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The influence of climate change on glacier geomorphosites: the case of two Italian glaciers (Miage Glacier, Forni Glacier)investigated through dendrochronology

L’influence du changement climatique sur les géomorphosites glaciaires : le cas de deux glaciers italiens (Glacier du Miage, Glacier des Forni) analysés par dendrochronologie
Valentina Garavaglia, Manuela Pelfini et Irene Bollati
p. 153-164

Résumés

Le changement climatique induit actuellement de nombreuses modifications à l’environnement alpin : les glaciers classés comme géomorphosites sont affectés par un important retrait et de nouvelles aires sont progressivement disponibles pour être étudiées et valorisées. Un examen des formes de relief liées à l’érosion et aux dépôts glaciaires a été effectué pour documenter les conséquences du réchauffement climatique sur la végétation ; la colonisation des surfaces récemment déglacées est désormais plus rapide. Les recherches sur l’évolution des géomorphosites glaciaires sont importantes pour la connaissance scientifique et pour l’élaboration de « modèles d’évolution ». Utilisant les arbres qui poussent sur la surface des glaciers recouverts de débris rocheux, des investigations menées sur l’évolution « naturelle » des géomorphosites glaciaires sont présentées, permettant d’analyser les dynamiques passée et présente des zones proglaciaires. En outre, en étudiant les arbres qui poussent dans les zones proglaciaires des glaciers « blancs », il est possible d’appréhender les effets du changement climatiques sur la croissance des arbres qui colonisent ces aires. Ainsi, les nouveaux espaces qui apparaissent suite au retrait glaciaire peuvent être insérés dans les géomorphosites glaciaires, et utilisés pour affiner leur évaluation. Cet article montre, au final, l’intérêt de la dendrochronologie pour appréhender l’évolution des géomorphosites glaciaires face aux changements climatiques. Cette thématique est discutée sur la base des résultats obtenus à partir de deux sites d’étude : le glacier du Miage (Alpes occidentales) et le glacier des Forni (Alpes centrales).

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Notes de la rédaction

Article soumis le 3 novembre 2009, accepté le 22 février 2010

Texte intégral

The authors wish to thank the Stelvio National Park and Aosta Valley for permitting sampling activities. Moreover, thanks to Prof. P. Deline, Prof. B. Smith and the two anonymous reviewers for the useful suggestions in order to improve the first version of the paper. The authors would also like to thank the Editor-in-Chief G. Arnaud-Fassetta and the editorial staff of the Journal for the support provided.

Introduction

1In the Alps the impact of climate change is particularly significant owing to the great sensitivity of this environment. Changes in the Alpine landscape are mainly due to glacier shrinkage: glacial retreat is accompanied by a fragmentation of ice masses into glaciers of reduced extension. It causes transformations from valley glaciers into glaciers and glacierets, extensions of proglacial areas and recolonisation by vegetation, and an increase in supraglacial debris coverage that transforms “white glaciers” into debris covered glaciers (Benn and Evans, 1998; Pelfini et al., 2007). Glacier geodiversity (sensu Panizza and Piacente, 2003) is strictly linked to glacier typologies and forms related to their present and/or past passage. In the Italian Alps, several types of glaciers are present: large valley glaciers (e.g., the Forni Glacier, central Italian Alps), cirque glaciers (e.g., the Sforzellina Glacier, central Italian Alps), glacierets (e.g., the Calderone Glacier, Italian Appennines, even if classification is still pending) and debris covered glaciers (e.g., the Miage and the Belvedere glaciers, western Italian Alps; Pelfini and Smiraglia, 2003). Glacial geomorphosites are an important component of the Alpine environment and considering the geomorphosite definition proposed by M. Panizza and S. Piacente (2003), they well represent the four attributes suggested for their assessment: i) The scenic attribute is represented by spectacular landscapes and confirmed by the increasing interest in mountain regions, in mountain sports and recreational activities; ii) Tourism and industrial activities, such as production of hydroelectric energy, are factors which define the economic value of glacial geomorphosites. In fact, the economy of several mountain regions is strictly related to exploitation of glaciers: they represent water reservoirs but also attract tourists all year round, hikers in spring, summer and autumn and skiers in winter; iii) People living near glacial systems have been influenced by glaciers throughout history, influencing costume, arts and, as mentioned, economic activities; iv) Some Alpine glaciers were theatres of war, during the First World War, where fierce battles were fought, contributing to the culture.

2All the parameters suggested by M. Panizza (2001) for definition of scientific attributes are well documented in glacial geomorphosites (Pelfini and Smiraglia, 2003). They have a significant educational value as examples of geometric forms that correspond to the World Glacier Monitoring Service’s classification; they are sensitive indicators of climate change, witnesses of the effects of global warming; the dating of their morainic deposits allows the reconstruction of past glacial dynamics (paleogeomorphological evidence) and finally life outposts role contribute to promote their ecological value (Panizza, 2001; Gray, 2004).

3Several works have noted glacier sensitivity to climate change and vulnerability, and promoted their conservation and preservation, as well as evaluation of human impact (Bini, 2005; Pelfini et al., 2005; Smiraglia et al., 2006). When a glacier is classified as a geomorphosite, its limited temporal persistence must be especially considered a component of the scientific attribute as “model of evolution” (Pelfini and Smiraglia, 2003). As a consequence, given their rapid evolution, assessment of glacial geomorphosites requires a detailed analysis. For example, concepts such as “integrity” and “rarity”must be revaluated for some glacial tongues, as was the case for the Calderone Glacier (central Italian Appennines; Pelfini and Smiraglia, 2003). It can be defined as “rare” because it is the last glacier still existing in the Appennines, even though its recent division into two ice aprons does not permit to label it as “integer” and it may be considered to be two glacierets (Pecci et al., 2008). Nevertheless, the glacial retreat may be considered not only a reduction or loss of glaciarised areas but also the creation of new territories influenced by glacier-related processes. Proglacial areas are a clear example of portions of the glacial system not directly part of the glacier but highly influenced by its dynamic. These areas may be considered and their value may be quantified: the retreat of the glacial front leaves traces of the erosional and depositional processes and the vegetation dynamic enables investigation of the rate of glacier retreat and of ecesis (time taken by trees to successfully germinate on a bare surface; McCarthy and Luckman, 1993). Global warming is, in fact, responsible not only for glacier shrinkage but also for the vegetation dynamic, influencing, for example, the vegetation succession and accelerating plant colonisation and development. It seems that vegetation starts to colonise deglaciated surfaces in only one year (Cannone et al., 2008) and an upward movement of high mountain plants has been empirically determined (Pauli et al., 2003; Caccianiga et al., 2008; Leonelli et al., 2009).

