Pegasus Group considers the mechanics and value of arboricultural assessments
Section 197 of the Town and Country Planning Act 1990 gives local authorities a duty to ensure that when they grant planning permission for developments, adequate provision is made for the tree preservation or planting through preservation orders or planning conditions.
The environmental impact assessment (EIA) process evaluates the potential biophysical, social and other effects of a development to avoid, mitigate or offset significant adverse effects. Its function is to identify problems, recommend solutions and promote and maximise proposals’ positive effects.
Arboricultural inputs play an increasingly important role in informing the design process and demonstrating the interrelationship between trees and development has been fully considered and is sustainable. An arboricultural impact assessment (AIA) is an important tool in the process.
Trees are important assets in rural and urban landscapes. Their benefits are:
- social: trees line our streets forming prominent features in parks and gardens that create aesthetically pleasing and peaceful environments. Trees are landscape features and strengthen landscape character and sense of place. Research has found positive links between trees and human wellbeing, with corresponding reductions in the rates of non-communicable diseases such as cancer.
- Economic: they provide fuel, timber and food.
- Ecological and environmental: they contribute to regulating air quality, provide food, and habitat. They support a wide range wildlife and are important in supporting biodiversity and ecological networks.
Trees also have perceived negative qualities, including:
- damage to buildings and structures from root and canopy encroachment
- inconvenience of leaf litter and honey dew
- overshading and overbearing effects
- unwanted wildlife such as loafing birds and insects
- risk of harm to people and property.
An AIA can help ensure the benefits of trees and hedgerows are retained and maximised while the perceived negative aspects are avoided or minimised.
BS5837: 2012 - Trees in Relation to Design, Demolition and Construction – Recommendations, is the nationally recognised standard that sets out best practice for taking into account and retaining suitable trees in proximity to development.
What is an AIA?
An AIA is undertaken to establish how the design of proposals will impact trees and how trees will impact the development and follows the BS5837 2012 framework. An initial tree survey provides a detailed baseline of tree related constraints.
An AIA should follow an iterative process which identifies impacts at an early stage and feeds them into the design process to adjust proposals accordingly.
The AIA evaluates the direct and indirect effects of proposals on trees and recommend mitigation where the design cannot be adjusted.
The assessment should take into account the effects of any tree loss required to implement the design and any potentially damaging activities proposed in the vicinity of retained trees. Key considerations for an AIA include:
- root protection
- changes in soil levels
- installation and layout of underground and over ground services
- demolition of existing buildings and surfaces
- sunlight and shading of buildings and open spaces
- construction site access, layout and materials storage (buildability)
- post development pressures for felling
- direct and indirect damage;
- possible replacement planting, including species selection.
BS.5837: 2012 recommends an AIA should include:
- a tree survey plan and schedule of data
- a plan showing trees identified for retention, loss or pruning works
- an evaluation of potential impacts on each tree
- an evaluation of tree constraints and a draft tree protection plan
- issues to be addressed in an arboricultural method statement.
Value of an AIA
Many development sites have trees and hedgerows which provide ecological and landscape benefits. Local and national policy encourage new development to protect and conserve site features, where possible, and typically ecology and landscape assessments in an EIA will identify important trees and hedgerows for retention. The AIA is key to ensuring important hedgerows and trees on site are retained, protected and incorporated in the development.
An AIA forms a useful tool in ensuring that development maximises trees’ benefit to society while minimising potential adverse effects through considered design. It uses information from the tree survey, and the initial designs for the development, to evaluate potential conflicts and issues at an early stage in the design process.
In summary, a successful AIA will help ensure new development:
- retains important trees and hedgerows, whether for landscape, heritage or ecological purposes
- protects retained trees and hedgerows during construction and minimises the potential for post development pressures to fell trees
- sensitively integrates trees
- has a harmonious relationship with retained trees
- complies with national and local policies
- contributes to sustainable development.
This article was written as a contribution to the EIA Quality Mark’s commitment to improving EIA practice.
