Black poplar  (Populus nigra)

Not listed under any major conservation designations.

Black poplar, thought to be Britain's most endangered native timber tree (3), has a wide, rounded crown and dark grey fissured bark, with many swellings ('bosses') on the trunk (2). The deep green leaves are roughly triangular or oval in shape and become yellow in autumn (4). The flowers occur on 3-5cm long catkins (2), and male and female flowers are produced on separate trees; male flowers have red anthers and female flowers have green stigmas(2). Old specimens often develop an obvious lean (5), and older branches are frequently pendulous (6).

The native subspecies of black poplar, Populus nigra betnifolia, is locally frequent in parts of lowland England and Wales, rarer in the north of England and Scotland, and rare in Ireland (6) (7), and also occurs in western Europe. At present the British population numbers just 2000 to 3000 trees (3). Elsewhere, black poplar is widely distributed but increasingly scarce throughout much of Europe reaching into central Asia and North Africa. It is generally absent from the far north of Europe (8).

Typically inhabits lowland floodplains (8) in river valleys (4) and needs open areas to allow germination (8). It also occurs in hedges and roadsides, and by ponds. Furthermore, it is sometimes planted in urban areas (6).

This deciduous tree produces catkins in March and April, before the first leaves appear, and is pollinated by the wind (2). The fruits are green capsules that open up to reveal the very small seeds that have wispy hairs attached (4), which aid their dispersal in the wind (9). In order for this tree to regenerate, male and female trees must be fairly close together, and fertilised seeds must fall on bare soil that is still moist in June (5).

The timber, which is springy and light, is highly resistant to fire, and has been used for a variety of purposes, including floorboards, clogs and arrows that were found on the Elizabethan galleon, the Mary Rose (5).

The preferred habitat of this species has become very rare across Europe as floodplains have been modified and drained for agricultural purposes or succumbed to development pressures (10). Other threats include hybridisation with introduced poplars, which degrades the gene pool, competition with hybrids, and reductions in the groundwater table, which results in trees drying out and dying (8).

Plans to try to recreate the flood plain forest habitat favoured by black poplar, a habitat that is largely extinct in the UK, have been put forward (5).

See the website of the Botanical Society of the British Isles at:
http://www.bsbi.org.uk

Information authenticated by Tim Rich of the National Museums and Galleries of Wales.

• Anther: part of the stamen (the male reproductive organ of a flower) that produces pollen. (See http://www.rbgkew.org.uk/ksheets/pdfs/flower.pdf for a fact sheet on flower structure)
• Deciduous: a plant that sheds its leaves at the end of the growing season.
• Hybridisation: cross-breeding with a different species.
• Stigma: the receptive part of the female reproductive organ of a flower. Pollen germinates on the stigma. (See http://www.rbgkew.org.uk/ksheets/pdfs/flower.pdf for a fact sheet on flower structure).

1. National Biodiversity Network Species Dictionary ( July 2002) http://www.nhm.ac.uk/nbn/
2. Press, B. (1992) Field Guide to the trees of Britain and Europe. New Holland (Publishers) Ltd., London.
3. Cheshire Wildlife Trust (April 2002): http://www.wildlifetrust.org.uk/cheshire/bpoplbap.htm
4. Coombes, A. J. (1992) Eyewitness handbooks, Trees. Dorling Kindersley, London.
5. Mabey, R. (1996) Flora Britannica. Sinclair-Stevenson, London.
6. Milne-Redhead, E. (1990) The BSBI Black poplar survey, 1973-1988. Watsonia18: 1-5.
7. Hobson, D. D. (1993) Populus nigra L. in Ireland- an indigenous species? Irish Naturalist's Journal24: 244-247.
8. WWF. Freshwater species, black poplar: flagships for floodplain forests. (April 2002): http://www.panda.org
9. Tabbush, P. Dynamic processes in riparian ecosystems- implications for P. nigra gene conservation strategies. European forest genetic resources programme. (April 2002): http://www.ipgri.cgiar.org/networks/euforgen/networks/poplars/Network_ouputs/pninsitu.htm
10. Cagelli, L. & Lefevre, F. (1995) The conservation of Populus nigra L. and gene flow with cultivated poplars in Europe. Forest Genetics2 (3): 135-144. http://www.tuzvo.sk/~paule/FG95/obsah23.htm