4In this work we present some results obtained from tree ring analysis in order to illustrate the role of dendrochronological investigations in the study of glacial geomorphosites, especially in relation to their evolution. The research was carried out on the Miage Glacier, the most representative Italian debris covered glacier (Aosta Valley, western Italian Alps) and on the Forni Glacier (upper Valtellina, central Italian Alps; fig. 1), one of the best examples of valley glaciers in the Italian Alps. Particular attention has been paid to the evolution of proglacial areas. On the Miage debris-covered glacier, trees growing on the debris coverage and in the proglacial area were sampled in order to investigate recent glacier dynamics, whereas on the Forni Glacier, the tree vegetation colonising the glacier forefield was studied in order to evaluate the colonisation rate in relation to global warming. In detail, the main goals of this work are: i) to underline how glacier responses to climate change are accompanied by tree responses and how both reflect/record the evolution of geomorphosites; ii) to demonstrate how tree ring analysis can reveal more information about recent surface dynamics in debris-covered glaciers, about glacial stream activities and the modification of proglacial areas, increasing the ecological value of glacial geomorphosites; iii) to show how glaciers and forefield areas may evolve, considering both the degradation of some parts of the geomorphosites and the generation of new ones; iv) to show that the evolution of a glacial geomorphosite, as a consequence of climate change, does not necessarily mean its degradation. Dendrochronology is the method proposed to achieve the above objectives, because of the significant colonisation by vegetation in the selected areas and the amount of data available related to these sites.

Fig. 1 – Panoramic views of the two study areas.
Fig.1 – Vue panoramique des deux zones d’étude.

Fig. 1 – Panoramic views of the two study areas. Fig.1 – Vue panoramique des deux zones d’étude.

A: The Forni Glacier (central Italian Alps; photo by V. Garavaglia). B: The Miage Glacier (Aosta Valley, Western Italian Alps; photo by E. Motta).
A : Le Glacier des Forni (Alpes centrales italiennes ; photo V. Garavaglia). B : Le Glacier du Miage (Alpes occidentales italiennes ; photo E. Motta).

Study areas

5The Miage Glacier (~ 11 km2; Aosta valley, western Italian Alps; fig. 1B) flows for 6 km along the Veny valley; it originates at an altitude of 4800 m a.s.l., running from the Mont-Blanc Massif and it reaches 1775 m a.s.l. at its terminus (Diolaiuti et al., 2005). Two main lobes and a central smaller one characterise the shape of the tongue. Debris coverage starts at 2400 m a.s.l., rapidly forming a continuous layer that developed during the 17th century and it is nowadays supported by rock and debris falls onto the glacier surface (Deline and Orombelli, 2005). Several glaciological studies have been carried out at this site to evaluate surface velocity, calving processes (Diolaiuti et al., 2005) and surface elevation changes (Thomson et al., 2000). Moreover, the Miage Glacier presents a debris cover colonised by tree vegetation [principally Larix decidua Mill. and Picea abies L. (Karst.)] which has already been studied using dendrochronology (Pelfini et al. 2007) to investigate glacier evolution and surface dynamics.

6The Forni Glacier (upper Valtellina, central Italian Alps) is the biggest Italian valley glacier, with a surface of ~ 12 km2. It flows in a valley with a 2.5 km glacial forefield (fig. 1A) and the major late Holocene advances are marked by frontal moraines dated to AD 1859, 1913-14, 1926 and 1980 (Pelfini, 1992). It is a geomorphosite whose scientific, historical and cultural values have been valorised by a glaciological hiking trail, providing a good example of an opportunity to observe glacial geomorphosite evolution. This trail has been threatened by slope instabilities related to lateral moraine degradations (Pelfini and Smiraglia, 2007). The rapid glacial retreat is creating a wide proglacial area where moraines, erosional and depositional forms are well visible and where herbal, shrub and tree vegetation are developing. The ecological value of the Forni Glacier has been enhanced by linking geomorphological and glaciological investigations to zoological ones: a study on Carabid beetle (Coleoptera) assemblages along a chronosequence of the glacial forefield contributed to the investigation of landscape and habitat change in response to global change and to glacier retreat (Gobbi et al., 2007).

Methods

7The dendrochronological methods presented here were applied to obtain information about the evolution of geomorphosites. In relation to debris coverage of the Miage Glacier and its proglacial area, the results from dendrochronological research carried out to investigate the debris-coverage dynamic have already been presented in a previous work - Pelfini et al. (2007). Nevertheless, in order to respond to the goal of this work, a summary of the whole dendrochronological research is proposed, integrating a recent study on the proglacial area (Garavaglia et al., in press b) and data about monitoring of ice cliffs.

8In order to investigate recent glacier surface dynamics, one hundred and fifty-three larches were sampled: 11 on the northern lobe (A, fig. 2), 41 on the southern lobe (B, fig. 2) and 101 in the proglacial area (D, fig. 2). Moreover, nine larches were also sampled on the inner lateral moraine (C, fig. 2) since they have been clearly bent by the glacier movements. The cores were taken near the stem base crossing the stem through the pith. For comparison with tree-ring data from supraglacial trees, three reference chronologies were built using 57 samples, based on undisturbed larches growing outside the glacier, in areas not directly influenced by glacial dynamics. Samples were prepared following standard procedures (Schweingruber, 1987). They were crossdated using reference chronologies to check the correct dating of each ring. Crossdating was performed both visually on screen and statistically using, respectively, TSAP and COFECHA software (Holmes, 1983).

Fig. 2 – Sampling areas (A, B, C and D) for the dendrochronological study on the Miage Glacier (adapted from Pelfini et al., 2007).
Fig. 2 – Zones d’échantillonnage (A, B, C et D) pour l’étude dendrochronologique du Glacier du Miage (adapté de Pelfini et al., 2007).

Fig. 2 – Sampling areas (A, B, C and D) for the dendrochronological study on the Miage Glacier (adapted from Pelfini et al., 2007). Fig. 2 – Zones d’échantillonnage (A, B, C et D) pour l’étude dendrochronologique du Glacier du Miage (adapté de Pelfini et al., 2007).

The picture at the top left represents the ice cliff on the northern lobe of the glacier (photo by E. Motta).
L’image en haut à gauche représente le front de glace du lobe nord du glacier (photo E. Motta).

