Click on the ‘Results’ button. For each test (trunks and branches) the app will work out your lichen indicator score (LIS) and the NAQI score (Nitrogen Air Quality Index). The LIS is based on the difference between the presence of N-tolerant and N-sensitive lichens on three aspects of the trunk or on three zones of the branch.
The app will produce the LIS and the NAQI automatically.
Doing it manually - the range of lichen indicator scores (LIS) is given on the Y axis (from -3 to 3). Read across the graph until you meet the broken line drawn for branches or soild line for trunks. Drop down a line perpendicular to the X axis and this is your NAQI. A simple description of air quality is indicated by the coloured zones (e.g. a LIS of “2”, based on branches, meets the line for branches in the green zone (left side of the graph), which is indicative of a clean site with negligible gaseous N pollution; a LIS of “-2” meets the line for branches in the salmon pink zone, which is indicative of a very N polluted site).
The LIS for a site can vary from +3 for clean (low concentrations of gaseous N compounds) sites where only N-sensitive indicator lichens are present, to -3 for very high concentrations of gaseous nitrogen compounds sites where only N-tolerant indicator lichens are present.
Transitional sites may have both N-tolerant and N-sensitive taxa present, especially where conditions are changing.
If you compare the NAQI based on LIS for trunks with the LIS for branches and find that the LIS for branches is lower than that of the trunks, it suggests that conditions are deteriorating in your site.
However, there may be sites where conditions are improving (e.g. sites formerly affected by acid rain where there is very little lichen cover on the trunk, and yet the branches have N-sensitive taxa present).