Northwestern Italian Alps Research Articles

Seasonal course of photosynthetic efficiency in Larix decidua Mill. in response to temperature and change in pigment composition during senescence

This manuscript presents a study aimed at characterizing the seasonal course of photosynthetic capacity of an alpine deciduous conifer, European larch (Larix decidua Mill.), based on chlorophyll fluorescence measurements and photosynthetic pigment analysis. The study focused on the characterization of autumn senescence events which (contrary to bud-burst) are still scarcely investigated. The study was conducted on two natural European larch stands in the northwestern Italian Alps during two consecutive years. The results show that photosynthetic efficiency as assessed by fluorescence measurements was controlled by variations in air and soil temperature. Photosynthesis responded to variations in maximum air and soil temperature in a delayed way, with a varying lag depending on the seasonal period considered. The analysis of photosynthetic efficiency and pigment decline at the end of the growing season identified two senescence phases. During early senescence, plants manifested only the beginning of needle decolouration, while during late senescence pigment degradation led to a loss in photosynthetic efficiency. This behavior indicates that the beginning of needle yellowing and the decline in photosynthetic efficiency can occur at different times-a finding that should be considered in order to improve models of ecosystem processes.

Management tradeoff between endangered species and biodiversity conservation: The case of Carabus olympiae (Coleoptera: Carabidae) and carabid diversity in north-western Italian Alps

The worldwide loss of biodiversity is of great concern, and this has lead to strong policy frameworks to promote the maintenance of biodiversity through protecting species and habitats in many countries. Often however, rare species with legal protection provide a conservation focus, and therefore may dictate management policy. Co-occurring species, especially those without formal protected status, may contribute significantly to overall biodiversity, but may nonetheless receive limited attention. In such cases, conflicts may arise between the needs of individual species and those of wider biodiversity. We examine such a conflict in alpine ground beetles of the Sessera Valley (NW Italian Alps). This area is the type locality of the endangered species Carabus olympiae Sella, 1855, an endemic species known only from two restricted sites in the Alps. In order to assess priorities for C. olympiae conservation we used habitat suitability modeling, and identified potential indicator species that could serve as an indicator of the occurrence of the target species. In order to assess priorities for ground beetle diversity conservation we described the local ground beetle community by calculating abundance, species richness, average taxonomic distinctness (Δ+), taxonomic distinctness (Δ*) and functional diversity (FD). The best management option for the conservation of ground beetle diversity was found to be maintenance of unforested habitats, in particular pastures, which showed the highest values for all the parameters considered. Forested habitats (artificial plantation and beech forest) had the lowest ground beetle diversity. However, the preferred habitat for C. olympiae was beech forest, especially at medium altitudes (800–1400m) and with sloping terrain. Moreover, C. olympiae presence could be indirectly assessed by the co-occurrence of four indicator species: Tanythrix senilis, Carabus depressuss, Cychrus italicus and Pterostichus appenninus. Our main conclusion is that the most promising landscape-scale approach to preserve both the relict steno-endemic species C. olympiae and the high local syntopic ground beetle diversity is to maintain traditional pastoral activities along with the preservation of the unmanaged beech forests.

Soil development and microbial functional diversity: Proposal for a methodological approach

