BS 5837:2012 Tree categorisation method and Tree Quality Assessment

As part of your bs5837 tree survey, trees should be categorised using the U,A,B,C categorisation types below.

The British Standard states that trees must be categorised in a way that should assist those within local government authorities to help form a well-balanced/unbiased judgement.

Category and definition Criteria (including subcategories where appropriate)

Tree Categorisation – Category U

  1. Trees unsuitable for retention.
  2. Those in such a condition that they cannot realistically be retained as living trees in the context of the current land use for longer than 10 years
  3. Trees that have a serious, irremediable, structural defect, such that their early loss is expected due to collapse, including those that will become unviable after removal of other category U trees (e.g. where, for whatever reason, the loss of companion shelter cannot be mitigated by pruning)
  4. Trees that are dead or are showing signs of a significant, immediate, and irreversible overall decline
  5. Trees infected with pathogens of significance to the health and/or safety of other trees nearby or very low-quality trees suppressing adjacent trees of better quality.NOTE Category U trees can have existing or potential conservation value which it might be desirable to preserve.

Tree Categorisation – Category A

  1. Trees of high quality with an estimated remaining life expectancy of at least 40 years. Mainly arboricultural qualities- Trees that are particularly good examples of their species, especially if rare or unusual; or those that are essential components of groups or formal or semi-formal arboricultural features (e.g. the dominant and/or principal trees within an avenue)
  2. Mainly landscape qualities- Trees, groups or woodlands of particular visual importance as arboricultural and/or landscape features
  3. Mainly cultural values, including conservation- Trees, groups or woodlands of significant conservation, historical, commemorative or other value (e.g. veteran trees or wood-pasture)

Tree Categorisation – Category B

  1. Trees of moderate quality with an estimated remaining life expectancy of at least 20 years.  1 Mainly arboricultural qualities- Trees that might be included in category A, but are downgraded because of impaired condition (e.g. presence of significant though remediable defects, including unsympathetic past management and storm damage), such that they are unlikely to be suitable for retention for beyond 40 years; or trees lacking a special quality necessary to merit the category A designation.
  2. Mainly landscape qualities- Trees present in numbers, usually growing as groups or woodlands, such that they attract a higher collective rating than they might as individuals; or trees occurring as collectives but situated so as to make little visual contribution to the wider locality
  3. Mainly cultural values, including conservation- Trees with material conservation or other cultural value See Table 2

Tree Categorisation – Category C

Trees of low quality with an estimated remaining life expectancy of at least 10 years, or young trees with a stem diameter below 150 mm.

  1. Mainly arboricultural qualities- Unremarkable trees of very limited merit or such impaired condition that they do not qualify in higher categories
  2. Mainly landscape qualities- Trees present in groups or woodlands, but without this conferring on them significantly greater collective landscape value; and/or trees offering low or only temporary/transient landscape benefits.
  3. Mainly cultural values, including conservation- Trees with no material conservation or other cultural value. See Table 2.

Important to note: BS Standard demands meticulous care and attention is required when evaluating young trees, especially where they occur as individual specimens.

Where there are less than 150 mm stem diameter at 1.5 m above adjacent ground level, it might be acceptable and relatively straightforward to mitigate their loss, if necessary, with a similar new tree planting.

Alternatively, it might be practicable to relocate such trees within the site (e.g. using a tree spade). Whilst the presence of young trees of good form and vitality is generally desirable (i.e. those trees which have the potential to develop into quality mature specimens), they need not necessarily be a significant constraint on the site’s potential.

Where remaining contributory years’ score is provided within the ‘Findings’, and where further investigative works are required, these scores are preliminary only and based on an incomplete inspection.