Abstract
Very little is known of the earlier lichen flora of the Padanian Plain, the most heavily anthropized and industrialized part of Italy, which is currently extremely poor. Terricolous lichens in particular are the most sensitive to threats, and have almost totally disappeared from the western Padanian Plain. This paper reports new findings of 20 terricolous lichen species, several of which are rare or poorly known in Italy or are of some phytogeographical interest because they are found at lower altitudes than their usual distribution (i.e. Cladonia coccifera, Cladonia uncialis). In addition, Cladonia humilis is new for Lombardy and two other species, Cladonia portentosa and Stereocaulon condensatum, are reported for the second time in the same region. The significance of these species is discussed with regard to their historical records from the same area and their current altitudinal distribution; they were probably much more widespread in the past, but the decline and disappearance of their habitats in lowland areas have been followed by their own disappearance in many localities. A modification of the rarity status of some of these species in the considered phytoclimatic belts, based on the new records, is proposed.
Introduction
Very little is known of the earlier lichen flora of the Padanian Plain, which is currently extremely poor, mainly due to air pollution and almost total deforestation (Nimis Citation1993; Nimis and Martellos Citation2004). Especially in Lombardy, the most heavily industrialized region of Italy, vast parts of the lowlands are now deprived of their native lichen flora (Nimis Citation1993); the features of this part of the region are not favourable to lichen diversity (Nimis and Martellos Citation2004).
Unlike epiphytic lichens, which have essentially no competitors on their elective substrates, terricolous lichens are exposed to strong competition with vascular plants, and are not able to overcome them because of their smaller size and slower growth rate (Scheidegger and Clerc Citation2002); therefore, they are often more vulnerable and less represented. Furthermore, particularly sensitive or rare species are unable to recover after their disappearance due to disturbance, even when the causes of their disappearance have ceased (e.g. Sparrius Citation2011; Leppik et al. Citation2013). On the other hand, their physiological characteristics, which make them more stress-tolerant than phanerogams, and their independence from the substrate for their sustenance, allow them to colonize habitats that are prohibitive for plants, making them important pioneer organisms; these habitats are characterized by, for example, oligotrophic soils, severe edaphic conditions and extreme climates (Scheidegger and Clerc Citation2002). Habitats with these features are becoming increasingly rare due to anthropization and agricultural exploitation, leading to loss of natural habitats, pollution and eutrophication; the terricolous lichen diversity in them could be used to infer information about the whole diversity they host, their stability and the anthropogenic influence acting on them (Scheidegger and Clerc Citation2002).
At present, in the western Padanian Plain, such habitats are even scarcer than in the other, less anthropized, phytoclimatic belts of Italy. Realistically, this lack of suitable habitats is the reason for the absence of studies focused on terricolous lichens in this part of Italy, together with the high level of anthropization; here, they were included in very few studies, only in some areas of conservation concern (Valcuvia Passadore et al. Citation2002a,Citationb; Gheza, Assini, and Valcuvia Passadore Citation2015).
The aim of this paper is to describe recent findings of terricolous lichen species that are new or poorly known in the Padanian Plain, or which are interesting because they are recorded outside their previously known distribution in Italy; some implications of their presence at low altitudes are discussed.
Materials and methods
Study area
The study area is located in the western Padanian Plain (northern Italy), mainly along the valley of the Ticino river, which is the natural boundary between the two regions of Piedmont and Lombardy. Thirteen sites selected for this research are located here and included in two regional natural parks; two additional sites are located in the Lomellina, south of the previous sites, and not included within protected areas but occurring in a military base and in a private hunting preserve (Table. ). The lichen flora of the latter has been previously described in detail by Gheza, Assini, and Valcuvia Passadore (Citation2015).
Table 1. The 15 sites selected for the study of terricolous lichens in the study area, listed from south to north.
According to Rivas-Martìnez, Penas, and Diaz (Citation2004), the bioclimate of the study area is temperate continental in the low and medium plain and temperate oceanic in the high plain. Following the phytogeographic subdivision of Italy stated by Nimis and Martellos (Citation2004, Citation2008), the lower plain falls into the Padanian region and the upper plain into the sub-Mediterranean region; however, this separation is considered artificial, because the Padanian differs from the sub-Mediterranean only in having heavier anthropization (Nimis and Martellos Citation2004).
