Juniperus communis L.
Common Juniper, Bastard’s bane, Dwarf Juniper, Meryw, Aiteann, Iubhar Creige CUPRESSACEAE SYN.: none
Status: Serious decline over the last 25 years UK BAP Priority species since 1999 805 10 km squares 1987-1999 Lead partner: Plantlife International Schedule 8 Wildlife and Countryside Act
UK Biodiversity Action Plan (BAP)
These are the current BAP Targets following the 2001 review:
T1 - Maintain the current range of Juniper. T2 - Maintain the overall population size of Juniper. T3 - Achieve natural regeneration of Juniper populations at sites under direct conservation management. T4 - Maintain, or re-establish, populations at sites not under direct conservation management. T5 - Restore representative tree-line Juniper populations.
Progress on targets can be viewed by clicking on: http://www.ukbap.org.uk.
The full Action Plan for Juniperus communis can be viewed by clicking on: http://www.ukbap.org.uk.
PLEASE NOTE: In this dossier, the main emphasis is on Juniperus communis ssp. communis, although there are sections that include information about the other sub- species, their taxonomy and distribution. Generally, a reference to Juniper or Juniperus communis means the whole species, and references to sub-species are made explicit.
Contents
3 Ecology & Life Cycle...... 23 4 Habitat Requirements ...... 32 4.1 Communities & Vegetation ...... 32 4.2 Summary of Habitat Requirements ...... 35 5 Management Implications ...... 35 6 Threats / Factors Leading To Loss or Decline or Limiting Recovery ...... 38 7 Current Conservation Measures ...... 40 7.1 In situ Measures ...... 40 7.2 Ex situ Measures...... 41 7.3 Research Data ...... 41 7.4 Monitoring Juniper & the Common Monitoring Standard ...... 42 8 References ...... 42 9 Acknowledgements ...... 45 10 Contacts...... 45 11 Links...... 46
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3 Ecology & Life Cycle This section is written with particular reference to Juniperus communis ssp. communis.
Juniperus communis ssp. communis reproduces mainly by sexual means in drier areas and at lower altitudes. However, in the Lake District and Scotland, where the ground is boggy and individuals are of more prostrate varieties, it can be exceedingly difficult to distinguish individuals (Smith, 1980) and it is likely that there are large clones. Experiments in Canada on rooting cuttings of J. communis ssp. depressa have also shown that ability to root is greater in northern populations and in females (Houlé & Babeux, 1994).
Vegetative reproduction is commoner in old declining stands (Falinksi, 1980). Layering does sometimes occur even on the drier chalk grasslands in the south of England. Larger, aging bushes collapse, the branches touch the ground, and occasionally re-root, as shown by a much more vigorous and greener branch. However, in these dry situations the re-growth does not always persist after the centre of the bush has died.
Juniper is wind-pollinated. The male flowers open in spring and there are pollen sacs attached to each of the cone scales (see Figure 12). Clouds of pollen can sometimes be seen in windy conditions. Pollen sticks to the receptive droplets on the female flowers (see Figure 13) and as the pollen tube elongates the berries begin to develop. In the first year the berries (strictly speaking cones or galbuli) are green but they progressively ripen and turn purple after fertilization at the beginning of the second year – mostly around August to November (see Figure 14).
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Figure 12 – Male cones of Juniperus communis in spring with cone scales and pollen sacs. Left – pollen sacs full; right – pollen sacs discharged. (Photographs by Lena Ward).
Figure 14 – 1st year Juniper berries Figure 13 – Receptive droplets on (green) and 2nd year berries (purple) in female cone flowers of Juniper in autumn. (Photograph by Lena Ward). spring. (Photograph by Lena Ward).
Figure 15 – Sections of 1st year (green) and 2nd year (purple) Juniper berries in autumn. (Photograph by Lena Ward).
