Urban trees surrounded by less asphalt grow taller and stronger

Urban areas are increasingly recognizing the importance of trees in mitigating the effects of climate change and enhancing the quality of life for city dwellers. Recent research from the University of Gothenburg has provided valuable insights into how urban trees contribute to cooler air temperatures and the conditions they need to thrive.

Role of trees in urban climate

Trees have a well-established role in urban environments, particularly in the context of climate change. As global temperatures rise, urban trees offer much-needed shade and contribute to lowering air temperatures.

However, the research team, led by Janina Konarska, emphasizes that the benefits of trees are maximized when they are given suitable conditions to grow. A crucial factor in the efficacy of urban trees is the extent of paved surfaces surrounding them.

The study highlights that trees need adequate space, free from asphalt, to maximize their growth and cooling effects. “Our research shows that an important factor is how much of the area around the tree is paved,” says Konarska.

Urban trees with less asphalt

The study found that trees with additional grassy areas around their trunks, especially those aged 20–30 years, showed significantly better growth and cooling effects.

“We found in our study that 20–30-year-old trees surrounded by grass were on average 2.6 meters taller and the crown was 1.3 meters wider than nearby trees growing with paving close to the trunk. The trees also had a crown that was 61 percent denser and provided twice as much cooling,” says Janina Konarska.

Surface cover and tree health

The research assessed the impact of surface cover around tree trunks on species like pin oak, horse chestnut, and common lime. It considered various factors such as crown density, tree growth, and transpiration rates.

The findings indicate that the type of surface cover significantly influences these parameters and, consequently, the tree’s ability to impact the microclimate through shading and cooling.

Asphalt surfaces near trees lead to several challenges. “The air above an asphalt surface will be warmer than the air above grass or soil. A hardened surface also prevents rainwater from reaching the roots, impacting the growth of the tree,” Konarska adds. This effect varies across tree species, with some like the horse chestnut being less affected by hardened surfaces.

Urban tree planting best practices

Given the expenses involved in planting and nurturing trees in urban areas, it’s crucial to optimize their growth environment. The study underscores the importance of not only the choice of tree species but also the management of the area surrounding the tree trunk.

“You have to do the best you can when planting trees in urban areas. If it is difficult to create open spaces around the trees, it is a good idea to invest in better soil and preferably to water the tree,” says Lasse Tarvainen, an environmental scientist at the University of Gothenburg.

In summary, the research from the University of Gothenburg serves as a call to action for city planners, environmentalists, and the public. It highlights the need for thoughtful planting and maintenance of urban trees to harness their full potential in cooling and beautifying our cities.

As Tarvainen notes, “It is important that we take care of the trees, they are valuable in many ways.” This study lays the groundwork for more sustainable urban planning, where trees play a central role in creating healthier, more livable urban spaces.

The full study was published in the journal Landscape and Urban Planning.

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