Disclaimer: The views and opinions expressed in this article are those of the author and do not necessarily reflect the views of the Arboricultural Association.

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Arbs at the sharp end of environmentalism

Author:  Brynley Andrews
Last Updated:  07/06/2019
Figure 1: Sheffield City tree removal programme

Figure 1. The Sheffield city tree removal programme means the loss of carbon sequestration assets and a negative contribution to the main environmental fight. Conserving big trees in built-up areas isn’t easy. However, it is possible and with an environmental profit if the methodology of management is low carbon. (Source: Wikicommons: accessed 29.3.19)

Arboriculture in the UK is underplaying its environmental role and missing the opportunity to help maximise the provision of ecosystem services in urban areas.

Maybe this is because arboriculturists (arbs) have not yet shrugged off the mindset that they are a hybrid discipline of silviculture and amenity horticulture, and have not fully embraced being environmentalists. Arbs should readjust their perspective to reflect their position at the sharp end of tactical urban ecosystem services provision. Correspondingly, arbs should be mostly concerned about the major, serious environmental issues, climate change and air-pollution, and the best way to act on this is by advocating and using tree canopy cover (TCC) as a method of analysing sustainable development in every area and on every project.

Tree canopy cover targets

General public awareness of the importance of the urban forest is growing: social media groups of tree enthusiasts espouse the value of ecosystem services and rage at developers and local authority planners for allowing our greenspaces and streets to be ruined by tree removals. Highly respected figures such as Sir David Attenborough warn of a catastrophic collapse of civilisation; and the consensus of scientific opinion, i.e. the United Nations Intergovernmental Panel on Climate Change (IPCC), tells us that there is no documented historic precedent for the action needed at this moment, and we have just 12 years to make massive and unprecedented changes.

The position of arbs within communities and society offers us a unique opportunity to improve TCC on a daily basis without any need for discussion with other players who might slow us down. If we arbs don’t set TCC targets, who will? No one else has our unique conservation mindset and is in the same position to make such a big difference. Factoring in the local TCC targets and the need for low carbon management to every scenario we encounter should be a knee-jerk reaction. It is a basic truism to state that if we are not part of the solution, then we are part of the problem.

Setting clear TCC objectives for every area and project is our method of contributing the most we can to a sustainable environment. Every community, be it district, county, city, town or parish, and project must step-up to the mark and set TCC targets. The Forest Research study by Dr Kieron Doick (Doick et al. 2017) of about 300 UK towns and cities provides a solid start for assessment and target setting for the rest of the c.43,000 cities, towns and village-parishes in the UK (Towns UK, 2019).

Arbs already play the major role in enabling increased TCC. However, the past mindset may be holding us back from truly engaging with the need to maximise ecosystem services performance, for the betterment of all life on Earth. We can do this using i-Tree software (thanks to the sponsors and geniuses behind it) and studies in the UK such as those by Dr Doick, backed up with on-the-ground surveyassessment data and computer-aided-design software for individual sites; and then we can set targets everyone can understand.

Sustainable development

Sustainable development (SD) of urban areas is our field of operation; true SD must include measurement and management of TCC. Using TCC as an indicator of the efficacy of SD policies is entirely fitting because the very concept of SD is derived from Scandinavian forestry practice (Grober, 2007). However, currently TCC as a measurement metric of sustainable development has lost out to grey infrastructure initiatives and this needs to be put right, by applying the original conceptual basis for SD.

Our objectives should be to increase our TCC in both urban and rural settings to at least 20% in inland urban areas and 15% for coastal areas (Doick et al., 2016). There are those who are well ahead on this; the Mayor of London and the London Plan propose targets for increasing TCC by 5% before 2025 and a further 5% by 2050 from the current 22% (LTOA, 2019). Using the Doick et al. study and/or locally derived data, we have the basis to enable a solid common-sense metric for measurement of the efficacy of sustainable development policies that the public can see happening on Google Earth and planners or architects can factor into their designs.

The natural role of an arb-professional is to champion trees. It used to be all about ‘visual amenity’ and habitat value, with other rather esoteric biophilic psychological attachments. It is now much more: the whole ecosystem services issue has brought every tree value together into one big powerful term. And science tells us that mitigating carbon and pollution emissions are the biggest environmental challenges facing life on Earth.

