A love letter to city trees

There’s a tree at the Botanic Gardens that I love to sit under.

The love of my life and I met this tree while celebrating our first anniversary. Its branches are sprawling and knotted beautifully. There’s nothing like sitting in its shade to write about the world.

Trees deserve our love. They keep our soil stable and our minds well. We often underestimate how much being near a tree improves your mental wellbeing. Even on dark days they bring a unique feeling of peace.

We’ve depended on trees to build boats and explore the oceans. We’ve used them to cook our food or warm our homes or be our homes. Our ancestors were protected from predators by a trustworthy trunk. Trees were our guardian before we had the technology to spend our lives on the ground.

Our scientists and experts are urging people to ask trees to be our guardians again. This time, it’s to help our cities thrive. Cities like Wellington face unique problems as storms get stronger and temperatures soar from fossil fuels being burned. As we face a frighteningly warmer world, the time has come to ask trees for their help.

Trees slow stormwater

The city ground acts nothing like a forest floor. It doesn’t absorb water and release it underground. It locks water out from the dirt. If dirt is a sponge, our concrete paths and paved roads are a waterslide.

Cities stop flooding by moving water with gutters, pipes, storm drains, and sewers. This system is built for regular storms, not what’s coming.

All the pollution we’ve added to the air make storms stronger. Pollution warms the air, which turns more water into steam. More water in the air means a powerful storm has more liquid to drop. If the world keeps polluting like New Zealand is, Wellington storms will drop 30% more water by the end of the century.

Trees can help us adapt. Their branches and leaves hold a lot of water and stop it hitting our drains all at once. When their trunks are surrounded by sponge-like ground (think dirt or gravel), their root systems move more water away from overloaded sewers.

City forests help a lot in a major storm. Tree canopies are estimated to stop around a third of heavy rainfall hitting the ground. Get enough trees in a city and our sewers become harder to overwhelm.

Trees keep us cool

Planting a ngahere (forest) through central Wellington can keep us comfy in hotter summers, too.

Cities have a habit of getting really hot. Concrete is great at absorbing heat, something urban planners call the “urban heat island effect”. Cities without enough tree cover get way warmer than surrounding rural areas with a better balance of plants and pavement. Cities also stay hotter further into the night. The pavement warms neighbourhoods like a hot stone. That keeps temperatures unbearable for longer.

We will need to deal with a warmer world, even if we stop polluting today. Past pollution is already raising temperatures. That heat is, unfortunately, baked in. We must stop polluting so temperatures won’t rise any further. While we do that work, we must also find solutions for living in a warmer world.

Planting forests in cities is a fantastic solution. The Parliamentary Commissioner for the Environment says that tree shade can make the air nearly 4.5 degrees cooler. If everywhere in Wellington had tree cover like Thorndon, we’d be very well prepared for a warming world.

Without more trees, sweltering temperatures will lead to serious discomfort for the millions living in New Zealand cities. Partnering with plants will make the blistering heat on the horizon more bearable.

We thrive when trees thrive

I could write another thousand words exploring how cities are better with trees. They clean our air and bring beautiful birdlife. Having a tree as a neighbour is definitely better for you. We’re happier when we share our place with plants.

Right now, cities aren’t designed for trees. Artificial lighting can stop trees from growing as large. We stop rainwater from reaching them by covering their trunks with pavement. Poorly made city environments stress the hell out of trees.

Ironically, this design stresses the shit out of us, too. Artificial lighting messes with sleep. Noise harms our health. This environment isn’t good for anyone. If we rebuilt our city so trees will thrive, people will thrive, too.

Wellington’s missing canopy

Wellington is the only city in New Zealand where trees aren’t in decline. Our neck of the woods has maintained a healthy 30% of its land area covered in leaves.

I am so grateful that we have the Botanic Gardens, Zealandia, and the treasured Town Belt. We’re enveloped by rākau (trees) like a comfy blanket.

In the hills of Highbury or Aro Valley, tree cover is between 54% and 71%. It’s fantastic.

However, tree-less urban islands sit amongst the leafy suburbs. Pipitea has less than 3% tree cover. Only ~1% of Rongotai is covered. We must change this to adapt to a warming world.

Even if we magically stop belching carbon today, summer will still get hotter. Storms will get stronger.

The more pollution we create, the more power is added to natural disasters. Stopping our pollution is incredibly important. We must also prepare for the warmer future that’s already on its way.

Trees are our guardians against climate change. If we start now, we could foster thriving canopies across the central city. More kererū and kākā will move into Manners Street or Martin Square.

The best time to plant a tree was 30 years ago. The second best time is right now. By the time the climate gets truly weird, we should have a forest of leafy protectors to weather the storms with us.