The Black Walnut of Campagne Rohner

Lausanne's own walking tour of its finest trees finishes at a tree from the wrong continent. Black walnut is an eastern North American species, and this one has stood above the Ouchy lakefront for about 150 years. It is large for a species that rarely gets the chance here. The city's heritage-tree register measures the trunk at 3.46 metres round and the tree at 27 metres tall. Lausanne Tourisme, which made it the fifth and final stop of its tree walk, gives 3.50 metres and 25 metres. That is the ordinary gap between two people with a tape and a clinometer, and both agree on the age. Telling it apart from the European walnut most people know takes a second look. The city's own description points at the leaflets, more slender than those of Juglans regia, and at bark built on a different pattern. What the tourist office adds is that a walnut of this size in the middle of a city is rare in itself. One caveat, and it belongs to us rather than to the tree. The city names the site Campagne Rohner; the tourist office calls the same patch of green Rhodanie Park. Species, age and girth match closely enough that this is almost certainly one tree described twice, but we could not confirm the two names cover exactly the same ground, so the pin marks the area around Place de la Navigation rather than the trunk itself.