Giovanni Leonelli

Climatic and Environmental Influences on Mountain Pine (Pinus montana Miller) Growth in the Central Italian Alps

ABSTRACT In this paper we analyze upright mountain pine (Pinus montana Miller) radial growth responses to climatic and environmental factors in a valley of the Central Italian Alps. This valley is characterized by intense geomorphological dynamics that can mostly be traced back to instability processes and particularly to debris flows. Here, there are also less active areas that allow undisturbed tree growth and permit dendroclimatic research to be performed. The relationship between climatic factors and radial growth in mountain pine was established by Pearsons correlation and response functions using four chronologies. Two were built using trees located on opposite valley slopes; the other two from the valley bottom. One of these last two is constructed with trees growing in areas occasionally affected by sheetfloods. We found that the climate of the summer months has the strongest influence on tree-ring growth: especially May and July mean temperatures and June precipitation. In contrast, the chronology built with trees located in the valley bottom in an area affected by sheetfloods, shows different climate-growth relationships especially concerning summer precipitation. The burial made by silt layers and the more impermeable conditions of the substrate seem to be the main factors regulating tree growth in this area. Comparing this chronology with the reference chronologies, we found that some years with growth anomalies in the disturbed site correspond to debris flow events dated by previous studies in nearby fans. This paper points out the potential use of mountain pine for dendroclimatic reconstruction and the influence of soft slope processes on tree growth.

The influence of glacier surface processes on the short-term evolution of supraglacial tree vegetation: The case study of the Miage Glacier, Italian Alps

Supraglacial debris cover allows vegetation to colonize glacier surface, and whenever it is enough stable and thick, also shrubs and trees can germinate and grow. Supraglacial tree growth and distribution patterns on the glacier are closely connected with the debris-covered glacier dynamics and evolution. The aim of the research reported here was to evaluate the tree age and tree distribution patterns on the glacier tongue and the influence of ice-cliff backwasting, close to glacier terminus, on tree loss. We analysed the fragile and fast-changing environment that is present on the lower ablation sector of the Miage Glacier (Mont Blanc Massif, Italian Alps) where some ice cliffs are present and backwasting and downwasting phenomena occur. Tree features and short-term evolution were analysed with respect to glacier variations (mainly surface displacements and ice ablation) and geometry changes of the two most representative ice cliffs. The supraglacial trees’ life time resulted to be mainly controlled by glacier surface displacements and by the occurrence of backwasting and downwasting processes, whereas tree germination was associated with fine debris presence. These factors, controlling plants’ life and growth on the glacier, are an actual limit when supraglacial trees are analysed to reconstruct past environmental changes occurred on the glacier tongue. Moreover, we found that a large number of trees die under conditions of dominating backwasting inducing the loss of debris substrate (condition met especially on the northern glacier lobe). Instead, in the case of prevalence of downwasting (condition mainly observed on the southern glacier lobe), trees more easily survive and flow downvalley transported by the glacier flux.

The role of Ecological Value in Geomorphosite assessment for the Debris-Covered Miage Glacier (Western Italian Alps) based on a review of 2.5 centuries of scientific study

Ecological attributes of geomorphosites play a significant role as one of the characteristic components of their scientific value, hence influencing their global value. Ecological attributes can, however, act independently and inform other attributes which characterise scientific and additional values and the sites potential for use. Within the framework of active geomorphosites, environmental changes and recent dynamics can be reconstructed through tree-ring analysis. Glacial geomorphosites are one of the most significant examples of this biotic–abiotic relationship. Among glacial geomorphosites, debris-covered glaciers represent key sites at which to evaluate an ecological attribute. The Miage Glacier, the most representative Italian debris-covered glacier, is an important site for multidisciplinary scientific research, enhancing its global value as a complex geomorphosite. The Miage Glacier has been selected as a study site, firstly to characterise the evolution of scientific research across the last 250 years and then to quantify the ecological support role (ESR) and its influence on the other attributes. The ESR’s importance in assessing global geomorphosite values was estimated by studying its variation and the variation of the related attributes as a consequence of an increase in scientific knowledge over time. The ESR variation displays a positive effect on scientific value, in particular, and generates more differentiation between defined sites and visitor trails, thus influencing site selection.