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The berries of Juniperus communis contain from one to five seeds, usually three (see Figure 15). However, many seeds that appear intact on the outside may not be so inside, e.g. at Porton Down only 3.7% of 417 seeds sampled from 40-year old bushes in October 1998 were normal. This abortion appears to relate to predation, failure of pollination and the nutritional status of the bush. It also varies geographically, empty seeds being much commoner in the south of the range (García et al, 2000). Older bushes have fewer good seed than younger bushes (Dearnley & Duckett, 1999; Ward, 1981; Diotte & Yves, 1989). In the UK seeds are killed by several species of insects / mites e.g. Juniper Seed Chalcid (Megastigmus kuntzei), Juniper Shield Bug (Elasmostethus tristriatus), Juniper Berry Miner (Argyresthia praecocella). The Juniper Berry Mite (Trisetacus quadrisetus) inflicts the most serious damage, and has been recorded affecting 82% of berries.
The seed bank type of Juniperus communis is classified as transient (Thompson et al, 1997) meaning that the seeds persist in the soil for less than one year. This fits reasonably well with incidental information, as very occasionally young Juniper does reappear on recently extinct sites. Most records of Juniper appearing spontaneously are apparently from bird dispersal.
Seed germination of Juniperus is complex and not convenient for artificial manipulation for sowing (Pack, 1921). The seeds from berries ripening in the autumn require a long period of after-ripening, and as few as 1% germinate without an after-ripening period. The embryo shows root and shoot dormancy (Sebastian, 1958) and the seeds require two winters before they germinate in spring (in April - May in southern England). Germination has been reported to vary greatly according to the specific treatment and seed source (Johnsen & Alexander, 1974). This variability is considered to be an ecological adaptation that increases the chances for a species to establish in unpredictable habitats and those that result from catastrophic events (Broome, in press). A suggested procedure is two periods of cold stratification at 90 days for 3.5oC separated by 60-90 days at 20oc diurnally. This resulted in successful germination of 70-75% of the seeds over 20-30 days. Broome (in press) recommends that seeds are removed from the fruit and soaked in 1% citric acid solution for 4 days before being stored in well-aerated conditions at 4oC for 30 weeks to break their dormancy. If seed is left out of doors in compost and kept free of rodents, a few will germinate in the first year, most in the second year, and several more over the next two-three years. In germination experiments at Lochaber, seedlings continued to emerge for 5 years with a peak in germination at 2 years and 7 months (Broome, in press).
Ripe berries are dispersed by birds in the autumn, and there is extensive literature on this subject, especially for Spain (Garcia, 2001; Garcia et al, 2001). Bird dispersers mainly belong to the Turdidae (Thrush family) and large flocks of fieldfares are particularly important in spreading Juniper to new sites. Some berries are attacked by insect pests, and are then less attractive to birds (García et al, 1999), so favouring the dispersal of undamaged cones. Some berries fall to the ground beneath the bushes. Others persist uneaten on the tree, often turning brown; such berries usually containing fewer fertile seeds. Berries on the ground and those accessible on the bushes are also eaten by rodents such as voles and wood mice (King & Wilson, 2001). Rosen (1988) reports that domestic sheep may also serve as a dispersal agent since Juniper is often associated with sheep droves.
Young seedlings of Juniper are slow growing and are most often found in un-grazed situations in communities with much bare ground or little competition from other vigorous plants -usually due to low nutrient conditions (Vedel, 1961). There are usually vigorously fruiting, but not old, parent bushes within a few hundred metres of young seedlings. Regeneration with many age classes on one site is unusual in southern England unless there is continual erosion of the ground or intermittent periods of grazing (Ward, 1981). A good example of natural regeneration on eroding steep roadside banks showed how pioneer Juniper on these new sites had produced numerous seedlings
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locally (Banks, 2001). It will be interesting to see how well these seedlings survive. Mice and voles eat both young seedlings and seeds (Barrett, 1997). Most of the younger stands of Juniper in the south regenerated after rabbits were lost by myxomatosis in 1954-5 (e.g. Porton Down). Regeneration continued for a narrow time span of about 11 years and then apparently ceased because of competition from other plants. Rabbits returned in the mid 1970s and caused serious damage (see Figures 16 & 17).
Young seedlings are vulnerable to summer drought (Garcia et al, 1999; Rosen, 1988 & 1995), and we may speculate that this climatic factor might have implications for Juniper with any future global warming. Conversely, where seedlings are grown in very moist conditions as in plant nurseries, they may succumb to Phytothphora, Phomopsis and other fungi. This may happen in some conditions in the wild.