The aim of the work was to propose a new methodological approach that relates soil microbial functional diversity to soil development under different moisture regimes. As soil evolution proceeds through an increasing niche separation we expect a link between functional diversity and soil development. Shannon's (H') and Gini (D) diversity indices were calculated using eight enzyme activities (β-cellobiohydrolase, N-acetyl-β-glucosaminidase, β-glucosidase, α-glucosidase, acid phosphatase, arylsulfatase, xylosidase and butyrate esterase) in order to assess functional diversity at different scales, from soil horizons (α-diversity) to soil profiles (β-diversity) under different moisture regime (γ-diversity) and belonging to different taxonomic levels. In addition, the ratio of acid phosphatase to chitinase was calculated as a potential index of soil development. Eight soil profiles were selected: four in Northwestern Italian Alps or Northern Apennines with Udic soil moisture regimes (Typic Haplocryod, Mollic Haplocryept, Lithic Dystrudept, Lithic Cryorthent) and four in Northeastern Italy where in two cases the water table near the soil surface strongly affects the Ustic soil moisture regime, and intrazonal Aquic regime or Aquic conditions develop (Typic Haplustept, Typic Ustipsamment, Aquic Ustipsamment, Typic Psammaquent). D ranged from 50 to 95%, while the H' ranged from 3 to 2.4 in Lithic Cryorthent and Typic Psammaquent, respectively. Under Udic moisture regime an inverse relationship between soil profile development and the diversity index was observed. However the lowest the diversity in the profile, the highest the variability of the values obtained within horizons in the soil profile suggesting a link between differentiation of soil horizons and biochemical properties. The Aquic conditions interfere in establishing the relationship between soil profile development and the microbial functional diversity since H' and D increased in Typic Psammaquent with respect to Typic Haplustept (H' from 2.4 to 2.6 and D from 52.2 to 60.4). Finally, the phosphatase/chitinase ratio was related to soil development since the lowest values were obtained in the upper horizons of Typic Haplustept, Typic and Aquic Ustipsamment (from 2.0 to 4.0), while the highest values were obtained in deep horizons of Typic Haplocryod and Lithic Dystrudept (e.g. 39.2 in Bs2 and 28.0 in Bw1). In conclusion, microbial functional diversity assessed using Shannon or Gini diversity indices and phosphatase/chitinase ratio measured at different scales from soil horizons to soil profiles under different moisture regime and belonging to different taxonomic levels, may represent a new approach to establish the interrelationship between pedogenetic processes, soil development and soil microbial functions.

A new experimental snow avalanche test site at Seehore peak in Aosta Valley (NW Italian Alps)—part I: Conception and logistics

Abstract Experimental test sites are important to understand the physical flow processes occurring within an avalanche. They can be at different scale: laboratory or real scale. In Europe, a dozen of real-scale test sites have been realized, though at present only a few of them are still operative. The primary goal is to measure avalanche dynamical variables under controlled conditions. Not all the observed phenomena have been fully understood yet and more work is needed especially regarding small to medium avalanches. The aim of this paper is to present a new experimental test site at a real scale in order to study specific topics: the dynamics of small and medium avalanches, the avalanche release processes and the interaction between avalanche flows and obstacles. The test site, called Seehore, is located in Aosta Valley in the North-western Italian Alps. The slope, with an elevation difference of about 300 m (from 2300 to 2570 m asl), has a mean slope angle of about 28°. Avalanches are artificially released on a routine basis to secure the ski-runs, as the site is located within a ski resort (Monterosa Ski); they are usually dense slab avalanches of small or medium size, but also a powder cloud may occasionally form. The site is instrumented with a steel obstacle, described in details in a companion paper, which measures the effects of avalanches impacting on it. Before, during and after each artificial release physical properties of the snow in the avalanche release, track and deposition zones are recorded; front velocity, erosion and deposition mass are estimated by field surveys or by videogrammetry and terrestrial laser-scan measurements.

Does natural reforestation represent a potential threat to dung beetle diversity in the Alps?

Traditional agro-pastoral practices are in decline over much of the Alps, resulting in the complete elimination of livestock grazing in some areas. Natural reforestation following pastoral abandonment may represent a significant threat to alpine biodiversity, especially that associated with open habitats. This study presents the first assessment of the potential effects of natural reforestation on dung beetles by exploring the relationships between the beetle community (abundance, diversity, species turnover and assemblage structure) and the vegetation stages of ecological succession following pastoral abandonment. A hierarchical sampling design was used in the montane belt of the Sessera Valley (north-western Italian Alps). Dung beetles were sampled across 16 sampling sites set in four habitat types corresponding to four different successional stages (pasture, shrub, pioneer forest and beech forest) at two altitudinal levels. The two habitats at the extremes of the ecological succession, i.e. pasture and beech forest, had the greatest effect on the structure of local dung beetle assemblages. Overall, dung beetle abundance was greater in beech forest, whereas species richness, Shannon diversity and taxonomic diversity were significantly higher in pasture, hence suggesting this latter habitat can be considered as a key conservation habitat. Forests and pastures shared a lower number of species than the other pairs of habitats (i.e. species turnover between these two habitats was the highest). The two intermediate seral stages, i.e. shrub and pioneer forest, showed low dung beetle abundance and diversity values. Local dung beetle assemblages were also dependent on season and altitude; early-arriving species were typical of pastures of high elevation, whereas late-arriving species were typical of beech forests. It is likely that grazing in the Alps will continue to decrease in the future leading to replacement of open habitats by forest. This study suggests therefore that, at least in the montane belt, reforestation may have potentially profound and negative effects on dung beetle diversity. Maintaining traditional pastoral activities appears to be the most promising approach to preserve open habitats and adjacent beech forests, resulting in the conservation of species of both habitats.

