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Trees: When Quality is more important than Quantity

Special Reports

by Mark Chester - Cedarwood Tree Care

The value and importance of trees, especially within the urban environment, is widely recognised and appreciated. Indeed, London Mayor Boris Johnson has set ambitious targets for increasing green spaces by 5% by 2025, including the planting of some 10,000 extra trees. This is to be welcomed. Indeed, once this target has been met, he wishes to go further, with another 5% by 2050. Trees are important. However, I recognise the importance of looking behind the headline numbers to what is being achieved.

There is a principle of Right Tree Right Place. This principle requires a careful assessment of locations and the tree to be planted to ensure it is suitable for the setting. Back in the ‘noughties’, I was managing trees for a large Midlands local authority. My area included housing estates dotted with numerous ornamental trees, which seem to be so popular in such settings. It was becoming very apparent that many of these popular ornamental specimens, which had been planted back in the 1970s and 1980s, were struggling to cope with the harsh urban conditions being faced more recently. There may have been quantity in planting; there was a distinct lack of quality.

A single specimen of one of the larger trees, such as London Plane, Beech, Lime or Birch, allowed time and space to mature, can contribute more than a score of smaller, ornamental trees. It can also live for much longer. In terms of numbers, planting the score of trees may indicate greater activity.

During my time in this role, I experienced dry springs, and it takes a tree particularly suited to the dry, warm conditions to be able to thrive. Many people like smaller trees such as cherry and apple with their spring blossom. However, shallow-rooted, these trees are ill-equipped for our modern weather patterns. The larger Lime trees and London Planes, which take space but make a positive contribution to the quality of air, and can last for several centuries.

There are proposals to build a motorway service station to support the M42 in Warwickshire. Part of the proposed site is covered by ancient woodland. This is woodland which has existed continually since 1500, ie the days when Henry Vlll was on the throne. It is valuable, and irreplaceable. The developer has sought to reassure concerned parties with the statement that they would be planting more trees than need to be felled to accommodate the services, parking and infrastructure. This comment suggests that they really haven’t appreciated the asset they have. To put this in to context, the late Professor Oliver Rackham identified that a single 500-year-old oak tree is ecologically more valuable than one hundred 400-year-old oak trees. These trees are not readily replaceable.

How often do we hear of developments with tree planting schemes where the numbers of trees being planted are presented as a headline figure? Road widening is often accompanied with the news that thousands, even millions of trees, are to be planted as part of site works. Sounds impressive, until it transpires that many of these are one year old ‘whips’, typically a metre in height. There is nothing wrong with such plantations as landscape features. There is a different, however, with them and planting specimen landscape trees. One element that can be overlooked is that, as part of the management of these features, many of the trees will need to be felled to reduce the density as they become larger.

I have been involved with the management of several woodland sites, within the context of exploring development potential. One aspect which they have in common is natural regeneration which is resulting in such dense vegetation that ground cover is shaded out and there is a lack of wildlife and biodiversity. Plantations tend to have little diversity, and the crowding often results in etiolation, with tall, thin trunks ill-equipped to sustain the tree in to the future. In such cases, the best option is to go in with the saw and start to cut down some of the individual saplings. With fewer trees, there is more space for those remaining to develop further and opportunity for ground cover plants, which provide diversity both in terms of species mix and wildlife habitation, to become established.

It is better to plant fewer trees and see them established, than to plant many only for them to suffer post-planting and to decline.

One of the problems with ‘headline’ planting is that there may be little consideration for the longer-term management of the trees. I survey trees on a site in my adopted county of Herefordshire, where there has been considerable investment in regeneration in recent years. Work has not been done on a shoestring, and some substantial trees have been planted as part of site landscaping works.

This included planting a small group of Birch trees within raised containers. The trees were delivered in wire cages, which help to keep the soil around the roots secure. These cages need to be removed prior to planting. Not only had the cages been left in place, but the gravitational effect of water in raised containers, which requires more regular watering, had been overlooked. Without the required irrigation, the trees declined and were dead within two years of being planted.

