Response of epiphytic lichen communities to decreasing ammonia air concentrations in a moderately polluted area of The Netherlands.

Decreasing local ammonia air concentrations in a moderately polluted area in The Netherlands were accompanied by a rapid increase in nitrogen-sensitive species (acidophytes) and a decline of nitrogen-tolerant macrolichens (nitrophytes). This paper presents data on the relationship between nitrophyte abundance and species abundance for three ecological groups of epiphytic lichens: nitrophytes (positively correlated with ammonia), acidophytes (negatively correlated) and neutrophytes (which have an optimum at medium concentrations) and suggests ammonia dependent optimum curves for these groups. In this study neutrophytes were found to die-off massively at sites with a decrease of the ammonia air concentration over the period 1996-2003.