Non-stationary Responses of Tree-Ring Chronologies and Glacier Mass Balance to Climate in the European Alps

Abstract Tree-ring width and glacier mass balance are two highly sensitive climatic proxies which are often used as indicators of biological and geophysical changes in high-altitude ecosystems. Tree-ring data have been widely used to reconstruct past temperatures and also to reconstruct past glacier mass balance. Here we show that tree-ring chronologies from a high-altitude Pinus cembra L. dendroclimatic network and glaciers from the same region in the European Alps have non-stationary responses to air temperature, and have also been responding non-proportionally to temperature extremes in recent decades. Both ring-width chronologies and the mass-balance series of some glaciers from the same region have shown an increasing sensitivity to summer (JJA) temperatures. Our results demonstrate that the sensitivity to climate of tree-ring chronologies and glacier mass balance may change over time and has been increasing in recent decades, posing some limitations to tree-ring-based glacier mass-balance reconstruction. Moreover, we found these reconstructions in the European Alps are more reliable for large rather than for small glaciers, and may not be able to reveal years of extreme ablation that could have occurred in the past.

Early stages of soil development on serpentinite: the proglacial area of the Verra Grande Glacier, Western Italian Alps

PurposeClimate change is driving strong variations in mountain habitats, such as glacier retreat, which is releasing large surfaces soon colonized by vegetation and attacked by weathering and pedogenesis. Many proglacial soil chronosequences have been studied in different parts of the world, but no study is available on early soil development and pedogenesis on serpentinite.Materials and methodsWe analysed the development of the main chemical (pH, organic matter, nutrients and exchangeable cations) and morphological properties in three soil chronosequences in the Verra Grande Glacier forefield (Italian side of the Monte Rosa Group, Western Alps), characterized by slightly different parent materials (pure serpentinite or serpentinite with small gneiss inclusions) and topography (steep lateral moraines or flat basal till).Results and discussionOrganic matter accumulation, acidification and base and metal leaching are the most important pedogenetic processes active during early stages of soil formation on serpentinite in the upper subalpine altitudinal belt. These processes are associated with minor changes in color and structure showing weak mineral weathering. Biocycling of nutrients is limited on pure serpentinite because of weak primary productivity of the plant community. Pedogenesis is quite slow throughout the forefield, and it is slowest on pure serpentinite. On flat surfaces, where slow erosion permits a fast colonization by Ericaceae, the podzolization process begins after few centuries since moraine deposition, while on steep slopes more time is required.ConclusionsPedogenesis on serpentinite is extremely slow. The fast colonization by grassland species increases the speed of pedogenetic trends where serpentinitic till is enriched by small quantities of P-rich gneiss. The encroachment of forest-shrub species increases the speed of pedogenetic trends thanks to a strong nutrient biocycling.

INFLUENCE OF CLIMATE AND CLIMATE ANOMALIES ON NORWAY SPRUCE TREE-RING GROWTH AT DIFFERENT ALTITUDES AND ON GLACIER RESPONSES: EXAMPLES FROM THE CENTRAL ITALIAN ALPS

Abstract. Climate change and climate anomalies are inducing strong variations in the high‐mountain environment, driving the responses of physical and biological systems differently. This paper assesses tree‐ring growth responses to climate for two Norway spruce (Picea abies (L.) Karst.) sites at different altitudes from an Ortles‐Cevedale Group (OCG; internal zones of the Central Italian Alps) valley site and reports some examples of climate impact on glacier dynamics in the OCG in recent decades. Growth–climate relationships between tree‐ring chronologies and meteorological data were established by means of Pearsons correlation and response functions. In the high‐altitude chronology we found a strong signal of July temperatures, whereas the low‐altitude chronology also contained a signal of summer precipitation. Climate anomalies occurring in these months proved to influence tree growth at the two sites differently. In summer 2003 extreme climatic conditions established over Europe and the Alps, strongly affecting physical and biological systems. Spruce responses to the climate anomaly of 2003 were more evident with a one‐year lag. The high‐altitude site profited from the warmer growing season, whereas trees at the low‐altitude site experienced water stress conditions and their growth was strongly inhibited also in the following year. Glacier mass loss in the OCG in 2003 was the highest since yearly measurement started. The examples reported confirm the strong and even divergent variations affecting the Alpine environment, induced by recent climate change.

