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Tree Data: How Relevant Collection and Use ..

Special Reports

by Mark Chester - Cedarwood Tree Care. Processing tree data, whether by collecting it through tree surveys (often the work of the consultant), or interpreting the information as a tree officer, has been a fundamental element of my work as an arborist. In the early days, the specification was generally agreed by others. 

However, increasingly I am finding myself responsible for setting the parameters.

As trees become more prominent both in terms of their contribution to the landscape and the obligations on land owners to ensure they are maintained in a safe condition, so there are increased requests for inspections and management reports. The client in these situations is generally a lay person when it comes to a technical appreciation of the tree resource. Ultimately, the information usually required is along the lines of knowing what trees they have and what is the condition?

The basic survey relates to the condition of the tree in terms of safety. This explores the physiological state of the tree, looking at cavities, weak forks and side branches that are too large for the tree and more vulnerable to breaking. The vigour of the tree is also assessed, as this is a good way to identify a tree in decline. The most important data with such a survey (apart from accurately identifying the position of each tree) is whether an individual tree needs pruning (or felling) and how urgent the work is.

When I look at a tree, I assess both safety work and pruning which would be beneficial to the tree, also helping to avoid problems later on. When trees are growing in open settings, there is a tendency for lower branches to become over-dominant and compete with the central leader. This detracts from the ability of the tree to fully develop. There is also the longer term risk of the larger branches becoming too heavy for the tree to sustain. As a purist, I seek a pruning solution. However, for those with limited resources, I appreciate that this action is less of a priority and guide the focus accordingly.

Whilst the data collected is not complex in itself, the process of collating it can easily become  complicated. I recently surveyed trees for a housing association whose sites covered much of the West Midlands region. I inspected some 1000 trees across 80 different sites. To make it easier to identify the sites with trees requiring more urgent attention, I provided mini reports for each site with colour coding to highlight where priority work was located.

For the planning scenario, the client is often required by the local planning authority to provide details of the trees on the proposed development and how they contribute to the setting. The key data relates to the size of each tree (the trunk diameter is used to calculate the space that should be allocated to the tree whilst crown spread indicates the physical space presently occupied), how important its’ retention is to the site in terms of aesthetics and future life span. The data that needs to be collected is more detailed than is the vase for the basic condition assessment, although that information is still included.

These surveys are defined by BS5837:2012 and the reports generated tend to be subject to more scrutiny that the basic condition assessments, as they accompany planning applications which are being considered by the local planning authority. Recommendations and priorities are still required. However, seeking to allocate a retention category for a tree is a subjective judgement and I am always conscious that I could be called to explain my recommendations. The general principle is that the more important trees should be retained within a site. The reality is that often this is not possible as other priorities determine the outcome. Regardless of whether a tree is being retained or not, the retention category to which it is allocated should be the same.

I once surveyed a site for a local authority where the terrain consisted of reclaimed land which was now public amenity space. It contained landscaping and
tree planting which dated from the 1970s. The surrounding area was residential. I had been provided with a proposed layout which did not allow for any trees to be retained, even though some of them were, in my opinion, of high quality and worth retaining. It became apparent later on that the main reason for my report was to provide the local authority with a detailed audit of the tree cover to enable appropriate mitigation planting as the site was to be cleared and completely
redeveloped. I am actually relieved that I didn’t know this when I was surveying the trees and making recommendations for the retention of the better specimens.

It does concern me that some of the data I am instructed to collect is little more than a box-ticking exercise. For every site with a population of high quality trees whose retention is highly desirable, there is a site where one is identifying little more than scrub and self-set trees of very limited merit. I sympathise with clients who are required to provide a report, by a suitably qualified consultant, on trees on site, where it is clearly evident that there is practically nothing to report. How often has a self-set Sycamore or Goat Willow in the corner of a derelict plot resulted in the planners insisting on a tree report? For one client, the planners stipulated a Landscape Appraisal before approving plans to regenerate an abandoned site covered in debris and scrubs.

The planning process can be costly, as applicants provide a list of reports considering site constraints, highways issues, bats and other ecological issues, along with design statements. As the costs of commissioning various specialists rise, the applicant is often faced with a rapidly shrinking budget, and seeks to limit further costs. This can result in less of a focus on what they actually want themselves. I recently surveyed trees for one aspiring developer seeking to regenerate a small piece of waste ground. I asked whether a landscape scheme had been commissioned. This had not been considered, as it was not on the listed of stipulated documents. Was it really necessary, given the costs already encountered? Is it not time, I suggested, for the applicant to decide what they wanted? Did they want to look at the existing surroundings, or would they prefer some colour? What trees and shrubs could enhance the setting? It is interesting, when someone has become accustomed to working within a framework of constraints, to grasp that they may be able to choose the landscape.