Geological substrates are composed of sediments of various ages and lithologies. In the high plain, the fundamental level of the plain is constituted by ancient Pleistocene terraces attributed to the ancient and medium Diluvium, mainly gravelly or pebbly (D'Alessio and Comolli Citation1996). In Lomellina, there are the remains of inland dunes made by siliceous sands attributed to recent Diluvium deposits subjected to aeolic shaping (Boni Citation1947; Bertossi Citation1950), which has now ceased. Finally, the fluvial valley of the Ticino River has a more recent origin, being constituted by Holocene pebbly, gravelly and sandy deposits of the recent Alluvium (D'Alessio and Comolli Citation1996).
The natural vegetation of the western Padanian Plain is now very limited; Sartori and Bracco (Citation1998) provide an exhaustive overview of it. In particular, the vegetation of the study sites considered here is characterized by the presence of dry grasslands and heathlands in the widest openings of the mixed wood of Quercus robur L. and Carpinus betulus L. which represents the climax of the vegetation in the Ticino river valley and in the low plain (Sartori and Bracco Citation1998). Grasslands referred to Corynephorion canescentis Klika 1931 are found both on diluvial inland sand dunes and on more recent alluvial deposits with various granulometry in the fluvial valley (Assini et al. Citation2013), whereas several communities attributed to Thero-Airion Tüxen 1951 (Assini and Sartori Citation2004) are found on the second substrate and in the diluvial high plain, but not on the inland dunes. Heathland fragments, often considered as a mere blanket of the wood margin, can be found on recent deposits in the fluvial valley, but proper heathlands referred to Calluno-Genistion pilosae Duvigneaud 1944 (Sartori and Bracco Citation1998) are found only on intermediate and old-age diluvial deposits (Cerabolini, Ceriani, and De Andreis Citation1998) on the basic level of the plain. All of these three habitats are listed in the “Habitat” Directive 1992/43/CEE (2330: inland dunes with open Corynephorus and Agrostis grasslands; 4030: European dry heaths; 6220: pseudo-steppes with grasses and annuals of the Thero-Brachypodietea) (Biondi and Blasi Citation2009), and are therefore of some conservation value. Their importance for the biodiversity of the Padanian Plain rests not only in the abundance of terricolous lichens, but also in the presence of various vascular plants occurring here at the southern limit of their area (Cerabolini, Ceriani, and De Andreis Citation1998; Assini and Sartori Citation2004; Assini Citation2007; Assini et al. Citation2013).
Lichen sampling
Fifteen sites (Table 1) were selected for a floristic study on terricolous lichens: 13 in open dry grasslands (two with only Corynephorion, five with only Thero-Airion and six with a mixture of them) and two in heathlands (Calluno-Genistion). All the study sites were selected on the basis of their relevance in coverage and richness of the cryptogams in the herbaceous layer of the vegetation and because they represent quite well-preserved fragments of those habitats.
Terricolous lichens were exhaustively collected in each site and identified in the laboratory by means of a stereomicroscope and chemical reagents, following the keys of Nimis (Citation1986), Nimis and Martellos (Citation2004) and Smith et al. (Citation2009). Nomenclature follows Nimis and Martellos (Citation2008).
Records of the considered species from Lombardy and Piedmont were examined from both the available literature and the specimens held in the cryptogamic herbarium of the University of Pavia (hereinafter: PAV), to check their currently known regional and altitudinal distributions. Particular attention was given to historical records from localities sited in the study area (Biroli Citation1808; Cozzi Citation1917; Bertossi Citation1950; Giacomini Citation1958; Corbetta Citation1968), which have been examined critically.
A rarity spectrum based on the commonness–rarity categories stated for the phytoclimatic regions of Italy by Nimis and Martellos (Citation2008) was calculated for each site. The nine rarity categories are defined as follows: absent, extremely rare, very rare, rare, rather rare, rather common, common, very common, extremely common. As several species considered “absent” by Nimis and Martellos (Citation2008) in the Padanian and the sub-Mediterranean regions were found in some sites, when calculating the spectra they have been merged in the category “extremely rare”, to avoid the nonsense of the presence of “absent” species. Therefore, for these newly found species, the assignment to the “extremely rare” category is proposed on the basis of the criterion stated in ITALIC (Nimis and Martellos Citation2008) for which a species is to be considered “extremely rare” if it is known from fewer than five sites (in the considered belt).