Figure 2: The City of London Urban Forest Strategy

Figure 2. The City of London Urban Forest Strategy leads the way in the UK. The mission statement summary says it all: ‘Plant more, protect more, maintain better’. However, ‘fossil fuels’ and ‘low carbon’ don’t get a mention – a flaw in an otherwise great strategy. (Source: City of London Urban Forest Strategy: www.london.ca/residents/Environment/Trees-Forests/Documents/London%20Urban%20Forestry%20Strategy%20Final.pdf. Accessed 30.3.19)

Being part of the solution

Climate change and pollution are the enemies and our best weapon against them is judiciously increasing TCC. Being part of the solution means helping decisionmakers. When I suggested to my own local authority that action to improve TCC was required, I provided the following recommendations, specific to South Somerset.

Set a strategic objective for 30% urban and 10%+ rural canopy cover. Achieve the objective by doing the following:

  • use canopy cover as a sustainability metric;
  • apply the highest-quality conservation measures to existing trees and woodland;
  • identify vulnerable trees and woodland and create protocols for their conservation;
  • transfer resources from environmentally negative activities, such as grass cutting, to positive action like tree planting;
  • require 30% mature-tree canopy cover on new developments;
  • require retention of grade A and B (BS5837, 2012) quality trees on development sites, or require canopy-cover equivalent compensatory planting for any essential loss; and
  • encourage urban and rural landowners to judiciously plant trees.

Many of the recommendations I gave are already in place, but not necessarily always applied. An extra advantage of making the role of TCC more widely appreciated is that the tree officer’s role gains in importance; the advantage to consultants is that making these issues official (or even unofficial) policy sets clear benchmarks to apply; and contractors get to do tasks they know are environmentally beneficial and can invest in low-carbon machinery and vehicles knowing they give competitive advantages.

The economic costs of carbon and pollutant emissions are of the highest order – £trillions globally. Any solutions will be cost-effective if carbon and pollution inputs are factored in, by which I mean that the fossil fuel used by internal combustion engines (ICE) is part of the problem and needs to be balanced against the benefits. For example, a tree team that uses fossil fuels – and of course they all still do – is possibly causing more carbon/pollution harm than the benefits produced by the trees they work on. The science behind this statement is that when carbon atoms emitted by ICE combine with atmospheric oxygen, the combined atomic weight increases greatly: for every 1kg of fossil fuel we use we put about 2kg of carbon, plus pollutants, into the atmosphere (Energy & Carbon Conversions, 2008). On this basis, arguably doing nothing but essential tree work, which includes planting, is the best tree management policy, until ICE is replaced by electric power.

This puts greater emphasis on the need for trees to be low maintenance, at least until ICE power is replaced by renewably generated electrical power. Then theoretically there would be no negative input however much energy is used for tree works. Total electrical battery power for our activities is probably at least a decade away; in the meantime minimising fossil fuel use is all we can do.

Table 1: Pollutants and their effects on health.

Resultant health issues
Carbon monoxide (CO)

Causes the blood to be unable to carry oxygen and this lack of oxygen causes the body’s cells and tissue to fail and die.

Nitrogen dioxide (NO2)

Diaphoresis, chest pain and persistent dry cough, all of which may result in weight loss and may also lead to right-side heart enlargement and heart disease in advanced cases. Prolonged exposure to relatively low levels of nitrogen oxide may cause persistent headaches and nausea.

Ozone (O3)

Ground-level ozone can harm lung function and irritate the respiratory system. Is linked to premature death, asthma, bronchitis, heart attack, and other cardiopulmonary problems.

Particulate matter less than 2.5 microns (PM2.5)

Can cause short-term health effects such as eye, nose, throat and lung irritation. Can also affect lung function and worsen medical conditions such as asthma and heart disease. Possible increased respiratory and cardiovascular hospital admissions, emergency department visits and deaths.

Long-term exposure may cause increased rates of chronic bronchitis, reduced lung function and increased mortality from lung cancer and heart disease.