As I mentioned earlier, the data parameters for planning reports are established by the British Standard. However, for safety and other assessments, the data being collected can be set by the client, especially if they have specific requirements. Often the client seeks guidance requiring the data that should be collected, and I have frequently been asked to design the template for their approval. Relevant data collection is important to provide an informed survey. However, if one is being required to collect additional data, this can affect costs and represent inefficient use of resources.

I was invited to tender for a survey of trees on a housing estate for the estate manager. The purpose was to inform safety management of the trees. However, I was asked to identify the species of each tree down to the cultivar. With some trees such as Maples and Cherries, this can be very difficult and a task which only the specialist who deals solely with Maples or Cherries can complete with confidence. I was also required to measure tree canopy spread to the nearest metre, with a 10% margin of error. This is a level of detail rarely required with a planning report which is considering the amount of space an individual tree may need in order to be successfully retained. Requiring it for a safety assessment would not, in my opinion, enhance the management of the stock but would increase surveying time, and therefore, costs.

When I am surveying trees, the surveying process takes a certain amount of time and data being collected needs to be relevant to the situation, with discretion regarding when to add extra information in the field (such as the proximity of a particular tree to a footpath where roots may be a future problem, or branches growing over a roof, with leaf fall blocking guttering, both of which may need specific management solutions. Timing of inspections is key for me to establish the condition of the trees. It is harder to assess vigour when a deciduous tree is dormant. I have been instructed to survey trees in the middle of winter, and the
results are inevitably limited.

One headline statistic that is often favoured relates to tree planting. Organisations love to quote the numbers of trees they are planting. They make for great photo opportunities and public relations material. We have the London Mayor’s office aiming to plant 10,000 trees within London during the current mayoral term, and during the winter of 2014-2015, the Tree Council set the target of planting one million trees. It is great to see trees and establishing the next generation receiving publicity and political support. However, without careful management, many trees struggle to become established. Indeed, the last audit, back in 2006 (published in the paper ‘Trees in Towns ll’, found that as many as 25% of the young trees being planted by highways authorities were dying within two years.

I have been exploring this because I am involved in two projects where the aim is to improve both the survival rates and the vigour of younger trees, two elements which are integral to enhancing the urban forest. A problem with planting trees solely to meet a target is that there may be insufficient time and
thought given to selection of the location, the species and future contribution. If there is insufficient space for a tree then planting one to tick the relevant box will achieve little. Similarly, selecting small ornamental trees such as Cherry and Apple which tend to be shorter-lived and reach maturity when only several metres in height can result in their being overwhelmed by surroundings.

Trees need space to fully develop, and it is disheartening to see a group planted so closely that they will limit the future growth of each other.Similarly, planting without reference to surrounding features such as overhead power lines which need to be maintained free of vegetation can result in lost opportunities to establish the specimen trees of the future.

Incidentally, the two projects I am connected with involve training in the various skills of establishing young trees and separately providing a platform whereby the management of the young trees can be monitored for effectively and adjusted as required. Issues such as watering can affect the establishment of young trees, and over-watering is as detrimental as insufficient application. The operator records their action during irrigation and records the condition of each tree. This needing further attention can then be identified for further action.

These two projects may be considered pioneering. However, another one, whilst being new application is definitely using established technology. Chlorophyll fluorescence is present in the foliage of all plants, whether trees or not. In a healthy plant, the fluorescence is able to absorb more light than is the case for a plant in decline. Stress from excess or insufficient water, compacted ground or damage from the application of a herbicide can all be identified from the fluorescence which responds more quickly than is evident from the external appearance of the plant. With this data being collated and interpreted, one can gain a more complete understanding of the condition and health of the plant concerned.

Whilst the collection and correct interpretation of relevant data helps to enhance efficient management, there can be costs in cutting corners. This is particularly the case when dealing with tree-related subsidence claims. Trees can cause damage to property both directly and indirectly, and in such situations, appropriate management should be explored. This can involve felling trees growing close to walls and installing root barriers to restrict rooting activity.

However, I have encountered numerous instances where trees are pruned or felled based on limited or inconclusive evidence. Why does this matter? There is a tendency to attribute blame to trees in the first instance. Where the tree isn’t culpable, or is only a contributing factor, the removal can be regarded as the solution and further investigative work delayed. In addition, with felling of the tree being blamed, an amenity feature is lost.