Larix decidua δ18O tree-ring cellulose mainly reflects the isotopic signature of winter snow in a high-altitude glacial valley of the European Alps

We analyzed the chronologies of cellulose stable isotopes (δ13C and δ18O) and tree-ring widths from European larch (Larix decidua) in a high-altitude site (2190ma.s.l.) at the bottom of a glacial valley in the Italian Alps, and investigated their dependence on monthly meteorological variables and δ18O precipitation values. The δ18O of tree-ring cellulose appears to be strongly driven by the δ18O of winter snowfall (November to March), which suggests that larch trees mostly use the snow-melt water of the previous winter during the growing season. This water, which also comes from the slope streams and from the underground flow of nearby steep slopes, infiltrates the soil in the valley bottom. The tree-ring cellulose δ18O values were also found to be influenced by the August precipitation δ18O and mean temperature. The associated regression model shows that the δ18O chronology from the tree rings explains up to 34% of the variance in the winter precipitation δ18O record, demonstrating the potential for reconstructing the δ18O isotopic composition of past winter precipitation in the study region. Unlike most other tree-ring studies that focus on growing season signals, in our study the summer signal was small and the winter signal dominant due to the special conditions of the glacial valley. Site topography, geomorphology and soil characteristics in particular influence the stable isotope signal in tree-ring cellulose.

The influence of topographic variables on treeline trees under different environmental conditions

Abstract Aiming to analyze the site conditions of treeline trees at the highest elevations, we investigated 360 km of treelines in the Upper Valtellina, Italian Alps. We analyzed approximately five trees per km and determined the environmental factors limiting treeline elevation by distinguishing between geomorphologic constraints (mean elevation 2355 m), climatic constraints (2530 m), and human impacts (2335 m). Up to 82% of the 1814 analyzed treeline trees were influenced by geomorphological constraints, whereas human impacts influenced only 3% of the trees. Climatic treelines (15% of trees) were most common in the western sector. Moreover we analyzed the frequency distributions of elevation, slope, and aspect. Elevation was the most important variable that was also strongly associated with climatic treelines. The slope variable was more strongly associated with treelines limited by geomorphology than by climate. By reconstructing the altitudinal dynamics at the Mt. Confinale study site, we found rates of an ongoing treeline upward shift of up to 2.6 m/y in the period 2000–2009. Our results indicate that climatic conditions related to the ongoing air temperature rise in this region will likely enhance the treeline shift, especially at high elevations (>2400 m a.s.l.) and on non-extreme slopes (<45°).

Directions in Geoheritage Studies: Suggestions from the Italian Geomorphological Community

In recent years, more and more attention has been focused on geological and geomorphological heritage. This has led to several investigations within the framework of conservation projects, both at administrative and scientific levels, involving national and international research groups whose purposes are the promotion of Earth Sciences knowledge and the conservation of geological heritage. This paper presents an overview of research and conservation projects in Italy, focusing mainly on geomorphological heritage. Members of the AIGeo Working Group on “Geomorphosites and cultural landscape” analysed the historical development of these research projects in order to identify possible innovation strategies to improve the awareness and knowledge of geodiversity and geoheritage of a wider public.

Il segnale climatico e le sue variazioni negli anelli di accrescimento degli alberi da siti estremi al contorno della regione mediterranea

Climatic signal and its variations in the tree rings from extreme environments bordering the Mediterranean region.Tree rings from climatically extreme environments, such as the Alpine treeline the arid and desert environments, allow the annually-resolved reconstruction of the climatic parameters most limiting tree growth in these areas. Climate proxies from the regions bordering the Mediterranean basin could provide a valuable contribution to palaeoclimate reconstructions in the area. Recent tree-ring chronologies of alpine conifers from the Italian Central Alps and discontinuous upper-mid Holocene chronologies of Cupressus dupreziana from the Libyan Sahara, confirm the possibility of obtaining meaningful palaeoclimatic information and quantitative reconstructions of the diverse climate parameters from annual tree rings. The Alpine tree-ring chronologies contain a summer-temperature signal, while the Libyan chronologies highlight the fluctuations of water availability in the Central Sahara over time. The information contained in these records can therefore contribute to a better definition of the past Mediterranean climate, showing how, by using dendrochronological data from sites limited by temperatures and by precipitations, relevant climatic information can also be derived from the bordering regions.