Effects and implications

  • Loss of sensitive lichen species

Overview: evidence, processes and main impacts

Hedgerows can support N sensitive epiphytes. Species diversity is often restricted by the absence of a source of appropriate seed, caused by the use of highway management herbicides, and cutting restricting seed and berry production.

Hedgerows containing evergreens will be sensitive to ammonia, especially during the winter when low temperatures compromise assimilation leading to toxicity and exacerbation of winter desiccation.

Pollutant type and risk

Type of N depositionForm of NRisk areas

Dry deposition

Gaseous

NH3Hedgerows in rural areas with elevated background concentration.  Higher dry deposition is found close to point sources e.g. intensive livestock units.
 NOxHedgerows close to combustion plants, and major roads and urban areas.

Wet deposition

precipitation and occult

(cloud, mist)

Ammonium, (NH4+)

Nitrate, (NO3-)

in varying proportions

High, wet N  deposition areas,

Indicators of N enrichment

  • None available

Example evidence of species specific responses

  • None available
Critical Load/Level