Trees, hedges, shrubs, meadows—they are all excellent for biodiversity and creating healthy environments, but trees in particular offer unique benefits not found in other planting options. In fact, humans need trees for health.
So, why should you prioritise planting trees over hedges, shrubs, or meadows?
The old saying goes that the best time to plant trees was 20 years ago, and the next best time is today. Established trees yield the most benefits, often termed as ‘ecosystem services’ (e.g. carbon capture, rainwater interception, pollution barriers, etc.). Planting trees now will put the wheels in motion on a green legacy that will continue to grow and benefit future generations.
Why do humans need trees for health?
Natural air conditioning
Climate change will affect the UK’s weather significantly. We can expect hotter, drier summers and more frequent and intense weather extremes. Harnesssing trees’ natural thermo-regulating capacity will be incredibly important in the coming years. As a result, natural air conditioning is perhaps one of the most crucial factors when considering the benefits of trees. It can be categorised into three main areas—cooling humans, cooling buildings and reducing the urban heat island effect across cities. Hedging or other types of green spaces do not offer this benefit to the same degree.
- Cooling Humans: It has been discovered that trees can lower surface temperatures by up to 12°C. As temperatures rise and hotter summers become more common, planting trees in areas where people walk and gather can help keep them cool. This aids in preventing heat-related illnesses, thereby reducing the need for healthcare interventions.
- Cooling Buildings: It’s not just outdoor temperatures that trees can influence. As trees decrease local air temperature, they effectively cool buildings and provide shade for them. This cooling effect can significantly cut down air conditioning costs in buildings during summer. A recent Forest Research study estimated the monetary value of tree-induced cooling on a single 12.68 heactare NHS woodland site at £7,529 per year.
- Reducing the Urban Heat Island: Urban trees assist in minimising heat retention in densely populated areas through evapotranspiration. Planting more urban trees can effectively decrease the number of deaths caused by heat waves.
Warmer and wetter winters are another predicted outcome of climate change. Flooding is an increasingly common phenomenon in the UK, causing significant damage. As of 2023, floods account for £740 million in annual damages. Predictions indicate a potential 13% surge in annual flood damages in the UK if global temperatures rise by 2.5°C. Addressing flood preparedness has been highlighted in the NHS England Third Health and Care Adaptation Report. Additionally, at least one study has flagged it as a concerning area for healthcare sites.
A recent Forest Research study quantified the monetary value of flood mitigation by trees at a single NHS site, estimating it at £2,126 per year.
Trees contribute to flood mitigation in two ways:
- Interception: Tree canopy cover intercepts rain before it reaches the ground, allowing it to evaporate into the atmosphere. Larger trees, with more extensive and densely packed leaves, excel at this process. In our bundles trees that are most effective at intercepting rain are beech, birch and wild cherry.
- Uptake and infiltration: tree roots (both dead and living) help aerate the soil. The soil structure tree roots create can act as a sponge full of connected channels. Mature trees possess extensive root systems capable of retaining water and swiftly directing it from the surface deeper into the ground. Areas with trees generally have greater infiltration rates than lawn or pasture without trees. This is because trees create more stable, porous soil.
Humans need trees for mental and physical health
Humans need trees for health and proximity to nature has demonstrated significant benefits for mental and physical wellbeing. Specifically, spending time in woodland areas has been found to stabilise blood pressure, reduce stress levels, and induce a sense of calm. In contrast with blue spaces or other green spaces, trees release phytoncides into the air. These are volatile organic compounds which have been shown to help both immune response and the nervous system and are mood enhancing. Moreover, interactions with these chemicals have been shown to bolster anti-cancer cells and expedite post-surgery recovery.
A UK study conducted by Forest Research revealed that visiting woodlands significantly enhanced mental health and could potentially save the NHS approximately £185 million in annual treatment costs. One contributing factor to this positive health impact might be the way trees release particularly high levels of phytoncides. These are naturally occurring substances believed to alleviate stress and enhance immune function in individuals.
Trees also contribute to reducing staff absences due to sickness. Employees with views of trees took an average of 11 fewer sick leave hours annually compared to those without such views. This translates to an estimated saving of around £1,600 (approximately $2,000 as reported) per employee. In 2019 the Centre for Sustainable Healthcare produced the Space to Breathe report which looked at the importance of green space for NHS staff. The report found over 80% of staff wanted to spend more time in green spaces.
As a result of these positive effects on mental and physical health, trees are also believed to have an equigenic effect. Equigenesis occurs when something disrupts the relationship between economic disadvantage and poor health outcomes in favour of better health equality amongst all economic groups. Access to trees promotes better health especially amongst economically disadvantaged groups. Trees are not a luxury when humans need trees for health.