9Two main approaches were adopted to identify growth disturbances related to debris instability and glacier dynamics: i) a tree-ring growth series analysis, based on ring width measurement, in order to detect the pointer years and abrupt growth changes; ii) a visual assessment of growth disturbances using skeleton plots.

10Pointer years are those when more than 75% of the samples show the same interval trend: a positive trend indicates a growth release, a negative one shows growth suppression (Huber and Giertz-Siebenlist, 1969). In the southern proglacial area, tree cores were principally collected at sites of visible damage and changes in growth direction related to runoff variations. A detailed analysis was carried out on scars, generally due to the impact of boulders and blocks coming from the glacier surface, and compression wood, produced by a tree in order to recover its vertical position when tilted by glacier pushing, boulder fall, debris flows, substrate instability, etc. As supraglacial trees move downvalley, depending on the glacier surface velocity, they represent data recorders until they reach the glacier front or marginal ice cliffs. Ice cliffs cyclically open along the tongue boundaries and here the debris-covered glacier loses ice mass (Benn and Evans, 1998) because of the absence of continuous debris coverage. Ice cliffs evolve in time and may disappear or may be modified by backwasting and downwasting processes (sensu Benn and Evans, 1998). The ice cliff retreat may affect trees, and monitoring activities were carried out in order to obtain some information about the backwasting rate (fig. 2). A previous study was undertaken by G. Diolaiuti et al. (2005) on the ice cliffs affected by calving at the Miage lake, where during the hottest periods some form of calving takes place several times a day. During summer 2004 a loss of 1900 m3 of ice had been estimated and forecast, whereas an exceptional detachment of 10,000 m3 occurred, also affecting tourists near the edge of the lake (Smiraglia et al., 2008). Using laser measurements, during summer 2006 and 2007, the ice cliffs backwasting rate was estimated on the northern lobe of the Miage Glacier and, in summer 2007, the number of trees growing within 12 m of the ice-cliff boundary was counted. Using the ice-cliff retreat and the number of larches growing on borders, the tree loss was estimated.

11On the Forni Glacier forefield a 2 km-long longitudinal profile was defined, extending between 2100 m a.s.l. and 2400 m a.s.l. Eight plots were investigated with a surface area of 400 m2 each, about 200 m apart (fig. 3). For each sample area, an increment core was extracted from the trees presumed oldest and detailed information was collected about vegetation coverage, soil, and geomorphology. The sampling strategy was designed with the objective of collecting samples from areas that well represent the entire glacial forefield. A total of 35 cores were extracted: 20 from Picea abies L. (Karst.), 15 from Larix decidua Mill. Growth curves were built using WinDENDRO (Regeant Instrument Inc., 2001) software, with a precision of 0.01 mm. They were crossdated using reference chronologies from other research (unpublished data) to check the correct dating of each ring. Crossdating was performed both visually on screen and statistically using TSAP and COFECHA software, respectively (Holmes, 1983).

Fig. 3 – A simplified sketch of the Forni Glacier forefield. Black squares represent the sampling plots where the dendrochronological sampling was realised, whereas the black lines represent the dated moraines.
Fig. 3 – Schéma simplifiée de la zone proglaciaire du Glacier des Forni. Les carrés noirs représentent les plots où l’échantillonnage dendrochronologique a été réalisé. Les lignes noires représentent les moraines.

Fig. 3 – A simplified sketch of the Forni Glacier forefield. Black squares represent the sampling plots where the dendrochronological sampling was realised, whereas the black lines represent the dated moraines.Fig. 3 – Schéma simplifiée de la zone proglaciaire du Glacier des Forni. Les carrés noirs représentent les plots où l’échantillonnage dendrochronologique a été réalisé. Les lignes noires représentent les moraines.

Results

Dendrochronological investigations on the Miage Glacier

12The tree age and the temporal and spatial distribution of growth anomalies in supraglacial larches highlight the great growth variability in relation to local conditions and provide details about the evolution of the glacier surface in the second half of the 20th century. Growth anomalies are due to glacier movements which induce growth disturbances. The glacier surface dynamic in debris-covered glaciers is mainly associated with up and down movements related to differential ablation, mass wasting processes, glacier slide and flow, and with debris movements. Moreover uplift and downlift of the glacier surface reveal the passage of kinematic waves, produced by mass balance variations (Smiraglia et al., 2000). A previous investigation (i.e., Pelfini et al., 2007) showed how supraglacial trees can not only record the passage of a kinematic wave but how they also represent a means of detecting the different times of arrival in the two lobes of the glacier. The concentration of growth anomalies revealed a delay of few years in reaching the northern lobe (1989-1993), compared to the southern one (1984-1990). Moreover the growth disturbance affected trees for a longer time in the southern lobe (7 years) than in the northern one. This corresponds to an uplift of the glacier surface as demonstrated also by glaciological investigations (Smiraglia et al., 2000). The kinematic wave, that crossed the glacier tongue in the 1980s (Giardino et al., 2001), seems to have moved more slowly on the northern lobe than on the southern.

13The continuous monitoring of the ice cliffs enabled an estimate of their evolution for the period 2006-2007. Field data suggest that the retreat of the ice cliff located on the northern lobe was about 20 m/a and, more particularly, 5.8 cm/day between 25 May 2006 and 10 June 2007 and 8.3 m/a (12.7 cm/day) between 10 June 2007 and 14 August 2007 (Brioschi, 2007). As a consequence of this retreat, more than one hundred larches died, falling from the ice cliff margins and reducing the tree coverage (Pelfini, 2008). The fallen specimens also included very young trees and seedlings.

14The second approach regards the potential of the trees located in the proglacial area as a recorder of glacial drainage variations (Garavaglia et al., in press b). In this case the growth anomalies allowed us to detect glacier runoff variations. The maximum tree age (about 30 yrs) suggested that since 1977 (minimum age) the southern proglacial area has not been affected by significant fluctuations in the glacial front, as generally has been observed in debris-covered glacier behaviour (Benn and Evans, 1998) in mass-wasting events or in great stream-flow activities. The tree-age spatial distribution enabled us to reconstruct the changes in shape and dimension of single geomorphological units affected by glacial stream activity and snow coverage disturbances. It was possible to identify different degrees of stability among the geomorphological units. The dendrochronological results identified areas characterised by a more intense stream activity before at least 1977, between 1977 and 1982 and after 1982 (these dates are minimum ages; fig. 4).

Fig. 4 – Sketches of the proglacial area of the southern Miage Glacier lobe.
Fig. 4 – Cartes simplifiées de la zone proglaciaire du lobe sud du Glacier du Miage.