Results
Commented floristic list
Cetraria aculeata (Schreb.) Fr.
Found in one site. Lombardy: Dossi di Remondò. On open mineral sandy soil. Only in Corynephorion.
Previously reported in Lombardy only from subalpine and alpine environments (Anzi Citation1860; Giacomini Citation1940; Giacomini and Pignatti Citation1955, Citation1956; Pignatti and Pignatti Citation1958; Giacomini, Pirola, and Wikus Citation1962; Credaro and Pirola Citation1975; Kärnefelt Citation1986). It has never been accurately reported before in the lowland area, but was listed in relevés by Assini (Citation2007) from generic “inland sand dunes of Lomellina”. New for the Padanian phytoclimatic belt (cf. Nimis and Martellos Citation2008), where it should be considered “extremely rare”.
Even if it has not been found in the Piedmont sites, it is worth mentioning that Biroli (Citation1808) reported the species from the heathlands of the valley of Ticino River in Piedmont.
Cladonia cervicornis (Ach.) Flot. ssp. cervicornis
Found in four sites. Lombardy: Dossi di Cergnago, Ansa di Castelnovate; Piedmont: Tenuta Bornago, Barbelera. On pebbly, slightly humified soil. In Corynephorion and Thero-Airion.
Previously reported for the mountain regions both in Lombardy (Anzi Citation1860; Sandstede Citation1931; Rivellini and Valcuvia Passadore Citation1996; Rossi, Pirola, and Zurli Citation1998) and in Piedmont (Baglietto Citation1863; Baglietto and Carestia Citation1867, Citation1880), but actually already recorded “in ericetis Ticini” by Biroli (Citation1808). New for the Padanian phytoclimatic belt (cf. Nimis and Martellos Citation2008), where it should be considered “extremely rare”.
Cladonia chlorophaea s. lat
Found in eight sites. Lombardy: Molino d’Isella, La Promessa, Turbigaccio, Brughiera di Tornavento, Ansa di Castelnovate. Piedmont: Tenuta Bornago, Marcetto, Barbelera. On pebbly, slightly humified soil. In Corynephorion, Thero-Airion and Calluno-Genistion.
Cladonia coccifera (L.) Willd
Found in eight sites. Lombardy: La Fagiana, La Promessa, Brughiera di Tornavento, Ansa di Castelnovate; Piedmont: Tenuta Bornago, Marcetto, Barbelera, Baraggia di Pombia. On pebbly, slightly humified soil. In Corynephorion, Thero-Airion and Calluno-Genistion.
Previously reported for mountain regions both in Lombardy (Anzi Citation1860; Baroni Citation1893; Rivellini and Valcuvia Passadore Citation1996; specimens in PAV) and in Piedmont (Baglietto and Carestia 1876, Citation1880; Martel Citation1911; Cengia-Sambo Citation1931, Citation1933; Montacchini and Piervittori Citation1979; Montacchini et al. Citation1982; Piervittori, Tarchetti and Montacchini Citation1988; Piervittori, Isocrono, and Maffei Citation2001; Isocrono et al. Citation2003a,b), but actually already recorded from Lombardy and Piedmont Ticino areas by several authors (Biroli Citation1808; Cozzi Citation1917; Giacomini Citation1958). New for the sub-Mediterranean phytoclimatic region (cf. Nimis and Martellos Citation2008), where it should be considered “extremely rare” or “very rare”.
Cladonia coniocraea (Flörke) Spreng
Found as terricolous in four sites. Lombardy: Dossi di Cergnago, Dossi di Remondò, Ansa di Castelnovate; Piedmont: Tenuta Bornago. On slightly humified soil. Only in Corynephorion.
Cladonia fimbriata (L.) Fr
Found as terricolous in four sites. Lombardy: Molino d’Isella, Brughiera di Tornavento; Piedmont: Marcetto, Barbelera. On slightly humified soil. In Corynephorion, Thero-Airion and Calluno-Genistion.