Young Juniper plants are very vulnerable to damage, especially when they are shorter than the height of a grazing rabbit. They have less protective bark and may be more easily killed outright by ring barking. Very young seedlings do sprout again from the base but not so vigorously as Crataegus (Hawthorn), and a few persist for years as grazed plants a few centimetres tall. If grazing is relaxed these shoot up. However, where there is frequent serious grazing damage, Juniper is progressively killed and regeneration will be very poor (Morris et al, 1993; Gilbert, 1980). The greater number of sheep grazing in the Lake District together with an absence of Juniper regeneration is thought to be a cause of the imbalance of age classes, with the grazed older stands having poorer reproductive capacity (Dearnley & Duckett, 1999). In northern areas, particularly in Scotland, both deer and sheep browsing damage Juniper. Sullivan (2003) showed that pioneer plants suffered heavy browsing early on, although prostrate plants are heavily browsed throughout their life cycle, probably because of their accessibility. Miller & Cummins (1998) found that the Juniper was browsed in winter when other foliage was scarce. However, snow-lie does protect prostrate Juniper from browsing (Sullivan, 2003). Broome (in press) suggested that shelters 0.60 m in height should be used to protect Juniper from grazing as these improve plant growth. Although they have an effect on growth form, shelters should be removed at about five years. After removal, there was no evidence of collapse.
Juniper is shade intolerant at all stages of life, particularly at the young seedling stage. Although seedlings may initially be protected from grazing and browsing under older bushes, the older plants and seedlings may then die under the shade of successional yew trees (Watt, 1926) (see Figure 18). Juniper can survive under light shade, and in some cases the Junipers are drawn up and become very tall. For example, Humphrey (1996) showed successful establishment and growth in 20.5% daylight levels typical of 40 year old, thinned Scots pine woodland. In Scotland, Juniper may be an understorey in birch woodland e.g. Morrone Birkwood NNR. Sullivan (2003) showed that shading of woodland Juniper caused it to die (2% of surveyed woodland populations affected) and may be responsible elsewhere when deaths were unexplained, in 42% of surveyed woodland populations. Snow break in woodland populations was another important factor in branch death (Sullivan, 2003). Broome (in press) suggested that weed control was beneficial to the establishment and growth of Juniper.
The mean annual increment of growth of Juniper growing on Porton Down, measured for one hundred bushes, 40 years old, was 7cm, but individual growth varied according to the year, health and sex of the bushes from 1cm to as much as 28cm. This particular stand reached maturity after about 9 years for males and a little later for females (Ward, 1981). Other observations suggest that this time can be shorter for plants growing on better soils, while being much later for Juniper in alpine/northern conditions. In Scotland, the growth rate for Juniperus communis ssp. communis is typically 3-5 cm per year (Broome, in press).
The varieties of Juniper tend to grow at different rates, some are exceedingly slow growing, especially Juniperus communis ssp. nana, while some of the tallest Juniper
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1969
1973
1977
2002
Figure 16 – History of a Juniper population at Porton Down (note the same Yew tree on the downland in the background): 1969 – Population regeneration after rabbits died from myxomatosis in 1955; 1973 – growth continuing with foliage to the ground; 1977 – after serious rabbit attack; 2002 – surviving bushes (note 1 metre rule). (Photographs by Lena Ward).
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Figure 17 – Basal damage to Juniper by rabbits at Porton Down, Wiltshire. (Photograph by the late J.A. Grant, with kind permission of Lena Ward).
Figure 18 – Juniper in the process of being shaded out by successional change to Yew woodland at Stockbridge Down, Hampshire, 1985. (Photograph by the late J.A. Grant, with kind permission of Lena Ward).
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so far recorded in the UK reached about 6 m at Holystone Burn in Northumberland. The maximum height for a Juniper in Norway was 18 m. The Borders Forest Trust Survey (1997) found that the maximum spread can be considerable - an individual bush covered 35 m2.
Figure 19 – Dead and dying Juniper in an old population at Blakes Firs, Porton Down, Wiltshire, 1991. (Photograph by Lena Ward).
Figure 20 – The oldest recorded Juniper in the U.K. growing in Teesdale in 1987, with 255 annual rings. (Photograph by the late J.A. Grant, with kind permission of Lena Ward).