Fig. 4 – Sketches of the proglacial area of the southern Miage Glacier lobe. Fig. 4 – Cartes simplifiées de la zone proglaciaire du lobe sud du Glacier du Miage.

Dating tree-ring growth anomalies, three areas characterised by a more intense stream activity (before 1977, between 1977 and 1982, after 1982) were identified (redrawn from Garavaglia et al., in press b). Black circles represent the sampled trees. 1: proglacial area boundary; 2: hydrography; 3: scarp; 4: hiking trail; 5: sampled tree group; 6: spring; 7: bridge.
Trois zones caractérisées chacune par une dynamique spécifique ont été identifiées (avant 1977, entre 1977 et 1982, après 1982) en utilisant les anomalies de croissance des cernes (redessiné de Garavaglia et al., in press b). Les cercles noirs représentent les arbres échantillonnés. 1 : limite de la zone proglaciaire, 2 : hydrographie ; 3 : escarpement, 4 : sentier de randonnée pédestre ; 5 : groupe d’arbres échantillonnés ; 6 : source ; 7 : pont.

15The large number of growth disturbance indicators (39 dated scars, 62 trees with compression wood, eccentric rings present in practically all samples) suggests a continuous modification of the proglacial morphology and stability. Moreover, a correlation seems to exist between the influence of the glacier stream on trees and the Miage lake behaviour. The Miage lake has been affected by several drainage events during last century (Diolaiutiet al., 2005). Tree-growth anomalies seem to decrease in the years following the 1990 and 2004 lake outbursts (fig. 5). For example, in 2004, after a concentration of growth anomalies corresponding to the drainage of the lake, a decrease in tree ring anomalies can be observed. On the other hand, the 1986 event is followed by an increase in tree-ring anomalies, probably as a consequence of the flood events that characterised the Aosta valley in 1987 and 1988 (fig. 5). Moreover, as fig. 5 shows, a concentration of growth anomalies is evident during the periods 1988-1990, 1994-1998 and 2001-2002. The period between 1988 and 1990 in particular corresponds to the passage of a kinematic wave in the southern lobe, confirming that its consequences also affected the proglacial area.

Fig. 5 – Relation between growth anomalies (black bars) distribution and flood events (black stars). The grey dashed bars represent exceptional snowfalls and the grey bars are years characterised by the Miage marginal ice-contact lake’s drainage events.
Fig. 5 – Relation entre la distribution des anomalies de croissance (barres noires) et les événements de crue (étoiles noires). Les barres grises en pointillés représentent les années caractérisées par des vidanges du Lac du Miage.

Fig. 5 – Relation between growth anomalies (black bars) distribution and flood events (black stars). The grey dashed bars represent exceptional snowfalls and the grey bars are years characterised by the Miage marginal ice-contact lake’s drainage events.Fig. 5 – Relation entre la distribution des anomalies de croissance (barres noires) et les événements de crue (étoiles noires). Les barres grises en pointillés représentent les années caractérisées par des vidanges du Lac du Miage.

The recolonisation of Forni Glacier forefield

16The first results concerned tree age distribution and elevation: the maximum ages of the plots range from 8 to 71, at 2190 m a.s.l. and 2410 m a.s.l., respectively (tab. 1). As expected, as the altitude increases the tree age decreases (R2= 0.73 and R2= 0.68 for maximum plot age and average age of plots, respectively; fig. 6). A similar trend was identified in the average tree height, but in this case, the correlation is higher (R2= 0.89; fig. 7). Nevertheless, analysing the age and height trends, an outlier is present in both graphs: vegetation plot 2 presents higher tree-age values (~ 12 m) than other plots (tab. 1). The reason is probably related to its location: it is in fact at the margins of the valley axis and the trees in this position are subject to less direct influence by the glacier and glacier-related processes.

Tab. 1 – Distribution of sampled trees in the vegetation plots investigated in the Forni Glacier forefield.
Tab. 1 – Distribution des arbres échantillonnés dans la zone proglaciaire du Glacier des Forni.

Time frame

Total length variation (in m)

Annual change rate (in m/a)

1895-1970

- 1505

- 20.1

1971-1981

+ 303

+ 30.3

1982-2008

- 714.5

- 27.5

The average and maximum age and the height of the investigated vegetation plots are quantified.
L’âge moyen et minimum et la hauteur sont quantifiés.

Fig. 6 – Relation between sampled tree ages and altitude in the Forni Glacier forefield.
Fig. 6 – Relation entre l’âge des arbres échantillonnés et l’altitude dans la zone proglaciaire du Glacier des Forni.

Fig. 6 – Relation between sampled tree ages and altitude in the Forni Glacier forefield. Fig. 6 – Relation entre l’âge des arbres échantillonnés et l’altitude dans la zone proglaciaire du Glacier des Forni.

The tree age increases with altitude (R2= 0.73 for the maximum age and R2= 0.68 for the average age of trees).
L’âge des arbres augmente avec l’altitude (R= 0,73 pour l’âge maximum et R= 0,68 pour l’âge moyen des arbres).

Fig. 7 – Relation between the sampled tree average height and the altitude. The average tree height decreases with altitude (R= 0.89).
Fig. 7 – Relation entre la hauteur moyenne des arbres échantillonnés et l’altitude. La hauteur moyenne des arbres diminue avec l’altitude (R= 0,89).

Fig. 7 – Relation between the sampled tree average height and the altitude. The average tree height decreases with altitude (R2 = 0.89). Fig. 7 – Relation entre la hauteur moyenne des arbres échantillonnés et l’altitude. La hauteur moyenne des arbres diminue avec l’altitude (R2 = 0,89).