Tree cover serves to mitigate both diffuse and point source pollution by intercepting run-off into watercourses. Trees play a vital role in capturing and storing rainfall. Their root systems aid in soil consolidation, thereby reducing the transmission of waterborne pollutants attached to loose soil particles. In areas with impermeable paved surfaces, notably in car parks, trees are effective in curbing dispersion of vehicular pollutants into the broader environment.
Trees also contribute significantly to decreasing run-off by intercepting rainfall before it reaches the ground altogether. Trees with expansive leaf areas demonstrate the highest effectiveness in this regard.
UK woodlands presently store approximately 213 million tonnes of carbon. A recent study conducted by Forest Research estimated the value of carbon sequestration at just one NHS site to be £21,647 annually. Trees, being larger than other vegetation forms, have a greater capacity to store carbon, and their extended lifecycle ensures the long-term storage of carbon.
Air quality improvement
A recent study by Forest Research evaluated the annual value of air quality improvement from trees at a single NHS site, estimating it at £8,595. In addition to absorbing CO2, trees provide a shield against various air pollutants, including ozone (O3) and Nitrogen dioxide (NO2). The primary reason for trees’ beneficial impact on air quality lies in their function as physical barriers, effectively blocking pollutants from reaching people. Unlike low-level vegetation, trees, especially those with greater leaf area, have a more pronounced effect. Consequently, safeguarding existing mature trees holds immense importance as they currently serve as a protective shield against pollution.
Noise mitigation and screening
Trees aid in reducing noise originating from traffic and other external sources. The strategic planting of noise buffer strips can diminish noise levels by five to ten decibels for every 30-metre width of woodland. According to the 2023 study by Forest Research, the annual value of noise mitigation from trees at just one NHS site amounted to £2,109.
Shade and shelter
Apart from providing cooling effects, tree cover offers protection from the elements. This can potentially enhancing the utilisation of green spaces and reducing operational expenses. During summer, shade from tree canopies can reduce UV exposure by up to 50% compared to direct sunlight. Additionally, tree shade contributes to prolonging the lifespan of tarmac surfaces by mitigating heat exposure and subsequent degradation over time.
Tree shelterbelts are capable of decreasing wind speeds and establishing sheltered zones. Implementing windbreaks around buildings can also aid in cutting heating costs and conserving energy, particularly in areas prone to strong winds.
Protect and improve soil
Trees contribute to soil fertility by recycling organic matter through fallen leaves, aiding in moisture and nutrient retention. The establishment of an organic soil layer and the development of root systems also alleviate soil compaction, benefiting water infiltration. Furthermore, trees’ ability to absorb and retain rainwater helps reduce nutrient leaching from surrounding soil.
Trees serve as a prevention measure against soil erosion and topsoil protection. Their roots bind the soil, particularly on sloping ground prone to subsidence, providing bank stabilization applications.
Aesthetic and amenity value
Beyond the inherent beauty of trees, they offer diverse amenity benefits for healthcare settings. Vibrant blossoms, autumnal leaves, and even bark infuse colour into dull settings, softening building outlines, and minimising visual intrusion by screening roads or unsightly views. Moreover, trees create tranquil spaces for rest and relaxation, benefiting both patients and staff.
Trees can evoke a sense of pride and ownership while fostering community involvement in planting and maintenance. Over time, established trees become valuable assets for the site and potentially increase property value.
Biodiversity and wildlife
Biodiversity stands as a cornerstone for all life on Earth. Trees are a crucial part of this. Both wildlife and humans need trees for health and survival. Our human ecosystem relies on diverse services for clean air, fresh water, and food production. Areas covered by trees, even individual trees themselves, offer essential elements for our continued existence, while providing habitats for diverse wildlife. For instance, birch trees found in some of the tree bundles we offer serve as food and shelter for over 300 insect species. Tree planting initiatives substantially contribute to expanding biodiversity and fortifying resilience against climate change and natural habitat loss.
Woodland can be better than hedges in promoting biodiversity because it allows for the formation of an understory layer. This is the layer where vegetation and animals can thrive. Woodland also promotes healthy ecological succession where vegetation can change and develop over time more easily than in a hedge.
All the evidence points towards how humans need trees for health. Tree planting and woodland creation is not an instant win, but all woodlands have to start somewhere. Taking action to plant trees today will help ensure the future is more secure and positive. NHS sites in England can order their free trees from us now. You can also read about our various tree bundles.
It’s also important to remember that trees are not distributed evenly. They are needed the most in urban areas – where many healthcare sites are also found. You can use the Tree Equity Score tool to identify if your site falls into an area of low tree cover. https://uk.treeequityscore.org/
Still need support with deciding to plant trees? Join us online for one of our regular drop-in sessions.