Description:
This method was developed in France to provide a rapid assessment of air pollution particularly nitrogen over a large geographical area using 14 easily recognisable macro-lichen species associated with well defined phytosociological communities selected from the van Haluwyn and Lerond scale (1988). Land use in each unit was used as a basis for assessing nitrogen levels.
The area to be surveyed is plotted using a grid .834 km 2. Trees (number not specified but in van Haluwyn et al it is c. 10) with a diameter >0.3 m are selected (preferably oak) in the centre of each plot as far as possible and selected lichen species recorded on the trunk between 0.8-2 m above ground. Lichen species presence is used to define 5 pollution zones ranked from zone 1 coinciding with zone D in van Haluwyn and Lerond with presence of Diploicia canescens and Xanthoria parietina at high frequency, to zone 5 corresponding to zone F in van Haluwyn and Lerond distinguished by presence of Flavoparmelia caperata, Melanelia glabratula and absence of nitrophilous species of Physcia, Xanthoria and Diploicia. Zones are mapped and land management and topography recorded. Zone 1 coincides with high pigsty density and maize production and zone 5 coincides with protected areas (Giraudeau et al., 1997)
Previous experience:
This method has been used in a number of oceanic sites in France with similar lichen communities and zones mapped across urban and rural areas. (Lallemont et al. 1999). The method was tested across a woodland in Scotland adjacent to a poultry farm. In this context a low resolution of the method was found, with all sites scoring either 2 or 3. The method is therefore quick, but of rather low sensitivity and resolution.
Suitability to indicate atmospheric concentrations:
The method responds to NH3 concentrations, but has a low sensitivity to indicate concentrations.
Suitability to indicate atmospheric depositions:
Not known. Results have mostly so far been tested against land use rather than against N deposition.
Suitability to indicate environmental impacts:
By definition the method records an impact of N, however, it is currently rather uncertain regarding its implementation in the UK (where different key species occur).
Sensitivity to other factors:
The method has not been tested against other climatic factors.
Timescale:
The method scores lichens on trunks and therefore reflects changes in pollution climate over the previous several decades.
Limitations:
Surveys with this method have so far focused on areas with oceanic vegetation where trees a component of the landscape. Only selected species used, so that the method cannot be used to assess changes in other species or in total diversity. Not useful to assess changes in sites of nature conservation interest.
Expertise in field:
Easy to train observers to identify selected species.
Expertise in laboratory:
No laboratory work required.
Cost (per unit sample): £unknown
Cost Comment: Preliminary identification of area and grid sampling units 2-3 days. Sampling of 10 trees per unit area for selected species - approx half a day.
Robustness: 