Cladonia foliacea (Huds.) Willd
Found in 12 sites. Lombardy: Dossi di Cergnago, Dossi di Remondò, Molino d’Isella, Bosco Ronchi, La Fagiana, Turbigaccio, Ansa di Castelnovate; Piedmont: La Chiocciola, Tenuta Bornago, Marcetto, Barbelera, Cascina Casone. On sandy, pebbly and slightly humified soil. In Corynephorion and Thero-Airion.
The most widespread species in the study area. Already reported by Gheza, Assini, and Valcuvia Passadore (Citation2015) for the Padanian belt, where it should be considered “extremely rare” (cf. Nimis and Martellos Citation2008), whereas it could be considered “very rare” in the sub-Mediterranean belt.
Cladonia furcata (Huds.) Schrad
Found in five sites. Lombardy: Dossi di Cergnago, Dossi di Remondò, Molino d’Isella, Bosco Ronchi, La Fagiana. On sandy and slightly humified soil. In Corynephorion and Thero-Airion.
Cladonia humilis (With.) J.R.Laundon
Found in two sites. Lombardy: Ansa di Castelnovate; Piedmont: Tenuta Bornago. On sandy and pebbly soil. In Corynephorion and Thero-Airion.
Previously reported for Piedmont only by Coassini Lokar, Nimis, and Ciconi (Citation1986). New for Lombardy (cf. Nimis and Martellos Citation2008).
Cladonia parasitica (Hoffm.) Hoffm
Found as terricolous in one site. Piedmont: Baraggia di Pombia. On organic soil above a rotten stump. Only in Calluno-Genistion.
Widespread in Piedmont (cf. Nimis Citation1993; Nimis and Martellos Citation2008), but recorded mainly as epiphytic.
It is worth mentioning here that it was also found on Quercus robur in Bosco Ronchi, which represents the first record for the Padanian phytoclimatic belt (cf. Nimis and Martellos Citation2008), where the species should be considered “extremely rare”.
Cladonia portentosa (Dufour) Coem
Found in four sites. Lombardy: Dossi di Cergnago, Dossi di Remondò; Piedmont: Tenuta Bornago, Marcetto. On sandy or pebbly, mineral or humified soil. Only in Corynephorion.
Previously reported in Lombardy only for residual inland sand dunes in the Padanian phytoclimatic belt (Gheza, Assini, and Valcuvia Passadore Citation2015) and in Piedmont for the mountain regions (Martel Citation1911; Cengia-Sambo Citation1931, Citation1933; Montacchini et al. Citation1982; Isocrono et al. Citation2006). It should be considered “extremely rare” in the Padanian belt (cf. Nimis and Martellos Citation2008).
Cladonia pyxidata (L.) Hoffm
Found in nine sites. Lombardy: Dossi di Cergnago, La Fagiana, La Promessa, Brughiera di Tornavento, Ansa di Castelnovate; Piedmont: Tenuta Bornago, Marcetto, Barbelera, Cascina Casone. On sandy or pebbly, mineral or humified soil. In Corynephorion, Thero-Airion and Calluno-Genistion.
Cladonia rangiformis Hoffm
Found in 11 sites. Lombardy: Dossi di Cergnago, Molino d’Isella, Bosco Ronchi, La Fagiana, Turbigaccio, Ansa di Castelnovate; Piedmont: La Chiocciola, Tenuta Bornago, Marcetto, Barbelera, Cascina Casone. On rather evolved, humified soil. In Corynephorion and Thero-Airion.
The most widespread species in the valley of Ticino River.
Cladonia rei Schaer
Found in eight sites. Lombardy: Dossi di Remondò, Bosco Ronchi, Turbigaccio, Brughiera di Tornavento, Ansa di Castelnovate; Piedmont: Marcetto, Barbelera, Cascina Casone. On sandy and gravelly-pebbly, not or scarcely humified soil. In Corynephorion, Thero-Airion and Calluno-Genistion.
Previously reported for the montane belt both in Lombardy (Rivellini and Valcuvia Passadore Citation1996) and Piedmont (Cengia-Sambo Citation1934; Isocrono et al. Citation2003b). New for the Padanian phytoclimatic region (cf. Nimis and Martellos Citation2008), where it should be considered “extremely rare”.
