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Populus alba × P. tremula (P. × canescens (Aiton) Sm.), Grey Poplar

Account Summary

Deliberately planted introduction, very rare, possibly under-recorded.

15 August 1985; Leach, S.J., McMullin, A.S. & Wolfe-Murphy, S.A.; shore of Knockballymore Lough.

May to August.

This very vigorous hybrid, which originated in the continental Asian or European range of P. alba, is capable of producing viable seed which theoretically could allow mature specimens to successfully back-cross with either parent species. There is little or no evidence that this is happening in B & I, however, or else it is an extremely rare event. Even the spontaneous hybridisation of the parent species appears very rare and thus the trees we see are deliberately planted nursery stock. As might be expected, the foliage is intermediate between that of the parents; the leaves of long shoots (ie of rapid growth) are large and lobed, but not deeply so and they are covered on the undersurface with greyish down which readily rubs off. Leaves on short shoots are orbicular and quickly become almost glabrous.

The hybrid, like its parents, readily suckers and vegetative reproduction therefore appears to be its dominant mode of increase. The vast majority of trees in B & I are male, females being regarded as very rare (Meikle 1984).

Grey Poplar was introduced to B & I sometime around 1700 AD. Originally it was regarded as a timber tree on account of its rapid growth rate (Mitchell 1996, p. 278). However, foresters soon found that the hybrid proved difficult to propagate from cuttings, which is their normal method of stock production, and although it can grow on poor, sandy soils, it really requires better, more fertile, nutrient-rich, lowland soils than those usually available for timber plantations. Thus P. × canescens quickly fell out of favour for forestry purposes and nowadays it is planted purely for decorative amenity purposes, or in situations where rapid screening is required and the suckering drawback does not matter.

Fermanagh occurrence

There are only three sites in Fermanagh where this hybrid poplar has been recorded: two isolated stations in the southern lowlands, plus one on a landed demesne. Apart from the first record listed above the other details are: Aghavea Td, 2 km E of Maguiresbridge, 30 May 1990, RHN; Templehill Wood, Belleisle estate, 27 June 1992, RHN. In common with other deliberately planted woody species, it is very probably seriously under-recorded in our survey.

British and Irish occurrence

The New Atlas hectad map shows that elsewhere in Ireland this hybrid is only occasional, being rather thinly and widely scattered across the island. In Britain, it is common mainly in SE England, with occasional occurrences in the remainder of England and Wales, becoming increasingly scarce and coastal northwards to Inverness. The largest tree of this hybrid in B & I (ie 'the Champion tree'), is on the Birr Castle estate, Co Offaly; its height in 1999 measured 42 m (Johnson 2003).

Threats

None.