In one case, a tree was cited as causing the wooden floor in a village hall to lift, with invasive roots being blamed. It was only after the nearest tree had been
removed and the problem continued that the floor was lifted and a leaking water pipe found to be the cause. It is interesting, and shocking, the pressure which can be applied by the insurers and other professionals to action their recommendations for tree removals regardless of the evidence. One case I explored when in local government involved a Silver Birch tree cited as being responsible for causing a porch extension to come apart from the main house. Roots in the vicinity identified as being from a Birch was the basis of the claim. I arranged for the tree in question to be made subject to a Tree Preservation Order, and it was only when dealing with the subsequent appeal for refusal of consent (subsequently dismissed) that the subsidence specialists acknowledged that the extension was of
poor quality and not built on foundations and therefore affected by settlement. It had been a long journey, and one in which felling of the Birch would not have resolved the problem.

When damage does occur to a building, the Building Research Establishment (BRE) provides guidelines for appropriate action based on the severity of damage. I have encountered claims to fell based on two months of a twelve month investigation, threats to pursue recovery of costs if the alleged offending tree was not felled and pleas for action when the evidence presented was minimal. In one such case, the insurers offered to pay for felling a tree they had cited, before
exploring installing a root barrier. When the BRE guidelines recommend no action for movement of up to 20mm and one is presented with evidence of movement of 2mm, it is unclear to me how else I am supposed to respond as a professional.

In true CSI fashion, I seek to follow the evidence. Again from the annuls of local government and the world of Tree Preservation Orders, a request was received to fell a tree due to invasive roots blocking a drain. There was evidence of the invasive roots, but with a dozen trees of several species in the vicinity, it was unclear which one was the guilty party. Once this was established, we would have a basis to proceed. A specific tree had been identified in the applicant’s garden. Having agreed a course of action, the applicant let slip that they would appreciate this particular tree being removed due to the shade and leaf fall nuisance it caused; an ulterior motive!

In this case, the guilty party was found to be a neighbouring tree, for which consent to fell duly followed, a course of action which perhaps left the original applicant somewhat disappointed to still have their tree. However, this reinforced the need to establish the evidence. For me, data is not just figures but physical evidence and carefully assessing it can help to guide clients considering pursuing legal action. I have been asked to advise on whether a dead tree died from natural causes or the result of action by a third party such as a neighbour.

For those seeking to prepare a case, the information that cause of death was natural may disappoint, but it avoids embarrassment later on. One tree I looked
at for such evidence had girdled roots which had snapped in a winter storm! In that case, the guilty party was actually the nursery which had grown the tree and not re-potted it in time, and then sold it rather than scrapping poor stock!

I began this article by looking at data collection with reference to planning applications. When I am asked to provide a survey to BS5837:2012, I begin by asking whether a topographical survey has been undertaken to plot the positions of trees on site. I appreciate that the process of preparing an application for submission can be costly, and the topographical survey may seem as just another expense. I can work without this information, but having it enhances the accuracy of my work and it can provide important data. When I survey trees, I include all with a trunk diameter of 75mm or greater. This is not only the recommendation of the British Standard, but when trees are within a Conservation Area, all trees of this size and greater are subject to protection.

With one site I surveyed, a topographical survey had been commissioned, but only of the significant trees. Having surveyed all of those subject to protection, I then found that I had more trees in my survey than we in the topographical survey. There were some challenges with merging the two sets of data. Architects tend to plot trees as small round circles. This is fine for smaller trees. However, for larger trees, it can give a misleading picture and may encourage layouts to be drawn up which can only be implemented with some tree removal.

Finally, as an author, I need to be sure that my findings and recommendations are clear and unambiguous, regardless of the situation. After all, I am unlikely to be supervising programme of tree work undertaken based on my recommendations made months or even years ago. It can be interesting reading the conclusions made by others and exploring the evidence they have used. I was once asked to guide a residents’ group concerned by proposals to fell many trees within a park as partof regeneration works, for which a consultant’s report had been produced. The residents wished to ensure that any representation they made was based on sound professional advice. Whilst a number of ornamental trees reaching the end of their natural lives had been recommended for removal, so too were a row of mature weeping Willows, on safety grounds which seemed to be rather vague. Furthermore, the organisation which had commissioned the report cited that its’ author was ‘an approved consultant’. There is no national register of approved consultants, with the only comparable list being the Registered Consultants of the Arboricultural Association. In that case, the Willows were successfully retained.

This brings me to the value in my work, when a tree is retained based on my recommendations regardless of the original proposal. It is satisfying to return to a site months or even years after providing advice and seeing trees retained based on comments made previously. Whether I did the original survey or advised on recommendations made by others, it is so satisfying to see a tree standing because of my actions.

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