Cladonia squamosa Hoffm
Found as terricolous in seven sites. Lombardy: Dossi di hea headingCergnago, Molino d’Isella, La Fagiana, La Promessa, Ansa di Castelnovate; Piedmont: La Chiocciola, Tenuta Bornago. On slightly humified soil. In Corynephorion and Thero-Airion.
Cladonia symphycarpa (Flörke) Fr
Found in seven sites. Lombardy: Bosco Ronchi, La Fagiana, Ansa di Castelnovate; Piedmont: Tenuta Bornago, Barbelera, Cascina Casone, Baraggia di Pombia. On rather mineral soil. In Corynephorion, Thero-Airion and Calluno-Genistion.
Previously reported in Lombardy only in montane and alpine localities (Nimis and Tretiach Citation1993; Rivellini and Valcuvia Passadore Citation1996; Nascimbene, Thor, and Nimis Citation2012; specimens in PAV) and in the sub-Mediterranean belt in Piedmont (Re Citation1825). New for the Padanian phytoclimatic region (cf. Nimis and Martellos Citation2008), where it should be considered “extremely rare”.
Cladonia uncialis (L.) F.H.Wigg. ssp. uncialis
Found in two sites. Piedmont: Tenuta Bornago, Marcetto. On humified gravelly soil. In Corynephorion and Thero-Airion.
Previously reported in Piedmont only for the alpine belt (Allioni Citation1785; Biroli Citation1808; Pollini Citation1824; Baglietto Citation1863; Baglietto and Carestia Citation1867, Citation1880; Martel Citation1911; Cengia-Sambo Citation1931, Citation1933; Isocrono et al. Citation2003b; Isocrono et al. Citation2006) and considered restricted to the Alps in Italy (Nimis and Martellos Citation2008). New for the sub-Mediterranean phytoclimatic region (cf. Nimis and Martellos Citation2008), where it should be considered “extremely rare”.
Cladonia sp
Found in one site. Lombardy: Molino d’Isella.
Lepraria sp
Found in one site. Lombardy: Brughiera di Tornavento.
Stereocaulon condensatum Hoffm
Found in two sites. Lombardy: Dossi di Cergnago, Dossi di Remondò. On open mineral sandy soil. Only in Corynephorion.
Previously reported by Gheza, Assini, and Valcuvia Passadore (Citation2015) for the Padanian phytoclimatic belt; the only other citation for Lombardy has been resumed by Rivellini and Valcuvia Passadore (Citation1996) from Anzi (Citation1860), and refers to the alpine region. According to Nimis and Martellos (Citation2008) it would be restricted to the Alps in Italy, since all the other Italian findings refer to mountainous regions. It should be considered “extremely rare” in the Padanian belt (cf. Nimis and Martellos Citation2008).
Composition and distribution of the whole terricolous lichen flora
The whole floristic list includes 20 species, among which four (Cetraria aculeata, C. coniocraea, C. portentosa, S. condensatum) were exclusive to Corynephorion grasslands, while one (Cladonia sp.) was exclusively found in a Thero-Airion grassland and two others (C. parasitica, Lepraria sp.) were found only in one heathland each. Two species (C. parasitica, Lepraria sp.) have been collected only on ancient diluvial sediments of the fundamental plain level, two (Cetraria aculeata, S. condensatum) only on recent diluvial inland dunes, and three (C. humilis, C. uncialis, Cladonia sp.) only in the alluvial valley of the Ticino river.
Only fruticose and squamulose species were found; no crustose or foliose terricolous species were observed in the study sites. Furthermore, all the recorded species have green algae as photobionts; no cyanolichens were found.
Considering the different habitats, Corynephorion grasslands are the richest in species (7.88 ± 2.64 species per site, 17 species overall), Thero-Airion grasslands show a slightly lower lichen diversity (6.09 ± 2.43 species per site, 14 species overall) and the heathland is the habitat that is poorest in lichens (4.5 ± 2.12 species per site, eight species overall). Considering the different substrates, alluvial (6.81 ± 2.76 species per site, 15 species overall) and recent diluvial (8 ± 1.41 species per site, 11 species overall) substrates host a similar number of species per site but a different number of total species, whereas the ancient diluvial plain is poorer (4.67 ± 1.53 species per site, nine species overall). The number of species per site is reported in Table .