17Other aspects of the research regard the ecesis time, considered as an indicator of climate change. The ecesis value is an “estimate of the elapsed time between deglaciation (or moraine formation and stabilisation) and the germination of the first tree to survive and be sampled, i.e. the oldest tree in the surface” (McCarthy and Luckman, 1993). The minimum ecesis value and the average ecesis value were calculated on the basis of the maximum tree age in each plot and on the average tree age, respectively. More in detail, using the spatial position of the Forni Glacier terminus in 1998 (unpublished data, kindly made available by G. Diolaiuti), the distance of each vegetation plot from the glacial front in 1998 was calculated (tab. 2), and the relation between average minimum ecesis and elevations was investigated. Norway spruces present an average ecesis value between 52 years (plot 1, 2200 m from the glacier front) and 30 years (plot 5, 940 m from glacier front; tab. 2) with a significant statistical correlation (R2= 0.79; fig. 8) if related to the glacier front position in 1998. The same trend is visible from the minimum ecesis value in fig. 9: it varies between 41 years (plot 1) and 23 years (plot 5). The larches sampled also presented an average and minimum ecesis with trends similar to Norway spruces (fig. 8 and fig. 9). The average varies between 58 (plot 1) and 25 years (plot 6), the minimum between 48 (plot 1) and 20 years (plot 6). The data obtained are comparable with those found in the literature documenting other parts of the globe, despite the high variability of this parameter. Whatever value we consider and even if the ecesis rate is subject to some errors in estimation, a reduction in ecesis time from the Little Ice Age maximum and the present time seems evident. We can hypothesise several causes: i) the Little Ice Age corresponds to a period with a reduction of the tree line altitude and to an increase in the time necessary for seedlings to colonise the proglacial areas; ii) tree cutting may be supposed, even if no stumps are present in the area investigated; iii) the impact of glacial floods may have damaged and removed trees, reducing the tree age and the ecesis time; iv) in the Alpine mountain areas biological and abiotic processes are accelerating in response to global warming (Cannone et al., 2008). The results presented seem to favour this last hypothesis.

Tab. 2 – Average and minimum ecesis of the sampled plots in the Forni Glacier forefield, related to the distance of the sampling areas from the glacial front location in 1998.
Tab. 2 – L’ecesis moyen et minimum des plots échantillonnés dans la zone proglaciaire du Glacier des Forni, en relation avec la distance au front du glacier en 1998.

Average ecesis

Minimum ecesis

Vegetation plot

Distance from glacier front location in 1998 (in m)

Picea abies L. Karst.

Larix decidua L.

Picea abies L. Karst.

Larix decidua L.

1

2200

52

58

41

48

2

2050

62

45

62

45

3

1730

53

63

50

54

4

1600

54

56

35

50

8

1250

35

41

29

35

5

940

30

-

23

-

6

500

-

25

-

20

Fig. 8 – Average ecesis of Norway spruces and Larches in the Forni Glacier forefield.
Fig. 8 – L’ecesis moyen des Picea abies L. Karst et des Larix decidua Mil. échantillonnés dans la zone proglaciaire du Glacier des Forni.

Fig. 8 – Average ecesis of Norway spruces and Larches in the Forni Glacier forefield. Fig. 8 – L’ecesis moyen des Picea abies L. Karst et des Larix decidua Mil. échantillonnés dans la zone proglaciaire du Glacier des Forni.

1 : Norway spruces (Picea abies L. Karst) ; 2 : larches (Larix decidua Mill.).
1 : épinettes de Norvège (Picea abies L. Karst) ; 2 : mélèzes (Larix decidua Mill.).

Fig. 9 – Minimum ecesis of Norway spruces and Larches in the Forni Glacier forefield.
Fig. 9 – L’ecesis minimum des Picea abies L. Karst et des Larix decidua Mil. échantillonnés dans la zone proglaciaire du Glacier des Forni.

Fig. 9 – Minimum ecesis of Norway spruces and Larches in the Forni Glacier forefield. Fig. 9 – L’ecesis minimum des Picea abies L. Karst et des Larix decidua Mil. échantillonnés dans la zone proglaciaire du Glacier des Forni.

1 : Norway spruces (Picea abies L. Karst) ; 2 : larches (Larix decidua Mill.).
1 : épinettes de Norvège (Picea abies L. Karst) ; 2 : mélèzes (Larix decidua Mill.).

Discussion

18Glacier fluctuations are responsible for significant changes in the Alpine landscape, modifying continuously the appearance of glacial geomorphosites. The results of these changes need not necessarily be labelled as “degradation” and can be considered part of the geomorphosites, as consequences of climate change and/or natural evolution of the glaciers. Tongue retreat in debris free glaciers is accompanied by i) the formation of new surfaces where traces of the glacier passage are evident, with significant scientific and educational value ; ii) colonisation by vegetation, including trees. Dendrochronological dating allows us to reconstruct not only the glacial history (Winchester et al., 2001 ; Pelfini and Smiraglia, 1992) and the recent dynamic but also to investigate both the glacial retreat rate and the ecesis time, contributing to analyses of the rate of change in glacial geomorphosites and to assessment of the ecological value of glacial geomorphosites. The case study presented of the Forni Glacier highlights how glacier retreat creates new deglaciated areas recolonised by vegetation.

19Worldwide literature suggests that ecesis is significantly influenced by the local climatic conditions, which change dramatically from site to site (Koch and Kilian, 2005). According to these authors, the ecesis rate can change from 1 year to more than 70 years in different study areas of Andes, whereas it has been estimated between 6 and 30 years on Coleman Glacier, Mount Baker, USA (Heikkinen, 1984), between 10 and 20 years in the Canadian Cordillera (McCarthy and Luckman, 1993), between 10 and 20 years on Morteratsch Glacier (Swiss Alps ; Bleuler, 1986 ; Burga, 1999) and between 14 and 34 years on Ventina Glacier (Italian Alps ; Garbarino et al., 2010). The minimum ecesis value and the average ecesis value were calculated respectively on the base of the maximum tree age in each plot, and on the average tree age.

20The data obtained from the Forni Glacier agree with those in the literature, highlighting how the study of the ecesis enhances the role of proglacial areas as climate change indicators and as new parts of glacial geomorphosites or of geomorphological landscapes (sensu Reynard and Panizza, 2005), increasing the scientific and the educational value. On the Forni Glacier, tree ring analysis enabled gathering of data about the minimum interval time required for tree colonisation : probably due to global warming, seedlings are now also present near the glacial front (at altitudes of about 2400 m) and are colonising more quickly than in the past.

21The case study reveals the Miage as a good example of the transformation of a “white” glacier into a debris-covered glacier, partly as a consequence of global warming. The behaviour particular to a debris-covered glacier is documented by the different modifications of the landscape surrounding the glacier front. The loss of ice mass takes place at the ice cliffs where the glacial ice is not protected by debris and where the ablation rate increases (Benn and Evans, 1998). The dendrochronological investigation o the trees growing on the debris coverage, originally undertaken for glaciological purposes (see Pelfini et al., 2007), revealed the large amount of data on the glacier dynamic derivable from trees and the possibility of using such data to enhance the ecological value of a glacial geomorphosite (Garavaglia et al., in press a). Data from trees located in the proglacial areas provide more information about the glacier dynamics and also allow assessment of the influence of meltwater on vegetation growing near the glacier front, raising the importance of tree vegetation in assessing the geomorphosite’s scientific value. In the case of debris-covered glaciers, supraglacial tree life span is controlled by the glacier surface velocity and by downwasting and backwasting processes that also influence the geomorphosite ecological value.

