Mature trees are key to liveable cities – housing intensification plans must ensure they survive

The New Zealand parliament is about to have its third reading of an amendment bill informally known as the “housing intensification bill”. Its purpose is to relax the Resource Management Act (RMA), which currently restricts building height and intensity in cities, to meet the urgent demand for housing and address affordability.

While it is clear that housing affordability needs to be addressed to meet the needs of young and low-income New Zealanders, there are pitfalls to the speed at which the legislation is rushing through the system. Yes, we do need more houses, and we do need to intensify within our cities so that we don’t further impact the rural landscape as the tentacles of our cities spread into key food production and natural ecosystem areas.

However, we also need our cities to be built and expanded in a way that takes advantage of the benefits urban greening provides to infrastructure – for example improved water quality and a reduction in flood risk, energy costs, noise and air pollution – and the health and wellbeing of their inhabitants. Studies have shown blood pressure, respiratory illnesses, depression and anxiety are lower in neighbourhoods with more nature. Maximising benefits requires very intentional planning.

Previous amendments to the RMA removed general urban tree protection, which meant permission was no longer needed to remove trees on private land unless that tree was specifically protected (eg. on the notable tree schedule). This meant that only about 15% of trees on private land in Auckland were left with any protection, which is disastrous given that these trees make up 63% of the urban forest. Although it is difficult to pinpoint the scale of tree loss across the country since this 2012 amendment, we do know that some Auckland suburbs lost 35% of their urban forest between 2006 and 2016.

Given the well-defined and significant social, cultural, economic, and environmental benefits of trees in cities, the impacts of another amendment that allows further removal of vegetation to increase hard infrastructure are likely to be substantial and long-term. The “death by a thousand cuts” that occurs across New Zealand cities via tree felling during intensification cannot be undone. It is not enough to simply offset trees felled during development by planting seedlings in public spaces. The benefits reaped from a single, large tree – from carbon sequestration to enhanced biodiversity – cannot be replaced by minimalist landscaping, mown lawns, or even planting seedlings that can take 50-100 years to provide those same benefits.

Covid-19 lockdowns have demonstrated the importance of having nature in our neighbourhoods and have exposed the inequities of access to green space across our cities. Given the clear evidence of the mental and physical health benefits that nature and trees give people, reducing the urban forest and even exacerbating these inequities in health and wellbeing benefits seems like an astonishing misstep.

We can intensify and increase our housing stock while putting protections, and even enhancements, in place for our urban forests at the same time. These urban greening strategies can ensure that the people who live in these houses will have the health and wellbeing benefits of trees, making developments more liveable.

One guideline that has been proposed internationally is the 3:30:300 rule; three trees should be visible from every home, every neighbourhood should have 30% forest canopy cover, and each house should be no further than 300m from the nearest green space. This proposal fosters the idea of “access for all residents” and helps mitigate the inequities that remain with overall city canopy targets. It also requires developers and planners to consider the environment outside the building site itself.

Currently the proposed new amendments do not specify provisions around landscaping. Designing developments that keep some existing large trees in place can be achieved, and the benefits to the inhabitants and the city itself – although difficult to quantify in economic terms – clearly outweigh any extra costs incurred. Trees can be incorporated even into small sites, if we stick to the strategy of “right tree in the right place”.

Many of our cities have a focus on removing invasive predators, such as rats, to bring back our native birds under the government’s “Predator Free 2050” strategy; but birds need good vegetation structure and diversity, not minimalist landscaping. So, should we have provisions for minimum landscaping requirements in the amendment to the bill? Absolutely. We should also be specific about the type of landscaping required – compared to trees, mown lawns contribute very little to biodiversity and ecosystem services, such as mitigation of air pollution.

Specifying the amount of each site that is under a tree canopy would retain the largest benefits for the inhabitants, the birdlife and the city. Adoption of the “Urban Green Factor”, used in several European cities, would guide developers as to the relative value of different plants (eg. unmown native tussocks is better than mown lawn) and promote the use of green roofs and living walls.

There are several options for landscaping provisions that require some thoughtful discussion and new collaborative relationships to ensure urban greening is an integral part of a person’s right to a healthy home. Beyond that, cities need to be forward thinking, planning for equity in urban greening, and developing green corridors that allow wildlife to flourish throughout the city. Only then will our cities be truly liveable.

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