Table 2. Number of total, extremely rare and exclusive species per site.
According to Nimis and Martellos (Citation2008), three species (Cetraria aculeata, C. rei, C. symphycarpa) are new for the Padanian phytoclimatic region, and three other species (C. foliacea, C. portentosa, S. condensatum) are recorded there for the second time after the records by Gheza, Assini, and Valcuvia Passadore (Citation2015); two species (C. coccifera, C. uncialis) are new for the sub-Mediterranean region. One species (C. humilis) is new for Lombardy, and the record of C. portentosa reported here for Remondò is the second in the same region. The two records of S. condensatum from the inland sand dunes of Lomellina represent the second and third findings for the whole of Lombardy more than 150 years after the first report (Anzi Citation1860).
The rarity spectra (Figure ) show a very high percentage of extremely rare species, mainly in the sites located in the lower plain, which is mostly the result of the heavily depleted condition of the Padanian region, in which they are placed, resulting in high rarity values for species that are less rare in the sub-Mediterranean region. However, also, several sites in the sub-Mediterranean belt have quite high percentages of extremely and very rare species.
Fig. 1. Rarity spectra. Rarity refers to the phytoclimatic region where the site belongs, as stated by Nimis and Martellos (Citation2008), modified accordingly with the new records (i.e. “absent” species have been merged in the category “extremely rare”).
Discussion
Although the lichen flora of the Ticino Natural Park has been well studied recently (Valcuvia Passadore et al. Citation2002a, Citationb), the research presented here highlights the presence of several species previously not found or overlooked. These results could be a basis for reconstructing at least a fragment of the original composition of the terricolous lichen flora of the Padanian Plain.
The most interesting question is whether at least part of all those terricolous species that are restricted to mountainous regions today are truly limited by climate, or if they remain at high altitudes only because less pollution and anthropogenic disturbance are found there. Some historical and recent records suggest that the distribution of some species was wider in the past, extending to lowland areas. In fact, according to the altitudinal distribution stated by Nimis and Martellos (Citation2008), only three species (C. coccifera, C. uncialis, S. condensatum) found in this research are formally typical of higher altitudinal belts, but the number increases when considering the historical records of six other species in several sites of the same study area near the Ticino river (Cetraria islandica (L.) Ach., Cladonia amaurocraea (Flörke) Schaer., Cladonia arbuscula (Wallr.) Flot., Cladonia gracilis (L.) Willd., Cladonia pleurota (Flörke) Schaer., Cladonia rangiferina (L.) F.H.Wigg) (cf. Biroli Citation1808; Cozzi Citation1917; Giacomini Citation1958). Historical records from grasslands of the inland dunes of Lomellina are instead useless, because Bertossi (Citation1950) and Corbetta (Citation1968) overlooked lichens almost completely, reporting only the two most widespread species; several species unnoticed by them but reported in the present day (i.e. Cetraria aculeata, C. cervicornis, C. portentosa, S. condensatum) were certainly present, so it cannot be excluded that other species, that have since disappeared, could have been present but unseen by those authors in the past.
The occurrence of terricolous lichens seems related to the presence of residuals of dry grasslands and heathlands, which are the only habitats currently hosting them in the planitial regions of northern Italy. The integration between historical records and new findings from those habitats may help to better understand their importance. In fact, these habitats seem to have once hosted a higher lichen diversity than in the present day, including several species thought to be typical of mountainous regions in Italy (cf. Biroli Citation1808; Cozzi Citation1917; Giacomini Citation1958). The richest and best-known site was the Gallarate heathland (of which the site referred to as ‘Tornavento’ here represents the residual part), which extended far further until the first half of the twentieth century, before the noticeable enlargement of the Malpensa Airport occurred since the 1960s.