People with breathing and heart problems, children and the elderly may be particularly sensitive to PM2.5.

Sulphur dioxide (SO2)

Breathing in sulphur dioxide causes irritation to the nose and throat. Possible effects on reproductive and developmental issues. Children may be more sensitive to the effects of sulphur dioxide due to their smaller size.

Particulate matter greater than 2.5 microns and less than 10 microns (PM10)

As PM2.5

Table 2. Potential effects of climate change on public health in the 21st century.

Climate issue
UV radiation

Incidences of skin cancer and other diseases are likely to rise due to climate change. The young, elderly and outdoor workers are most vulnerable.

Changing temperatures

Higher-temperatures-related mortality is projected to increase steeply in the UK throughout the 21st century, from around a 70% increase in the 2020s to around a 540% increase in the 2080s.

Ozone pollution

Ozone is a respiratory irritant strongly affected by the climate.


Existing allergy sufferers may suffer from longer pollen seasons and more rapid symptom development.


Less disruption because less snow predicted.

Cloud cover

Reduced cloud cover could lead to increased health risks associated with UV including some skin cancers.

Wind speed and more storm events

Hazards and disruption of services because predications indicate the UK can expect stronger winds and more storm events.

Indoor environment

May exacerbate health risks associated with building overheating, indoor air pollution, flood damage and water and biological contamination of buildings.

Floods and droughts

More frequent floods and droughts would bring general disruption and associated hazards. Also, impacts on mental health and impacts from disruption to critical supplies of utilities such as electricity and water.

Increased risk from water- and food-borne diseases through changes in human behaviour associated, for example, with food hygiene.

Vector-borne diseases

It is likely that the range, activity and vector potential of many ticks and mosquitoes will increase across the UK by the 2080s. There is also the potential for introduction of exotic species and pathogens.


May lead to reductions in the availability of certain food groups, and reductions in the nutritional quality of dietary intake in some population groups. Increased temperature will allow pathogens such as Salmonella to grow more readily in food.

The human cost

To put the humanitarian toll of air-pollution and climate change into perspective, Tables 1 and 2 summarise the damage they cause to people’s health.


Arb professionals play one of the most important roles in combatting the most serious threats to humankind and all life on Earth as we know it. Those at the sharp end of urban forestry have a responsibility to be part of the solutions. Tree officers must set TCC targets and promote them as a lead metric for the sustainable development of their areas. Consultants and contractors must emphasise to their clients the need for TCC and set coverage targets for every project, and we must all minimise the use of fossil fuels. Otherwise we may find ourselves living a dystopian existence. Even if the worst-case scenario doesn’t pan-out, environmental improvement is still a worthy cause.


Doick, K., Davies, H., Moss, J.L., Coventry, R., Handley, P., Vaz Monteiro, M., Rogers, K., and Simpkin, P. (2017). The Canopy Cover of England’s Towns and Cities: baselining and setting targets to improve human health and well-being. www.researchgate.net/publication/322337570_The_Canopy_Cover_of_England’s_Towns_and_Cities_baselining_and_setting_targets_to_improve_human_health_and_well-being

Energy and Carbon Conversions (2008). www.knowlton.org.uk/wp-content/files/Energy%20carbon%20conversions.pdf

Grober, U. (2007). ‘Deep roots – A conceptual history of “sustainable development” (Nachhaltigkeit),’ Wissenschaftszentrum Berlin für Sozialforschung. www.researchgate.net/publication/254461192_Deep_roots_A_conceptual_history_of_’sustainable_development’_Nachhaltigkeit

LTOA (2019). Web page accessed 29.3.19. www.ltoa.org.uk/news/159-calculate-londons-tree-cover

Towns UK (2019). Online list accessed 31.3.19. www.townscountiespostcodes.co.uk/towns-in-uk/

Brynley Andrews
Brynley Andrews MSc,CEnv, MArborA

Brynley is an independent arboricultural and green infrastructure consultant based in Somerset who is a passionate but realistic environmentalist.

This article was taken form Issue 185 Summer 2019 of the ARB Magazine, which is available to view free to members by simply logging in to the wesbite and viewing your profile area.