Trees: More than shade – a climate change ally

Trees do so much in our lives – providing shade, food and keeping our environment green. However, trees give us more than that. In a changing climate plagued by heatwaves, floods, and air pollution, their ability to improve air quality and mental and health well-being is priceless.

Not everyone in South Africa, however, is lucky enough to enjoy the benefits of trees. In townships, with improper housing, space, soil, and water, and where poverty reigns, trees are a luxury.

Therefore, education is key and the more communities learn about the importance of trees, it can go a long way to mitigate the impact of climate change.

Dr Peter Johnston, a climate impact scientist from the University of Cape Town, says that when it comes to trees and climate change, there are two key points: trees help reduce carbon dioxide in the atmosphere, but the most important benefit is that they lower temperatures, clean the air, and are aesthetically pleasing.

“So, trees become quite emotional, they’re part of our environment. We should be planting them, but we must be careful not to disrupt the ecology, especially in vulnerable areas, by planting the wrong trees in the wrong places.”

Johnston explains that everything revolves around the carbon cycle, and trees are carbon sinks. They absorb carbon dioxide, which is then converted to carbon. The carbon is stored in the tree, and the tree releases oxygen.

Do trees really create cooler, cleaner green spaces?

The South African Weather Service’s Air Quality Information System currently shares air quality data for 215 monitoring stations across the country.

To demonstrate Johnston’s claims, we looked at 2024 satellite and air quality data for two listed areas in Sedibeng, Gauteng: Vanderbijlpark CW5, a middle-income urban area and Sharpeville, a nearby low-income residential area.

Vanderbijlpark CW5 (left) and Sharpeville (right) in the Sedibeng district in Gauteng. The circles highlight a 1 km area around each air quality monitoring station. Insets show satellite data for vegetation in June and December 2024.

Satellite data revealed the stark difference in green cover between the two areas. The middle-income, urban CW5 had a green cover of about 24% in the dry winter months, which almost doubled to a lush 46% in December. The Sharpeville area, in contrast, had just 10% cover in June and a thin 22% cover in December.

Various studies have shown that green spaces can reduce the harsh effects of urban heat islands where the dense concentration of heat-absorbing surfaces like asphalt and concrete can noticeably raise temperatures.

Green spaces can reduce heat by as much as 1℃ in the summer and also help retain heat in the winter.

And while we should always be cautious in assuming a connection between factors, the greener CW5 had an average December temperature of 24.83℃ compared to the slightly warmer 24.95℃ in Sharpeville. Similarly, Sharpeville’s average temperature in June was 11.2℃ compared to CW5’s cosy 12.5℃.

While these differences are small, increased tree cover also seems to have a modest effect on air quality and a reduction of pollutants from fossil fuels.

The charts above show the actual values in concentrations of pollutants in June and December for the CW5 and Sharpeville stations. In both areas, pollution was considerably less in December than in June, which supports the position that more vegetation could potentially improve air quality.

While we see reduced pollution in the greener leaf-on season, the actual levels of gases NO² (nitrogen dioxide) and SO² (sulfur dioxide) are much higher in Sharpeville than in CW5. While we might want to interpret this as a positive consequence of more green cover in CW5, the type of industries and activities around Sharpeville would play a larger role in the higher numbers.

When we look at the air quality data for various stations across the country, we see a similar trend: An increase in vegetation seems to help in reducing pollution.

While SO² and PM2.5 show reduced levels, there was no significant drop in NO².

Urban green spaces are not magic air filters, and while they can lessen the impact of polluting industries and activities, it would require a lot of trees to nullify the overall effect of pollution.

Trees that heal

Trees, however, can still do a lot of good. A phytotherapist based in Tshwane, Dr Sharon Maphaha, says trees are essential for human health, mental well-being, and climate regulation.

“From improving air quality to reducing stress levels, trees and green spaces have profound benefits that impact our daily lives.”

Maphaha says that in areas where trees and green spaces are limited, people experience several challenges:

Poor air quality: High levels of pollution increase the risk of respiratory illnesses.
Increased mental health issues: Lack of greenery is linked to higher stress and anxiety levels.
Higher temperatures: The absence of trees exacerbates heat-related illnesses.
Reduced biodiversity: Fewer trees mean fewer birds, insects, and pollinators, which impacts ecosystems.

Maphaha explains that trees act as natural air purifiers by absorbing harmful pollutants such as carbon dioxide, sulphur dioxide, and nitrogen oxide while releasing oxygen.

They also trap airborne particles like dust and smoke, reducing the risk of respiratory issues.

“Certain herbal trees, such as eucalyptus, neem, and tulsi (holy basil), offer additional respiratory benefits,” Maphaha says and adds that eucalyptus, for example, is known for its ability to clear nasal congestion and support lung function.

“Exposure to green spaces has been shown to reduce stress, anxiety, and depression. Spending time around trees lowers cortisol levels and promotes relaxation. Certain herbal trees, such as lavender and chamomile, emit soothing aromas that help alleviate anxiety and improve sleep quality.”

She notes that by planting more trees, cities can reduce temperatures and lower energy consumption.

Planting the right trees

According to Lungisani Zondi, senior horticulturist at the South African National Biodiversity Institute (Sanbi) in Roodepoort, Gauteng, when planting a tree, it’s important to consider the mature size and root system, as some trees have aggressive roots that can damage buildings and drainage pipes.

“Other trees are sensitive to frost. Others are very slow-growing. These are some of the basic things one needs to consider when planting a tree.”

Zondi suggests some common trees suitable for planting around homes, such as boer-bean (Schotia brachypetala), Cape Ash (Ekebergia capensis), Vachellia Karoo (Sweet Thorn), and kiepersol (Virgilia oroboides). These trees provide shade, beauty, and ecological value while being safe for planting around homes in Mzansi, as long as they are appropriately spaced from buildings to allow for healthy growth.

In short, trees do offer some benefits, but they’re not a one-size-fits-all solution for air pollution or extreme heat.

Johnston adds that if society could stop using fossil fuels and switch to renewable energy, we wouldn’t have to worry about planting trees.

“Planting trees is important, but it’s not going to solve the climate crisis,” he says. “The real solution is stopping the use of fossil fuels. However, it may already be too late.”