Populus nigra

Taxonomy 

The Black Poplar, Populus nigra L., is a distinctive and characteristic feature of the countryside. It was popularised in the 1980s by Edgar Milne-Redhead, who organised a recording project via the pages of the Daily Telegraph. The Western European Black Poplar is Populus nigra L. ssp. betulifolia (Pursh) Dippel. The closely related ssp. nigra occurs in Eastern Europe and Russia, and has entirely glabrous leaves and stems; ssp. caudina (Ten.) Bug. grows in the Mediterranean region and has caudate leaf bases (Fl. Europeaea). There are a number of varieties and hybrids of Black Poplar that are widely planted. The most common are the Lombardy Poplar P. nigra ‘Italica’, which is a fastigiate form, and the Hybrid Black-poplars, Populus x canadensis Moench., which are crosses with the American tree P. deltoides (Eastern Cottonwood). The ‘native’ Black Poplar, P. nigra ssp. betulifolia, is distinguished in the British Isles by having characteristically diamond-shaped leaves (cuneate leaf-bases) without glands, no balsam smell, a distinctive outline with downswept branches, and it often has burrs on the bark of the trunk.

Chromosome No.: 2n = 38 (Stace 2010).

Populus nigra

Photography: A.J.Lockton

Distribution 

It is widespread throughout the lowlands of the British Isles, except in the northern and western isles of Scotland. It is also found throughout western Europe. Like many tree species, it is often planted and it is quite impossible to tell where it was originally native.

BSBI Hectad Map 

Click on the map to view full-size on the BSBI Maps Scheme website.

Status 
  • Origin: native throughout its range, but often planted as well.
  • Rarity: it has no rarity status, being quite a widespread tree, but it is rarely common, with just a few specimens dotted around the landscape.
  • Threat: not threatened, although concern has been raised about the small number of female plants that are to be found. It is not entirely apparent if there are viable ‘wild’ populations in Britain or Ireland or whether it depends entirely on planting to survive.
  • Conservation: it was at one point a UK BAP species, but is no longer considered a Priority Species at the national level. Some local BAPs include it, but without any particular reason except sentiment. Several county recorders have included it as an axiophyte, but as more than 10% of specimens in any area are probably planted (and therefore ecologically meaningless), it might not warrant such inclusion.
Ecology 

Because it appears to have effectively died out in the wild, the ecology of the Black Poplar in the British Isles is little known. It occurs mostly in the floodplains of lowland rivers, often on river banks and by the side of drainage ditches. This suggests that it should be a plant of W6 Alnus glutinosa-Urtica dioica woodland, which is the typical vegetation of eutrophic river floodplains; but Rodwell (1991) only lists it for W5 Alnus glutinosa -Carex paniculata woodland, which is a woodland of much less fertile soils. That difference may hold the key to its decline as a wild plant, if it is less able to compete in the highly modified and eutrophicated environment of modern rivers.

As a native tree, the Black Poplar is host to a large number of pests and predators. A curious one is the aphid Pemphigus spyrothecae, which forms twisted galls in the petioles (see below). Unfortunately (for identification purposes), it is not entirely host-specific so it also infects hybrid poplars and related taxa (Redfern & Shirley 2002).

Populus nigra

Further Work 

Despite many years of active recording, several county recorders have reported finding ‘new’ sites for P. nigra which have obviously been there for decades, so it is well worth looking out for trees where there are no dots yet on the map. A lot of Black Poplars have been planted recently under conservation schemes, often in places that are ecologically inappropriate. It would be of some interest to know how these trees have fared. The most interesting thing to know about this species is whether there really are viable, wild populations anywhere in the British Isles. Then we could mark native and planted trees differently on the map.

References 
  • Milne-Redhead, E. 1990. The B.S.B.I. Black Poplar survey, 1973-88. Watsonia 18, 1-5.
  • Redfern, M. & Shirley, P. 2002. British Plant Galls. Field Studies 10, 207-531.
Citation 
Lockton, A.J. (date accessed). Species account: Populus nigra. Botanical Society of the British Isles, www.bsbi.org.uk.

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