essentialARB visits a site in London where Arboraeration’s unique TRU Tree Radar is helping developers protect trees from harm. 

TO the rear of a residential housing block in Plaistow, East London, the canopies of three London plane street trees throw shade across four back-to-back units of single-storey garages. Separated by driveways, each unit is three garages deep and each has a tarmac or reinforced concrete base.

The owners, a local housing association, are looking to redevelop the site, but before any work begins they need to know where the London planes are rooting, so that any new foundations – in this case pilings – if installed, cause minimal disturbance to them.

To facilitate an accurate but non-invasive Root Protection Area (RPA) investigation, the housing association has employed the expertise Arboraeration. Invited to the site to see a new piece of kit at work, essentialARB finds James Abbott inside the shell of one garage, pushing a three-wheeled cart frame slowly across a pitted concrete floor.

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At first glance, the cart looks similar to a child’s all-terrain pushchair. The frame supports a square white tub suspended just above ground level. Curls of wires feed up through the frame into a grey unit supported at handlebar height. The white tub contains a TRU Tree Radar 900 antenna, suspended just above the ground to reduce interference from any objects on the surface. The wires connect the antenna to a receiver unit, which in turn is connected to a tablet.

The TRU Tree Radar works like this: the antenna scans through almost any surface by sending out a series of short pulses, electromagnetic waves or ‘decibels’, which are then reflected back to the receiver by any object in its path down to a depth of 1.5 m. The receiver feeds this data to the tablet and in Scan Mode the tablet shows the radar’s base parameters as a series of thick, wavy grey layers. When flipped into Graph Mode these layers form either a series of roughly equal triangular peaks and troughs or a flat line along a fixed central line.

James is moving slowly to fine-tune the decibel depth, or ‘return’ data (anything reflected back), so that the flat line begins to resemble a series of peaks and troughs. 

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“If the line is flat,” he says, “we reduce the depth the radar is scanning to. The deeper the scan, the less definition on the return. It is a balancing act.”

This pre-scan calibration is performed at all sites whatever the surface. Concrete, tarmac, metal, or clay, sandy and loamy (or other) soils, even moisture content, all impact the readings the radar makes.

In Plaistow, the client has supplied CAD drawings of the proposed redevelopment. Arboraeration has divided the site into a linear grid and James will walk the radar back and forth along the grid lines, intercepting (at 90 degrees) any tree roots larger than 15mm in diameter.

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A resident asks James what he is doing. James explains that he is here to scan the roots of the street trees. “Are they going to cut them down?” asks the resident.

“I am 99.99% sure they won’t be cutting the trees. If they were doing that, there would be no point in me being here.”

The resident wants to feel heard and James encourages them to explain why they think the trees and garage units should remain: air quality, letting natural light in to west-facing apartment windows and (mostly) secure storage space. Satisfied, the resident moves on and James says that this often happens.

“I tend not to be told much about the projects we work on, so that when this does happen I can plead ignorance and not get involved.”

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For any new development or redevelopment in pre-planning phase, the British Standard BS 5837:2012: Trees in Relation to Design, Demolition and Construction states that steps must be taken to ensure that any trees within the proposed development zone are protected. The Standard calculates a tree’s Root Protection Area (RPA) as a circle whose radius is 12 times the stem’s diameter, 1.5 m above ground level, to a depth (subsurface) of 60 cm. This is the same for all trees, regardless of age.

“The majority of tree roots are within a metre of the surface, especially smaller roots that are further away from the stem. These [London plane] canopies spread about five metres out from the trunk, but roots could easily spread up to twelve to fifteen metres for a significant sizeable tree.”

During the course of the morning, James will scan up to twelve metres from the London plane trunks, more if the ground is accessible. “While the scans are on the tablet, it is hard to get a good impression of the data. The small triangular peaks should indicate tree roots. Any anomalies, such as cabling or pipes below the concrete are filtered out during the data processing and filters are applied using tree maps to make sure the information fits with their position.”

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Once a survey is completed, James sends the scan data back to the office, where his brother David Abbott will analyse and collate it into a Tree Root Survey Report (with maps) to send back to the client.

One day’s worth of scanning can mean up to three days of report writing. Speaking from Arboraeration’s office in Redhill, David says: “It is office-intensive and slightly more onerous than air-spade reports. But both are useful tools in their own right.”
Since taking delivery of the TRU unit in January, it has been employed in RPA investigations at least once a week, sometimes more. 

“This is way more than we thought we would use it during the first year.”

