make it impossible to maintain such a clear distinction. At present, in Britain, three subspecies are accepted, but many people simply record the species. The three subspecies are:-
- ssp. communis
- ssp. nana (J. & C. Presl) Nyman
- ssp. hemisphaerica (J. & C. Presl) Nyman
Chromosome No.: 2n = 22 (Stace 2010).
Photography: S. Pilkington
Juniper is unusual in having only immature foliage. Mature leaves in the Cupressaceae are scale-like and appressed to the stem. In most species the immature needle-like leaves soon fall off, but in juniper they persist indefinitely.
Common Juniper is widely but unevenly distributed throughout the British Isles, mostly in grazed grasslands. Ssp. communis occurs throughout the range of the species, whereas ssp. nana is restricted to the west and the north. The ssp. hemisphaerica is recorded only in Pembrokeshire and Cornwall. It is one of the most common and widespread tree species in the northern hemisphere, occurring throughout much of Europe, North America and Asia, and even into North Africa.
Click on the map to view full-size on the BSBI Maps Scheme website.
Juniperus communis
Juniperus communis ssp. communis
Juniperus communis ssp. nana
Juniperus communis ssp. hemisphaerica
Juniper occupies many niches in vegetation communities: it can be the dominant canopy shrub in scrub, or it can be a small, ground-hugging plant in heaths or short grassland. Thomas, El-Bargathi & Polwart (op. cit.) describe it as occurring in calcareous, dry grasslands in the south of England; and on wet, calcareous to acid soils in Scotland and the north. They list the following NVC communities for it: CG7, CG13, H7, H12, H14, H15, H20, W11, W13, W17, W18, W19 & W21.
- Origin: native.
- Rarity: not rare or scarce.
- Threat: listed as Least Concern by Cheffings & Farrell (2005) but with a Change Index of -0.42 it is apparently declining quite rapidly.
- Conservation: UK BAP. Several counties list it as an axiophyte. Juniper is listed as a priority species on the UK Biodiversity Action Plan (Anon. 1998), on the grounds that it is declining. This is partly attributable to changes in land management (mainly loss of low-intensity grazed grasslands), but also apparently to poor reproductive capacity and competition with other plants, which is largely climate-related (Thomas, El-Bargathi & Polwart 2007). Due to its conservation status, Juniper is now often planted in the wild, particularly in southern England, and it was recorded as alien in 42 hectads in the New Atlas (Preston, Pearman & Dines 2002). It may have been planted in some of its 705 native hectads as well.
Photography: S. Pilkington
It would be interesting to study the responses of Juniper to climate change and agricultural practices but, unfortunately, it is such a charismatic species that any natural changes are likely to be masked by conservation action - at least in England & Wales, where populations tend to be small. For the Maps Scheme, we do not distinguish between wild and planted populations, but anything that is planted in a garden or other obviously horticultural site should not be recorded at all. If it is planted in the wild, it should only be recorded if it persists for at least a few years. County recorders should try to maintain information on the extent of the introductions that occur.
- Anon. 1998. UK Biodiversity Group Tranche 2 Action Plans Vol. 1 – vertebrates and vascular plants. Publicity & Grants Team, English Nature, Peterborough.
- Thomas, P.A., El-Bargathi, M., & Polwart. 2007. Biological Flora of the British Isles: Juniperus communis L., Journal of Ecology 95, 1404-1440.
Login to post comments