Lichens

N deposition :: Lichens (general)

Impact Type: Deposition of pollutant

Key Concerns:

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.

N deposition :: a lichen

Impact Type: Deposition of pollutant

Key Concerns:

Schistomatomma graphidioides is a lichen growing on parkland trees that appears to be threatened by nitrogen deposition. It is listed under the UK Biodiversity Action Plan. The key concern is fertilisation of parkland combined with intensive grazing or the application of organic manure to neighbouring agricultural land leading to elevated levels of nitrogen deposition from ammonia, as well as nitrogen oxides from roads.

Additional Comments:

NH3 :: a lichen

Impact Type: Direct exposure to pollutant

Key Concerns:

Xanthoria parietina is an orange-grey crustose lichen which can occur on acid substrates, trees (i.e. oaks and limes) which have acid bark or rocks (Bates & Farmer 1992), which are exposed to NH3 . This is probably due to the alkalising effect of the NH3 (van Dobben & ter Braak 1998).

Additional Comments:

Acid deposition :: Usnea species

Impact Type: Deposition of pollutant

Key Concerns:

The Usneaceae are characterised by a broad strap based thallus attached usually to trees, by a basal sheath. Usneas have a filamentous thallus with primary and secondary branches and are known as the beard lichens. They often cohabit tree trunks with mosses preferring damper regions especially the west coast. Those growing on trees as opposed to rocks or fence posts will be semi protected by the filtering effect of the tree canopy from direct effects of the H+ ions (Gilbert 1968).

Acid deposition :: Ramalina species

Impact Type: Deposition of pollutant

Key Concerns:

Ramalinas belong to the family Usneaceae, having a fruticose strap shaped thallus. The many species of Ramalinas show a preference for either rock or bark, the chemistry of which may buffer acid deposition. Few if any studies have investigated the effects of wet acid deposition on Ramalinas

Acid deposition :: Lichens (general)

Impact Type: Deposition of pollutant

Key Concerns:

Studies suggest that atmospheric SO2 and NO2 are the two most important factors in determining levels of lichen biodiversity (Hawksworth & Rose 1970a,b, Richardson 1988, van Dobben et al. 2000). Species that are sensitive to SO2 and NO2, also tend to react negatively to NH3, due to the effect of NH3 on bark pH rather that any toxicity (van Dobben & ter Braak 1998, 1999).

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