My son is a landscape architect and when I lament at why cities generally don’t have enough trees, he tells me that it isn’t as simple as just planting them to green-up a city. It’s not easy to grow trees in an urban concrete environment. The obvious problem is sufficient water and room—for the tree and its roots to grow. Tree roots don’t grow that deep, but they spread wide—often as wide as the upper canopy—in search of water and nutrients. Urban soils are often too compact or full of rubble to permit the tree to flourish. In addition urban-sourced toxins find their way to the tree’s root system. De-icing salt, used in most north temperate cities is particularly damaging to trees. Mindy Maslin, project manager for the Pennsylvania Horticultural Society’s Tree Tender program, cited a study, which showed that a city tree’s life expectancy averages less than 10 years for a sidewalk cutout tree; but five times longer if planted in a lawn.
On March 16, 2016, Rotterdam, a below sea level seaport city, will plant a “bobbing forest” of twenty floating trees in Rijnhaven, a downtown harbour basin on the Maas (Meuse) River, which flows into the North Sea at Rotterdam via the Rhine-Meuse-Scheldt delta. A saltwater wedge intrudes variously into the harbour, depending on tidal forces, wind and the flow of the river.
Dobberend Bos (“bobbing forest”) was conceived by the art collective Mothership, and inspired by the work of sculptor Jorge Bakker. In the 1970s, Bakker created “In Search Of Habitus,” which featured miniature trees attached to buoys in an aquarium. Dobberend Bos recreates Bakker’s piece on a grander scale, toward sustainable green construction, writes Robert Montenegro of BigThink.com. Rijnhaven will host Dobberend Bos and other installations until 2018.
Three years ago, Mothership constructed a prototype under the supervision of Rotterdam’s engineering department, Rotterdam University, Delft University of Technology, and Van Hall Larenstein University of Applied Sciences. They examined which type of tree could survive in the buoys (recycled from the North Sea) and whether the sea buoy could keep the tree balanced.
There were challenges, writes Adele Peters of FastCoExist.com. “The trees have problems with sea sickness,” said Everaert, founder of Mothership. “When there are waves, you see the sea buoys dancing on the water, and the trees are really moving roughly.” Researchers determined that not all trees can root and grow in the buoy. The Dutch Elm (Ulmus x hollandica ‘Major’) proved sturdy and thrived in the floating buoys. This species could also handle some saltwater.
The tree buoys had to balance and float a 6-meter (20-foot) tree as well as maintain its freshwater supply. Mercon, a steel construction company, modified the standard sea buoy so that it could withstand forces caused by weather, water, and the tree itself.
As with ‘In Search of Habitus’, Dobberend Bos is an initiative that could also question and alternate the relationship between human and nature. How do people, cities and nature relate to one another?
The project is part of an overall initiative to create a greener Rotterdam. Creators hope to “evoke questions about the relationship between city dwellers and nature” and raise awareness of environmental sustainability, according to their project’s website.
I talk about the role of trees in maintaining a balanced hydrological cycle—including their role as “rainmakers”—in my upcoming book “Water Is…The Meaning of Water”. Not only do forests make rain; they function as biotic pumps, carbon sinks and havens of biodiversity. Their essential role in maintaining local and global climate—via their integral part in water exchange—makes the planting of trees far more than an ecological aesthetic. They are an essential part of creating and maintaining our global ecological health.