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The Benefits of Trees

Special Reports

by Mark Chester - Cedarwood Tree Care


In previous articles, I have explored how trees contribute to our landscapes, methods for valuing them, the role of Tree Preservation Orders complete with the challenges of managing trees subject to them and how to successfully establish the next generation of trees, especially within our urban settings. The underlying principle linking all of these topics is how trees benefit us. Some of the benefits are more obvious, others may be surprising.

Trees help to clean the air. They remove carbon dioxide which is then used to convert water to sugars, in the presence of light, the well-known process of photosynthesis. The process of gaseous exchange (by which oxygen, the by-product of photosynthesis, is released and CO2 is absorbed), involves the release
of water. Called evapotranspiration, this has a valuable cooling effect. This has such an impact that in urban settings, it can reduce the need for air conditioning. During 2015, a team of volunteers carried out a survey of the trees within London as part of the i-Trees Project. This seeks to evaluate the population and benefits which can be attributed to it. The data collated has valued London’s trees as an asset worth some £6 billion. Lower energy costs from the cooling effects of evapotranspiration reducing the need for air conditioning is estimated to be worth more than £200 million per year in London alone!

Whilst the London I-Tree report, hot off the press in December 2015, may represent a more recent approach to appraising the financial benefits of this urban forest, many of the benefits it cites have been apparent for decades. Research from the 1980s demonstrated that when patients in hospital recovering from surgery have access to views of trees and green spaces, recovery times are reduced and mental health is improved.

Whilst our roads are often devoid of trees, and road-side trees face an increased threat of being felled, the benefits of trees to drivers can easily be overlooked. Trees help to reduce stress levels among drivers, whether travelling locally facing the commute home before or after a hard day at work. It is often said that by highways engineers that trees in the highway, and especially those at road junctions, can contribute to conditions that detract from road safety. However, there is evidence that their presence is calming to drivers and when they are around junctions, drivers need to be more careful before making manoeuvres.

Cars, and especially those with diesel engines, release pollutants in to the atmosphere. These tend to have a negative impact on the health of those living and
working by the roads. Tree lovers have known that trees help to improve the quality of the air, and trees such as Birch and London Plane have been widely planted due to their ability to remove pollutants from the air. Backing this with scientific evidence strengthens the argument that trees are important and should be incorporated in to the landscape, and especially the urban environment, wherever possible, even where space is limited.

Research by Professor Roland Ennos working with the University of Manchester, has demonstrated the dramatic effect of planting trees in road-side settings. In a trial using Birch trees in raised containers by a main road in Manchester. Professor Roland took samples of residues of pollutants within eight properties before the trees were placed in the pavement outside, and then several weeks later, after the trees had been in situ for a period. The reduction in particles being deposited in each of the homes was stark. The impact of having the trees between the road and the properties was significant, and he concluded that every resident living by a road should request a Birch tree outside their home. For those worried about the negative impact of having trees near to properties, Birch are one of the most appropriate of trees to select.

Often, to facilitate collections of motorists, for example at retail and business parks, we need to construct car parks. These can easily become deserts of concrete and tarmac, heat islands which detract from the enjoyment of shopping or employment. How often do architect drawings of proposed developments show attractive avenues of mature trees, designed to enhance the setting and enable it to fit in to the surrounding landscape? Sadly, without care, this intended feature can so easily fail to materialise, as the trees, which are often planted at the very end of the construction process and left to fend for themselves, struggle to become established. Those that do become established can be seen as a maintenance problem, subject to regular pruning which restricts their growth so that they are unable to reach their potential. The idyllic plans have by this time long since been forgotten and an opportunity to create an urban oasis has been lost.

The social scientist Dr. Kathleen Woolf has shared research from the United States exploring the role of trees and vegetation in contributing to the retail experience in urban settings. The research found that retailers were reluctant to have trees by their outlets, concerned that the trees would deter shoppers. This is a sentiment that I have experienced myself. However, the research identified that shoppers found settings with trees to be more appealing than outlets without them. This is again a sentiment that I would concur with. The disparity between the retailers and their customers is interesting. It is more straightforward for developers to develop sites with no trees. However, when trees are successfully retained, they can provide such a valuable feature of maturity that it is worth the effort.

Why does the focus on retaining existing trees rather than planting replacements, matter? It depends in part on the qualities of the existing trees, but often sites contain established trees, either as individual specimens or groups. These trees are often mature and established on the site, suited to the existing site constraints. They provide a maturity which would take newly planted trees years, even decades, to reach. I have previously worked for several local authorities where the policy regarding the felling of trees was to plant two replacements for every one that is felled. This can sound impressive, and one may argue that it contributes to the sustainable management of the urban forest, expanding the tree population.

The drawback is that all too often, the trees being felled are substantial specimens, field trees which can live for several centuries, such as London Plane, Beech, even Sycamore. Attaining heights of sometimes more than thirty metres when mature, these trees are not readily replaceable, and even planting several replacements, of several metres each in height, is not comparable. The replacement species are often not comparable. I have seen ornamental trees such as Rowan, the Mountain Ash, and flowering apples, planted to replace the field trees. These ornamental trees are unsuited to the harsh urban environment. They tend to have short lives and a smaller stature.

