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Critical levels (CLEs) of atmospheric ammonia based on biodiversity changes have been mostly calculated using small-scale single-source approaches, to avoid interference by other factors, which also influence biodiversity. Thus, it is questionable whether these CLEs are valid at larger spatial scales, in a multi- disturbances context. To test so, we sampled lichen diversity and ammonia at 80 sites across a region with a complex land-cover including industrial and urban areas. At a regional scale, confounding factors such as industrial pollutants prevailed, masking the CLEs. We propose and use a new tool to calculate CLEs by stratifying ammonia concentrations into classes, and focusing on the highest diversity values. Based on the significant correlations between ammonia and biodiversity, we found the CLE of ammonia for Mediterranean evergreen woodlands to be 0.69 μg m−3, below the previously accepted value of 1.9 μg m−3, and below the currently accepted pan-European CLE of 1.0 μg m−3. [Copyright &y& Elsevier]

Abstract: The effects of land-use on species and communities are usually studied by considering high-intensity land-use gradients. However, in many Mediterranean Europe areas, the traditional land-use regime is of low-intensity, including low-impact forestry practices and extensive livestock pasture. This low-intensity land-use is associated with ‘High Nature Value Farmlands’, which occupy more than 50% of total farmland area in Mediterranean areas. The objective of this work was to determine the effect of traditional low-intensity land-use on epiphytic lichen communities in Mediterranean cork-oak woodlands. We intend to investigate the value of lichen communities as early indicators of the effects of land-use changes. For that, lichens were sampled along a gradient of low-intensity land-use that included forestry and pasture activities. As lichen diversity variables we considered: (i) total species richness, (ii) total species frequency (LDV), and (iii) richness and frequency of functional groups dividing species according to their eutrophication-tolerance. We found an increase of total species richness with an increase of land-use intensity which is opposite to expectations and which was shown for first time in lichens. The increase in total species richness was due to an increase of the number of eutrophication tolerant species accompanied by the maintenance of the sensitive one when we analyzed the lichen-data at the functional response group level. These results fit with the intermediate disturbance hypothesis that predicts higher diversity under an intermediate disturbance due to the coexistence of species with contrasting ecological requirements. Traditionally managed cork-oak woodlands with low-intensity land-use can thus support a high diversity of lichen species. An important outcome was that we confirmed the importance of using ecological indicators based on functional-groups for monitoring changes in ecosystems and, since lichens responded to low levels of land-use intensity, we have also shown the possibility of using lichens as early indicators of the impacts of low intensity land-use. [Copyright &y& Elsevier]

Nitrogen (N) has emerged in recent years as a key factor associated with global changes, with impacts on biodiversity, ecosystems functioning and human health. In order to ameliorate the effects of excessive N, safety thresholds have been established, such as critical loads (deposition fluxes) and levels (concentrations). For Mediterranean ecosystems, few studies have been carried out to assess these parameters. Our objective was therefore to determine the critical loads of N deposition and long-term critical levels of atmospheric ammonia for Mediterranean evergreen woodlands. For that we have considered changes in epiphytic lichen communities, which have been shown to be one of the most sensitive to excessive N. Based on a classification of lichen species according to their tolerance to N we grouped species into response functional groups, which we used as a tool to determine the critical loads and levels. This was done under Mediterranean climate, in evergreen cork-oak woodlands, by sampling lichen functional diversity and annual atmospheric ammonia concentrations and modelling N deposition downwind from a reduced N source (a cattle barn). By modelling the highly significant relationship between lichen functional groups and N deposition, the critical load was estimated to be below 26 kg (N) ha-1 yr-1, which is within the upper range established for other semi-natural ecosystems. By modelling the highly significant relationship of lichen functional groups with annual atmospheric ammonia concentration, the critical level was estimated to be below 1.9 µg m-3, in agreement with recent studies for other ecosystems. Taking into account the high sensitivity of lichen communities to excessive N, these values should be taken into account in policies that aim at protecting Mediterranean woodlands from the initial effects of excessive N. [ABSTRACT FROM AUTHOR]

In spite of the relative importance of groundwater in coastal dune systems, the number of studies concerning the responsiveness of vegetation to ground water (GW) variability, in particularly in Mediterranean regions, is scarce. In this study, we established 5 study sites within a meso-mediterranean sand dune Pinus pinaster forest on the Atlantic coast of Portugal, taking advantage of natural topographic variability and artificial GW exploitation, which resulted in substantial variability in depth to GW between microsites. Here we identify the degree of usage and dependence on GW of different plant functional groups (two deep-rooted trees, a drought adapted shrub, a phreatophyte and a non-native woody invader) and how GW dependence varied seasonally and between the heterogeneous microsites. Our results indicated that the plant species had differential responses to changes in GW depth according to specific functional traits (i.e. rooting depth, leaf morphology, and water use strategy). The species comparison revealed that variability in pre-dawn water potential (ψpre) and bulk leaf δ 13C was related to microsite differences in GW use in deep-rooted (Pinus pinaster, Myrica faya) and phreatophyte (Salix repens) species. However, such variation was more evident during spring rather than during summer drought. The exotic invader, Acacia longifolia, which does not possess a very deep root system, presented the largest seasonal variability in ψpre and bulk leaf δ 13C. In contrast, the response of Corema album, an endemic understorey drought adapted shrub, across seasons and microsites seemed to be independent of water availability. Thus, the susceptibility to changing GW availability in sand dune plant species is variable, being particularly relevant for deep rooted species and phreatophytes, which have typically been less exposed to GW fluctuations. [ABSTRACT FROM AUTHOR]