Biology and conservation status of Juniperus macrocarpa Sm. in Sardinia

The present Ph.D. thesis aimed to provide a better understanding of Juniperus macrocarpa and the habitat that it characterizes (Juniperus spp. habitat; European priority habitat) in Sardinian coastal dunes, as well as to achieve results useful to support in situ and ex situ conservation actions. In particular, the specific aims of the thesis were: (1) to analyse morphological variation in seeds of Mediterranean Juniperus taxa (at inter- and intraspecific level) and morphometric differences in J. macrocarpa seeds collected in different populations, seasons and sources; (2) to evaluate the effect of the collecting season, source, laboratory pre-treatments and temperatures on seed viability and germination of J. macrocarpa; (3) to investigate factors affecting seedling emergence, survival and growth of the species; (4) to explore the floristic variability of the habitat in Sardinia in relation to geographic, climatic and human variables, as well as the potential effect of human disturbance and sampling period on key plant parameters; and finally (5) to assess the conservation status of this habitat in Sardinia. In the first chapter, a statistical classifier for Mediterranean Juniperus taxa based on seed morphometric parameters analysed by image analysis techniques, was tested at interspecific, specific and intraspecific levels. Analysed seeds came from galbules of Juniperus taxa collected from different regions of the Mediterranean Basin and galbules of J. macrocarpa collected in 2010 from four Sardinian populations, in two seasons and in plants and soil. Two taxonomic treatments for Juniperus genus (Flora Europaea and The Plant List) were compared and inter-population, seasonal and source variability in seed morphology were analysed. High percentages of correct identification were reached for both taxonomic treatments at specific and intraspecific level and from the comparison among taxa of the J. oxycedrus, J. communis and J. phoenicea complexes. Moreover, this statistical classifier discriminated J. macrocarpa seeds collected in spring better than those collected in autumn, but it seemed not to be able to discriminate those seeds collected from plants and soil, nor those ones collected in different populations from the same geographical region. In the subsequent chapter, seed viability and germination phenology of J. macrocarpa were investigated. For this purpose, ripe galbules in four localities and in two seasons, both from plants and soil, were collected. In order to verify the presence of physiological dormancy, warm (W) and cold stratification (C), two combinations of them (W+C and C+W), and no pre-treatment (control) were applied. After pre-treatments, seeds were incubated in a range of constant (10–25°C) and alternating (25⁄10°C) temperatures. Seed viability was low (ca. 40%) and the source (plant or soil) had not a significant effect on it, but it varied significantly according to season, showing lower percentages for seeds collected in autumn than in spring. Seed germination was low (ca. 10%), the control and W were the most effective on stimulating germination, while C negatively affected germination. The best temperatures for germination were 15 and 20°C and seeds collected in spring showed higher germination percentages (ca. 11%) than in autumn (ca. 7%). Seeds of J. macrocarpa are dormant and the results of this study suggested the presence of secondary dormancy induced by cold stratification. The germination phenology all along the dispersal season (from autumn to spring) was illustrated, as well as the potentiality of this taxon to create a soil seed bank. In the third chapter, factors affecting emergence, survival and growth of J. macrocarpa seedlings, were investigated. For this study, permanent plots were placed and periodically monitored. Within them, besides seedling parameters (emergence, survival and growth), several biotic and abiotic variables (solar radiation, tree cover, herbaceous plus scrub cover, distance from the closer J. macrocarpa female, number of galbules on the soil and event number of herbivore trace) were measured. Linear mixed-effects models were used to test the relative importance of different groups of explanatory variables on seedling parameters. A total of 536 seedlings were marked, most of which emerged in winter. The "microclimate" was the best fit model explaining emergence, highlighting the positive relation between the number of emerged seedlings and tree cover. Survival was very low and most of the seedlings died in the first months from emergence, reaching the highest mortality rate in the first summer. High values of both herbivory and solar irradiation increased mortality risk. Our results confirmed that J. macrocarpa is a slow growing species, and no seedlings reached the subsequent size class. Moreover, growth depended on suitable microhabitats, and in particular it was positively related to tree cover, hours of sunlight, and herbaceous plus scrub cover. Despite these relevant results, long-term studies are needed to identify key issues in the life cycle of J. macrocarpa (e.g. germination, fitness, and recruitment). In the last chapter, the floristic variability of Juniperus spp. habitat in Sardinia in relation to geographic, climatic and human variables was explored. Two data sets were created: the first one by inputting phytosociological relevés available in literature and our own relevés; the second one by including for each relevé geographic, climatic and floristic variables, as well as sampling period and human disturbance as categorical variables. The floristic composition differed among sites and this variation was mainly ruled by a latitudinal gradient linked to a climatic gradient. Regarding the results of key parameters in the evaluation of the habitat quality, floristic richness was positively influenced by low and medium level of human disturbance; the endemic taxa cover was positively related to a medium level of human disturbance, while the alien taxa cover was positively related to recent samplings. The conservation status of Juniperus spp. habitat in Sardinia following the IUCN protocol we also assessed. Preliminary results showed that this habitat should be considered as endangered (EN) at a regional level. In conclusion, our results gave new findings for the recovery and conservation planning of the species and the habitat under study. Specifically, we found that spring was the best season for seed collection. We also suggest: autumn as the period for planting or sowing, with planting being preferable to sowing; shielding plants from solar radiation under canopy; the application of techniques such as organic blanket when sowing is the selected option. In addition, in order to improve the conservation status of Juniperus spp. habitat, we advise management measures such as the eradication of alien taxa, as well as interventions aimed to reduce human impact on the dune systems.