Considering those ancient records critically, some considerations can be made. The records of C. arbuscula and C. rangiferina, not currently found, could even be misidentifications of C. portentosa, which is found today at least in the valley of Ticino; but misidentifications of C. amaurocraea and C. gracilis are more unlikely. The disappearance of such species, now restricted to the mountains in Italy, could be due not only to the habitat loss, but also to global warming, which is known to affect terricolous lichens (Aptroot and Van Herk Citation2007); this topic requires further research in the Padanian Plain.
The peculiarity of the lichen flora of the inland sand dunes of Lomellina represents a relict of the previous conditions (for a comparison with central European inland sand dunes see Gheza, Assini, and Valcuvia Passadore Citation2015). Through previous centuries, those species closely linked to these geomorphological formations have certainly parallelled the disappearance of these formations caused by the spread of agriculture (cf. Boni Citation1947; Bertossi Citation1950; Corbetta Citation1968), but, just like the dunes themselves, they were surely much more widespread, at least in Lomellina and in the surrounding regions that hosted dunes of the same age (for a discussion about the origin and age of these dunes see Boni Citation1947).
Leppik et al. (Citation2013) found that terricolous lichen communities in Estonian calcareous grasslands were mainly soil-type specific, but were also affected by historic disturbances and land use change. Effects of these events are detectable at several study sites, because the reduction of occurrence and the disappearance of terricolous lichens are linked to the progressive diminution and loss of their habitats. For example, today the area occupied by the “Gallarate” heathland is vastly decreased, and most of the historically recorded species are no longer present.
The occurrence of anthropogenic disturbance is suggested in several sites also by the presence of the ruderal C. rei, which is particularly abundant in formerly disturbed sites, such as Tornavento, La Promessa and Dossi di Remondò. In the last of these sites, the grassland has been the site of military exercises for several decades, which have probably made a fundamental contribution to maintaining open bare sand areas, which are important for the maintenance of Cetraria aculeata too. In Dossi di Cergnago, where the environmental conditions are almost identical to Remondò but no heavy disturbance occurred, Cetraria aculeata and C. rei are absent.
Finally, a practical observation underlines the persistence of interesting lichen floras in these habitats in well-preserved areas with forbidden access: a private hunting preserve and a military base in inland dunes (Dossi di Cergnago and Dossi di Remondò, 11 species overall) and a private estate (Tenuta Bornago, 13 species) in the Ticino fluvial valley. Conversely, the exploited, disturbed and reduced areas in the high plain (La Promessa and Tornavento) show a lower terricolous lichen diversity.
Conclusions
This research has shown the presence of terricolous lichen species not found previously in the Padanian Plain and, in some cases, generally considered montane–alpine species at these latitudes. Together with several historical records, these findings highlight the possibility of a broader distribution for these species, at least in the past.
The fate of terricolous lichens in this part of Italy is strictly connected to the fate of the habitats where they can develop (cf. Scheidegger and Clerc Citation2002). Here, these habitats are represented by dry grasslands and heathlands, which have become very rare and fragmented due to anthropogenic disturbance (Sartori and Bracco Citation1998), and which are therefore considered nature fragments of conservation concern, both for the biodiversity that they host as habitats for relict populations and, in some cases, for their location at the southern limit of their areal (Cerabolini, Ceriani, and De Andreis Citation1998; Assini and Sartori Citation2004; Assini Citation2007; Assini et al. Citation2013). A lichen flora showing elements of phytogeographical and conservation interest could be added to the motivations supporting the conservation claims of such habitats.
This research focused on an area that is relatively rich in residual grassland and heathland habitats, but restricted to part of the western Padanian Plain; other residual habitats suitable for terricolous lichens may be present in more or less distant areas of the plain, and so further work is advisable to better clarify whether in these fragments of lichen-rich habitats we can find a realistic representation of the primitive lichen flora of the ancient Padanian Plain.
Acknowledgements
I warmly thank Prof. Mariagrazia Valcuvia Passadore (University of Pavia) for her help in the identification of some critical specimens and Prof. Sonia Ravera (University of Molise) and an anonymous reviewer for their helpful remarks on an earlier version of this manuscript. I am grateful to Mrs Alida Piglia for some valuable suggestions about the English style and to Dr Anna Letizia Magrassi, Dr Francesca Cattaneo and Mrs Rosanna Zavatarelli for their help in finding the bibliographic material.
Related Research Data
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