Populus nigra (Black poplar)
Black poplar is one of the rarest native trees.
The native black poplar (Populus nigra subsp. betulifolia) is a rare native tree, scarcely seen today, but is making a recent resurgence in popularity thanks to conservation efforts. The UK black poplar is a subspecies of P. nigra only found in the very far north west of Europe in parts of France, Great Britian and Ireland. It can be distinguished from the continental subspecies (P. nigra subsp. nigra) and hybrids (Populus x canadensis) in that it has downy shoots (fine hairs covering the undersides of leaves, petioles and sometimes twigs) and is often heavily burred along its trunk. The black poplar is dioecious, meaning that trees are either male or female. This has thought to be part of the reason for the tree’s population decline. For successful pollination to occur, male and female trees need to be in close proximity to one another. However, historically the female trees with their fluffy seeds were considered a nuisance, and so many were felled or replaced with male trees. This has led to a disproportionately large population of male trees across the country, with far fewer female trees. In addition to the discouragement of female trees, the native habitat of poplar trees has also become scarce. Black poplar likes to grow close to rivers, near floodplains or in wet woodlands. This is because for successful germination seeds need an area of moist exposed bare soil and once germinated the seedlings need plentiful light to grow.
All these factors have contributed to the continual decline of the species in the UK. Furthermore, many of the old black poplars are reaching their final years and becoming weak and fragile.
Black poplars are easily grown from cuttings, which is how many of them have been historically grown. We know this because, as in the case of Sussex, where genetic tests have been done, although there may be a few dozen mature individuals growing, only a small handful in this population are genetically different. This means the genetic diversity within the black poplar population is smaller that what may have originally been thought.
The upside to the ease with which black poplars can be propagated means that conservation efforts can be used to increase the population of the tree. An example of this is at Wakehurst in Sussex, where there is a large conservation effort to increase the black poplar population across Sussex. Here there are propagation beds with each of the clones found in Sussex. Hundreds of cuttings are planted each year in raised beds, which are then distributed to various land owners, who will help to increase the population of this rare, impressive tree.