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The life span of Juniper in open unshaded conditions is about 100-120 years on the southern chalk, and stands with many dead and dying bushes can be found where the population was roughly even-aged (see Figure 19). In the south a bush with 130 annual rings has been recorded at Porton Down and one with 145 annual rings has been found on the Cotswold limestone. The oldest Juniper so far recorded by Ward had 255 rings (and therefore a minimum age of 255 years) and was from Teesdale (see Figure 20). No doubt other older specimens will be found. There is a suggestion that faster-growing bushes have shorter life spans than slower-growing ones (Ward, 1981). Many Juniper plants, however, do not live to their maximum life span as they are shaded out by encroaching scrub and secondary woodland. This can happen relatively quickly – in as little as 30-50 years in vigorous mixed scrub stands with Hawthorn, Ash, Whitebeam, etc. Stands amongst Yew live longer as Yew is so slow growing but are inevitably killed by the dense shade. Nearly all the old Juniper (in southern England) have serious cankers and rots in the roots and butts. Although there have been no studies to date of the life span of Juniper in Scotland, in more extreme situations it probably lives longer than Juniper in the south of England (MacDonald, pers. com.). However, it is very difficult to age bushes of J. communis ssp. nana because of the form of the stems, the way wood is laid down and the occurrence of layering.
Juniperus communis ssp. communis is a dioecious plant with the sexes occurring on different bushes. The sex ratio within populations on the chalk, especially those that are grazed or damaged by rabbits, is usually biased in favour of males. Ward (1981) recorded a ratio of 1 M: 1.26 F (+ 0.49 unknown sex) in young Juniper at Porton Down in 1971, but after rabbit attacks during the late 1970s the sex ratio became 1 M: 0.58 F (+ 0.17 U). For the same years on this site a very old Juniper stand had ratios 1 M: 0.62 F (0.38U) in 1971 and 1 M: 0.59 F (0.26 U) in 1979. Joensalo (2000) also found that females of Juniperus communis ssp. nana were differentially grazed. However, this bias to females does not always hold true. Falinski (1980) observed that females predominated in very old stands, while Marion & Houlé (1996) did not find any consistently obvious differences in sex ratios and growth. In Scotland, although Sullivan (2003) attempted to determine sex, this was not possible for 79% of plants surveyed because of the relatively short period of time in which the male cones were present. Males are therefore under-represented in his analysis. However, the measured proportion of female plants was only 15%.
There is relatively little information about metapopulation dynamics of Juniper. However, it is thought to be very important in the conservation of Juniper as it seems to be a mobile species, which rarely regenerates in the same place as the parent plants, but exploits new favourable situations within the general area of bird dispersal movements. This is less obvious in a relatively long-lived plant like Juniper, as the persistence of the adult plants long after conditions have become unsuitable for regeneration means that conservationists have not always appreciated the rather different likely requirements. Taken in a broad sense, the general and progressive reduction in Juniper populations that we now observe means than the seed resources for new colonization are declining and new habitats cannot be exploited. These new habitats are nowadays rather rare and therefore we can predict the serious and future retrenchment of Juniper back to its heartlands and to extinction (Ward, 1981).
Gene flow has been little studied, but the variability within populations is striking - a good feature for conservation. Greeve et al (1998) found that gene flow in the Netherlands populations were high, at 9.27 migrants per generation. Population size was not significantly correlated with the proportion of polymorphic loci, mean effective number of alleles or the mean observed heterozygosity. Their estimated parameters of gene diversity and gene flow showed that the Juniperus communis populations studied shared a common gene pool, regardless of the fact that most of them are isolated and disjunct today.
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Juniper, as the only native member of the Cupressaceae family, has a specialized plant feeding specific fauna of insects and mites in the UK, (Ward, 1977). There are 42 species including those from introduced ornamental Junipers. A few more species have been recorded since then, mostly introductions. These insects are distributed according to their individual climatic requirements. Some species are of Mediterranean origin and occur on downland Juniper, while others are of arctic alpine origin. Thus the fauna of Juniper in the Lake District and northern England is less interesting than that of either the south or the Scottish mountains. The different species are specialized to feed on all parts of the Juniper. Those feeding on berries and seeds may cause damage, but equally some species are in need of conservation themselves as the Juniper microhabitat declines. Juniper wood decays very slowly and has few wood-feeding insects; it appears to have chemical defences against both wood-rotting fungi and termites in southern Europe. In Scotland, Sullivan (2003) showed that the largest Juniper populations had most diseases and insect herbivory. This is also likely to apply to fungal pathogens.