The Impact of Overgrazing on Dung Beetle Diversity in the Italian Maritime Alps

Dung beetles (Coleoptera: Scarabaeidae) are undoubtedly the most typical and ecologically relevant insects of grazed alpine habitats because they provide valuable ecological services such as biological pest control and soil fertilization. Despite the great ecological contribution of these insects to pasture ecosystem functioning, little is known about their direct or indirect relationships with pastoral activities. The main aim of the study was to assess whether dung beetle diversity was influenced by different intensities of cattle grazing. Dung beetle communities of two adjacent alpine valleys within the Maritime Alps Natural Park (north-western Italian Alps), representing overgrazed and ungrazed pastures, were studied by pitfall trapping. A hierarchical design (three levels: valleys, transects, and replicates) was established for additive partitioning of γ-diversity and Indicator Species Analysis. Evenness and Shannon diversity were significantly higher at the ungrazed than at the overgrazed site because abundances were much more evenly distributed at the former than at the latter site (where one species was dominant over all the others). Dung beetle abundance and species richness of the overgrazed graminaceous pasture vegetation types were in most cases significantly lower than those of the ungrazed nongraminaceous vegetation type. In the additive partitioning of γ -diversity analysis relative to the whole study area, the randomization procedure indicated that the contribution of β to γ-diversity was significantly different from that expected by chance, suggesting that one or more environmental factors has intervened to change the partition of total diversity in the system considered. The analysis of the preferences and fidelity of species (Indicator Species Analysis) showed that only one species chose overgrazed pastures; all the others positively selected the ungrazed site, or the only ungrazed pasture vegetation type (Rumicetum alpini Beger) occurring at the overgrazed site. Results conformed to evidences that overgrazing represents a serious threat to the conservation of alpine dung beetles. To conserve local dung beetle assemblages, especially in protected areas, cattle overgrazing should be avoided. This does not mean, however, that pastoral activities are incompatible with biodiversity conservation. The contemporaneous presence of wild ungulates and low intensity extensive pastoral activities may be useful to preserve both local dung beetle assemblages and alpine pasture ecosystems.

Modelling soil removal from snow avalanches: A case study in the North-Western Italian Alps

Snow avalanches can exert considerable erosive forces on soils. If a snow avalanche flows directly over bare ground, basal shear forces may scrape away and entrain soil. Sediments mix up with the avalanche body and may be found within the run-out snow deposit. Based on a previous field campaign aiming to quantify the amount of sediments trapped within avalanche bodies for the study site of Lavancher, in the Aosta Valley, NW-Italy, we developed here a soil erosion model, which we preliminarily applied to that site. An already developed and tested 1-D avalanche dynamics model was modified to include soil erosion. Soil removal was triggered according to two different mechanisms, namely excess of shear and critical velocity. We used equations from the available literature to model the shear stress exerted by the avalanche flow upon the ground underneath. Critical threshold for soil removal of either shear or velocity were also retrieved from the available literature, possibly depending upon soil texture and geotechnical properties. The model performs well in reproducing soil removal for three wet-dense avalanches that occurred in the study site. Use of excess of shear mechanism to evaluate erosion seems more robust, as less dependent upon flow velocity, utmost uncertain. Albeit more accurately measured events of soil eroding avalanches seem necessary to test its performance, the model can be used henceforth as a basis for further refinement concerning geomorphologic contribution of avalanches. ► We set up a model to mimick soil erosion by snow avalanches. ► We use both excess of shear and critical velocity erosion mechanism. ► Application to three avalanche events indicates acceptable performance. ► Excess of shear seems less sensitive to model's output than critical velocity. ► Soil water content and temperature may control rate of erosion.

