There are fourteen species of whitebeam trees that are found only in the UK(1). Many of these endemics, like the Lancaster whitebeam, are confined to very small areas of limestone habitat. Each species can be distinguished from the others only by subtle differences in size, growth pattern of the tree and the shape and structure of its leaves.
The Lancaster whitebeam grows up to 5 metres in height. It has broad leaves with prominent veins. The upper two-thirds of the leaf margins have jagged teeth. The leaves have a covering of woolly, white hairs particularly on their lower surface. These hairs give the leaf undersides a silvery-white colour.The upper surface is more grey-green. Small white flowers are produced in flat-topped bunches in late spring and are followed by crimson berries in late summer/autumn.
The berries are eaten and dispersed by birds and this is thought to be the main way that whitebeams of all species colonise new areas.Main Habitat(s): Limestone cliff and scree; limestone pavement; woodland edge and open limestone woodland.
This species is endemic to Britain and is restricted to limestone areas around Morecambe Bay.
It is a British Red Data Book species (2), where its status is given as Low Risk Near Threatened.
The region supports the only natural population of this species in Britain (2). The populations in Lancashire are, therefore, of at least national, if not international, importance.
The species has been recorded from 35 sites in eight 10 km squares around Morecambe Bay (6). It is estimated that there are around 2000 trees in total in this area.
The tree occurs in Lancashire in six 2 km squares in the Arnside-Silverdale AONB (3). The coastal cliffs from Warton Crag to the county boundary north of Silverdale support a significant population.
Current factors affecting the Species
The species is not considered to be currently under significant threat. However, there are a number of factors that restrict its numbers and could affect its survival.
Where the plant occurs in woodland it prefers relatively open situations and is vulnerable to becoming shaded out by other trees. Lack of management or inappropriate management of sites could in the long-term lead to loss of the species from certain sites.
Crevices in bare rock provide opportunities for new saplings to become established but in parts of its range this potential habitat is being lost due to the spread into the wild of non-native Cotoneaster sown by birds feeding in gardens.
Competition from regenerating garden whitebeam species may also be having an effect. Three whitebeam species [Swedish whitebeam (Sorbus intermedia), common whitebeam (Sorbus aria) and Sorbus croceocarpa] have been found regenerating successfully in Lancaster whitebeam habitat within the Arnside-Silverdale AONB.
Additional ecological factors that have been implicated in the decline of other native endemic whitebeams include grazing, disease and low seed productivity. More research will be needed to assess the relative importance of each of these factors with respect to the Lancaster whitebeam.
Current Action / Mechanisms
Many of the sites supporting populations of this species enjoy some measure of statutory protection as SSSIs or indirectly through Limestone Pavement Protection Orders.
Other sites have been identified as Biological Heritage Sites using the Guidelines for Site Selection, (Guideline Ff1)(4).
Management for nature conservation takes place on the SSSIs, National and Local Nature Reserves and on National Trust land where the whitebeam occurs. However, specific objectives for the species need developing within most of these sites.
Survey results were reported by Tim Rich in 1986 and 1992 (5,6).
Objectives, targets and proposed actions for Lancaster whitebeam in Lancashire
References & additional reading:
1. Stace, C.A. (1991) New Flora of the British Isles. Cambridge University Press.
2. Wigginton M.J. (1999) British Red Data Books: Vascular Plants, 3rd Edition, Joint Nature Conservation Committee.
3. Livermore L A & Livermore P.D. (1987). The Flowering Plants and Ferns of North Lancashire, L A Livermore & P.D. Livermore.
4. Lancashire County Council (1998). Biological Heritage Sites Guidelines for Site Selection, Lancashire County Council.
5. Rich, T.C.G. & Baecker, M. (1986) The distribution of Sorbus lancastriensis E.F Warburg. Watsonia 16: 83.
6. Rich, T.C.G. & Baecker, M. (1992) Additional Records of Sorbus lancastriensis E.F Warburg (Rosaceae). Watsonia 16: 139 140.
Date: April 2001.