There are also specialized fungi, including in particular species of rust fungi, Gymnosporangium, which cause perennial galls on Juniper and sporulate in spring, with characteristic yellow finger-like projections (see Figure 21). These spores infect young growth of species of Rosaceae in summer spreading back to Juniper later in the season. The fungus usually only kills branches and does not often kill an entire bush. Gymnosporangium was not observed in prostrate Juniper in Scotland, although it was recorded in woodland and open ground Juniper (Sullivan, 2003). There are many other fungal species including some serious pathogenic species such as Juniper Blight Phomopsis juniperova. Juniper Blight occurred in 31% of all populations surveyed in Scotland (Sullivan, 2003), with an average of 23% of plants affected, making it the most commonly found cause of fungal disease. Juniper is also a good host for species of lichens but little is known about these.
Figure 21 – Gymnosporangium sp., a rust fungus, at the perennial galling stage with spores on yellow fruiting bodies, on Juniper in April, Mardale Banks, Cumbria. (Photograph by Lena Ward).
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4 Habitat Requirements Juniper occurs in a wide variety of plant communities as it can grow on both acid and alkaline soils throughout the British Isles from sea level to the highest montane areas (Rodwell, 1991a, b & 1992). Juniper can be a pioneer element of all types of open ground communities except for those in wet areas, and is especially characteristic of free-draining soils. It is limited by shading, and cannot persist in dense woodland.
The typical habitat of Juniperus communis ssp. communis in southern England is on chalk grassland, in open chalk habitats in quarries and in successional stages to woodland from these habitats. In the north of England there are also large stands on limestone pavements and scars. Juniper also occurs abundantly in some acidophilous heath communities. The most important in England is that of Borrowdale volcanic slates, followed by Bannisdale slates / Coniston flags, and whin sill (dolerite) and millstone grit - important in the Teesdale area. Often Juniper occurs in areas that were mined in the past. There are also smaller stands on the sides of eroded streams, e.g. in Northumberland. In the highlands of Scotland Juniper is common in open pine woodlands as in the Caledonian Forest, and also in birch woodlands. In some areas there are almost pure Juniper stands with very few tree species. There are also the uncommon but important Juniper sites on dunes in northeast Scotland recognized by the EEC Habitats Directive. Juniperus communis ssp. nana is scattered in exposed habitats through northwest Scotland and the Outer Isles.
Figure 22 – Juniperus communis ssp. communis in Pine woodland (NVC W19) in the Caledonian Forest, Loch Eilen, 1993. (Photograph by Lena Ward).
4.1 COMMUNITIES & VEGETATION National Vegetation Communities (NVC) communities in which Juniper is a dominant woody species are the most important for conservation (Ward, 1994). These occur in woodlands, grasslands and heaths. The three major communities with Juniper as the
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dominant species are described first, and then other communities mentioned in Rodwell (1991a, b & 1992) are listed briefly. A full detailed list of all 66 communities and sub- communities from the original data in all samples used in the construction of the NVC is provided by Wilson & King (2001).
IMPORTANT JUNIPER COMMUNITIES W19 Juniperus communis ssp. communis - Oxalis acetosella woodland Juniperus communis ssp. communis is the most abundant woody species in this community though some stands have an open over-canopy of Betula pubescens (Downy Birch). The Juniper may be patchy, but the bushes are not widely scattered. The bushes may have very diverse forms, and can be affected by browsing by stock or deer. Vaccinium myrtillus and Calluna vulgaris and ferns may be prominent. The grasses present are Agrostis capillaris, A. canina and Anthoxanthum odoratum, while Oxalis acetosella, Galium saxatile and Potentilla erecta are common.
This is a community of higher altitudes in the colder parts of northwest Britain on a wide variety of soils (Rodwell, 1991a). All the soils are free draining, but are not extremely dry because of the heavier rainfall in these areas. The community is represented in northern England, although its greatest area of abundance is in the Scottish Highlands. Whether it is a climax montane scrub is uncertain because of past destruction of the tree canopy in which pine and birch would have been abundant. Where trees are not present at lower levels then seral processes do not occur and the community is like a climax community.
