Tree versus gravity

With a girth of 527 cm and a height of 40 metres, this character happens to be the oldest and largest Canadian poplar in the Brussels Capital Region. This silent witness to the history of the Josaphat Park bears a certain resemblance to the tower of Pisa, is prone to shedding the odd branch and suffers from a touch of fungus. But he’s firmly rooted in the ground and knows how to stand up for himself. In other words, he's still got some good years left.

In the late eighteenth century, many Canadian poplars (also called Carolina poplars) were planted in Belgium. Judging from the size of our friendly giant in the Josaphat Park, one might imagine that he had been here long before the park was created in 1905. In reality, this veteran of the Region is no more than 80 years old. He was planted in the 1940s-50s in the lower section of the park, at the edge of one of the three ponds, from where he has watched the surrounding park grow increasingly beautiful. He has endured multiple phases of restoration, as well as the creation of the poultry yard and the playground nearby.

His rapid growth is all thanks to an ideal situation for a tree of this type: down in a valley, in an area of deep and rich soil that is sometimes wet and even underwater, at the edge of a pond from which the roots can pump plenty of water, and with full exposure to light. This is how he has been able to assume the characteristic form of a Canadian poplar. His crown is wide and spreading. The main branches are high, 8 metres from the ground, overhanging the adjacent chestnut tree.

This poplar has been under supervision for a while, as it has a number of serious defects. He is being closely monitored by the Region as well as by the municipality of Schaarbeek and is regularly subjected to mechanical testing and tomography (a type of ultrasound). But as long as he doesn't pose a danger to walkers, he will not be felled.

In the meantime, the old boy is doing his best. High up in the crown, he forms thickened growths to cover his wounds. He appears to be trying to isolate the fungus (polypores) that afflicts him. To combat his tendency to slouch, he generates terrific counterweights. This reaction wood that grows up from the roots functions a bit like the bases of the towers of fortified castles. It is the tree's own solution for remaining stable, and an effective weapon against gravity.

A protective perimeter has been installed around the tree: to protect everyday visitors, but also, and above all, the roots of the tree. Although invisible to the eye, they are under the ground directly beneath the crown, hidden just a few centimetres beneath our feet. They play an essential role in supplying water and food for the tree. And of course, they serve to firmly anchor this colossus in the ground. The roots are powerful, yet delicate: they risk suffocation if the earth above them becomes too heavily compressed. If you happen to walk under this tree, try not to tamp down the dirt. The smallest injury could open the door to disease, fungi or parasites. This is actually the reason why, in many parks, you are not allowed near the foot of certain trees.

A spirit of freedom

Poplars have been on our planet for over 100 million years. The name comes from Antiquity: some claim it is derived from ancient Greek, while other historians swear by Latin.

The ancient Greek word pappalein means to move or shake in the wind. The word certainly captures the restless impression made by the crown of this large tree with its dense foliage. The leaves dangle from a long stem, which allows them to dance in the wind. The Canadian poplar is always the first to rustle at the slightest breeze: you can recognise it by the sound of its leaves.

The Latin word populus means people, nation or state. In ancient Rome, it referred to the gatherings of the free men. The Romans planted poplars in places where the people gathered. Much later, at the time of the American Revolution, and later also the French Revolution, the tree was planted in great numbers as a symbol of freedom. It won a place in the hearts of the revolutionary French, second only to the lime tree.

But while the lime tree is still associated with freedom, this connotation has been lost for the poplar. It probably has to do with the fact that there are only a handful of poplars left that would have been around to witness the Revolutionary era. Poplars rarely grow older than 250 to 300 years. By contrast, lime trees can easily reach a thousand years of age.

Exceptional qualities

The Canadian poplar is a hybrid tree, a cross between two species: the populus deltoides from North America, and the black poplar (populus nigra) from Europe, making it an indigenous species for us.