Conclusions

22Global warming has already impacted several World Heritage sites and the UNESCO-World Heritage Centre (2007) considers that in the future years it will impact many more. It is impossible to stop glacial retreat and the vulnerability of glacial systems is becoming more and more evident. This study shows how glacial geomorphosites and their forefield areas evolve in time and are affected by processes that on one hand degrade and/or destroy some parts, while on the other hand also creating new landforms. Both the glacial geomorphosites analysed show the effects of global warming and the differences in their responses illustrate the difficulties encountered in evaluating their status and state of conservation. The research presented here highlights how important it is when evaluating glacial geomorphosites, to consider not only the abiotic elements, but also the biologic component, which is fundamental both for the ecological attribute and scientific value, especially concerning the glacier fluctuations, the present dynamic and the rate of different natural processes (e.g., glacier retreat and ecesis). The results confirm how the glacier response to climate changes is accompanied by tree layer modifications and how trees can be used in order to understand the evolution of glacial geomorphosites. Both glaciers examined illustrate the role of tree vegetation in assessing the ecological and scientific value of glacier geomorphosites. The tree vegetation dynamic reveals the rapid rate of evolution of glacier geomorphosites, a phenomenon that should be monitored not only for better planning conservation and tourist promotion but also for evaluating how to reassess glacier geomorphosites as they respond to change. Protection and management of glacial geomorphosites could then also be adapted to the glacial dynamic : the “results” of changes (extension of proglacial areas, ice cliffs evolution, etc.) may be investigated to improve the site value, supported by scientific investigations as already presented.

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Bibliographie

Benn D.I., Evans D.J.A. (1998)Glaciers and glaciation. London, Arnold, 734 p.

Bini M. (2005) – Glacial landforms in the Apuan Alps (Tuscany- Italy) : features in danger of extinction. Il Quaternario 18-1, special issue, 175-178.

Bleuler R.M. (1986)Jahrringanalysen von Lärchen in Gletschervorfeldern. Dissertation, university of Zurich, 89 p.

Brioschi D. (2007)Evoluzione recente dei lobi frontali del ghiacciaio del Miage (Ao) - Influenza sulla vegetazione arborea epiglaciale e uso del larice per indagini dendroglaciologiche. Master thesis, università degli Studi di Milano, 167 p.

Burga C.A. (1999) – Vegetation development on the Glacier Forefield Morteratsch (Switzerland). Applied Vegetation Science 2, 17-24.

Caccianiga M., Andreis C., Armiraglio S., Leonelli G., Pelfini M., Sala D. (2008) – Climate continentality and treeline species distribution in the Alps. Plant Biosystems 142, 66-78.

Cannone N., Diolaiuti G., Guglielmin M., Smiraglia C. (2008) – Accelerating climate change impacts on alpine glacier forefield ecosystems in the European Alps. Ecological Application 18, 637-648.

Deline P., Orombelli G. (2005) – Glacier fluctuations in the western Alps during the Neoglacial as indicated by the Miage morainic amphitheatre (Mont Blanc Massif, Italy). Boreas 34, 1-12.

Diolaiuti G., Kirkbride M., Smiraglia C., Benn D.I., D’agata C., Nicholson L. (2005) – Calving processes and lake evolution at Miage glacier, Mont Blanc, Italian Alps. Annals of Glaciology 40, 207-214.

Garavaglia V., Pelfini M, Bollati I. (in press a) – Dendrogeomorphological investigations for assessing ecological and didactical value of glacial geomorphosites. Some examples from the Italian Alps. In Regolini-Bissig G., Reynard E. (Eds.) : Mapping Geoheritage. Travaux et Recherches, 35, Lausanne, Institut de Géographie.

Garavaglia V., Pelfini M., Motta E. (in press b) – Glacier stream activity in the proglacial area of an Italian debris covered glacier : an application of dendroglaciology. Geografia fisica e dinamica quaternaria.

Garbarino R., Lingua E., Nagel T.A., Godone D., Motta R. (2010) – Patterns of larch establishment following deglaciation of Ventina glacier, central Italian Alps. Forest Ecology and Management 259, 583-590.

Giardino M., Mortara G., Bonetto F. (2001) – Proposta per la realizzazione di un catalogo aerofotografico dei ghiacciai italiani. Supplementi di Geografia Fisica e Dinamica Quaternaria 5, 89-98.

Gobbi M., Rossaro B., Vater A., De Bernardi F., Pelfini M., Brandmayr P. (2007) – Environmental features influencing Carabid beetle (Coleoptera) assemblages along a recently deglaciated area in the Alpine region. Ecological Entomology 32, 682-689.

Gray M. (2004)Geodiversity : valuing and conserving abiotic nature. Wiley, Chichester, pages.

Heikkinen O. (1984) – Dendrochronological evidence of variations of Coleman Glacier, Mount Baker, Washington, USA. Arctic Antarctic and Alpine Research 16, 53-64.

Holmes R.L. (1983) – Computer-assisted quality control in tree-ring dating and measurement. Tree-Ring Bulletin 43, 69-78.

Huber B., Giertz-Siebenlist V. (1969) – Unsere tausendjährige Eichen-Jahrringchronologie, durchschnittlich 57-(10-50-) fach belegt. Akademie der Wissenschaftenzu Wien, Mathematisch-Naturwissenschaftliche Klasse. Akademie-Verlag, Sitzungber 178 (H1-4), 37-42.

Koch J., Kilian R. (2005) – ‘Little Ice Age’ glacier fluctuations, Gran Campo Nevado, southernmost Chile. The Holocene 15, 20-28.

Leonelli G., Pelfini M., Morra di Cella U. (2009) – Detecting climatic treelines in the Italian Alps : the influence of geomorphological factors and human impacts. Physical Geography 30, 338-352 (doi : 10.2747/0272-3646.30.4.1).

McCarthy D.P., Luckman B.H. (1993) – Estimating ecesis for tree-ring dating of moraines : a comparative study from the Canadian Cordillera. Arctic and Alpine Research 25, 63-68.

Panizza M. (2001) – Geomorphosites : concepts, methods and examples of geomorphological surveys. Chinese Science Bulletin 46, 4-6.

Panizza M., Piacente S. (2003)Geomorfologia culturale. Pitagora, Bologna, 350 p.

