Is the diversity of epiphytic lichens a reliable indicator of air pollution? A case study from Italy

doi:10.1016/j.envpol.2006.03.030

Environmental Pollution

Volume 146, Issue 2, March 2007, Pages 317-323

https://doi.org/10.1016/j.envpol.2006.03.030 Get rights and content

Abstract

This work provided additional information for a better interpretation of lichen diversity values in biomonitoring studies of air pollution. The effects of 12 predictive variables were estimated for the Genova province (NW Italy) by means of a non-parametric model. The diversity of epiphytic lichens was strictly correlated with mean annual rainfall and mean annual temperature. Different variables were found to affect the lichen diversity in urban vs. forested areas. In urban areas, air pollutants, mainly SO₂, are still the main limiting factor, even if under ameliorating conditions this relationship becomes less significant. In forested areas, harvesting and forest fires showed a predominant effect, suggesting the need to develop a more defined sampling protocol to estimate atmospheric pollution in such ecosystems.

Introduction

During the last decades, SO₂ has been the main pollutant affecting the distribution of epiphytic lichens in urban and industrial areas (Hawksworth and Rose, 1970), and these organisms have been widely used as biomonitors of this pollutant (for a recent review see Nimis et al., 2002). However, new policies on emission control led to a consistent decline of SO₂ concentrations in most industrialized countries (Bates et al., 2001, Greenstone, 2004) and lichens recolonized many conurbations worldwide (e.g. Rose and Hawksworth, 1981, Seaward and Letrouit-Galinou, 1991, Hawksworth, 2002, Loppi et al., 2002c). Nevertheless, decreased lichen abundance and spatial trends of lichen diversity are still detected around urban and industrial areas (Giordani et al., 2002, Gombert et al., 2004), supporting the idea that anthropogenic variables are still responsible for lichen decline, irrespective of natural succession of epiphytic communities (Purvis et al., 2003). However, missing a clearly dominant limiting factor (SO₂ in the case of lichens – Seaward, 1993, Van Dobben et al., 2001), the variables involved are complex and difficult to model for biomonitoring purposes (cf. Seaward, 2004), and this is particularly true for areas with a high climatic variability and sharp environmental gradients, such as the Mediterranean basin, or in forest ecosystems, where interactions among factors are particularly complex and hardly detectable (Giordani et al., 2001, Brunialti and Giordani, 2003, Pinho et al., 2004).

If we wish to continue using lichens as pollution monitors in a rapidly changing environment, it is fundamental to answer three questions: (1) what pollutant is the primary cause of lichen damage? (2) what are the pollutant levels damaging lichens? (Nimis and Purvis, 2002), and (3) is lichen biomonitoring a reliable tool to estimate the effects of atmospheric pollutants outside urban and industrial areas, such as in forest ecosystems?

This paper reports a case study undertaken to evaluate (1) the influence of the main gaseous air pollutants (SO₂, NO_x, CO) on the diversity of epiphytic lichens in a complex Mediterranean area (Genova Province, NW Italy), and (2) the effectiveness of lichen diversity to assess the effects of air pollution in the survey area. To achieve these goals, two rather neglected methods were used respectively in the sampling phase and in the statistical analysis of the data: a stratified random sampling strategy, mainly based on land use classification, to emphasize local ecological differences, and a non-parametric multiplicative regression (NPMR) analysis (McCune et al., 2003) to minimize both the effect of the a priori assumption of a normal distribution of environmental variables and of an additive interaction among them.

Section snippets

Study area

The Genova Province (1835 km²) is characterized by a high variability in elevation (0–1800 m a.s.l.) and in related climatic parameters, such as mean annual temperature (10–14 °C) and rainfall (900–1800 mm). A sub-Mediterranean climate-type can be found along the coast, being more humid on the Thyrrenian side, and drier on the Padanian side. A montane climate-type is present inland at higher elevations. The population, consisting of about 1 million inhabitants, is concentrated in the capital town

Lichen diversity value

Table 1 summarizes the descriptive statistics of LDV measured in the survey area, in relation to the different ecological categories investigated. Among forested areas, chestnut and mesophilous oakwoods had the highest lichen diversity (mean LDV = 75 ± 48), but were highly variable (LDV in the range 0–160). Among non-forested sites, olive groves had the highest lichen diversity (mean LDV = 88 ± 22), whereas in urban areas the lichen diversity was generally very low (mean LDV = 19 ± 16, range 0–37).

Relationship between lichen diversity, pollutants and environmental variables

Table 2

Discussion

It is well known that although epiphytic lichens are valuable indicators of air pollution, other factors such as the scarcity of phorophytes (De Wit, 1976) and adverse microclimatic conditions in urban areas (Rydzak, 1968) may also influence the distribution of certain lichen species in polluted areas.

In the present study, the effect of 12 important predictive variables affecting the diversity of epiphytic lichens were estimated for the Genova province, a complex Mediterranean area. A high

Acknowledgements

This study was financed by the University of Genova in the framework of the research grant ‘Lichens as biomonitors of environmental alteration and naturality: standardization in Mediterranean areas’. The author is deeply indebted to Francesca Gallotti and Michele Molfino for help during fieldwork. Thanks are due to Giorgio Brunialti, Bruce McCune, Marco Ferretti and Pier Luigi Nimis for stimulating discussions and suggestions.

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Is the diversity of epiphytic lichens a reliable indicator of air pollution? A case study from Italy

Abstract

Introduction

Section snippets

Study area

Lichen diversity value

Relationship between lichen diversity, pollutants and environmental variables

Discussion

Acknowledgements

Atmospheric Environment

Lichenologist

Environmental Research

Environmental Research

Cryptogamie Mycologie

Environmental Pollution

Science of the Total Environment

Environmental Pollution

Environmental Pollution

Science of the Total Environment

Journal of Environmental Economics and Management

Environmental Pollution

Environmental Pollution

Science of the Total Environment

Environmental Pollution

Environmental Pollution

Contrasting fundamental and realized ecological niches with epiphytic lichen transplants in an old-growth Pseudotsuga forest

Bryologist

Mapping lichen diversity as an indicator of environmental quality

Applied Smoothing Techniques for Data Analysis

The effect of air pollution from nitrogen dioxide (NO2) on epiphytic lichens in Seville, Spain

Aerobiologia

Epiphytic lichens and air pollution in The Netherlands

Bibliotheca Lichenologica

Piano territoriale di coordinamento

The effect of air pollution from nitrogen dioxide (NO₂) on epiphytic lichens in Seville, Spain