The first thing you notice about it is the bark. It lets you recognise a poplar from afar. With age, the bark becomes dark grey and the furrows become larger and larger. It is reminiscent of the darker side of the black poplar, the tree often associated with Hecate, the goddess of the dead.

But this poplar isn't so shadowy after all. From both parents, he inherited a slightly rounded, triangular leaf, with a fairly sharp point and slightly serrated edges. His North American parent gave him jaunty foliage that changes colour when touched by a breeze: dark green and shiny on the surface, the leaves are pale green and matte on the underside.

At the end of the winter, the yellowish-brown twigs brighten the landscape. They herald the Earth’s awakening. Upon closer inspection, you will notice amber coloured orbs: these golden droplets of resin at the end of the twigs catch the light (in the case of our towering friend, you will probably need a telescope, since the smallest twigs grow at quite an elevation).

In Greek mythology, it is said that those droplets are the tears of the Heliades, the sun children and the daughters of Helios. One day their brother, Phaethon, borrowed the chariot of Helios. He lost control of it and burned everything in his path. He was fatally struck down by Zeus and thrown into the Eridan (the Po River). His sisters, who never stopped mourning their brother, were transformed into poplars. That is why poplars cry amber coloured tears: tears that are considered to have exceptional therapeutic powers.

The resin is found on the buds of the tree. It is harvested by bees and used to make propolis. Propolis is Greek for defender of the city. The bees use the resin to reinforce their hive and honey cells. Humans use the propolis to boost the immune system.

Already in ancient times, poplars were prized for the many therapeutic qualities that we still know today. The tree is at the origin of various remedies: it eliminates uric acid, stimulates the bladder, relieves rheumatism, soothes burns, ... The bark contains salicin*, an acid that forms the basis for aspirin.

Trailblazer

Poplars have a remarkable sex life. The sexes of this species are strictly separated. In layman's terms, it is often said that Mr and Mrs Poplar do not live under the same roof. They have a LAT-relationship. They reproduce long-distance.

In the springtime, Mr Poplar produces clusters of reddish petals that form a cylinder, which is called a catkin. The catkins hang from a stem. In order to use their pollen to fertilise a female flower on another tree, it takes an intermediary: the wind. The wind shakes the catkins so that they release their seeds. Mrs Poplar also has catkins, but they are finer and softer. They are formed by pale greenish-yellow flowers and are fertilised when the wind brings the male pollen to them. In May-June, Mrs Poplar releases downy puffs of seeds that are carried throughout the landscape on the wind.

In this way, the poplar is a trailblazer. At the slightest breeze, the seeds (more like feathers, really) take flight. They are quite light and covered with a silky down. They flood the countryside, far away from the tree. But they do need to quickly find a patch of bare, moist ground, as they are fragile and short-lived.

In order to secure their reproduction, poplars also spontaneously propagate through their roots. Over the centuries, the populus genus has naturally diversified. There are currently some thirty known species. Since the branches, roots and twigs are easily grafted, mankind has been able to create countless hybrids and crossbreeds. The Canadian poplar is one such hybrid that has found it easy to gain popularity in our region, as the black poplar has virtually disappeared.

If you're in the area, take a moment to admire this off-kilter giant. Enjoy his presence. Because although this species may once have been a trailblazer, it has become rare in the city. After all, patches of bare, wet soil are hard to come by in the urban world, and that includes in the parks as well as along the streets. And meanwhile, hardly any poplars being planted in Brussels anymore, while in fact, they could prove quite useful in swampy, flood prone areas in the Region.

• Salicin was first discovered in the bark of the willow. Just like the poplar, the willow is a member of the Salicales family.

(Story and photos created by Priscille Cazin https://www.sylvolutions.eu)
Photos by Gwen Breuls https://vimeo.com/gwenvideos) This portrait is enriched with an illustration from the Belgian Federal State Collection on permanent loan to the Meise Botanical Garden. See attached. Thanks to the library (heritage collection) for this contribution. https://www.plantentuinmeise.be/en/home/