Even so, the majority of Arboraeration’s investigations are still undertaken using an MBW soil pick (air-spade) and digging trial pits, as they were when essentialARB last met them in 2016. Back then, on the recommendation of an arboricultural consultant client, David and James were on day two of investigations into the RPAs of five trees that could be affected by the lines of new foundations it was hoped would be built during the redevelopment of a residential property in Maida Vale.

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While thorough, air-spade investigations can be both invasive and time-consuming. The continued volume of bookings could be because tree officers are still wary of the radar’s results.  “An earlier form of the system was brought into the UK to trial about 10 years ago,” David explains. “It didn’t do very well. The results plotted from the software didn’t show what people wanted it to show and people were unwilling to trial it again. The equipment and software has come a long way since then. When it first arrived we did many experiments, plotting grids and scanning an area and then excavating at marked locations. As long as it is calibrated for every new site and you spend the time analysing the data, the results are accurate.”

David first became aware of tree radar systems at Plumpton College, when studying for his Forestry and Woodland Management Foundation Degree.

“One course module on Urban Forestry covered RPAs. I never really looked into [the tree radar]. It wasn’t popular in the UK, there was little information on it and we were doing well with the projects and equipment we had.”

During the second half of 2019, Arboraeration had an increase in enquiries from developers keen to employ their services on large-scale projects, particularly investigating roots under car parks, pavements and alongside highways. “Digging up [street infrastructure] involves a lot of paperwork and expense, and then there are costs associated with reinstatement. For some of these projects, [working with the MBW soil pick] we would have been onsite for seven to ten days [at a time], a long time for anyone anywhere to be digging trial-pit holes.”

Forestry Journal:  David Abbott runs the operation from the firm’s offices. David Abbott runs the operation from the firm’s offices.

Looking into alternatives, David discovered that the TRU Tree Radar system had been used across the USA and Europe for around 15 years, the units owned mostly by universities for use in research projects. He spoke with TRU’s designer-manufacturer in Washington DC and placed Arboraeration’s order at the end of February 2020.

It was, he acknowledges, “a terrible time to spend a lot of money. It took almost a year to get the machine. Following the slowdown in manufacturing, Tree Radar could not get parts. Shipping was a nightmare, again because everything had slowed right down”. 

It was also not the best time for David, stranded in Canada for an extra six months as a result of travel restrictions imposed by the pandemic. One upside was that he received in-person training with TRU’s patented software at a centre in Vancouver. James learnt how to use the unit online and was trained by David once the unit finally arrived in the UK.

Prior to the pandemic, Arboraeration’s business grew steadily year-on-year as they added more services to complement their RPA investigations. First came DNA testing, useful when investigating the roots of multiple species or when trying to determine which tree may be causing damage to property. Then came ‘complete tree root health care’, where (following construction works) clients book a package of either shallow or deep decompaction to loosen and expand the soil, complemented with an application of biochar mulch or compost tea injections. While roots may not look damaged, compaction has still taken place, and compost tea injections are a good alternative for clients not wanting to add a layer of biochar mulch on top of a landscaped lawn.

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Arboraeration’s quietest year since launching in 2013 was 2020. Where work was booked, James spoke with customers and ran the onsite operations for air-spade surveys and digging trial pits. 

“I ran the day-to-day business side of things, quoting, invoicing and emailing responses to the enquiries. In some ways it worked well, I got up early and [from the data] wrote reports, plotting the roots along the scan lines and marking them up on plans and sending them off to clients.”

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Since January, Arboraeration has been advising clients that air-spade investigations work well across smaller, less complex sites and that TRU Tree Radar scans offer better value over larger sites. From working mainly in central London, James now works across England. Clients are also hoping he will take the radar to Northern Ireland and Switzerland.

Most enquiries still come directly through five or six arboricultural consultants, but architects and developers are getting in on the act, especially when planning departments want a developer to prove (or disprove) the presence of roots in certain locations. 

“Local authorities are being stricter on the implementation of legislation. Five years ago, a developer might have considered trees a hindrance. Now they ensure they are not damaged when retained on-site.”

From each new project carried out using the TRU Tree Radar, James learns something new. The hope is that in a year or two Arboraeration can invest in a second unit, the TRU

Tree Radar 400, capable of scanning between one to three metres in depth. This will be especially useful in urban areas where tree roots can do “weird things as a result of disturbances in the first metre of soil from utilities and drainage,” says James. “There are a couple of these units in the UK, but we don’t know of anyone who has both.”

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