The Critical Levels of Atmospheric Ammonia in a Mediterranean Holm-Oak Forest in North-Eastern Spain

Abstract

Despite recent regulations, atmospheric ammonia (NH3) emissions have not changed much over the last decades and excessive nitrogen remains as one of the major drivers for biodiversity changes. To prevent deleterious effects on species and ecosystems it is very important to establish safety thresholds, such as those defined by the Critical Level (CLE) concept, "the concentration above which direct adverse effects on receptors may occur, based on present knowledge". Empirical critical levels of atmospheric NH3 have mainly been reported for temperate forests and there is a lack of information for Mediterranean forests. Here, we provide a case study on NH3 CLEs for a typical Mediterranean ecosystem, the holm-oak (Quercus ilex) forest. To derive the CLE value, we measured NH3 concentrations for 1 year at a distance gradient in the forest surrounding a point source (cattle farm) and used diversity changes of lichen functional groups to indicate the onset of adverse effects. We estimate a NH3 CLE threshold of 2.6 µg m-3 , a value that is higher than that reported in other Mediterranean ecosystems and suggests that the site has been already impacted by NH3 pollution in the past. In a more general context, this study confirms the validity of lichen functional groups to derive CLEs in Mediterranean forests and woodlands and contribute to the body of knowledge regarding the impacts of NH3 on ecosystems.

Differential Response of Epiphytic Lichen Taxa to Agricultural Land Use in a Fragmented Forest in Central Argentina

“…In addition to the loss of habitat, agricultural activities, mainly intensive farming with fertilizers and intensive animal husbandry, have a great impact on the atmosphere (Fao, 2006). These activities are the main anthropogenic sources of atmospheric nitrogen compounds (Galloway et al, 2003) and their effects on terrestrial vegetation and lichens has been widely reported (Aguillaume et al, 2017;Boltersdorf and Werner, 2014;Frati et al, 2008Frati et al, , 2007Krupa, 2003;Paoli et al, 2010).…”

Diversity and floristic patterns of epiphytic macrolichens on white oak in the Klamath-Siskiyou region

“…Kappelle & Sipman 1992;Upreti & Chatterjee 2000;Oran & Oztürk 2012;Villella et al 2013b;Pérez-Pérez et al 2015;Marmor et al 2017;EI Mokni et al 2018). Oak-dominated habitats are often subject to intense anthropogenic influences that have substantial effects on lichen communities, such as burning, urbanization, and conversion to agriculture (van Herk 2001;Insarov et al 2010;Aguillaume et al 2017;Güvenç & Öztürk 2017). In the Pacific Northwest humans have recently repressed wildfires in oak-dominated habitats leading to invasion by other tree species, such as conifers (Sugihara and Reed 1987;Engber et al 2011).…”