W21 Crataegus monogyna-Hedera helix scrub This is a very mixed and extensive community including most of the seral thorn scrub and hedges in the British Isles. It is especially characteristic of the chalk and limestones of southern England (Rodwell, 1991a), though there are examples around Morecambe Bay.
Juniper is more often found in the Viburnum lantana sub-community, on the shallower, drier soils on steeper more exposed slopes than the scrubs where Crataegus is dominant. The diverse chalkland woody species such as Viburnum lantana, Cornus sanguinea, Ligustrum vulgare and Rhamnus catharticus are common. The scrub is more obviously seral than in the north, although succession may still be slow on very impoverished dry soils or sites where few trees invaded early on (Duffey et al, 1974). In quite a number of examples, grazing by rabbits or stock has prevented seral progression, and the Juniper then may be the major scrub species in CG7 (see below). Eventually bushes may die in the open of old age and disease.
H15 Calluna vulgaris-Juniperus communis ssp. nana heath. Prostrate Juniper occurs in a variety of dwarf sub-shrub heaths in Britain, but is more or less consistently dominant in the sub-shrub mat of the Calluna-Juniperus heath. Here it is accompanied by a distinctive element of oceanic hepatics, and Calluna vulgaris and Erica cinerea are especially frequent. This community is found at moderate altitude in the cool ocean climate on the western coast of the northwest Highlands and Islands (Rodwell, 1991). It is best developed on cool, shady slopes blown clear of snow, and is replaced at the junction of the sub-alpine and lower alpine zones by Juniperus-Oxalis scrub. There are stands, which are floristically and physiognomically intermediate between these two communities, with Juniper difficult to assign between communis and nana. This is a transitional community on the junction of the low alpine and sub-alpine zones. It can be seen as the north west Highland equivalent of the Juniperus-Oxalis scrub of the east central Highlands, though there it is ssp. communis that colonizes up to the limit of the forest zone.
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OTHER WOODLAND, GRASSLAND & HEATHLAND COMMUNITIES WITH JUNIPER W11 Quercus petraea-Betula pubescens-Oxalis acetosella woodland Juniperus communis ssp. communis occurs in the more open areas of this community, its increasing abundance often marking transitions to stands of the Juniperus-Oxalis woodland in the north.
W17 Quercus petraea-Betula pubescens-Dicranum majus woodland In Eastern Scotland Juniperus communis ssp. communis may occur in this woodland community, which can form mosaics with the more calcifugous stands of the Juniperus- Oxalis woodland.
W18 Pinus sylvestris-Hylocomium splendens woodland Juniper can be found as scattered bushes or in small patches in this community, and may become locally dominant in the absence of Pinus. These stands are best seen as mosaics with Juniperus-Oxalis woodland. They are a characteristic feature of higher altitude situations in eastern Scotland.
CG7 Festuca ovina-Hieracium pilosella-Thymus praecox/ pulegioides grassland Juniper invades along with other woody plants in the very early succession of the open vegetation of the Cladonia sub-community, and may form an open scrub as at Porton Down (Wells et al, 1976). Juniper may also invade the more typical limestone grassland communities in the south on the chalk or oolite. Where there are larger numbers of bushes that grow on to become the dominant element with other shrubs, this grades into the Crataegus monogyna-Hedera helix scrub described earlier. Juniper can persist as scattered bushes in limestone grasslands, but under severe grazing pressures may eventually become senescent and die without replacement by regeneration.
CG9 Sesleria albicans-Galium sterneri grassland Although Juniper is not included in this community in Rodwell (1992), it is considered an important colonist in some of these grasslands. The community occurs on free-draining but moist soils usually over drift-free Carboniferous limestone in the submontane and montane areas in the northern Pennines. The climate is cooler and wetter than that of the southern lowland calcicolous grasslands.
CG13 Dryas octopetala-Carex flacca heath Juniperus communis approaching ssp. nana in its procumbent habit occurs in the Salix repens-Empetrum nigrum ssp. nigrum sub-community. This community is restricted to calcareous lithomorphic soils in the cool oceanic lowlands of northwest Scotland.
