Pocket forests: a trending strategy to save Paris from heatwaves

The tree-planting method is borrowed from a Japanese scientific idea developed in the 1970s

Do you know what a “pocket forest” is? Well, according to volunteers and environmental activists, they could be the key to saving large cities from the harmful effects of climate change, such as heat waves.

A non-profit called Boomforest has been introducing precisely these ideas by encouraging volunteers to plant small, strategic sections in and around the city of Paris with the goal of creating mini forests. The first such tree-planting drive dates back to 2018 and the work and enthusiasm have slowly but surely been picking up since then.

The pocket forest concept actually originated in Japan, where during the 1970s a local botanist by the name of Akira Miyawaki concluded that the centuries-old forests growing around temples and shrines were much more resilient than recently planted forests.

Miyawaki claimed that densely planted indigenous species, grown in carefully prepared soil at four different heights to provide multiple layers of coverage, grew up to 10 times faster and captured more carbon than standard managed forests. And that even a forest as small as 100 square metres could host exceptional levels of biodiversity.

From City of Light to City of Green?

For all its charm and mystique, one problem that Paris consistently suffers from is its relative lack of green spaces. The latter has been ever more noticeable with the rise of temperatures in recent years and the resultant heat waves – magnified by a densely asphalted metropolis.

According to a 2016 study, cited by Resilience.org, the French capital had less than 10% of tree coverage on its streets, putting it well behind other major European cities.

Over the course of the twenty-first century, Paris’s average summer temperature is expected to rise as much as 5.3°C and the number of days per year with temperatures higher than 30°C could increase to forty-five days from the current average of ten days. Rising temperatures will come with more frequent and extreme storms, flooding, and drought.

Trees and plants, however, can provide a natural cooling effect due to something called transpiration, meaning most of the moisture that the plants consume they then evaporate through their leaves. Yes, exactly trees, just like humans sweat and this regulates their temperature.

This is where the Miyawaki method was adopted as a quicker way to greenifying parts of the city, while engaging residents in the deed and committing them to a greener future. After all, they are the ones who suffer the effects of urban heat waves most astutely.

Planting a single tree has been shown to have the same cooling effect as 10 air conditioners. But trees are also social organisms and fare much better when planted in the company of fellow trees. This is why these pocket forests are planted densely together. Besides, this helps in enriching biodiversity as it attracts other living organisms.

Paris City Hall has vowed to plant 170,000 trees in the French capital by 2026. However, that alone might not be enough, it is this citizen’s participation that can add to making a difference in the effort.