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Black Poplars.

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The Black Poplar is often said to be a rare tree in Britain but it is a confusing taxon and it's not straightforward to understand the value of individual trees.

To begin with, the common and, because of its columnar outline, easily identified Lombardy Poplar is a 'Black Poplar'. The species is Populus nigra but it is a sport 'Italica' of the wild tree which developed in Italy. Lombardy Poplars are all males.

The Black Poplar that we are concerned with is Populus nigra subsp betulifolia which is the subspecies that is native to NW Europe (including Britain). However, most of the trees of this taxon are what is called the Manchester Poplar which is a clone of a male tree that was taken in Manchester and widely planted. The BSBI map of Native Black Poplar distribution does not distinguish between this clone and otherwise native trees. The Manchester Poplar is often found in situations away from riversides and floodplains which is the habitat of the native tree which of course occurs as both male and female individuals. (Female trees produce large amounts of 'fluff' which is unpopular in urban situations).

I think that planted clones of a single tree from Manchester are of less importance than a truly native wild tree and the Collins Tree Guide casts doubt on there being any old trees that have not been planted. However there are several trees along the bank of Fairham Brook at Widmerpool that are believed by Charles Watkins of Nottingham University to be one of only three relict populations in England (the others being in Warwickshire and Devon). Engineering of rivers and streams has destroyed many populations. By relict population we mean trees that have survived since the last ice retreat. Seeds are said to germinate best in wet mud but the old fallen trees can produce roots and regenerate.

Clearly, the Widmerpool population is of great importance both culturally and scientifically. All other trees in Nottinghamshire (and the great majority elsewhere) have been planted but it is impossible without research on the genetics of the trees, to say whether these are the Manchester Poplar clone or not (unless a tree is female). Some may have been grown from seed, but it is much more likely that they are from cuttings, perhaps from a local (possibly native?) population in which case I would suggest they too are a priority for conservation.

Populus nigra subsp. betulifolia is a rare tree and in need of protection. Edgar Milne-Redhead found around 1,000 trees in a national survey in the early 1970s but he didn't include pollarded trees for some reason and neither did he include what he considered to be Manchester Poplars. A further study undertaken for a PhD at Nottingham University established that there were actually far more than this as if the Manchester Poplar (and pollarded trees) were included the national total would be 10-12,000.

This study (link below) states that the reason for the trees decline is six-fold:

• Clearance of floodpain forest
• Land drainage and river engineering operations
• An unequal number of male and female trees
• Unsuitable ground conditions for seed set
• Unpopularity of female trees
• The introduction of a faster-growing, more commercially viable hybrid species P. x canadensis

The Hybrid Black Poplar Populus x canadensis is much more common than the Native tree. It is the hybrid between Populus nigra (the particular race or subspecies is not known) and the North America tree, Eastern Cottonwood P. deltoides.

References:

• https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/290320/sw1-022-tr-e-e.pdf
• Collins Tree Guide, Johnson & More; 2004
• New Flora of the British Isles, Clive A. Stace; 4th Edition 2019.