Regenerative urban greening in the face of a hotter, wetter UK

Right time, right place, right tree

Extreme climate events will result in tree sapling and mature tree losses. Storms and extreme wind damage trees, breaking stems and uprooting trees. Drought and heat waves change plant physiology and phenology, increasing tree mortality.     

In summer 2018, 89,000 tree saplings planted for High Speed 2 died. To water them would have cost £2million—replacing the dying plants was cheaper and a more ethical use of water resource during a heatwave. Spring 2020, the fifth warmest and sunniest spring on record, killed 4,000 saplings on Hackney Marshes in London. The winter storms in 2013-14 caused the greatest loss of mature trees in a generation.

The Royal Horticultural Society and the Millennium Seed Bank at Royal Botanic Gardens, Kew provide annual updates on suitable species that are adapting and can withstand the gradual process of climate change. As drier, hotter temperatures hit the south, we will have to look at our trees and planting trends.

Palm trees lining the Mall in London? The novelty of these trees as iconic visual indicators of a once-sought warmer climate—similar to Barcelona or Florida—would likely be short-lived. Palm trees do not provide enough shade nor capture carbon and would not be a sensible approach to adopt by local planning authorities. The Royal Palm absorbs less than 0.5kg of carbon.

The right time, place, and tree could be set out in legislation with rules against planting trees in peat areas, or in areas where the soil has organic surface areas less than 50cm thick. There could be future limits on our types of woodland with a new focus on broadleaved species. Oak, maple and disease-resistant ash trees would be the climate adaptation choice in southern and eastern UK. Oaks can absorb over 41kg of carbon. By 2050, beech trees would only do well in north and west UK.

Rising temperatures and reduced frosts in winters could mean a decline in traditional orchards in southern England. But where apples, pears and plums are disappearing, we could see more citrus trees planted in their place, with home-grown oranges, lemons and even limes in some plots.   

The future is green

To avoid becoming ghost cities, and uninhabitable during summer months, cities must manage urban heat island effects. Regenerative Urban Greening is a design and placemaking movement that aims to regenerate and reactivate the worst heat island cities, by replacing hectares of grey infrastructure with green-blue infrastructure and vegetation-clad buildings. The former early-century network of grey infrastructure transport routes could be a thing of the past and no longer dominating urban areas, nor dictating the placemaking design process. Instead, Regenerative Urban Greening schemes could be designed around macro-scale connecting urban floodplains and woodlands. Transport routes could be truly green!

Many British cities could take their design cues from the early vertical forest architecture of Singapore, such as PARKROYAL Hotel, and Milan. The concept of vertical greening and the understanding of green infrastructure has been established as critical for human habitation. We could see a boom in tall buildings, placed amongst swathes of urban green floodplains and woodlands to help address rising sea levels, extreme rains, and provide shade and respite from the heat. First envisioned in 2013, this is xeriscaping, an approach that reduces the resources and water requirements of green infrastructure in urban areas. We could see it embedded in planning legislation. 

Not just a pretty space

From dealing with water run-off and pollution, to green corridors, and increased urban food production, we could see urban parks that are functional, and more than just a pretty green space – providing shade, cooling, connection to nature and wildlife, and local produce.

Take a long look at the landscaped lawn. One day it could be a distant memory, having been replaced by rain gardens, meadows and species-rich grasslands, even in urban areas, and tree planting. 

Urban tree planting should focus on species that provide shade and function within extensive chains of rain gardens. Urban areas could have designated Primary Shade Routes—cool and green corridors for people’s active travel so that they can move using whichever mode they choose in relative comfort during the common heatwaves and heavy downpours. Maturing trees would provide dense canopies for shade and be part of a linear rain garden.

Greener, by law

We’ll need to take note of future climate change and biodiversity crises across the country. Would a future UK Government finally implement a National Forest Programme? Green Belts—the planning mechanism to prevent urban sprawl across the countryside—could be replaced by Forest and Woodland Belts. These could look like substantial areas of undeveloped countryside given over to a nation-wide, macro-scale, 100-year tree planting programme. Would their number and size have greater capacity than original Green Belts and envelope all English major cities and towns?

Forest and Woodland Belts could help with providing flood mitigation, clean air, green and cool spaces for people and wildlife. The south of England will be the most affected by searing temperatures and extreme rainfall; Forest and Woodland Belts could be the most prevalent there. As we travel further north, it could be rare to see south of Sheffield the ‘millennium-romantic’ landscapes –the formerly managed open landscapes of agricultural countryside, large fields, and lengths of hedgerows. We could see them replaced by substantial areas of phased national tree planting, interspersed with permanent grassland and rough grazing pasture, providing carbon storage.

And with more extensive and intensive tree planting programmes, we could see a new timber industry, and a symbiotic relationship between people and the woodlands and forests. The idea of a Garden City is well known now – would this design principle resurge in a new Forest Town format?  

Each year, we’re seeing devastating climate change-related impacts around the world, from polar icecaps melting at a terrifying pace, to wildfires in US, Turkey, and Australia, and flooding in Germany, and London. A biodiversity crisis is a climate crisis. We have to take note of the impacts on nature, our horticulture, and landscapes. Mitigating them means future generations will be able to survive in public spaces that just a few decades before, were not intolerable to live in.