Climate change increases the urgency to have sufficient green in cities. This requires different trees and many more green roofs and walls. The experts of Wageningen University & Research are searching for such other trees and lists the knowledge about trees and plants.
Green in cities is facing difficult times. This is a fact. Current plants and trees are usually unable to withstand the climate change that lays ahead: more and longer periods of drought, peaks in rain showers, as well as periods of extreme cold in winter.
Green in the city is then important to keep town life pleasant because trees and plants are cooling cities. They are evaporating water, which immediately reduces temperature by a few degrees. And trees are also blocking solar radiation resulting in streets heating up less. And shade is in any case pleasant in case of heat.
And green roofs and walls are also catching rain; this means that all water does not directly flow into the sewage system. This avoids the need to increase the capacity of the sewage system with the advent of more heavier rain showers. And green against walls and on roofs also has an insulating effect; this reduces the need for cooling or heating.
Trees for extreme weather
The scientists of WUR are therefore searching for trees that are doing well under extreme conditions; trees that can resist heat as well as frost. This means that palm trees are not suitable because they cannot withstand frost. The scientists are searching for new cultivars in, e.g., South-east Europe such as a different oak or maple variety. They are testing these in the Netherlands and try to find out whether the new varieties could result in new pests and diseases emerging.
Demonstrating advantages of green roofs
Where trees are already a logical choice in cities, this is not yet the case for green roofs and walls. This makes it important to provide information about the advantages and disadvantages. In addition to water collection, isolation and temperature reduction green walls and roofs are also muffling noise. And roofs last longer because the plants are protecting the roof material from UV light. The only disadvantage is that plants on or against a building are more expensive than plants next to the building.