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Although the black popular can be found nearly all over Europe, it is one of the rarest and most endangered trees. The main reason is the eradication of the alluvial areas, which are the natural habitats of this quick growing giant. But the cultivation of hybrid poplars also contributes to the decline of this species which is threatened with extinction.
Fig. 1 - Native black poplars are also endangered because of a
possible cross breeding with hybrid poplars.
Photo: Daniela Csencsics (WSL)
World wide there are around 60 species of poplar. They belong to the willow family. The quick growing black poplar needs only 30 to 50 years to grow into a majestic tree of around 30 m in height and 2 m in trunk diameter. Two different forms distinguish this species of tree.
The former is now only to be found occasionally, along river banks and on flood plains. The latter along roads. In spite of their quick rate of growth black poplars can reach an age of 100 to 150 years.
The dark grey, almost black bark with its furrowed structure gave this species of popular its name. Its crown is wide, but irregular, and the trunk is often gnarled and covered with burls. The unusual trunk form is characterized by a board like root base.
Fig. 2 - A black poplar (Populus nigra) with its typical burls,
which not all trees have.
Photo: Daniela Csencsics (WSL)
The buds are close together, sticky and brownish in colour. The 8 to 12 cm long leaves which twist around their stems are diamond shaped, nearly triangular with long drawn out points. The catkins of the black poplar are around 10 cm long and appear in April growing on separate trees according to gender (dioecious). Poplars reproduce not only by means of fluffy seeds which float out of the burst fruit capsules (so called poplar snow) but also vegetatively through shoots and suckers. To preserve this tree species, tree nurseries propagate black poplars by means of cuttings or grafting.
The usefulness of black poplar timber is limited not only because it is bent, knobbly and knotty, but mainly because it is not very durable. The light wood, which has a dark centre, is soft and easy to work with and is mainly used for making palettes, chests, and matches and pressed wood. Wood carvers carve mainly clogs. The use of the downy seeds is also interesting. They are used as fillings for cushions and covers as well as insulation material. That is why poplars in North America are often known as “Cottonwood”.
Like many willow species the black poplar is a typical tree species of alluvial forests. These forests provide habitats for a large number of insects. The black poplars are special favourites of the following insects: the poplar longhorn; poplar leaf beetle; poplar leaf roller; poplar hawk moth as well as the poplar lutestring and the poplar twig borer. Many species of birds use the crown as a nesting place. The fact that the black poplar is able to remove heavy metals out of the soil is also of ecological importance.
|Fig. 3 - Koehler's Medicinal Plants (1887)|
According to Greek mythology the poplars emerged from the Heliades, the sisters of Phaeton, the son of the sun god Helios. As he was not able to rein in the horses after they bolted with their father’s sun coach he was hit with a punishing lightning bolt by Zeus. Out of grief over their dead brother the Heliades turned into black poplars. That is why this species of tree was associated with death during antiquity.
4000 years ago the Greek Doctor, Galen, recommended a cream made out of black poplar buds for inflammation. Today the poplar cream is still used for skin inflammation and haemorrhoids. Tanning agents and ethereal oils, whose substances are fever reducing and disinfecting, are extracted out of the buds. Napoleon was responsible for a rapid spread of the Lombardy poplar in the 19th Century. He had his military roads lined with this quick growing species of tree, which originated in Italy, for better orientation in winter and shade in summer.
Native black poplars are not only endangered because of their declining habitat – the alluvial forests – but also because of a possible cross breeding with hybrid poplars. Therefore as many pure black poplars as possible should be cultivated and planted. However, this is not easy as it is very difficult to ascertain the purity of this species on its appearance alone.
Scientists of the WSL working together with the ETH on the project "Promoting rare tree species" (SEBA) tested over 1’000 poplar samples using genetic methods (DNS Analysis). Within a few weeks using only a few milligrams of wood it could be seen whether the samples, which had been collected in different Cantons, were really pure black poplars or hybrids. What is encouraging is that these typical alluvial forest trees are more wide spread than once imagined. A prudent estimate of numbers is around 65’000 black poplars.