Why have we stopped planting big trees in towns and cities?

Large trees of 20-30m create cooling shade and vast habitat

Platanus x hispanica, plane trees in Bordeaux

By chance, this year I’ve found myself in cities during the three heatwaves and the one thing I noticed is how much I sought out the shade of large trees. In fact, it was the only place I could find any kind of reprieve from the burning, sweat inducing sun.

I’m talking about towering trees over 20-30m tall with the same spread. Trees that form cavernous understories to cool huge areas of towns and cities, sometimes by up to 10C.

Red flowered horse chestnut between apartment low apartment blocks in Bordeaux, France

Trees like the hybrid plane Platanus × hispanica, oak, sweet chestnut and various cultivars of horse chestnut, Aesculus spp. Plane trees are a hybrid of Platanus orientalis and Platanus occidentalis, which themselves are large trees that can be seen around city streets.

Why and when did we stop planting these trees? Given they cool our streets, are drought tolerant even in long periods of heat and create huge habitats for thousands of species high in their branches. Oak alone we know supports over 2,000 species.

Sadly, we seem to have stopped sometime toward the end of the last millennium. Deemed too large for modern society, too intrusive with their shade. Instead, we’re making streets as narrow as possible and filling them with tiny little ornamental cherries and amelanchier. Beautiful and useful trees but their impact is significantly reduced by their scale.

Tall shade giving trees fill parks in sunbaked Syracusa, Sicily

As the climate warms, the UK and other northern European countries can learn from our southern neighbours. Here big trees are used to great effect in parks and around the countryside to shade people and understory plants.

A walnut shading forbs and grasses in Sicily

Many trees are more drought tolerant than we might think and southern drier regions help inform us what trees can tolerate. Above is a walnut with more space around it, the mix of shade and light allowing for plants to grow beneath. Below are enormous elderflower around Mount Etna growing to well over 10m tall and wide. Here summers can be very sunny, hot and dry.

Elderflower grow to huge proportions in hot Sicily

I do understand the challenge, in the rush for space for buildings it’s easy for politicians and developers to brush aside green infrastructure. Making new roads wider to accommodate trees up to 30m wide with buildings either side may sound like a challenge too far for many.

Things like longterm maintenance to reduce canopies and worries about trees falling on buildings all put a stop to architects and planners planting these trees. Fear around what will survive - even though with eyes open we can see what will survive in regions to our south. Also what has survived past heatwaves and drought. these Victorian era trees all lived through the heatwave of 1976, the heatwave global warming deniers are so keen to harp on about.

It can go wrong without plant expertise, here birch are seriously struggling in July. I always thought these silver birch outside Tate Modern were planted (in 2000) with far too little root space and surrounded by too much concrete, which acts like an oven.

20th Century architects and planners didn’t get everything right. I’d suggest they planted the big trees too close together, preventing other understory plants growing well beneath them. They also planted the same species in monoculture avenues, rather than mixed planting. Both of these decisions will have reduced wildlife value - but we live in a different time with better knowledge of nature’s decline.

By spacing out a mix of different big tree species, it means we can also underplant them with smaller shade tolerant trees, shrubs and perennials. Giving them plenty of root space is critical.

Green Park in London where large trees are underplanted with lawn that goes dormant in summer.

To cope with the hot summers it feels like we’re missing out on one of our cheapest natural assets: big trees. Look at European cities with mature big trees and how well they work. I would also argue the obvious: slotting green space between buildings is better for our health. Better for a feeling of space, better to cool living areas naturally, better for bringing biodiversity close to our homes.

What do you think? Can we make room for big trees in our towns and cities once again? Should we? Or am I barking up the wrong trees? Has our need for buildings outgrown the possibility of big trees in urban areas? Are they actually just too big to grow around houses and workplaces?