Since the official opening of Amaliaplein, the trees in it have faced a hard time because of the high groundwater level. We even installed a drainage system to make it easier to process the surplus groundwater, which was already causing trees to die. We also placed air pipes into the ground to provide additional oxygen for the trees. Despite these measures, another eight trees have died in Amaliaplein. How is that possible? ‘We know an awful lot about trees’, says Jasper Zwetsloot, technical supervisor for green landscaping at the City of Amsterdam. ‘But you can’t take anything for granted with nature.’ Despite this, we have made several modifications for the trees that we are now replacing. The new planting will be on a mound, a raised bed that prevents the groundwater from having too much effect on the tree. There will also be extra aeration around the roots.
The work started with the removal of the existing trees. The trees are cut down by saw first in order to make it possible to use the digger to remove the tree stumps from the ground. We then prepare the planting site for the new tree by adding fresh soil. And that’s no easy feat: in Amsterdam, we use around 18 m³ of fresh soil for every tree we plant, providing the equivalent of around 20 years of nutrition for the tree. ‘That does seem a lot, it’s true’, says Zwetsloot, ‘but a tree can easily live for 80 years. That means we have to change the soil every 20 years or inject additional fertiliser.’
Wire and straps
The root ball of a new tree is reinforced with wire at the nursery in order to facilitate transport. However, it is important to cut the wire before planting the tree because the roots would otherwise be unable to grow. Zwetsloot: ‘After that, we anchor the tree by inserting stakes into the ground and securing the root ball by means of a lashing strap. You can’t see anything because it happens underground.’ All of these efforts are made in order to enable the Pendula, Prunus, Quercus (oak) and Betula (birch) trees to thrive. ‘We’re only using more expensive, multi-stemmed trees here. They’re not something that every project can afford’, says Zwetsloot. He’s pleased that they are being used. ‘When they arrive here, they’re already around 4 m tall and look really impressive. Just look at them!’
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