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Sorbus bristoliensis 

Scope: Global
Language: English
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Taxonomy [top]

Kingdom Phylum Class Order Family
Plantae Tracheophyta Magnoliopsida Rosales Rosaceae

Scientific Name: Sorbus bristoliensis Wilmott
Common Name(s):
English Bristol Whitebeam
Taxonomic Source(s): The Plant List. 2016. The Plant List. Version 1.1. RBG Kew. Available at: http://www.theplantlist.org/.

Assessment Information [top]

Red List Category & Criteria: Endangered D ver 3.1
Year Published: 2017
Date Assessed: 2015-07-31
Assessor(s): Rivers, M.C. & Beech, E.
Reviewer(s): Rich, T.C.G., Mikoláš, V., Meyer, N. & Allen, D.J.
Contributor(s): Wigginton, M.J.
Justification:

The species is a restricted species endemic to the Avon Gorge in western England. It qualifies as Endangered (EN D), as it has a low population size of about 306 individuals, of which 150 are mature. In addition, it has a highly restricted extent of occurrence and area of occupancy (<8 km2). There are no significant widespread current threats, and there is no continuing decline or severe fragmentation. The population is currently healthy and regenerating. It is considered well protected as the whole population is found in the Avon Gorge SSSI, and the main threat to the species is possible mismanagement of its habitat.

Previously published Red List assessments:

Geographic Range [top]

Range Description:This species is endemic to western England, where it is recorded from the Avon Gorge near Bristol, where it is found on both the Somerset and Gloucestershire sides of the Gorge (Houston et al. 2008). The distribution is very small and both the extent of occurrence (EOO) and the area of occupancy (AOO) estimated to be less than 8 km2.
Countries occurrence:
Native:
United Kingdom (Great Britain)
Additional data:
Estimated area of occupancy (AOO) - km2:8Continuing decline in area of occupancy (AOO):No
Estimated extent of occurrence (EOO) - km2:2.3
Continuing decline in extent of occurrence (EOO):No
Number of Locations:1
Lower elevation limit (metres):5
Upper elevation limit (metres):110
Range Map:Click here to open the map viewer and explore range.

Population [top]

Population:There were 262 trees known in 2006 and there is evidence of regeneration in the population (Houston et al. 2008). In the Red List for England the population estimate is 291, based on field data collected in 2013 (Stroh et al. 2014). In 2016, 306 trees were known (L. Houston and T. Rich pers. comm. 2016). It has been suggested that the population in Leigh Woods has been increasing by ~10% per decade since the 1970s (Houston et al. 2008; Rich et al., 2010). The age of one tree was more than 227 years old, however the mean estimated age of cored mature trees are 89 years (Houston et al. 2008). There are an estimated 150 mature individuals.
Current Population Trend:Increasing
Additional data:
Number of mature individuals:150Continuing decline of mature individuals:Unknown
Extreme fluctuations:NoPopulation severely fragmented:No
Continuing decline in subpopulations:No
Extreme fluctuations in subpopulations:No

Habitat and Ecology [top]

Habitat and Ecology:The species grows as a tree to at least 15(-22) m tall. It is found on rocks and quarries, screes and slopes, and also occurs in woodland as a tall tree. On the Bristol side of the gorge it is scattered in secondary woodland and scrub. It is found on Carboniferous Limestone rocks, screes and shallow rendzina soils on the slopes. Soil depths range from 2-10(20) cm and can be rooted directly into crevices. Fruiting appears to be dependent on ecological conditions and some large shaded trees produce no fruit. A variety of birds and small mammals were seen to eat Sorbus bristoliensis fruits (Rich et al. 2010).
Systems:Terrestrial

Use and Trade [top]

Use and Trade: No information available.

Threats [top]

Major Threat(s): Whilst a number of threats have been identified, none are considered to be significant or likely to impact all individuals. Some trees have been felled during work to improve public safety and access. Reintroduced cattle grazing may affect a proportion of the population. Given that virtually all of the trees except those in gardens occur within the statutorily protected areas of the Avon Gorge SSSI and SAC, there are few obvious threats to its long term survival other than mismanagement (Rich et al. 2010). Goat grazing for conservation purposes resulted in ring-barking of some trees in 2016. Trees seem partially susceptible to a fungus disease which weakens but does not kill them (L. Houston pers. comm. 2016).

Conservation Actions [top]

Conservation Actions: The entire population is found within statutorily designated sites including Avon Gorge SSSI (Rich et al. 2010). There are ex situ collections held at Bristol University Botanic Garden, Cambridge University Botanic Garden, Ness Botanic Garden, Westonbirt Arboretum, the National Botanic Garden of Wales, and elsewhere. Some seed has been deposited in the Millennium Seed Bank, Wakehurst Place (Houston et al. 2008). Sorbus bristoliensis is recorded as present in an ex situ seed bank collection (ENSCO 2015).

Sorbus bristoliensis was listed as Endangered in Oldfield et al. (1998), in the Red List of Great Britain in 2005 (Cheffing and Farrell 2005), and as Vulnerable in the Red List of England in 2014 (Stroh et al. 2014). It is listed as a UK BAP priority vascular plant species (JNCC 2010).

Citation: Rivers, M.C. & Beech, E. 2017. Sorbus bristoliensis. The IUCN Red List of Threatened Species 2017: e.T34741A81171372. . Downloaded on 12 December 2017.
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