Monitoring snow avalanches in Northwestern Italian Alps using an infrasound array

Abstract Risk assessment of snow avalanches is mostly related to weather conditions and snow cover. However, a robust risk validation requires avalanche activity data, in order to compare predictions to actual events. For this purpose in December 2009 we installed a temporary 4-element, small aperture (150 m), infrasound array in the northwestern Italian Alps. The array was installed south of Mt. Rosa, at an elevation of 2000 m a.s.l. in the valley of Gressoney, Italy, where natural avalanches are expected and avalanche control by explosives is regularly performed. A multi-channel correlation analysis is carried out on the continuous infrasound data set recorded by the array as a function of apparent velocity, back-azimuth and frequency of recorded infrasound. This allowed detectionof infrasonic signals propagating across the array from the background noise. During the 5-month-long experiment, 343 infrasonic events have been detected and characterized. These include sharp infrasonic transients (99 events) produced by explosions during avalanche control as well as longer lasting signals (244 events) possibly caused by avalanches. Although only few of these events were validated by direct avalanche observation, obtained results are promising and encouraging application of infrasound for long-term avalanche observation on wide areas, as the peak in avalanche activity in winter 2009–2010 was observed shortly after the infrasound events peaked as well.

Properties, best management practices and conservation of terraced soils in Southern Europe (from Mediterranean areas to the Alps): A review

Terrace soils are distinctive features of the agricultural landscape in Europe. Due to their historical and aesthetic significance, they are a resource for agriculture and tourism: however they are also a challenge for land conservation and management. Nevertheless, the fundamental role of terrace soils for agricultural quality and natural hazard prevention has not been fully investigated.In the past, terraced slopes became ideal sites for human settlement and agricultural activities. At present, they are often used for high quality crops that grow on soils with specific chemical and physical properties. The filling material used for building terraces is a human-reworked substrate, where pedogenesis occurs under a strong human influence. This leads to soils with a generally limited pedogenic development and coarse texture, although, often, with good productivity. When abandoned, terraces are subjected to progressive decay due to erosion processes and slope failures.This review focuses on terrace soil properties, conservation and management in Southern Europe. In particular, it reports some examples from the northwestern Italian Alps, where terraced slopes are characterised by ancient origin and, presently, are subjected to specific practices for their preservation. The different effects of land degradation at hill slope scale may be mitigated through appropriate management practices favoring the terrace walls maintenance, drainage optimization, and the presence of a spontaneous vegetation cover. These subjects require careful planning and conservation measures that could be collected in “best practices” guidelines for farmers, landowners and decision-makers.

Runoff regime estimation at high-elevation sites: a parsimonious water balance approach

Abstract. We develop a water balance model, parsimonious both in terms of parameterization and of required input data, to characterize the average runoff regime of high-elevation and scarcely monitored basins. The model uses a temperature threshold to partition precipitation into rainfall and snowfall, and to estimate evapotranspiration volumes. The role of snow in the transformation of precipitation into runoff is investigated at the monthly time scale through a specific snowmelt module that estimates melted quantities by a non-linear function of temperature. A probabilistic representation of temperature is also introduced, in order to mimic its sub-monthly variability. To account for the commonly reported rainfall underestimation at high elevations, a two-step precipitation adjustment procedure is implemented to guarantee the closure of the water balance. The model is applied to a group of catchments in the North-Western Italian Alps, and its performances are assessed by comparing measured and simulated runoff regimes both in terms of total bias and anomalies, by means of a new metric, specifically conceived to compare the shape of the two curves. The obtained results indicates that the model is able to predict the observed runoff seasonality satisfactorily, notwithstanding its parsimony (the model has only two parameters to be estimated). In particular, when the parameter calibration is performed separately for each basin, the model proves to be able to reproduce the runoff seasonality. At the regional scale (i.e., with uniform parameters for the whole region), the performance is less positive, but the model is still able to discern among different mechanisms of runoff formation that depend on the role of the snow storage. Because of its parsimony and the robustness in the approach, the model is suitable for application in ungauged basins and for large scale investigations of the role of climatic variables on water availability and runoff timing in mountainous regions.