H7 Calluna vulgaris-Scilla verna heath Juniper is very rare in this community in the area of the Lizard Peninsula in Cornwall, and is probably ssp. communis although small in size. Elsewhere this community occurs around the coast, and is the extreme maritime fringe of British sub-shrub vegetation.
H12 Calluna vulgaris-Vaccinium myrtillus heath Scattered bushes of Juniperus communis ssp. communis can be found in some situations around the eastern Highlands in this community. This is the typical sub-shrub community of acid to circum-neutral, free-draining mineral soils in the cool and wet sub montane zone. Sometimes found in association with Juniperus-Oxalis scrub, the community is widely distributed in southeast Scotland, the Lake District, parts of Wales and the southwest peninsula, and the North York Moors.
H14 Calluna vulgaris-Racomitrium lanuginosum heath (dwarf mountain heath) This community includes sparse records of Juniperus communis generally as ssp. nana. It is the typical shrub community of base poor soils at moderate to fairly high altitudes in the cool oceanic climate of the mountains of northwest Scotland. It sometimes gives way
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at lower altitudes to prostrate vegetation in which J. communis ssp. nana becomes very common and often co-dominant with the stunted heath.
H16 Calluna vulgaris-Arctostaphylos uva-ursi heath Juniperus communis ssp. communis occurs very occasionally in this community in the east central highlands.
H17 Calluna vulgaris-Arctostaphylos alpinus heath Juniperus communis ssp. nana occurs in some stands, but the generally small contribution of this plant to the vegetation here helps distinguish it from the Calluna- Juniperus heath. The community is confined to northern Scotland.
H20 Vaccinium myrtillus-Racomitrium lanuginosum heath Juniperus communis ssp. nana occurs locally in this community type, which is strongly centred in northwest Scotland on humic base-poor soils on fairly exposed slopes at moderate to high altitudes. In the former, J. communis ssp. nana occurs in the Viola riviniana-Thymus praecox sub-community.
H21 Calluna vulgaris-Vaccinium myrtillus-Sphagnum capillifolium heath Juniperus communis ssp. nana (and Arctostaphylos species) are occasional in this community of mixed sub-shrubs. In fact their absence helps separate the community from the Calluna-Juniperus heath. The community occurs widely but locally through the northwest Highlands and on the island of Skye.
4.2 SUMMARY OF HABITAT REQUIREMENTS The habitat requirements of Juniper in Britain are described below in Table 4.
Table 4 - Habitat features important to Juniper communis ssp. communis in Britain.
TYPE DESCRIPTION Physical and Steep eroding slopes. topographical Bare ground. Seedlings may appear during and just after severe grazing, but only persist when grazing by domestic stock/rabbits is reduced or absent. Older plants can withstand grazing and browsing. Seedlings do not tolerate long dry periods in summer. Vegetational and Production of fertile seed is more reliable from young structural bushes. Open/bare ground communities for regeneration and persistence (does not normally regenerate in deep grassland). Full light to slight shade only, dies in later stages of succession, therefore not in woodland unless very open, or at and above the tree line. Large stands required to ensure the survival of associated insects. Chemical Thin nutrient poor soils either acid or alkaline.
5 Management Implications The regeneration of Juniper is the most critical factor for management of lowland Juniperus communis ssp. communis. Of course, it will not matter if there is no regeneration at any one time, but only if this state continues throughout the reproductive life span of a stand of Juniper. At the present time, most of our younger
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Juniper populations in England date back to a regeneration phase that was caused by the loss of rabbits from myxomatosis in 1954-55 (preceded by very heavy grazing) creating ideal open ground conditions for young seedlings. However, considering the life span of Juniper is somewhere between 100-130 years in the south, and knowing that the majority of current Junipers are approaching 50 years in age with declining seed production, it is obvious that regeneration should be promoted vigorously now. The point is given even more force by the realization that Juniper in unmanaged mixed scrub stands in southern England will die much earlier because of shading.
A detailed and tested prescription for management of natural regeneration is not yet available. There have been a number of not very successful experiments, but deductions from their results and from general knowledge suggest the following requirements for chalk downland Juniper:
A nearby population of healthy, fruiting Junipers.
Open bare ground or short slow-growing vegetation and nutrient poor soils produced by: