Imagine a city without trees…

Suzanne Simmons, Projects Director at Trees for Cities, explains why the Covid-19 crisis may well shape our response to urban trees and green space supply

Perhaps the only way we can understand a city without trees is to compare urban areas that possess a wealth of tree cover with those that have a dearth. If you live in a UK city this may be more or less apparent depending not only on what city you live in, but also which part you live in. With more than 80 per cent of the population now classed as city dwellers, it has become increasingly urgent that we make space for trees and recognise the benefits and the cost savings they can bring to the environment, businesses and communities when planned carefully. Recognising these benefits and the cost savings they bring at decision-making, funding and planning level will demonstrably create healthier, resilient and more prosperous cities.

At Trees for Cities we choose to operate in urban areas that score highly when checked against multiple deprivation indices and we aim directly and indirectly to tackle certain inequalities through our tree planting programmes. This includes focussing attention on priority areas with low tree canopy cover, poor access to green spaces and nature, and poor air quality. These indices can all lead to poor quality health and wellbeing and a disconnectedness with nature. Research illustrates that there is nearly always a correlation between areas that are socio-economically deprived and areas with greatest environmental deprivation. That correlation can be further focussed on trees, where all deprived UK areas demonstrate low levels of canopy cover.

Tree canopy cover is a useful indicator of the extent of the presence of trees across a city, and it has become a default methodology of assessing urban tree numbers. Measuring tree canopy cover has become easier, providing accurate, simple, fast and replicable digital mapping. Replicability therefore allows easy comparisons and can support identification of opportunities for organisations to track changes in canopy cover over time and against targets, which in turn can demonstrate effectiveness of tree planting programmes.

Measuring tree canopy cover can also be a useful way of targeting funding to areas that are deficient in trees and it further supports, by default, Trees for Cities’ efforts to focus tree planting in mainly deprived city regions. By focussing on urban areas of deprivation when we plant trees, Trees for Cities is able to tap in to the wider benefits trees bring when developing partnerships at local level. This means we are not only filling canopy cover gaps on a plan, but also we can directly locate our tree planting in areas with high levels of air pollution, develop improved opportunities for connectedness with nature through planting programmes in schools, and improve amenity and biodiversity through tree planting on local community green spaces.

Cost benefits
In addition to tree canopy cover, we are now more able than ever before, to accurately quantify the cost effectiveness and multiple benefits trees can bring to urban environments. In doing so, we recognise the value of trees as Natural Capital and can demonstrate how trees can mitigate against the impacts of a changing climate on cities.

By measuring the added value of trees in monetary terms, the case for new trees can be presented as an opportunity for real financial gain, which is likely to be met positively by potential partner organisations, decision makers and funding agents on top of other, less easy to quantify benefits, such as aesthetics and biodiversity. In effect, trees should be viewed as ‘assets that increase in value over time’ because unlike grey infrastructure, they bring indirect and deferred benefits .

The real cost benefits may only become apparent after 50 years, but they continue to increase for another 150 years before levelling off. The key to accruing maximum benefits is ensuring the tree survives its first fifty years. So a 100 year old tree has around 4 times the cumulative benefits of a 50-year-old tree and at 200 years it will have achieved between 20-40 times the benefit of a 50-year-old tree.

Whilst quantifying benefits of trees in a qualitative way, may humanise the reasoning for planting trees in urban spaces, but putting a financial benefit on trees is often essential when tapping into strategic budgets. If we do not provide a value for the urban forest and each tree within it, then it will be allotted a value of ‘£0’, should removal be proposed. It is therefore important to recognise the financial value of trees directly and indirectly before they are removed and ensure that if felled, trees are replaced and adequately compensated, financially and qualitatively.

If we possess the science and data for the performance of urban trees, then we can use that information to underpin simple messages for decision makers. The obvious benefits of trees may be easy to communicate, but it is the less obvious benefits alongside the direct and indirect costs saved that create compelling arguments for planting and protecting urban trees.

When the well-understood benefits of urban trees on thermal comfort are translated to costs saved through, for example, a reduction in air conditioning costs in summer and a reduction of heating costs in winter, the argument can then be made in monetary terms alone. It is these facts translated to tangible scenarios that make a more compelling case for decision makers.

Treeconomics identified the following headlines for GreenBlue Urban in 2018:

• a 10 per cent increase in urban green space can postpone the onset of health problems by up to five years;
• students who have a green window view recover from mental fatigue faster and thus pay attention for longer;
• research has indicated that a 10 per cent increase in tree canopy was associated with roughly a 12 per cent decrease in crime;
• particulate levels on tree-lined streets can be up to 60 per cent lower than those without trees;
• a series of international third-party studies have shown that trees can increase property prices anywhere from five per cent to 18 per cent;
• there is up to a 24 per cent reduction in particulate matter near a mature tree;
• trees can help reduce stormwater runoff. For every five per cent of tree cover, stormwater runoff is reduced by two per cent.

So how can we deliver greater numbers of urban trees to bring those increased and much needed benefits to our towns and cities? The 25 Year Environment Plan set out to create a more cohesive and joined up approach to tree cover and has a stated aim of delivering one million urban trees.

To enable this action, Defra recently consulted on the England Tree Strategy. A natural progression would now be for every urban local authority to have their own dedicated tree strategy, linked closely to a landscape scale strategic plan. The Tree Council call for the use of tree strategies to afford good management by taking ‘the benefits and risks of trees into account, setting long-term goals to drive up tree numbers and canopy cover, diversify the tree stock, and protect existing trees for future generations’.

To ensure the benefits of trees are fully utilised moving into an uncertain future, Doik et al (2016)  recommend that trees and cities with a current average Tree Canopy Cover of 20 per cent should be setting a five per cent increase as the minimum standard over a 10-20 year span. Whilst Forest Research has called for all local authorities to commit to a minimum 30 per cent tree canopy cover target for new development land.

In its Environment Strategy, Greater London Authority has set a target to increase canopy cover from current 21 per cent to 31 per cent by 2050. Manchester City of Trees set its target to plant up to ‘three million trees within 25 years, of which one million trees to be planted by 2024, and a further two million by 2050’. These targets are currently filtering through to detailed local policy; a list of those local authorities who already have tree strategies can be found here.  

As we navigate the uncertainties of Covid-19 an emerging realisation is how big a role trees and urban open spaces play in our daily lives and just how particularly important well stocked and well connected green space is for exercise and general health and well-being, especially when our leisure choices are severely curtailed and our urban climate is changing.

There will be many lessons learnt from the Covid-19 crisis and it may well shape our response to urban trees and green space supply, to meet growing demands for outdoor exercise, healthy air, safer, cooler streets and green spaces, more biodiversity and more attractive places to live and work. If trees present a solution to current and anticipated future urban problems, surely now is the time to plant, protect and promote. A city without trees is a place that no one wants to live in.