Pinus sylvestris forest regeneration under different post-fire restoration practices in the northwestern Italian Alps

It is frequently believed that a post-fire environment requires immediate actions in order to be restored. Salvage logging followed by plantation is a common post-fire restoration practice in many forests of the northwestern Italian Alps. The objectives of this study were to assess the impact of active and passive management techniques on the restoration of a burned area of the Aosta Valley and to determine which approach is the most suitable for enhancing Pinus sylvestris regeneration after stand replacing wildfires. The influence of five management options (no intervention; salvage logging; broadleaves plantation; Larix decidua plantation; P. sylvestris or Pseudotsuga menziesii plantation) and environmental variables on natural regeneration structure and composition was evaluated through direct gradient analysis. Pinus sylvestris and Populus tremula were the dominant tree species (40 and 29%, respectively) in the regeneration layer. Density, size, and structural diversity of natural regeneration were higher in the no intervention area. The proximity to forest edge was found to be the most important environmental variable. This study provided evidence that taking advantage of natural restoration processes may be a suitable alternative strategy to the active restoration practices adopted according to the Aosta Valley policy of post-fire management.

Conservation value of artificial subterranean systems: A case study in an abandoned mine in Italy

Subterranean ecosystems often harbour unique and specialised biocoenoses of considerable scientific interest and high potential conservation value. In view of the peculiar species assemblage in the abandoned tunnels of a talc mine complex in the north-western Italian Alps (Germanasca Valley, Province of Turin, NW Italy), the aims of the present work were (i) to investigate the subterranean invertebrate fauna, (ii) to assess the impact of tourism activities on the invertebrate fauna, and (iii) to assess the conservation value of the terrestrial invertebrate community and associated habitats. The study was carried out at four sites: one tunnel restored for tourism purposes; two abandoned tunnels; and a wild cave. The results of several statistical analyses, including ANOVA, PCA and CCA, showed that the eutrophic conditions induced by past human activity could improve the quality of the subterranean habitat. On the other hand, a massive intervention for tourism purposes could seriously jeopardise the survival of the most sensitive species. The increased thermic instability and mean temperature had a significant negative effect on the local populations of cave-dwelling arthropods, whose ecological optimum is determined primarily by low thermic instability, cold temperatures and intermediate conditions of eutrophy. On the basis of our results we strongly recommend to avoid thermic isolation of any part of tunnels, as it is the primary factor affecting the most sensitive species.

Description and numerical modelling of the October 2000 Nora debris flow, Northwestern Italian Alps

The Nora alluvial fan, which is located in the Orco River valley (Piedmont region, Italy), was affected by a debris flow of approximately 10 000 m3 in October 2000. The event was triggered by heavy rainfall that affected the whole Piedmont region at that time. The mobilization of the water-satured altered gneissic bedrock and colluvium in the upper zone of the Nora basin resulted in the detachment of a debris slide, which rapidly evolved into a channelized noncohesive debris flow. As information from post-event surveys and two pre-event digital elevation models (DEMs), with different resolutions, were available for the study site, the dynamics of the event has been numerically back-analyzed using the numerical code RASH3D. The obtained results have shown both the capability of the code to simulate the dynamics of a noncohesive debris flow, including the final deposit depth distribution, and the importance of on-site surveys and digital elevation model (DEM) resolution in interpreting numerical results and the associated calibrated rheological parameters.

Investigating the relationship between raw milk bacterial composition, as described by intergenic transcribed spacer-PCR fingerprinting, and pasture altitude

To assess the bacterial biodiversity level in bovine raw milk used to produce Fontina, a Protected Designation of Origin cheese manufactured at high-altitude pastures and in valleys of Valle d'Aosta region (North-western Italian Alps) without any starters. To study the relation between microbial composition and pasture altitude, in order to distinguish high-altitude milk against valley and lowland milk. The microflora from milks sampled at different alpine pasture, valley and lowland farms were fingerprinted by PCR of the 16S-23S intergenic transcribed spacers (ITS-PCR). The resulting band patterns were analysed by generalized multivariate statistical techniques to handle discrete (band presence-absence) and continuous (altitude) information. The fingerprints featured numerous bands and marked variability indicating complex, differentiated bacterial communities. Alpine pasture milks were distinguished from lowland ones by cluster analysis, while this technique less clearly discriminated alpine pasture and valley samples. Generalized principal component analysis and clustering-after-ordination enabled a more effective distinction of alpine pasture, valley and lowland samples. Alpine raw milks for Fontina production contain highly diverse bacterial communities, the composition of which is related to the altitude of the pasture where milk was produced. This research may provide analytical support to the important issue represented by the authentication of the geographical origin of alpine milk productions.

