The former roof park in Bospolder-Tussendijken is teeming with life in 2030. It is the place where food and firewood are grown and stored.
Lees dit artikel in het Nederlands. Collages by Golnar Abbasi & Arvand Pourabbasi.
The first carbon neutral neighbourhood in the Netherlands runs entirely on renewable energy sources: wind and solar energy on the one hand, human power and fire on the other. Wind and sun do not require fuel, but are not available on demand. Human power and fire are, but they need fuel: food and firewood. Whether they are carbon neutral or not depends on how the fuel is grown.
In industrial society, both food and firewood are dripping with fossil fuels. In 2015, the production of 1 calorie food in Dutch agriculture and horticulture required an average of 6 calories of petroleum, while in 1950 this ratio was still 1 to 1. This increasing dependence on fossil fuels is due to mechanization of agriculture, the use of artificial fertilizers, and energy-intensive cultivation in horticultural greenhouses. The Dutch diet also contains many ingredients that come from abroad, so that the transport of food adds even more oil consumption.
Biomass has similar problems. In principle, the combustion of biomass is carbon neutral, because it releases greenhouse gases that were extracted from the atmosphere by the tree. But trees are pulled out of the ground and cut into pieces with powerful machines, and firewood is transported all over the world. This is only possible because of fossil fuels. In addition, the global character of the firewood trade makes it virtually impossible to assess the durability of wood. If an old-growth forest is cut down on the other side of the world and then replaced by agriculture or urbanisation, the carbon emissions of that firewood are twice as high as those of coal.
The roof park
In order to keep the fuel for both fire and people carbon neutral, the neighbourhood decided to produce food and firewood locally as much as possible. In this way, energy consumption for transport is avoided and wood and food can be harvested by hand.
Bospolder-Tussendijken has an ideal place to grow firewood and food: the former roof park, built on the old railway yard. In 2020, a neighbourhood garden had already been set up in the roof park, including 25 allotments. That concept was expanded considerably, so that half of the park now consists of vegetable gardens and orchards. The other half is occupied by a coppice forest.
A human powered lighting tower on top of the roof park.
The conversion of the roof park was one of the larger works that were required to make the neighbourhood carbon neutral. In order to make the best use of the sunlight, a slope with terraces has also been built on the south side of the roof park. As a result, the size of the roof park doubled to 20 hectares, at the expense of the four-lane motorway next to the original park. The residents also reinforced the roof construction so that it can support a thicker layer of earth.
Coppice forest
The fire plays a crucial role in the first climate-neutral neighborhood in the Netherlands. Thermal energy consumption - for cooking, heating and showering - is too high for wind, sun and human power. To maximize the wood harvest, the residents created a coppice forest.
Most people, when thinking of a forest, imagine a collection of tall, large-diameter trees. But until the early twentieth century, about half of the forest area in the Netherlands consisted of coppice forests. In a coppice forest, the trees are cut just above ground level, after which several new shoots emerge on the trunk. These thin branches are then harvested every few years and tied together into bundles, which provide energy for cooking, heating and showering.
A newly cut plot in a coppice forest. Photo: Ruud Knol (CC VY-SA 4.0).
Coppicing offers interesting benefits. Wood can be harvested without killing the tree: the trunks (the "stools") can live for hundreds of years. Because the roots are already developed, coppice grows much faster than an upright tree, which increases the wood yield. In addition, coppice is easy to harvest and transport without large machines: human power, a machete and a donkey are all that is needed. Finally, the wood can also be used for other purposes, such as basket weaving.
In addition to coppice, the Netherlands also had many pollard trees. The only difference with coppice is that the trunk is cut at a height of about 2 meters, so that the shoots are not eaten by animals. Line plantings of coppice and pollard trees were also common along roads, waterways and plot separations. The neighbourhood has brought back that traditional landscape. Firewood is grown not only in the roof park, but in every possible free space in the city.
Planting trees along the streets was not self-evident. In 2020 there was so much infrastructure in the ground that there was no room for the roots of trees. Ten years later, however, all that infrastructure has become superfluous: electricity is now generated locally in each household, gas is no longer used, the sewage system is gone, and all communication is wireless.
Urban agriculture
If food is grown using fossil fuels, as is common in industrial agriculture, human power is no longer a renewable energy source. That is why Bospolder-Tussendijken decided to produce as much food as possible in the neighbourhood itself, without machines, chemical pesticides or fertilizers. Mostly vegetables and fruits are grown. The vegetable gardens also contain a number of fruit walls and solar greenhouses, which create a micro-climate for growing southern crops.
A fruit wall in the Netherlands, dating from the early 18th century. Photo: Cultural Heritage Agency of the Netherlands.
The neighbourhood also produces meat and dairy products. There are cows in the orchard, and pigs, sheep and chickens between the coppice trees. Fattening farm animals with specially cultivated crops such as grain and soy is only possible thanks to fossil fuels. In Bospolder-Tussendijken, the cows eat grass, while the pigs and chickens are fed harvest and kitchen waste. The animals also supply the necessary fertilizers for both the vegetable gardens and the coppices. The roof park also has a public dry toilet for extra fertilization.
Cooling
The space under the park, which was occupied by large shops in 2020, was converted into a huge root cellar. Before the arrival of electricity, people kept all kinds of vegetables as well as pickled foods in underground spaces where the temperature is relatively low and stable. Because there is a layer of earth on top of the building, cooling requires no extra energy from October to May.
Only the summer months require extra energy input to avoid food waste. That energy comes from human power, or -- if the weather is good -- from solar panels. Conventional cooling systems use coolants, which emit a lot of greenhouse gases. To avoid this, the neighbourhood opted for compressed air cooling: a simple technology based on the principle that a drop in air pressure also decreases the air temperature.