Thursday, 31 May 2007

The invisible tree

Writing in 1996, the author Richard Mabey referred to the native black poplar as the invisible tree. Here was a tree of immense presence and with a strong cultural history, that had ‘passed so thoroughly out of common knowledge’. How could we have let this happen?

The black poplar (Populus nigra subsp. betulifolia) is a tree of deep alluvial soils, largely restricted to lowland river floodplains across southern Britain, northern France and western Germany. As our landscape has changed over recent centuries, so the drainage of land has seen the loss of black poplars from large parts of their former range. The most recent estimates suggest that there may be only 7,000 individuals left in Britain, most of which are males (black poplars are dioecious, the male and female catkins appearing on separate trees). The loss of these majestic trees had largely gone unnoticed until, in 1973, Edgar Milne Redhead, recently retired as deputy curator of the herbarium at Kew, took an interest in the species. Milne Redhead’s work revealed the extent of the loss and demonstrated that the remaining individuals had almost certainly originated as cuttings from a population of just 600 trees. Most of the trees were isolated and there was little hope that they would be able to secure natural pollination and seed set without intervention. There was also the threat of hybridisation with the various Italian black poplars favoured by local councils for tree planting schemes. The almost complete absence of seedlings within Britain is something that has been noted by many authors.

Here in Norfolk, the most recent survey revealed just 54 male trees, together with an impressive female tree on the village green at Old Buckenham. A map included in the most recent county flora shows that most of these trees are in the central southern part of the county, while just over the border into Suffolk there are many hundreds of trees. However, to really appreciate this tree at the landscape scale you have to visit the Vale of Aylesbury, where the presence of these trees can really be felt. The short trunk section, with its rough bark and bosses, almost always leans at an angle, supporting above it a rich green and luxuriant canopy.

The conservation of the black poplar will require a careful balancing act, securing the future of the species by establishing more individuals, while at the same time ensuring that these individuals are planted correctly within a cultural landscape. Many of the cultural traditions associated with the tree stem from its scarcity and position within the landscape (as boundary markers or centrepieces for village festivities) and so newly established trees must fit into this pattern.

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