The maintenance of extensively exploited pastures within the Alpine mountain belt: implications for dung beetle conservation (Coleoptera: Scarabaeoidea)

The abandonment of marginal areas and the decline of traditional small-scale cattle-breeding is bringing about substantial changes in many areas of the Alpine mountain belt. Extensively exploited pastures, which were colonized by typical ecological communities, are now being replaced by shrublands and forests. In this paper, we evaluate the effectiveness of the maintenance of small pastures for dung beetle (Scarabaeoidea: Geotrupidae, Aphodiidae, Scarabaeidae) conservation in a protected area of the north-western Italian Alps. From July until September 2007, we studied the dung beetle coenosis in the main habitats of the mountain belt: beech forest, scots pine forest, mountain pine forest and pasture. Twenty-three species were sampled. We compared abundance, species richness, α-diversity, evenness and species turnover between the four habitat assemblages and performed a correspondence analysis based on dominance patterns of the three families. Two main ensembles were identified: a pasture ensemble, highly diverse and dominated by Scarabaeidae, and a closed habitats ensemble, less structured and dominated by Aphodiidae and Geotrupidae. Combining habitat specificity and fidelity, the IndVal method showed that half of the species collected made a strong habitat selection toward pasture, while only C. granarius (Aphodiidae) was a reliable indicator of woody areas. We therefore conclude that the loss of extensively exploited pastures may bring about fundamental changes in dung insect communities. In protected areas, a management policy intended to preserve the traditional, sustainable human activities within the mountain belt is highly recommended for the conservation of these insects.

The impact of forest ski-pistes on diversity of ground-dwelling arthropods and small mammals in the Alps

Forest clearing for winter sport activities is the major force driving loss and fragmentation of the alpine forests. The establishment of ski-pistes involves impacts on every ecosystem component. To assess the extent of this threat we studied ground-dwelling arthropods (namely ground beetles and spiders) and small mammals (shrews and voles) at two ski resorts in north-western Italian Alps by pitfall trapping. Diversity parameters (mean abundance, species richness and Shannon index) of spiders and macropterous carabids increased from forest interior to open habitats (i.e., ski-piste or pasture), whereas parameters of brachypterous carabids significantly decreased from forest interior to open habitats. Diversity parameters of macropterous ground beetles were higher on pastures than on ski-pistes. Small mammals were virtually absent from ski-pistes. Observed frequencies in the three adjacent habitats were significantly different from expected ones for the bank vole Myodes glareolus and the pygmy shrew Sorex minutus. Generalized linear models showed that abundance, species richness and diversity of spiders and macropterous carabids of ski-pistes were best modelled by combination of factors, including grass cover and width of the ski-piste. Indicator Species Analysis showed that species that significantly preferred ski-pistes were less than those preferring pastures, and species which were exclusive of ski-pistes were very few. To retain arthropod ground-dwelling fauna of open habitats environmentally friendly ways of constructing pistes should be developed. After tree clearing, only the roughest ground surfaces should be levelled, in order to preserve as much natural vegetation as possible. Where necessary, ski-pistes should be restored through the recovery of local vegetation.

An analytical model of the effects of catchment elevation on the flood frequency distribution

The effect of temperature on the flood frequency distribution in mountainous basins is examined through a minimalist analytical model. The conceptual hypothesis on which the model is grounded is the existence of a subtractive mechanism that reduces the basin‐contributing area in flood formation to the fraction of basin laying below the freezing elevation at the time of occurrence of each precipitation event. This fraction depends on the watershed hypsometric curve and on the seasonal evolution of temperatures. Under this hypothesis, the probability distribution of the annual maximum discharge is analytically derived, based on simple assumptions on the stochastic process of precipitation. The shape and the moments of this distribution explicitly relate to basin hypsometry and to the seasonality of temperatures. Qualitative results show that the simple causative mechanisms can explain the attenuation of flood quantiles in high‐elevation basins. Model application to 57 watersheds in the Northwestern Italian Alps effectively demonstrates the role of the hypsography in explaining the spatial variability of the mean of the flood distribution.

