Questions: What are the most relevant environmental variables influencing the distribution and the species richness of epiphytic lichens in heterogeneous areas of the Mediterranean region? What is the relative importance of substrate- vs. environmental-related variables? How do climatic and disturbance factors interact?
Location: The study was carried out in the Liguria region (northwestern Italy). This is a complex region where steep environmental gradients occur over a few kilometres of longitude and latitude.
Methods: Data on lichen species frequencies, collected on the basis of stratified random sampling, were analyzed using non-metric multidimensional scaling (NMS) and DCA. Indicator Value Analysis (IVA) analysis was used to find indicator species for the environmental predictors.
Results: In the survey area, epiphytic lichen distribution depends on both substrate- and environment-related factors. Climatic variables (in particular average yearly temperature and rainfall), anthropogenic pressures (particularly harvesting and atmospheric pollution), bark pH and texture were associated with the main axes of variability in the dataset. Mean annual rainfall is the best predictor for epiphytic lichen richness in the survey area. The particular effects of the Mediterranean region (e.g. the influence of forest fires) and of heterogeneous areas (the variability of diversity in relation to habitat) were pointed out. Several indicator species, closely linked to particular ecological conditions, were found for both substrate-and environment-related variables.
Conclusions: The main variables involved seemed to be the same reported for other areas, but their relative importance and their spatial scale of action were in some cases different, probably due to the geomorphological and climatic heterogeneity of the survey area. The significant influence of climatic predictors and disturbance factors on epiphytic lichens was confirmed, suggesting that these organisms may be used successfully to describe ecological trends in natural environments, also providing practical information at ecosystem level.
Nomenclature: Nimis (2003).
Abbreviations: NMS: Non-metric Multidimensional Scaling. IVA = Indicator Value Analysis.