Evaluation of lichen diversity as an indicator of environmental quality in the North Adriatic submediterranean region

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Abstract

In 2000, a standardized sampling protocol was developed by a group of European researchers to provide a repeatable and objective strategy for mapping lichen diversity as an indicator of environmental changes; this protocol is nowadays adopted in the guidelines to air quality bioindication in Italy.

The present paper shows the results of a study of epiphytic lichen diversity performed according to both the new protocol and the standard methodology previously used in Italy; diversity values are based on frequency counts of all lichen species within particular sampling grids positioned on the trunks and divided in subunits. The survey was carried out in 61 sampling sites of two areas of the Friuli Venezia Giulia region (Italy) and Slovenia, characterized by similar climatic conditions and a wide range of anthropic pressure. Biodiversity values obtained following the two sampling methods are highly statistically correlated; this suggests an interpretative continuity of lichen diversity data for biomonitoring purposes. Lichen communities and diversity values occurring in natural areas, far from heavy human influences, are investigated by means of multivariate analysis of floristic relevés of 11 sites. Diversity values scored in natural areas are rather variable, and are mainly influenced by the different vegetation types, Parmelion communities having lower diversity values than communities with Xanthorion elements. Evaluation scales of environmental alteration based on lichen diversity in the North Adriatic submediterranean bioclimatic area are provided. Some critical aspects of the sampling strategies are discussed.

Introduction

The definition of standardized, objective and widely applicable sampling strategies represents a crucial step in the development and spreading of biomonitoring investigations of environmental quality. The use of lichens in monitoring the terrestrial environment is well recognized and widespread all over the world for many years. Lichens are a consortium of fungal and photosynthetic partners (algae and/or cyanobacteria), characterized by a notable sensitivity to environmental stress such as pollution and climatic changes. Thanks to this susceptibility, lichens are among the most widely used indicators of environmental quality and in particular of air pollution by phytotoxic gaseous substances (i.e. SO2 and NOx) (e.g., Hawksworth and Rose, 1970, Ferry et al., 1973, Markert, 1993, van Dobben et al., 2001, Nimis et al., 2002).

Starting from the 1950s, several approaches to biomonitoring with lichens were proposed, based on different parameters such as number of species, abundance or cover, poleophoby indices, and on different sampling areas (e.g. Barkman, 1963, De Sloover and Leblanc, 1968, Hawksworth and Rose, 1970, Herzig et al., 1987, Van Haluwyn and Lerond, 1988, Nimis et al., 1989, Nimis, 1999b). The Swiss approach (Ammann et al., 1987, Herzig et al., 1987, Herzig and Urech, 1991), based on the evaluation of frequencies of epiphytic lichens within a sampling grid positioned on the part of the tree trunks with the highest lichen coverage, was widely adopted with some modifications in different European countries, and was recognized by national government authorities in Switzerland, Germany (VDI, 1995) and Italy (Nimis, 1999b). However, the use of different sampling grid sizes made collected data not comparable. Furthermore, the selection of sampled trees and the location of the sampling grid were criticized as being too subjective.

Within the international workshop supported by NATO in 2000 (Nimis et al., 2002), a new sampling method, largely based on the Swiss approach, was proposed to assess repeatable lichen diversity values by means of a more rigid and objective strategy (Asta et al., 2002). This method was adopted in 2001 by the Italian Agency for the Protection of the Environment and for Technical Services (APAT) (ANPA, 2001), substituting the guidelines by Nimis (1999b).

The application of the new sampling method implies some problems, the main one being the lack of evaluation scales to assess magnitude of environmental alteration based on lichen diversity values in different bioclimatic areas. Epiphytic lichen communities are affected by different ecological variables: atmospheric pollutants, chemical and physical properties of the substratum, eutrophication, light and water availability, climatic factors. The interpretation of lichen diversity in monitoring environmental pollution is nowadays based on the evaluation of deviations of the communities from “normal” or “natural” conditions (Asta et al., 2002, Loppi et al., 2002, Nimis, 1999a). This is however a very critical topic, both for the difficulty in the operational definition of “naturality” and “alteration” concepts and for the statistical necessity to have a large amount of lichen diversity data.

The aim of this paper is to test the applicability of the sampling method proposed by Asta et al. (2002) and officially adopted in Italy from 2001 onwards, and to provide a regional scale of environmental alteration based on lichen diversity in the North Adriatic submediterranean bioclimatic area.

Section snippets

Survey area

The Province of Trieste (NE Italy) (Fig. 1) hosts about 240,000 inhabitants, most of which are concentrated in the large urban area of Trieste. The southernmost part of the Province can be divided in three main districts: (a) the Karst district, characterized by limestone as substratum and a mixed, more or less open, deciduous woodland, with small scattered villages, and an elevation ranging from about 300 to 560 m; (b) the town of Trieste and its industrial zone, located in a coastal area of

Relationship between LB and LDV data

The two sets of lichen diversity values of the 214 trees sampled following the methods by Nimis (1999b) and Asta et al. (2002) were compared by means of linear regression analysis. LB and LDV values of trees have a highly significant correlation (r=0.9495; p-value<0.001) (Fig. 2). In the first portion of the graph, corresponding to LB values lower than 10, the values obtained by the two methods are very similar and often coincident, while with increasing LB values the dispersion of

Conclusions

The sampling method of Asta et al. (2002) proved to be applicable for assessing lichen diversity in this study. This method, with its peculiar high degree of objectiveness and repeatability, represents a fundamental statistical approach for routine investigations of lichen diversity in environmental monitoring; however, some main critical aspects must be stressed. In the present work, the sampling of a station by two operators following this method is time-expensive, requiring twice time than

Acknowledgements

The authors are grateful to Dr. Luca Ianesch and Dr. Francesca Bellinzani (Trieste) for assistance in fieldwork, and Dr. Paola Ganis (Trieste) for suggestions for data analysis. Particular thanks go to the anonymous reviewers for their useful comments to the manuscript. This work was founded by the Province of Gorizia (Italy) and ELETTRA GLT S.p.A (Brescia, Italy).

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