S. Impagliazzo’s research while affiliated with University of Naples Federico II and other places

The Holocene palaeofires in Southern America has been generally attributed to climate until the middle Holocene and to human activities for later periods. Soil charcoal analysis and extensive AMS dating were carried out on six soil profiles, between 3400 and 3900 m a.s.l. in the Guandera Biological Reserve (Western Cordillera Real, North Ecuador). AMS results showed an ordered stratification of charcoals allowing a fire history reconstruction over the last 11,700 cal BP.The reported fire occurrences fit well with Holocene global scale arid periods. The association between fires and climate signals suggested a marginal role of humans in the environmental history of the studied area. Here, the human inference started at ca 2500 cal BP, but became considerable only in the last millennium.

The present study represents the first attempt of reconstructing fire history through soil charcoal dating. The investigated area is located in the Guandera Biological Reserve (western Cordillera Real, northern Ecuador). Six AMS radiocarbon dating, performed at the base of five soil profiles allowed a fire phase to be identified during the Pleistocene–Holocene transition. A strong correspondence was highlighted between the age of the Guandera fires and the El Abra stadial, which is considered the Younger Dryas equivalent in South America. This local evidence of fires contributes to define the geographic area in which the El Abra stadial was recorded and suggests a wider use of the soil charcoal analysis.

Indications for the speed and timing of past altitudinal treeline shifts are often contradictory. Partly, this may be due to interpretation difficulties of pollen records, which are generally regional rather than local proxies. We used pedoanthracology, the identification and dating of macroscopic soil charcoal, to study vegetation history around the treeline in the northern Ecuadorian Andes. Pedoanthracology offers a complementary method to pollen-based vegetation reconstructions by providing records with high spatial detail on a local scale. The modern vegetation is tussock grass páramo (tropical alpine vegetation) and upper montane cloud forest, and the treeline is located at ca. 3600 m. Charcoal was collected from soils in the páramo (at 3890 and 3810 m) and in the forest (at 3540 m), and represents a sequence for the entire Holocene.The presence of páramo taxa throughout all three soil profiles, especially in combination with the absence of forest taxa, shows that the treeline in the study area has moved up to its present position only late in the Holocene (after ca. 5850 cal years BP). The treeline may have been situated between 3600 m and 3800 m at some time after ca. 4900 cal years BP, or it may never have been higher than it is today. The presence of charcoal throughout the profiles also shows that fires have occurred in this area at least since the beginning of the Holocene.These results contradict interpretations of palaeological data from Colombia, which suggest a rapid treeline rise at the Pleistocene–Holocene transition. They also contradict the hypothesis that man-made fires have destroyed large extents of forest above the modern treeline. Instead, páramo fires have probably contributed to the slowness of treeline rise during the Holocene.

Natural hybridization between plant species often occurs in disturbed habitats and it is generally considered a threat for rare and endangered species. A different situation occurs in Mediterranean food deceptive orchids, where hybridization is a common phenomenon, as a natural consequence of their unspecific pollination system.Here, we present molecular and ecological evidence from a hybrid zone between Orchis mascula and O. pauciflora in order to address the consequences of hybridization on local orchid evolution and to assess conservation priorities for hybrids and hybrid zones in orchid conservation programs.We find that, although hybrids among the two target taxa are formed relatively frequently, hybrid zones often consist of F1 individuals, whereas backcrosses and later generation hybrids appear to be either rare or absent, presumably as a consequence of post-zygotic reproductive barriers acting in these food-deceptive orchids. Experimental evidence further indicates that hybrids are less fit than the parental species in attracting pollinators and that parental taxa exhibit higher or similar fitness in sympatry compared to allopatric populations. Since introgression is not frequent as indicated by molecular analyses, fitness and phenotypic trait differences observed among sympatric and allopatric populations of the parental taxa may be a consequence of pollinator-mediated selection.Our experimental data confirm that hybridization is a natural phenomenon in food-deceptive orchids and that it does not pose a threat to their survival. Furthermore, sympatric zones provide the stage for evolutionary processes in orchids, and this peculiarity should be taken into account when devising orchid conservation strategies.