Late Holocene glacial and periglacial evolution in the upper Orco Valley, northwestern Italian Alps

The sediments present in some areas of the Orco Valley provide indications on climatic variations that occurred during the last 6000 years on the southern slopes of the Alps. In particular, distribution and ages of peat layers help define periods and extent of glacial fluctuation in the last 2200 years. Sampling of soils involved in periglacial processes provided a basis for development of a chronological framework of late Holocene environmental change. The data indicate a trend toward cooler climate in the second half of the Holocene. A strong relationship exists between phases of River Po flooding and expansion/retreat phases of the Swiss glaciers: major glacial advances were coeval with periods of intense flooding of the River Po, whereas the phases of glacial retreat coincided with periods of little flooding of the Po. Only in three cases do relationships between glacier activity and floods show weak correlations; two of the cases relate to the warmest periods in approximately the last 2200 years, while the third is the present period. Paleoclimatic evidence from the study region indicates the relatively warm Roman Period between about 2200 and 1900 cal yr BP appears to better represent modern conditions than does the Medieval Warm Period.

Labile nitrogen, carbon, and phosphorus pools and nitrogen mineralization and immobilization rates at low temperatures in seasonally snow-covered soils

Surface mineral horizons from four ecosystems sampled in the northwestern Italian Alps were incubated at −3 and +3°C to simulate subnivial and early thaw period temperatures for a seasonally snow-covered area. The soil profiles at these sites represent extreme examples of management, grazed meadow (site M) and extensive grazing beneath larch (site L) or naturally disturbed by avalanche and colonized by alder (site A) and the expected forest climax vegetation beneath fir (site F). Changes in labile pools of nitrogen (N) and phosphorus (P) were active at all sites at both temperatures during 14 days of laboratory incubation. Ammonium was the dominant inorganic form of total dissolved N (TDN), being equivalent to 1.8–9.8 g N m−2 within the mineral horizon. Gross rates of ammonification were similar at the two temperatures but significantly (p<0.05) greater in soil from beneath fir than in the other three. Nitrification occurred in all soils and displayed a wide range in rates, from 2 to 85 mg N m−2 day−1, and was least in the two most acid soils, A and F. Immobilization of NH4 + as microbial N was greater in the fir soil than in the other three. Also, the fir soil showed greatest gross ammonification and least accumulation of NO3 − and greatest tendency to retain N. This high N retention capacity in the climax ecosystem contrasted with the managed systems characterized by higher nitrification rates and greater potential spring NO3 − loss. Dissolved organic N ranged between 30 and 50% of the TDN, while dissolved organic P was greater than 70% of total dissolved P (TDP). The dissolved organic compounds were important components of the labile pool, in equilibrium with a large reserve of organic N, and may significantly contribute to the soil N availability at low temperatures.

High-pressure metamorphism of the Lanzo peridotite and its oceanic cover, and some consequences for the Sesia–Lanzo zone (northwestern Italian Alps)

This paper presents new data on the Alpine high-pressure evolution of the Lanzo peridotite massif and its metasedimentary cover (Western Alps). Field relations in the northwestern Lanzo massif show that the serpentinized part is covered by a metasedimentary sequence including local occurrences of metaophicarbonate, metabasalt, calcschist, metaquartzite and gneiss. Remnants of granulite-facies mafic gneiss associated with metaophicarbonate are found within the serpentinite. Major element garnet zonation profiles in metaquartzite and mafic gneiss were used to explore the contrasting origin of metasediments. Bell-shaped Mn zoning in garnet from metaquartzite indicates a one-stage Alpine metamorphic evolution, while inverse zoning in garnet of the mafic gneiss shows that the protolith equilibrated under high-grade metamorphic conditions in pre-Alpine times, similar to kinzigites within the neighbouring Sesia zone. Phase equilibria in metaquartzite and mafic gneiss point to 500 ± 50 °C at pressures of 0.9 to 1.3 GPa for the Alpine metamorphic equilibration that contrasts with the 550–620 °C and pressures in excess of 2.0 GPa obtained for kyanite + talc + chloritoid and talc + chloritoid + garnet domains in a metagabbro dike from the internal part of the Lanzo massif. These different P– T trajectories can be explained by a much stronger retrograde overprint at the basement–cover contact than in the internal part of the Lanzo massif.