So often, when we plant trees in urban situations, they are ill-equipped for the harsh environment that they will face, with little soil, lack of space, insufficient or
excess water and high temperatures. However, much work has been done in the past decade or so to improve the situation. Our knowledge of how trees can cope with the harsh urban environment, and which species are better equipped is informing planting selections. Subterranean infrastructure can enable soil to be stored in the area around a tree without the risk of compaction or subsidence.

I was able to apply this practically to a development involving car parking, again with a target for trees being planted (by the local authority), in part to replace some being felled to facilitate construction works. By using subterranean infrastructure and carefully positioning suitably selected trees, a quality scheme was provided which met the requirements of the local authority without compromising the number of parking places.

When trees are planted in to such infrastructure, the cost of the installation can be considerable, and may be in the tens of thousands of pounds. It is an opportunity to plant high quality specimen trees. Sadly, without care, considerations such as species selection and suitability to the site can be overlooked,
compromising the success of the scheme. One scheme I know of, around a prestigious office complex in a coastal setting, involved planting Beech trees as they
complemented the architecture. However, Beech dislikes salty air, and the trees were all dead within the first year following planting.

When I am preparing a planting scheme, I seek to use a variety of species (if one species is used for more than 10% of the total, there is a tree health risk). I look for trees whose qualities will enhance the immediate area, whether through air quality, shade, shelter or screening. If a tree (such as Alder) has the potential for height and dense shading, it should be planted away from people’s homes, otherwise it could have a negative impact on people’s lives.

When I am asked for advice in connection with trees on potential development sites, there is often the assumption that many of the trees need to be retained, and this will prevent development. The reality is that the British Standard which provides guidance for successfully retaining trees on development sites seeks to identify the more important trees within each setting. I begin by assessing each tree for its contribution to the setting and long-term suitability to the site. It is very much a case of quality, not quantity. I also consider how each tree will relate to the proposed development (perhaps that should be the other way round).

I have been surveying and assessing potential development sites for some fifteen years, both as a consultant and working as a local authority tree officer. Typically fewer than 20% of the trees surveyed have been of sufficient value to the setting to merit retention. On the occasions where this is not the case, the existing layout typically reflects the presence of a population of trees of merit. On the pure head count basis, it can seem, when only a small proportion of trees is being retained, that one is decimating the site. However, I have realised that this can be very misleading. I recently surveyed a site and identified nearly 70 individual trees, for which it was only realistic to retain between 15 and 20. The site included a group of some 20 self-set trees in a ‘mini copse’, on a site with some spectacular oaks. It was when I compared crown spreads that I appreciated some of the oaks individually covered more space that the group of 20 trees combined.

How often do we see development proposals presented with drawings showing high quality landscaping and scenes with established trees? The trees can so easily become an afterthought, an opportunity lost. Trees can enhance the retail experience, and a parking area with some carefully chosen and positioned specimens which can cope with the harsher conditions can provide the finishing touch, in a way which we may not even consciously appreciate. This is where, with space, Pear, London Plane and Hornbeam can make a great difference.

A prominent focal specimen tree can become a valued local feature, sometimes even when it is not a particularly outstanding example of the species. In my adopted county of Herefordshire, a small group of Lime trees in a grass verge in the city centre was threatened by proposed redevelopment. The trees were not fully mature, nor historically important. They simply happened to be in a prominent setting. Despite offers by the developers to plant replacements elsewhere, these trees became a high profile cause celebre, to the extent that the road scheme which threatened them was altered to minimise the number which needed to be felled, and replacements were planted in the immediate vicinity.

The replacement trees were also substantial specimens. I did note at the time that whilst the outcome was to be welcomed, it had taken a sustained public campaign to achieve. How many high quality trees are lost because they are less prominent or their contribution is not recognised? The large, more valuable trees take up space, and sadly without a full appreciation of their contribution, it can be harder to present the case for their retention.