Retaining trees provides immediate maturity to a development site. Larger trees are also best equipped for storm water infiltration. This is a factor which has been in the headlines increasingly over recent years, and torrential downpours throughout the UK have resulted in localised flooding. One of the main causes
recently has not been just the volume of water which has fallen, but also the short time scale in which it has arrived. During one deluge in Cockermouth in Cumbria, the volume of water flowing down the river through that town increased more than thirty fold. This is exceptional.

Tree lovers have known for decades that trees have a role to play in rain water infiltration and soil stability.

Their role in reducing storm water run-off in our urban environments is increasingly being recognised. There is limited research on this topic to date, but
Professor Roland Ennos, who is responsible for a number of projects relating to the urban forest, and is based at the University of Manchester, has identified a favourable effect when monitoring some trials. More research is needed but when large trees are in urban settings, they intercept rain water and slow its rapid movement.

Tree enthusiasts value and appreciate trees. However, their wider benefits are being more widely recognised. They can enhance the landscape and provide a more appealing and attractive environment in which people choose to live. In one project, in Merseyside, tree planting was funded to encourage urban renewal in the most deprived areas. A review of the project, presented at the Trees, People and the Built Environment conference held at Birmingham University in 2014, demonstrated how the areas selected for tree planted had developed in to attractive places to live, encouraging inward investment and employment.

Not only do trees help to transform derelict urban settings, they can also improve the environment. Extensive tree plantings have been undertaken on the sites former mining collieries and as part of the restoration of former land fill sites. Some trees, such as Alder, can not only tolerate harsh and otherwise inhospitable landscapes, they can also improve the soil through the removal of toxins, nitrogen fixation and increasing the organic content of the soil. This can enable otherwise derelict sites to be restored and brought back in to wider use. In additional, they can help to reduce soil degradation, which can otherwise damage valuable farmland.

Trees contribute to our enjoyment of the visual landscape. They also contribute to ecology. I referred earlier to the value of larger field trees, which are not as readily replaceable as some would wish. Some of the relationships that exist between trees and flora and fauna can be quite unique. These become more
important when we explore older trees, and the late Professor Oliver Rackham, who specialised in the study of ancient woodlands, observed that one hundred 400 year old oak trees were not comparable in terms of the habitat they could provide and wildlife sustained within their structure, to a single 500 year old oak. I find this fascinating, especially when one considers some of the suggestions put forward to seek to mitigate for the loss of habitat in connection with proposed developments.

A motorway service station has been proposed for a site in Warwickshire part of which is covered by part of an ancient woodland, which has existed there for five centuries. It is likely that there was woodland present when the Tudors were on the throne. This is an irreplaceable habitat, a feature which cannot be
replicated, and is unlikely to survive being relocated. The applicant has offered to plant more trees than are felled to facilitate the proposals. This is, to me,
comparable to offering to replace a Tudor building with a mock-Tudor structure. Whilst it can be possible to dismantle a building of historic important and rebuild it elsewhere, the same is not true for our ancient trees and woodlands.

A pear tree believed to be about 250 years old, again in Warwickshire, is threatened by the proposed HS2 railway line. Reassurance about the loss of genetic
information has been provided, and cuttings have been taken for propagation. This is fine, but will not compensate for the loss of the tree, its historic link and the habitat it provides. I am aware of several situations, involving the construction of bypasses, where through careful design, trees of importance have been successfully retained, to contribute to the setting and be enjoyed by future generations.

One element that I emphasise to clients is that if we are seeking to retain trees, let’s do this properly. I see little benefit in investing in tree protection measures
and designing a layout to accommodate trees if the trees concerned are damaged by the construction process and cannot be sustainably retained. I was therefore delighted to read about two different approaches to retaining locally important trees when they are in the route of proposed road construction.

In Torquay, the famous Pineapple Palm was relocated in 2014, finding a new home in a nearby meadow. In Powys, the challenges were somewhat different. The
tree threatened there is a 500 year old oak. It is not actually in the route of the proposed bypass, but rather close. The original plans would have taken the new road to within five metres of the tree, which is too close for such an historically important specimen. In 2015, campaigners asked for the route to be moved to provide the tree with more space, and earlier this year, the change was confirmed.

We can consider the benefits of specific trees, and sometimes simply their link to a bygone age. Charles Martell, a farmer based in Gloucestershire, appreciated
this as his work as a livestock haulier in the 1970s involved him visiting many farms in the Midlands. He has an interest in fruit trees, and especially apples and
pears. He could see a way of life being lost as orchards were being grubbed up or suffering from a lack of maintenance and the loss of skills as the generation of farmers who had previously appreciated the diversity of trees were retiring and dying out themselves.

