Abstract
- Zedda, L.: The epiphytic lichens on Quercus in Sardinia (Italy) and their value as ecological indicators. – Englera 24: 1-468. 2002.
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The lichens growing on Quercus ilex, Q. pubescens s. lat., Q. suber and Q. coccifera s. lat. were studied at 92 plots placed in 62 selected localities spread throughout Sardinia (Italy). Earlier reports of species in the island were taken into consideration. On all oak species, 331 lichen taxa were found. During the project Lecanora leuckertiana was discovered, as well as a new variety, Ramalina farinacea var. variolarica and a new chemotype of Lepraria nivalis. Further 75 taxa are new to Sardinia, 13 of which are also new to Italy (Chaenothecopsis vainioana, Lecania cf. lesdainii, Lecanora farinaria, L. hybocarpa, L. paramerae, Lepraria cf. nivalis, Lecidea hypopta, Ochrolechia cf. androgyna, Protoparmelia ochrococca, R. subfarinacea var. salazinica, Schismatomma cretaceum, S. niveum and Usnea madeirensis) and six are reported for the first time from the Mediterranean region. In the light of this the European distribution of Lecanora farinaria, L. leuckertiana, Ochrolechia cf. androgyna, Protoparmelia ochrococca and R. subfarinacea var. salazinica is reviewed. Information on the distribution and ecology (e.g. phorophyte preference, altitudinal limits, nitrophily, photophily, hygrophily, commoness-rarity status) of each taxon is given; in many cases such information was poorly known, especially for the Mediterranean region. TLC analyses were carried out for many difficult genera, whose chemistry had been hitherto not investigated in material from Italy, and in some cases in the Mediterranean region (e.g. Lepraria s. lat., Ochrolechia).
The lichen flora on Quercus in Sardinia appears to be very rich in comparison with those on oak reported from other European countries and Italian regions. 256 taxa were found on Q. ilex, 207 on Q. pubescens, 168 on Q. suber and 20 on Q. coccifera. The Lecanorales are the order represented by most species (69 % of taxa); the Parmeliaceae (46 taxa), Physciaceae (44 taxa) and Lecanoraceae (36 taxa) are the families to follow. Only 10 species were found on all oak species, while 99 colonize Q. ilex, Q. pubescens and Q. suber, but not Q. coccifera. These lichens are mostly widespread temperate species with wide ecological amplitudes. 64 taxa were collected exclusively on Q. ilex, 30 on Q. pubescens, 27 on Q. suber and 3 on Q. coccifera. Most of the taxa grow on trunks (287), while the flora is much poorer on twigs (159 taxa). The “rare” component reaches 44 % of the entire flora, showing its great importance for biodiversity.
A phytogeographical analysis of the flora is also presented. The most common chorotypes in the entire lichen flora on oaks are the widespread temperate (33.8 %), the suboceanic (32.9 %) and the Mediterranean-Atlantic (8.8 %). Quercus ilex hosts the highest percentage of suboceanic species (36.8 %) and the lowest of widespread temperate species (32.4 %). Q. pubescens hosts more temperate species (37.1 %) and less suboceanic (31.7 %). Q. suber has a high percentage of widespread temperate (46.4 %) and only 28.9 % of suboceanic species. Q. coccifera hosts 60 % of the widespread temperate and only 15 % of the suboceanic species . This indicates the more disturbed status of cork-oak stands and formations with kermes-oak. The Index of Microclimatic Dryness (IMD) (no. of widespread temperate species / no. of suboceanic species) is proposed for the first time and calculated for each plot. The index appears to be well correlated with the forest type: in well-preserved forests it shows a low value, while its value increases gradually in disturbed forest environments, from open woodland to pasture land.
The percentage occurrence of the different photobionts in the lichen flora was studied. The most interesting results are the higher frequency of lichens with Trentepohlia along the coasts of north-western and western Sardinia, where the climate is most humid, and in well-preserved montane areas. Lichens with cyanobacteria are restricted to well-preserved forests and avoid pasture land and littoral vegetation. Lichens with green algae are the only ones present in disturbed habitats and xeric conditions.
Crustose lichens are most common in the flora (51 %), followed by broad-lobed species (16 %). Fruticose- filamentose lichens and leprose lichens are the most sensitive to changes in environmental conditions, and are mostly restricted to forests with long ecological continuity. Only “saxicolous” Lepraria nivalis seems to be well adapted to disturbed conditions. Sorediate crustose lichens growing on trunks are in general more sensitive than lichens with other growth-form and reproductive strategy.
Quercus suber hosts the highest percentage of very nitrophytic lichens (7.1 %). The lowest percentage is found on Q. ilex (4.2 %), while Q. pubescens has an intermediate value (5.4 %). Q. suber and Q. coccifera, being most frequent in disturbed environments, host the highest percentages of moderately nitrophytic species (34.2 % and 67.9 % respectively).
Indicator species of old-growth and of disturbed conditions are recognized in the flora. The RIEC (Revised Index of Ecological Continuity) is calculated for all examined forests. The highest values (100) were obtained for the forests of the Marghine-Goceano and for the southern part of the Gennargentu (65). A few localities have values of 10-40. The greatest part of the investigated forests have no species faithful to old-growth forest, thus showing the presence of high disturbance due to human activities (e.g. frequent fires, overgrazing).
A hemeroby scale relative to oak forests in Sardinia based on the floristic and ecological studies of the present work, is proposed with seven degrees of hemeroby [H0 (absent) – H6 (high)]. The following parameters were taken into consideration: number of epiphytic lichen taxa/forest; RIEC value; Index of Microclimatic Dryness; number of species belonging to the Caliciales; percentage of nitrophytic species; indicator species. A hemeroby degree was attributed to the examined plots. The majority of the plots are included in the H4 degree.
A cluster analysis was applied to absence/presence tables for relevées carried out in different forest types of each oak species. From the analysis it appears that the lichen floras of forests at lower altitudes and of littoral forest are clearly distinct from those of inland and montane forests. Another distinction is due to the forest type, and the flora of well-preserved forest is usually separated from those of younger or more open woodland and pasture land. The cluster analysis applied to the species growing on trunks and present in the different examined plots shows clusters of nitrophytic species (Xanthorion), clusters of species typical of open and young woodland (communities with Parmelia, Pertusaria, Ochrolechia, Ramalina and Physconia species) and clusters of species typical of undisturbed forest (Lobarion communities and associations with Lepraria s.lat. species).
Finally, problems related to the conservation of lichens are treated.