This is where being able to apply realistic valuations to trees can be really useful. One of my earlier valuation commissions involved a 200 year old Yew tree which had suffered from unplanned and excessive pruning during utility work. The contractors offered to provide several saplings from a local nursery to compensate. Interesting! A single seven metre tall Yew tree can cost more than £9000, which places the offer in context.

I am a tree specialist, and appreciate the variations in impact that trees of different species and genera can make, and when a purchase makes a sound investment. Depending on whether one is valuing a tree for insurance purposes or compensation, or to provide a budget for planting replacement trees, there is a range of methods available for the arboricultural valuer. This can help to ensure that, when a tree of value is lost, the mitigation works are proportionate. If, for example, a mature London Plane (capable of living for more than 200 years) in a highways setting needs to be felled, the ‘two for one’ policy that many local authorities apply, aimed at enhancing the landscape, could result in short-lived ornamentals being planted. If, however, the London Plane has been valued, with a valuation of £5000, and this becomes the value of the mitigation works, the replacement trees are more likely to reflect the contribution of the lost tree.

We can value trees as individual (depending on if the valuation is looking at the physical cost of replacing a tree or compensating for loss). We can also value their wider contribution to the environment. Arborists in the US have explored the different ways in which trees enhance our lives, and the financial benefits. We
can now calculate how much carbon dioxide and air particulates trees within a particular area are absorbing from the atmosphere and the value of this. In New York, a city-wide survey identified that for every pound spent on planting and maintaining trees, several pounds of benefits were gained. This exercise, using a process called ‘I-Trees’, has been carried out in Torbay, where it identified that the borough’s trees contribute more than £400,000 of benefits in improved air quality and cooling .

Our urban settings are warm, and create heat islands. The effect of evapotranspiration, where water is released by a tree from foliage as oxygen is released and CO2 absorbed, cools the surrounding air. This, together with shading, can cool the day time temperature in urban settings by ten degrees Celsius. This not only improves the quality of life experience for those benefitting from the cooling and makes working conditions more acceptable, it also reduces the need for costly air conditioning and ventilation.

When it comes to planting the next generation of trees, quality does not have to involve high spending. Sometimes developers are surprised when I advise against costly landscaping proposals. Spending money on impact trees to demonstrate commitment to a site is very admirable. However, it can easily be a poorly focused investment. There are so many challenges on the journey to successfully establishing high quality trees, something that seems so straightforward
to many. It takes the informed eye to appreciate when one is sourcing quality stock and ensuring the trees are suited to the setting and equipped for the future.

Over the past decade, much work has been done identifying the obstacles to establishing the next generation of trees for the urban environment. Part of this has been publishing BS8545:2014 ‘Young Trees: From Nursery to Independence in the Landscape’ which, for the first time, provides a framework of best practice.

Finally, one element of managing trees which I have recognised is that the more visible contribution most trees make is to the visual amenity of their setting, in other words, they improve the landscape. As a tree care professional, I can be a purist when it comes to assessing trees. Seeing a poorly-pruned tree jars for me. The presence of structural weaknesses, for me, detracts from the contribution of a tree, as do dominant lateral (side) branches, when the main leader should be dominant. One thing that I appreciated, when managing the populations of trees across the urban midlands, was that many had such detractions. Faced with limited budgets, and without the option to replace the specimens showing the scars of modern life, it was preferable to retain them warts and all rather than to remove them. The challenge was then to ensure that the new trees, representing the next generation, were high quality specimens.

This is one of the reasons that I particularly enjoy providing landscaping schemes. There is something rewarding in choosing trees for a new site, whether it be one property or an estate, and to supervise selection, locations and planting arrangements. For whilst it is better to plant and successfully establish one tree, if I can extend this to more, I welcome the opportunity. There is also something especially rewarding to return to a site and see trees which are in place through my involvement. That, for me, is a sign of quality.

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