Question\ud Poikilohydric organisms can survive desiccation without damage and recover soon after re-wetting. In this work we explore the realized niches of epilithic, poikilohydric organisms, i.e. lichenized and lichenicolous fungi and bryophytes, grouped into 15 functional guilds based on growth form, reproductive strategy and photosynthetic traits. We hypothesize that in Mediterranean ecosystems, the distribution of these guilds is controlled by water availability and solar radiation, together with characteristics of the substrate.\ud \ud Location\ud Western Sardinia (Italy). The area hosts Mediterranean Quercus ilex forests on basaltic substrata within an agroforestry landscape.\ud \ud Methods\ud The presence or absence of species from each guild was recorded in 1025 small quadrats (10x10cm). Four environmental variables were measured: solar radiation, microtopography (potential water run-off), substrate roughness and number of cracks. The occurrence of each guild was related to environmental variables using non-parametric multiplicative regression, and ecological niches of the guilds were derived from those models.\ud \ud Results\ud The occurrence of all functional guilds varied significantly according to the selected environmental variables. In most cases, solar radiation was the most important variable; TI was included first in the model of two sorediate guilds, whereas four sexually reproducing functional guilds had surface relief as first variable. The growth forms were separated along a gradient of increasing solar radiation, whereas water run-off and surface roughness mainly discriminated reproductive strategies and photobionts. Vegetatively reproducing guilds with other photobionts than Euphyta-like pigments were confined to the border of the ecological space, defined by gradients of environmental factors, which was largely occupied by more competitive, sexually reproducing organisms.\ud \ud Conclusions\ud Functional traits of epilithic poikilohydric organisms were associated with ecological adaptations to the stressful environment of Mediterranean outcrops. We showed that their response in terms of probability of occurrence is coherent with quantitative gradients of solar radiation and water availability at the micro-scale

Summary1. We attempted to elucidate the roles of b-diversity components and similarity in shaping Lobaria pulmonaria lichen communities in Italian forests to provide scientific tools for improving their longterm conservation. 2. A total of 20 sites were selected by stratified random sampling, including five chestnut forests, seven beech-silver fir forests and eight oak forests distributed across 10 administrative regions of Italy. Site selection was based on a national data base including all the available records of L. pulmonaria in Italy. In each forest, four plots were randomly placed, and in each plot, 5-6 trees were randomly selected for lichen sampling. For each forest and plot, meaningful predictors of lichen patterns were quantified. In particular, factors indicative of both geographic conditions and forests structure were considered. The SDR simplex approach was used to estimate the relative importance of similarity (S), relative species replacement (R) and relative richness difference (D) to b-diversity and similarity, while a hierarchical partitioning (HP) method was used to evaluate the relative importance of environmental predictors in explaining their patterns. 3. A total of 201 lichens and three nonlichenized fungi were found, including 51 species of conservation concern. The components of b-diversity and similarity contributed to shaping L. pulmonaria communities at both forest and plot scales across Italy, resulting in nearly random compositions, that is, the species set on each tree was a random sample from the available species pool. Species replacement and similarity were generally associated with forest structure predictors, while richness difference was mainly associated with geographic predictors. The implication of this is that the long-term conservation of L. pulmonaria communities could be promoted by maintaining scattered nodes and appropriate habitat traits, especially in large forested landscapes where species turnover is higher. 4. Synthesis. In this work, we used a new approach for analysing a countrywide data set improving the ecological understanding of the dynamics regulating epiphytic communities. In particular, this study improves the understanding of the contribution of different components of diversity across two spatial scales and evaluates the relative importance of environmental predictors in explaining variation of each diversity component.

Rapid Biodiversity Assessments (RBAs) of lichen communities, obtained by means of simplified sampling lists based on morphospecies, showed good correlations with Lichen Diversity Values (LDVs), based on the complete identification of lichen species only when performed by operators with high levels of taxonomic knowledge. Furthermore, the use of highly simplified sampling lists did not lead to significant advantages in terms of time needed for field operations. This approach proved to be especially unreliable in high diversity ecological contexts where variation of morpho-structural composition within lichen communities is frequent (i.e. co-occurring crustose- and foliose-dominated communities); it may also lead to weak results if applied for conservation purposes. Hence, the use of simplified RBA sampling lists in lichen monitoring has to be carefully evaluated and, in any case, should be based on sound taxonomic knowledge on the part of those in charge of data collection. The proper assessment of descriptors of lichen abundance and/or frequency, however, strictly depends on the skill, taxonomic knowledge, and willingness to learn of the lichenologist-in-training.

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