Temperature in Tiny Forest on hot days is 20 degrees lower than on the street

Wageningen University & Research report after four years of research  

For four years, Wageningen Environmental Research conducted research into the Tiny Forest project together with about a hundred volunteers and students. This project was set up by IVN Nature Education to connect children with nature and to halt the loss of biodiversity in urban areas. A Tiny Forest is a dense mini-forest of approximately 250 square meters, in which a maximum of 600 indigenous trees are planted.  

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Tiny Forests help combat heat stress and drought  

Tiny Forests are a good solution in the fight against drought and heat stress in the city. Research by Wageningen Environmental Research shows that the temperature in the summer in a Tiny Forest can be more than 20 degrees lower than the temperature just outside the forest. These mini-forests in the city also absorb a lot of water during heavy rainfall, which is badly needed in an increasingly drier Netherlands. In addition, Tiny Forests boost biodiversity in the city, providing a home for birds and animals.  

Large temperature differences  

The research results offer hope for all densely tiled cities, which suffer higher temperatures every summer. To get an idea of whether a Tiny Forest can contribute to combating heat stress in urban areas, the soil temperature was measured in 2020 and 2021 at 11 mini-forests in and outside the Tiny Forest. The difference turned out to be particularly large, up to 20 degrees, on extremely hot summer days. The temperature in a Tiny Forest all year round is on average 7 degrees lower than on the street and in the summer about 10 degrees.  

In addition to heat, increasingly extreme precipitation is also causing problems in the petrified city. The water can no longer be drained during heavy showers and cannot be stored in the soil due to compaction. It has been calculated that the 11 Tiny Forests studied collected more than eight million liters of water between the time of their construction and the end of December 2021.  

Boost for biodiversity  

With the help of citizen science, scientific research carried out with the help of volunteers, it has been established that mini-forests help a lot with biodiversity. In total, 1167 species of plants and animals were observed in all Tiny Forests studied, excluding the planted trees and shrubs. An average of 270 species were observed per Tiny Forest. As a Tiny Forest gets older and therefore more overgrown, fewer spiders and ants are found and more benthic animals such as snails, woodlice and earthworms. The black road ant is the champion of the Tiny Forest, but researchers also saw many aphids and woodlice. Researcher Fabrice Ottburg emphasizes that these ordinary species also play an important role, ‘Large populations of ordinary animals live in a Tiny Forest. This is the bottom of the food pyramid and amphibians, songbirds and small mammals benefit from it.” 

CO2  

In addition to biodiversity, the average annual CO2 sequestration has been determined. This amounted to 127.5 kilos of CO2 per year for Tiny Forests aged 1 to 5 years. It is expected that this will continue to grow up to 50 years after planting to around 250 kilos of CO2 per year. Given that the average annual emissions of a person are about 4.4 tons of CO2, a Tiny Forest only makes a small contribution to reducing the CO2 concentration in the air. 

In total, about 170 Tiny Forests have been created in public spaces in the Netherlands so far, and ninety private individuals have planted one in their own garden.  

Photo: Fabrice Ottburg
Source: Wageningen University & Research