1,721,004 research outputs found
Past surface instability of Miage debris-covered glacier tongue (Mont Blanc Massif, Italy): a decadal-scale tree-ring-based reconstruction
No full textDebris-covered glaciers may host several biological forms that colonize the debris cover, especially if the glacier tongue reaches sufficiently low altitudes (down to about 1700 m a.s.l. at Miage Glacier, Western Italian Alps) thus allowing also tree growth. Supraglacial trees colonizing the debris-covered tongue are strongly influenced in growth and distribution by substrate characteristics and instability. The tree age distribution at Miage Glacier presents a positive gradient towards the glacier terminus, which was found to be related to the decreasing glacier surface velocity. By analysing tree-ring growth anomalies on the glacier and at a control site at the tree line over the 20-year period 1987-2006, it was found that trees growing on the glacier presented the highest percentages of abrupt growth changes (AGCs)>+70% with respect to the four previous years. Considering tree displacement on the glacier surface over the same 20-year period and the recorded AGCs, it was found that the central-lower portion of the southern lobe towards the margins was the most unstable. The temporal analysis of AGC>+40% confirmed a period of higher glacier surface instability, reaching a maximum in the years 1988 (on lobe S) and 1989 (on lobe N), probably related to the passage of a kinematic wave in the glacier tongue. Our analysis suggests that supraglacial trees hold useful information on the glacier tongue dynamics and that both AGC>+70% and AGC>+40% may be used as a proxy for substrate instability in spatio-temporal reconstructions in the Alpine environment
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
No full textClimate change and climate anomalies
are inducing strong variations in the highmountain
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 Pearson’s
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
First results of the participatory approach for monitoring supraglacial vegetation in Italy
No full textThe relationship between glacier fluctuations and vegetation dynamics makes the vegetation system a precious archive of data not only for studying climatic trends but also for assessing glacier history and recent movements. The increasing supraglacial debris coverage, that is currently affecting many glaciers, offers new habitats for animals and plants, including trees. On this basis, since 2011 the Italian Glaciological Committee has started a participatory project for annually monitoring the Italian supraglacial vegetation in order to record the progressive debris covered glacier surfaces colonization, in relation with glacier location, altitude, aspect. In the first three years of monitoring, the 27 observed glaciers have allowed to add new information for those glaciers where supraglacial vegetation was already known or studied (Miage, Brenva and Belvedere Glaciers) and to detect new glaciers presenting vegetation colonization
Variazioni climatiche recenti, ritiro glaciale e risposta della vegetazione arborea nell’alta montagna lombarda
No full textDendrochronological and dendroisotopic patterns from trees affected by glacier meltwater: the case study of Lago Verde ice-contact lake (Miage Glacier, Italy)
No full textNovel indicators of environmental change from trees in the debris-covered glacier foreland: the case study of the miage glacier (Mont Blanc Massif, Italian Alps)
No full textSupraglacial trees are a useful source of data for reconstructing past glacier surface movements and debris-coverage instability. Proglacial trees also represent a useful tool for the identification and dating of changes in the glacial stream discharge and wide-spreading of melting water. Dendroglaciology is currently applied not only for reconstructing glacier fluctuations but also for investigating glacier surface dynamics at decadal scale. Trees and dated tree-ring characteristics such as scars, growth rate and reaction wood may provide information about glacier movements, discharge and hydrology.
The Miage Glacier in the Mont Blanc Massif (Italy), represents a unique situation in the southern side of the Alps, due to the presence of abundant supraglacial vegetation. The density and distribution of trees is strictly linked to glacier surface velocity, thickness of debris-coverage, ablation rate, grain size distribution, slope and ice thickness, as documented by the results obtained during field surveys, data analysis and remote sensing techniques.
The most recent studies show that supraglacial trees can also be considered environmental and climatic stress indicators. Leaf VOC (Volatile Organic Compounds) emissions and tree-ring carbon and oxygen stable isotopes show significant differences in trees located on the supraglacial debris with respect to trees on the lateral moraine, and these results suggest the possibility to apply these techniques in the identification of areas affected by glacio-geomorphological and climatic stress.
Tree-ring characteristics may also be analyzed in order to reconstruct the past hydrology of debris-covered glaciers with annual resolution. In particular, trees fed by glacial meltwater of the Lago Verde (Miage Glacier) show that tree-ring cellulose is more depleted in δ18O compared to trees fed by other water sources and, moreover, tree-ring width is narrower in trees affected by lake-level fluctuations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
L’influenza della valenza ecologica sul valore globale dei geomorfositi attivi : il caso del Ghiacciaio del Miage nell’Espace Mont Blanc
No full text- …
