The Capital Tree

Strong and majestic, this giant is a symbol of the capital. It grows at the heart of the patchwork of 19 communes that is the Brussels Capital Region, right in the middle of a municipal park and the European quarter. Its roots are anchored in Brussels and extend to the edge of the commune of Etterbeek. Its trunk and crown grow alongside the Museum of Natural History, a federal institution. And its summit is eye-to-eye with the ‘Caprice des Dieux’: the hemicycle of the European Parliament.

This veteran has stood atop the hill, on a slope of the Maelbeek valley, for over 250 years. In 1851, it witnessed the birth of the first large public landscaped park of the capital: le Jardin zoologique d’Horticulture et d’Agrément de Bruxelles. It was a picturesque landscape at the time, accented by a few pavilions and greenhouses, made up of rugged outcroppings, curved paths and a shady walkway along bodies of water. This Oriental plane tree, also known as an Old World sycamore, has seen the development of the Leopold Park and the gradual transformation of the district into the headquarters of the EU. Its shadow has sheltered several generations of little ones

Today, its majestic, reassuring presence looms over the playground where children cavort. It overlooks the Friche Eggevoort where neighbourhood residents gather to grow vegetables. It watches students go by on their way to the Lycée Jacqmain, who jog around the park during gym class. It shelters researchers at the Museum, European civil servants and doctors at the hospital who occasionally come out to have a break in its shade. From the top of its canopy, perhaps you can even follow the debate inside the European Parliament.

In Greek mythology, the plane tree is associated with Europa, a young girl kidnapped and protected by Zeus, who had transformed himself into a bull. It is also the tree that protects Greece against the invasion by the Persian emperor Xerxes. Later on, through the work of the poet Paul Valéry, it became a symbol of European resistance against fascism. So it makes an auspicious tree for Brussels.

A forest of a tree

Unlike its neighbours on the Place Jourdan, its branches have probably never had to endure the chainsaw. It does not know the rough urban life that is the fate of plane trees in the city, often pruned so severely they resemble hat racks. It has grown freely and has always received the loving care of gardeners. With its trunk measuring over six metres in circumference, and a summit that rises to 30 m high, it has become a specimen of regional, federal and international renown. This living monument attracts the attention of many scientists. For over 30 years, the Region and the Belgian Dendrology Society have been very closely monitoring its growth.

This individual tree has never wanted for anything. It's has grown far away from the competition of other species, in a protected environment with abundant water and light. So much so that it has become a forest in its own right. It serves as shelter and cover for a multitude of living creatures. This gigantic ecosystem is home to mosses, lichens, and insects of all kinds. Several species of birds live in its hollows. A small mountain ash tree even grows at the fork of one of its main branches. According to Scandinavian and Germanic legends, this is a sign of miraculous properties. And perhaps this is true in other cultures as well …

If you ever walk under this plane tree when its foliage is at its prettiest, you may encounter an Asian man performing a curious ritual. He visits the tree, at the time of day when it produces the most oxygen, when the sun is at its zenith above the park. He comes to do exercises directly beneath the crown. He raises his arms very high, inhaling through his nose. And then he allows them to fall, gently absorbing the shock with his legs, and exhaling through his nose. He repeats this intriguing gesture for about 20 minutes. He told us that he can thus oxygenates every pore in his body. This sage turns out to be 80 years old: you would think he was barely 60. In reality, this gentleman is taking advantage of many other properties provided by the tree. As its vast foliage releases certain molecules into the air: phytoncides. These help the human body defend itself against viruses and bacteria and reduce the oxidation of its tissues. When its thick foliage is stirred by the breeze, it also produces negative ions: these microparticles reduce stress, and increase well-being and energy. And finally, the tree releases terpenes into the atmosphere. These are substances found in essential oils. They relax the nervous system and muscles. They stimulate white blood cells (lymphocytes), which eliminate toxins and reduce the activity of cancerous cells.

These benefits of hardwood trees for our bodies have been scientifically proven. They are much more powerful in the forest. The Asian gentleman did not travel into the forest but instead, carefully chose his own forest of a tree.

A gigantic column of water

Plane trees often indicate the presence of water. In ancient Greece, they were planted close to springs and wells so that water could be drawn in their shade. The Oriental plane tree in the Leopold Park is no exception to this reputation. It reminds us that the little Eggevoort tower at the bottom of the hill was part of a fishing domain in the 17th century. And it indicates that not far away, the Maelbeek still flows beneath the chaussée d’Etterbeek.

The seeds of plane trees are astonishingly tiny: measuring barely a millimetre. A seed like this has been transformed into a tree, 32 m tall. From the very beginning, it would have contained the complete architecture of the individual specimen, its genetic heritage. Thanks to this plan, the entire structure of the tree has been built over the years. This phenomenon is equally true of other trees, but in this case, it has turned into an individual of exceptional size: a gigantic column of water.

This column is driven by a huge force. In fact, the tree must pump water from several metres underground all the way to the leaves of its crown, over 30 metres high. This pump is able to function thanks to a dual mechanism. On one hand, the roots expend energy to absorb water and drive it upwards. In a sense, they prime the pump that irrigates the tree. On the other hand, the leaves evaporate moisture: this evaporation creates a tension that pulls the water upwards through the trunk, branches, and all the way to the summit. This tension, which drives the circulation like a motor, can reach a pressure of several bars.

Sometimes, the soil is dry and the temperatures high. At such times, the tension then becomes too strong. Bubbles form in the veins, a bit like those formed around the propellers of boats underwater. The ‘pipes’ (or ‘veins’) of the tree then become blocked by these bubbles and the sap can no longer circulate. To prevent this from happening, the pores of the leaves are able to close in order to restrict their evaporation.

Thus, the plane tree, and trees in general, are equipped with an ingenious self-regulation system. It allows the sap to circulate and adapts to extreme conditions in order to prevent the structure from being damaged.

The ‘camouflage’ tree

You are not likely to confuse the plane tree with other species. Its leaves, that resemble the shape of a hand, are highly recognisable. They have five main veins. In the hybrid plane tree, which is the type that you will most frequently see planted rows in the city, the points at the end of the veins tend to be square. While the Oriental plane tree has quite sharp, elongated points.

Its fruits are small, spiky spheres which remain attached to the branches for a long time. They are clearly visible in winter.

But above all, you can recognise a plane tree by its bark. It flakes off in large chips with curvy contours. Year after year, they reveal the warm tones of the skin of the tree beneath: creating yellow, beige and honey coloured blotches. Could the bark of the plane tree have inspired camouflage-print fabric? Do these patterns make this urban tree blend in, to the point that it sometimes becomes invisible?

(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/