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The plane truth: have you ever wondered what these ubiquitous trees were, and how they came to look that way? Swiss News went in search of the story ...

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Although they are aligned in single or double rows along Quai Gustave Ador, on the Left Bank (part of Geneva City's famous waterfront, known as the Rade) ... and despite pruning that results in their dense foliage being shaped like a tete de chat (cat's head) ... and notwithstanding their eye-catching trunks, which are patterned like military camouflage fabric, you still might not notice these trees during the summer.

You are, however, very likely to notice them in winter. The patchwork trunks stand out all the more at this time, with their denuded branches ending in gnarly "fists" that look as if they're ready to punch the sky.

Meet the Platanus, or plane tree. To tell us more about it, Swiss News visited Daniel Oertli, who heads Geneva City's parks department: the Service des Espaces Verts et de l'Environnement (SEVE). Of the 40,000 trees in the care of the service, some 4,200 are plane trees.

A "cultural thing"

According to Oertli, SEVE is in charge of Geneva City's parks and other public spaces, wooded areas, some forestland, as well as the parkland (but not individual plots) in four cemeteries. This Swiss-German, who hails from Winterthur, worked in park services in both Lausanne and Basel, prior to coming to Geneva.

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"You do find plane trees all over Europe; however, the further north you go, the fewer there are going to be. Even in the Swiss-German part of Switzerland--the trees you see along lakeside promenades are likely to be chestnut trees, not planes. And plane trees won't grow in the mountains. They are originally Mediterranean, so you find many in France, Italy, Spain and Portugal.

"To prune or not to prune, and pruning style, is a cultural thing," Oertli explains. "Geneva is part of a cultural region that is French, hence it is not surprising that it espouses a French style as regards plane trees."

He says two other popular pruning styles--besides tete de chat--are en rideau (curtain style) whereby the branches of rows of trees are pruned so that when they come into leaf, they will have a flat front like a garden hedge--although this does not tend to be found in Switzerland. There's also en parasol, which involves preventing the tree from growing upwards, by pruning so that foliage produces an umbrella effect--a good option for those wishing to have a completely shaded summer terrace.

No pruning at all

Oertli points out that Geneva City's plane trees are by no means limited to the Rade. And indeed, one finds avenues, like Boulevard Georges Favon, lined with them; as well as small groups of them here and there, such as next to Geneva's classical concert venue, Victoria Hall. And that's just pollarded trees--"pollarding" being the term for pruning that is used in relation to plane trees.

According to Oertli, there are also a great many un-pruned trees in the city, like the one on Place du Cirque in the Plainpalais area, which he estimates is 150 years old. It shows how unpollarded planes--which may live to be 200 to 300 years old--can grow to heights of 40 metres (over 130 feet) and look vastly different from their pruned relatives. In fact, the difference can be so striking that many people have no idea it's the same tree.

"For one thing, the foliage is nowhere near as dense. [An un-pruned tree] has lots of luminosity when you look up into it, which is not the case for the pruned trees. For another, a pruned tree will not grow to even half that height."

Come spring, un-pruned trees carry seedpods, something that pruned trees, which are just beginning to show a bit of leaf growth out their "fists" at that time of year, do not.

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Keeping things healthy

Oertli says that traditionally, most Geneva City plane trees are Platanus x acerifolia, called the "London plane" in English, and fewer than five per cent are the Platanus orientalis, which have slightly different leaves.

However, new trees are of the Vallis Clausa variety that is resistant to a deadly and virulent disease: canker stain. Ceratocystis platani is an air-borne wound fungus that thrives in humid conditions. "If fungus spores settle on an open wound, such as will result from pollarding, the fungus spreads very quickly and can decimate an entire tree within a couple of years."

The fungus, however, isn't active in temperatures below 5[degrees]C. "That's why we can only pollard in the dead of winter," Oertli says. The situation is closely monitored by relevant cantonal authorities, who sometimes issue canker alerts when no pollarding at all can take place.

"We follow cantonal authorities very closely on this one, and if there is any danger, we don't prune the plane trees," he says. Denuded of leaves, pollarded plane trees that have not received a seasonal trim look as if they have bristly hairs growing out of their gnarly, stubby fists.

Preserving and protecting

Meanwhile, the trees play a role in city life, not only for their distinctive presence, but for the very pruning that keeps them looking the way so many do. It's a big deal every year, with workers operating from hydraulic platforms mounted on the backs of trucks, and traffic lanes shut down on roads lined with the trees.

"And since cutting down trees is a subject that will raise public outcry, we do everything we can to prevent that," Oertli explains to me. "At the same time, huge branches on old trees--not just un-pollarded plane tress--can snap off, and come crashing down, putting members of the public at risk, or causing material damage. We hire arboristes-grimpeurs [tree climbers, requiring specialist training] who can climb up into a tree and attach ropes loosely to branches that could be in danger of cracking off and falling. Then the rope is monitored, and if it starts to become taut it's clear that the branch is holding because of the rope and something will have to be done."

Thinking back over his days in Basel and Lausanne, Oertli remembers that even only as far north as Lausanne "the number of plane trees wasn't comparable: Geneva is known for them. They're part of its heritage."
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Author:Mangotd-Vine, Gail
Publication:Swiss News
Date:Aug 1, 2011
Words:1037
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