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The city - our most important ecosystem?

Johan Kjellberg Jensen utomhus i grönska med en spårvagn i bakgrunden. Foto.
"We need to acknowledge how valuable a tree in the city can be – it's not just for decoration. It affects insects, birds, and human well-being", Johan Kjellberg Jensen says. Photo: Sara Håkansson

The city is the perfect place to study nature and how humans affect it, says Johan Kjellberg Jensen. In a new dissertation from the Centre for Environmental and Climate Science (CEC) at Lund University, he explores the interaction between plants, animals, and humans in the physical environment of cities. 

Many of us associate 'nature' with something we go to the countryside to experience. But nature definitely does exist in the city, albeit in a different form, and it is important, Johan Kjellberg Jensen emphasizes. 

“Cities are hotspots. Most people in the world today live in cities - that's where we encounter nature in our daily lives and that's where almost all the environmental impacts caused by humans are concentrated. This is why urban ecology is so interesting to study. City nature is also of great importance to us humans. People may not always realize how valuable it is", he says. 

Biodiversity can also be high in many urban areas, as cities have often been settled in places rich in nature. Therefore, a conservation perspective is also highly relevant in cities, he says.

In his thesis, which consists of six sub-studies, he takes a closer look at how urban ecosystems function. The main focus is on air pollution, the food chain and the link between trees, insects and spiders, and birds, but also on how humans – who greatly impact the urban environment – are in turn affected by urban nature.

The importance of native species

One of the results that surprised him the most was the importance of native species (species that have been in the ecosystem for over 700 years) for urban biodiversity (see link in fact box).

“I was surprised at how clear this effect was. Insects and spiders were significantly fewer on non-native trees, which are common in urban planning, compared to native ones", he says.

The correlation itself is not unexpected, but what became clear in the study led by Johan Kjellberg Jensen is that the so-called origin effect – whether a tree is native or not – is more important than the so-called city effect – whether a tree is in the city or the countryside.

“That was something new. The alien trees are also consistently negative over the years. Fewer birds want to build nests near them, and the chicks weigh less there.”

Thorough understanding of urban ecosystems

In another study (see link in fact box), he aimed to improve our understanding of what precisely affects animals in the urban environment. In the city, man-made disturbances, such as noise, artificial light, pollution, hard surfaces, little greenery, and a warmer climate, are concentrated in one place. Research has often assumed that the more disturbances, the stronger the negative effects should be. But Johan Kjellberg Jensen shows that this is not necessarily the case and that some effects in the city can cancel each other out.

“There is a lot of uncertainty when it comes to enhancing effects. In order to plan cities properly, it is important to have a thorough ecological understanding of urban areas, otherwise there is a risk of implementing the wrong measures", he says.

Greater well-being near urban nature 

Johan Kjellberg Jensen and his colleagues have also looked at how urban and rural children perceive nature and how they were affected by feeding wild birds, as a measure to increase their nature contact. Previously, researchers have argued that urbanization weakens our connection to nature, especially in children, and that it may make us less likely to spend time in nature or engage with environmental issues. However, Johan Kjellberg Jensen's team did not see any such links; children's species knowledge and attitudes towards nature were determined by other factors.

The same study also highlighted the importance of proximity to nature, and the quality of nature, for children – those who had greenery near their homes reported higher levels of well-being. When planning our cities, we therefore need to think about the ability of future generations to experience nature, Johan Kjellberg Jensen says.

“Urban nature is very important and we should not forget that cities are an environment we control to a large extent, they are constructed by people, for people. This means that we actually have great potential to create environments that favour both nature and people. But I think it will be difficult to build the much talked about green and sustainable cities with the current level of ambition; I think we have to rethink cities as a place if we want to get there", he says.

The thesis "Understanding the urban ecosystem: interactions between plants, animals, and people" - Lund University research portal