Despite having limited land himself, Charles still understood how to take bud grafts and began to build up his own collection of fruit trees, growing them in his own garden. I interviewed him in connection with his experiences, several years ago. He is most famous for producing cheeses, including the Stinking Bishop. This cheese derives its name from the rind which is washed in the Perry from the Stinking Bishop pear. The pear is thus named after a local farmer who lived in the 19th century, named Frederick Bishop, who gained the nickname due to his foul temper.

Appreciating what could so easily be lost, Charles recalled visiting one farm to collect stock, where his interest in the apples and pears was spreading. The stock duly loaded, the elderly farmer took him to visit the orchard, where there was a fine example of the Yellow Primrose. Charles looked down expecting to see a primrose in the grass, when the farmer showed him the last remaining Yellow Primrose apple tree. The narrow margins between retaining and losing heritage stood out for the next time that Charles visited this farm, the elderly farmer had died and he, Charles, was the only one to know where the Yellow Primrose was growing. He took a cutting to add to his collection, which is now at the Three Counties Showground in Malvern. This is more than simply creating a living museum. The long-last varieties can provide genetic variation and a diversity of tastes which could easily have been lost.

When it comes to our heritage, Britain contains a great resource in veteran and other ancient trees. In fact, it is estimated that as many as 75% of all of the ancient trees in Western Europe are within the British Isles. Many offer invaluable wildlife habitation, as well as incalculable links to the past. There is, for me,
something special about a tree which has lived for centuries, and maybe even more than a millennium. We owe much to the efforts of people such as Charles and the members of the Ancient Tree Forum in highlighting the importance of these special trees, and working to protect them.

In valuing trees, it is important to recognise that there can be challenges when we live near to them. For everyone who enjoys the shade of a tree, there is
someone who objects. Tree roots can invade drains and disrupt paths, and cause concerns about their safety. They can also be associated with structural
damage to properties. Over the past two decades or so, many trees have been needlessly felled on the basis of convenience or a disproportionate response to
management concerns. Felling trees often seems to be among the early options for many insurance claims even when the evidence to implicate the nearest
specimen is limited. In one case I am aware of, a mature oak tree was felled due to damage to the floor of a village hall. When the damage continued, further
investigations were instigated and a leaking pipe under the floor was found to be the cause. It was too late at this stage to bring back the oak! I have personally been involved in cases where felling or totally inappropriate pruning are requested and it is evident that those pursuing the matter have little appreciation of the value and benefits of the trees concerned or how to actually resolve the situation.

Fortunately, when it comes to the balance between tree safety and tree felling, common sense seems to be prevailing. The risk of being killed by a falling tree is roughly the same as winning the national lottery and then being struck by lightning, on the same day! Indeed, even across concentrated populations of trees, one often finds very few are unsafe. In one local authority where I worked, some 30,000 trees were surveyed, and fewer than 0.5% of them required urgent attention, i.e. within the following 3 months.

Trees enhance our environments, and whilst they can be unpopular when situated near to where people are living, that is often exactly where they are needed most. During my time as a tree officer for several local authorities, I regularly heard the comment from residents, whose own personal experience was being
compromised by the presence of a particular tree, ‘don’t get me wrong. I love trees. Just not that one, there!’ Actually, that is often where the tree helps the most.

The benefits of trees are being appreciated more than ever. The situation in Sheffield, where the local population is seeking to resist the felling of thousands of trees, shows a commitment to this valuable resource. Whilst I don’t know the specifics, some of the proposed felling would seem to be questionable based on reports in both national press and arboricultural journals, and the local MP has given his support to the public campaign.

We live in an increasingly crowded land, and the pressure for space in the urban environments can be considerable. Until recently, if the choice was between an extra parking space and planting a tree, often the parking space would be preferred. However, developments in subterranean infrastructure mean that we can now provide the space that trees need below ground without compromising the integrity of the built environment. I have been able to use the technology to include the planting of replacement trees within car parks and other settings with hard landscaping, and it has helped clients to secure planning approval where otherwise this would have been challenging.

Finally, as we consider the various benefits, there are those who seek to attribute a financial value to trees, and to their benefits. Many of us are familiar with the
phrase, ‘money doesn’t grow on trees’. Apart from being technically incorrect for paper money, it is possible to given trees a value, depending on the situation.
This can be the cost of replacing a specific tree, and makes me wonder how willing a resident seeking to fell a tree in order to install a new driveway (which was a frequent request when I worked for a local authority in the Midlands) if they were presented with an invoice for the actual cost of the tree in question. Some larger urban trees can attract values of £100,000 and more.

There are numerous situations where trees provide a very specific benefit, for which a particular value is required. This can include screening and providing a focal point. Attributing a financial value to such situations can require careful consideration of a range of factors including the condition of the original tree and the practicalities of replacing like for like. It can some as a shock when a party which has damaged a tree, whether accidental or deliberate, becomes aware of the cost of supplying and planting a replacement.

Trees are important to our quality of life, and as there is more technical evidence to support how much we benefit from them, so we are better equipped to
 espond to requests to fell, and to promote planting them, and keeping them. Everyone will benefit from that.

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