Impact Type: Deposition of pollutant
In recent years there have been a vast number of studies on the impacts of N on lichens particularly outwith the UK in Scandinavia and northern latitudes where lichens are of economic importance. One such study by Mots et al 2000 treated a low alpine commuity at 7, 35 & 70 kg N ha-1 a-1. Over 3 yrs there were no significant changes or species loss.
The most likely mechanism for effects of nitrogen deposition on lichens will be through competition with other plants favouring higher nitrogen inputs. In situations with very high nitrogen inputs epiphytic lichens may be out competed by algae (e.g. pleurococcus spp). With nitrogen inputs above the critical load for different habitats, species changes in the composition of higher plants may indirectly lead to loss of lichens. For example, in heathland habitats increased growth of grass species may limit substrate availability and reduce light levels at the ground resulting in a decline in lichens such as Cladonia spp.
Although effects of nitrogen deposition on lichens are expected, the scale of impacts is currently rather uncertain. In this context, critical loads should be applied on a habitat basis. Hyvdrinen and Crittenden (1998) have analyzed the linkage between atmospheric nitrogen deposition and tissue nitrogen in Cladonia portentosa.
|Critical Load/ Level|
No comparable habitat with established critical load estimate available