How to avoid or reduce effects of a development on ancient woodland

Ancient Woodland Inventory

Read how ancient woodland is categorised or make an enquiry about a specific piece of woodland

Find all areas designated as ancient woodland in Wales on the Lle website

What to do if your development is likely to produce ammonia near an ancient woodland

Ancient woodlands are being detrimentally impacted as a result of increasing concentrations of ammonia in the air and levels of nitrogen deposition - one of the greatest threats to ancient woodlands in Wales.

New developments should not lead to further degradation of ancient woodland sites resulting from significant increases in atmospheric ammonia concentrations and total nitrogen deposition. In recent years, we have seen an increase in planning applications for ammonia-emitting developments, such as intensive livestock units, in close proximity to sensitive sites.

Ancient woodland falls within the definition of a sensitive site in NRW’s guidance. We have produced guidance on ammonia assessments that should be used by applicants and decision makers as a key material consideration.

This consideration should be in the context of determining whether an ancient woodland site may be affected by ammonia from a development i.e. screening for ammonia assessment and how to undertake the assessment.

The following points should be considered when using the ammonia assessment guidance for impacts on ancient woodland:

  • Designated sites (SAC/SSSI) have been assigned Ammonia Critical Levels (1 or 3 ug/m3) according to their features. Some of these SAC/SSSI sites are ancient woodland and some are not.
  • Ancient Semi-natural Woodlands (ASNW), the highest level of category of ancient woodland, are ecologically functioning to such an extent that all warrant protection from ammonia pollution. If Natural Resources Wales have recent evidence of N-sensitive Lichens or Bryophytes in an ASNW then that ASNW is mapped as requiring assessment with an appropriately protective 1µg/m3 Ammonia Critical Level; if Natural Resources Wales have no recent evidence of N-sensitive Lichens or Bryophytes then that ASNW is mapped as requiring assessment with the ‘vascular plant protection’ Critical Level of 3µg/m3.
  • Plantations on Ancient Woodland Sites (PAWS), Restored Ancient Woodland Sites (RAWS) and Ancient Woodlands of Unknown status may be ecologically functioning, but may have suffered such significant disturbance during past afforestation that they no longer function as natural ecosystems. It is considered these sites are not required to be assessed for Ammonia Critical Levels (1 or 3 µg/m3).
  • Parkland and Wood Pasture with recent evidence of N-sensitive Lichens are also mapped as requiring assessment with the protective 1µg/m3 Ammonia Critical Level.

How to avoid and mitigate effects from development on ancient woodland

Mitigation measures will depend on the development and the potential adverse effect and could include:

  • improving the condition of the woodland by sympathetic management e.g. removal of non-native coniferous trees to improve functioning of ancient woodland;
  • putting up screening barriers within the development itself to protect woodland or ancient and veteran trees from aerial emissions such as dust and pollution
  • noise or light reduction measures such as directional lighting and acoustic fencing to reduce the risk of disturbance to mammals and nesting birds;
  • protecting ancient woodland by designing open space around them i.e. no development within the crown spread of a tree to protect ancient woodland trees from damage to tree roots;
  • identifying and protecting trees that could become ancient and veteran trees in the future and protecting them via a tree preservation order;
  • rerouting footpaths to avoid damage to ancient woodland flora and disturbance to wildlife;
  • removing invasive species to protect the functioning of the ancient woodland ecosystem;
  • stand-off or protection zones to protect ancient woodland from aerial emissions and disturbance from new development.

More guidance on mitigation measures can be found in section 6 of the CIEEM Ecological Impact Assessment Guidelines

How development can affect ancient woodland

Development proposals may adversely affect ancient woodland and the wildlife they support due to direct damage, fragmentation, or by aerial emissions. This can lead to:

  • damaging or destroying all or part of ancient woodland (including its soils, ground flora or fungi)
  • changes to the composition of woodland ground flora
  • reduced tree health
  • wildlife poisoning
  • loss of soil micro-organisms, affecting nutrient cycling
  • damaging roots and understorey (all the vegetation under the taller trees)
  • damaging or compacting soil around the tree roots
  • polluting the ground around ancient woodland
  • changing the water table or drainage of woodland or individual trees
  • breaking up or destroying connections between woodlands and ancient or veteran trees
  • reducing the amount of semi-­natural habitats next to ancient woodland
  • a change to the landscape character of the area
  • loss of soil and above ground carbon

New development near to an ancient woodland increases the probability of invasion of woodland by non-native plants by:

  • altered environmental conditions
  • altered hydrological processes
  • increasing density of human population
  • increasing fragmentation
  • nutrient enrichment
  • proximity of residential gardens
  • soil disturbance
  • increased recreational use

Read our Advice to planning authorities considering proposals affecting ancient woodlands


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