Trees as natural air conditioners, streets help to cool tens of thousands of them. But some fail | iRADIO
“The deep green leaves are starting to be replaced by wilting leaves, brown leaves. These are silver linden trees,” describes the arborist David Hora of the linden tree, which withers on Vinohradská street in the center of Prague in mid-August and does not help much in cooling its surroundings.
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“Just a silver linden, we found out that it doesn’t work in Prague. It tolerates temperature and moisture fluctuations more poorly than, for example, domestic species such as the heart-shaped linden or the large-leaved linden, which were reported as less suitable in the literature,” explains Hora, chief editor city manual planning the planting and care of tree rows in the streets.
“In the last 15 years, the weather fluctuations have been so great that we are starting to lose trees that have grown steadily for decades. We now have thousands of such trees around Prague. In order to prevent the loss of trees, we have to focus on new plantings so that they are able to withstand extreme fluctuations and have a little more reserves than trees that will grow in limited conditions,” influences Hora with regard to rising temperatures.
At the same time, under good conditions, a properly selected tree can already help mitigate the effects of climate change several years after planting better than some trees that have been growing in the city for decades.
A properly planted tree
Beyond the main road near the National Museum building, we come across other trees that resemble acacias.
“It’s not an acacia, it’s a jerlin. You can notice that the trees look relatively green, vital, and at the same time they don’t even have the tree bowl that we saw on Vinohradská,” Hora points out. The trees stand in the pavement. It looks like they’re peeking out of a trash can, but it’s a protective ring.
“The key to success is that the trees grow very well on a solid surface that seems to be completely inhospitable, there is a structure built underground that carries the pavement, distributes the load, and underneath is actually uncompacted soil. And the trees were planted here four years ago. During that time, both the trunk and the crown have doubled in size. If you think of a linden that was about 40 years old, these trees will easily overtake it in the next five years,” says David Hora.
A new mindset
Landscape ecologist Jan Richtr, co-author of the Prague manual, or rather the standard, notes that access to trees is fortunately improving. And there is an effort to work on their conditions. Provide more space for roots and better access to water.
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“The way of thinking about trees in the city has started to change, especially among technical infrastructure administrators. We are also starting to do several pilot projects in Prague, where we are also trying to bring in storm water. We have a system of regulating shafts, which can gradually drain the level of rainwater, for example, into the sewer. That means the tree won’t drown.”
We almost reached the end of Wenceslas Square, where there is a distinct water feature among the newly planted trees. A fountain that is at sidewalk level. Several children play in the water here during an August afternoon.
“Of course, we all know that. Water is cooling. And trees are a very successful and effective biological air conditioner. They need a flow of water from the ground to the crowns to bring nutrients to the leaves and synthesize properly. Then the water must be removed and removed by evaporation. We call this plant transpiration. Trees cool down and cool down their surroundings. This is the primary ecosystem service that we expect and need from a tree in an urban environment,” points out Jan Richtr.
Metropole is currently compiling a new database of all street trees. And he also has a project ready to try out new exotic species of wood.
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