Pauli H., Gottfried M., Grabherr G. (2003) – Effects of climate change on the alpine and nival vegetation of the Alps. Journal of mountain ecology 7, 9-12.

Pecci M., D’Agata C., Smiraglia C. (2008) – Ghiacciaio del Calderone (Apennines, Italy) : the mass balance of a shrinking Mediterranean glacier. Geografia Fisica e Dinamica Qiaternaria 31-1, 55-62.

Pelfini M. (1992)Le fluttuazioni glaciali oloceniche nel Gruppo Ortles-Cevedale (settore lombardo). PhD thesis, università degli Studi di Milano, Earth Sciences Department “Ardito desio”, 211 p.

Pelfini M. (2008) – Il contributo della dendrocronologia alla glaciologia. In Romagnoli M. (Ed.) : Dendrocronologia per i beni culturali e l’ambiente. Nardini Editore, Firenze, 33-46.

Pelfini M., Smiraglia C. (1992) – Alcune serie secolari di variazioni frontali dei ghiacciai delle Alpi Lombarde. Atti VI Convegno Glaciologico Italiano, Gressoney. Geografia Fisica e Dinamica Quaternaria 15, 143-47.

Pelfini M., Smiraglia C. (2003) – I ghiacciai, un bene geomorfologico in rapida evoluzione. Bollettino della Società Geografica Italiana XI (VIII), 521-544.

Pelfini M., Smiraglia C. (2007) – Incremento del rischio geomorfologico e turismo naturalistico. Il caso del “sentiero glaciologico” della Valle dei Forni (Alta Valtellina, SO). In Piccazzo M., Brandolini P., Pelfini M. (Eds.) : Clima e rischio geomorfologico in aree turistiche. Patron, Bologna, 95-116.

Pelfini M., Diolaiuti G., Smiraglia C. (2005) – I ghiacciai come beni geomorfologici dell’alta montagna alpina : identificazione e valorizzazione In Terranova R., Brandolini P., Firpo M. (Eds.) : La valorizzazione turistica dello spazio fisico come via alla salvaguardia ambientale. Pàtron, Bologna, 345-368.

Pelfini M., Santilli M., Leonelli G., Bozzoni M. (2007) – Investigating surface movements of debris-covered Miage glacier, Western Italian Alps, using dendroglaciological analysis. Journal of Glaciology 53, 141-152.

Regeant Instruments Inc. (2001)Windendro. User manual. Régent Instruments, Québec, 86 p.

Reynard E., Panizza, M. (2005) - Géomorphosites : définition, évaluation et cartographie. Une introduction. In Reynard E., Panizza M. (Eds) : Géomorphologie : relief, processus, environnement 3, 177-180.

Schweingruber F.H. (1987)Tree rings : basics and applications of dendrochronology. D. Reidel Publishing Company, Dordrecht, 276 p.

Smiraglia C., Diolaiuti G., Casati D., Kirkbride M.P. (2000) – Recent areal and altimetric variations of Miage Glacier (Monte Bianco massif, Italian Alps). Symposium at Seattle 2000. Debris-Covered Glaciers. IAHS Publications 264, 227-233.

Smiraglia C., Pelfini M., Dioliauti G., Belò M. (2006) – The recent evolution of an Alpine glacier used for summer skiing (Vedretta Piana, Stelvio Pass, Italy). Cold Regions Science and Technology 44, 206-216.

Smiraglia C., Diolaiuti G., Pelfini M., Belò M., Citterio M., Carnielli T., D’Agata C. (2008) – Glacier changes and their impacts on mountain tourism : two case studies from the Italian Alps. In Orlove B.S., Wiegandt E., Luckman B.H. (Eds) : Darkening Peaks. University of California Press, Berkeley, 296 p.

Thomson M.H., Kirkbride M.P., Brock B.W. (2000) – Twentieth century surface elevation change of the Miage Glacier, Italian Alps. Symposium at Seattle 2000. Debris- Covered Glaciers. IAHS Publications 264, 219-225.

UNESCO-World Heritage Centre (2007)Case studies on World Heritage and climate change. UNESCO World Heritage Centre, Paris, 88 p.

Winchester V., Harrison S., Warren C.R. (2001) – Recent retreat Glaciar Nef, Chilean Patagonia, dated by lichenometry and dendrochronology. Arctic, Antartic and Alpine research 33, 266-273.

Zouros N. (2005) – Assessment, protection and promotion of geomorphological and geological sites in the Aegean area, Greece. Géomorphologie : relief, processus, environnement 3, 227-234.

Zouros N. (2007) – Geomorphosite assessment and management in protected areas of greece. Vase study of Lesvos island : coastal geomorphosites. Geographica Elvetica 62, 169-180.

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Annexe

Version française abrégée

Les impacts du changement climatique sur les glaciers alpins induisent des changements environnementaux profonds : morcellement des corps de glace, retrait de leur front, extension concomitante des zones proglaciaires, etc. Ces transformations affectent des zones englacées classées comme étant des géomorphosites. Leur évolution rapide renforce la nécessité d’étudier comment, et à quel rythme, ces zones changent, afin de définir au mieux des stratégies de valorisation et de promotion touristique. Dans ce travail, nous détaillons comment investiguer les changements affectant ces géomorphosites glaciaires à travers l’étude des cernes de croissance des arbres. Pour cela, des arbres ont été étudiés 1) sur la couverture de débris d’un glacier couvert italien, 2) sur la marge proglaciaire de ce glacier couvert et 3) sur les pourtours d’un glacier italien non couvert. Nous tentons alors de montrer que les cernes de croissance, en révélant la réactivité du glacier, sont un critère témoignant de l’évolution du géomorphosite.
Les géomorphosites sur lesquels cette méthode fut appliquée sont le Glacier du Miage (Val d’Aoste, Italie), le plus imposant glacier couvert italien, et le Glacier Forni, dans la haute vallée de Valtellina (Alpes centrales italiennes ; fig. 1).
Les relevés effectués sur le Glacier du Miage, et plus particulièrement sur sa couverture de débris, ont montré des anomalies de croissance. La localisation et la datation de celles-ci révèlent le passage d’une onde d’affaissement qui a affecté le lobe septentrional (fig. 2) entre 1989 et 1993 ainsi que le lobe méridional entre 1984 et 1990. Cet affaissement et la perte de volume associée se sont organisés en lien avec l’évolution de falaises de glace, apparues dans la zone terminale. Le suivi de ces falaises a révélé un retrait de l’ordre de 5,8 cm/jour entre le 25 mai 2006 et le 10 juin 2007 et de 12,7 cm/jour entre le 10 juin 2007 et le 14 août 2007. D’après cette vitesse de retrait de la falaise de glace, plus d’une centaine d’arbres ont été perdus. Plus en aval, les arbres (Larix decidua Mill.) développés dans l’aire proglaciaire du lobe méridional témoignent de l’évolution géomorphologique du glacier. Affectées successivement par l’intense remaniement occasionné par les eaux de fusion, trois unités géomorphologiques ont été identifiées. Une carte diachronique permet ainsi de montrer la période lors de laquelle chaque zone fut remaniée : avant 1977 pour l’une, entre 1977 et 1982 pour une autre, après 1982 pour la dernière. Dans le détail, les cernes étudiés suggèrent une relation entre la localisation de ces trois unités et le drainage du lac de Miage, comme le suggèrent les observations menées après des événements récents. En effet, une diminution du nombre d’anomalies de croissance a été mise en évidence après les vidanges brutales de 1990 et de 2004 (fig. 5).
Dans le cadre des études menées sur la colonisation végétale des pourtours du glacier de Forni, un échantillon d’arbres regroupés selon huit stations échelonnées entre 2100 m et 2400 m d’altitude, a permis de quantifier la période d’ecesis. L’ecesis minimal varie de 23 ans à 41 ans pour les mélèzes et de 20 ans à 48 ans pour les épicéas (fig. 8 et fig. 9). Ces valeurs semblent bien inférieures à celles qui sont estimées pour la période du Petit Âge de Glace. Une hypothèse serait que le réchauffement actuel soit à l’origine de cette réduction, en accélérant les processus biotiques et abiotiques.
Au final, les résultats soulignent la réactivité et les modifications profondes des géomorphosites glaciaires face au changement climatique. La nature et le rythme de ces modifications ont pu être reconstitués grâce aux cernes de croissance. Outre une meilleure planification des stratégies de conservation et de valorisation touristique, ceci permet d’évaluer les changements (évolution d’une falaise de glace, extension de l’aire proglaciaire, biodiversité…) intrinsèques au fonctionnement du site. Ces changements doivent être évalués grâce à des études scientifiques qui permettront d’estimer, par la suite et au mieux, la valeur de ce géomorphosite.

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Table des illustrations

Titre Fig. 1 – Panoramic views of the two study areas. Fig.1 – Vue panoramique des deux zones d’étude.
Légende A: The Forni Glacier (central Italian Alps; photo by V. Garavaglia). B: The Miage Glacier (Aosta Valley, Western Italian Alps; photo by E. Motta).A : Le Glacier des Forni (Alpes centrales italiennes ; photo V. Garavaglia). B : Le Glacier du Miage (Alpes occidentales italiennes ; photo E. Motta).
URL http://geomorphologie.revues.org/docannexe/image/7895/img-1.jpg
Fichier image/jpeg, 184k
Titre Fig. 2 – Sampling areas (A, B, C and D) for the dendrochronological study on the Miage Glacier (adapted from Pelfini et al., 2007). Fig. 2 – Zones d’échantillonnage (A, B, C et D) pour l’étude dendrochronologique du Glacier du Miage (adapté de Pelfini et al., 2007).
Légende The picture at the top left represents the ice cliff on the northern lobe of the glacier (photo by E. Motta).L’image en haut à gauche représente le front de glace du lobe nord du glacier (photo E. Motta).
URL http://geomorphologie.revues.org/docannexe/image/7895/img-2.jpg
Fichier image/jpeg, 284k
Titre Fig. 3 – A simplified sketch of the Forni Glacier forefield. Black squares represent the sampling plots where the dendrochronological sampling was realised, whereas the black lines represent the dated moraines.Fig. 3 – Schéma simplifiée de la zone proglaciaire du Glacier des Forni. Les carrés noirs représentent les plots où l’échantillonnage dendrochronologique a été réalisé. Les lignes noires représentent les moraines.
URL http://geomorphologie.revues.org/docannexe/image/7895/img-3.jpg
Fichier image/jpeg, 204k
Titre Fig. 4 – Sketches of the proglacial area of the southern Miage Glacier lobe. Fig. 4 – Cartes simplifiées de la zone proglaciaire du lobe sud du Glacier du Miage.
Légende Dating tree-ring growth anomalies, three areas characterised by a more intense stream activity (before 1977, between 1977 and 1982, after 1982) were identified (redrawn from Garavaglia et al., in press b). Black circles represent the sampled trees. 1: proglacial area boundary; 2: hydrography; 3: scarp; 4: hiking trail; 5: sampled tree group; 6: spring; 7: bridge.Trois zones caractérisées chacune par une dynamique spécifique ont été identifiées (avant 1977, entre 1977 et 1982, après 1982) en utilisant les anomalies de croissance des cernes (redessiné de Garavaglia et al., in press b). Les cercles noirs représentent les arbres échantillonnés. 1 : limite de la zone proglaciaire, 2 : hydrographie ; 3 : escarpement, 4 : sentier de randonnée pédestre ; 5 : groupe d’arbres échantillonnés ; 6 : source ; 7 : pont.
URL http://geomorphologie.revues.org/docannexe/image/7895/img-4.jpg
Fichier image/jpeg, 192k
Titre Fig. 5 – Relation between growth anomalies (black bars) distribution and flood events (black stars). The grey dashed bars represent exceptional snowfalls and the grey bars are years characterised by the Miage marginal ice-contact lake’s drainage events.Fig. 5 – Relation entre la distribution des anomalies de croissance (barres noires) et les événements de crue (étoiles noires). Les barres grises en pointillés représentent les années caractérisées par des vidanges du Lac du Miage.
URL http://geomorphologie.revues.org/docannexe/image/7895/img-5.jpg
Fichier image/jpeg, 128k
Titre Fig. 6 – Relation between sampled tree ages and altitude in the Forni Glacier forefield. Fig. 6 – Relation entre l’âge des arbres échantillonnés et l’altitude dans la zone proglaciaire du Glacier des Forni.
Légende The tree age increases with altitude (R2= 0.73 for the maximum age and R2= 0.68 for the average age of trees).L’âge des arbres augmente avec l’altitude (R= 0,73 pour l’âge maximum et R= 0,68 pour l’âge moyen des arbres).
URL http://geomorphologie.revues.org/docannexe/image/7895/img-6.jpg
Fichier image/jpeg, 108k
Titre Fig. 7 – Relation between the sampled tree average height and the altitude. The average tree height decreases with altitude (R= 0.89). Fig. 7 – Relation entre la hauteur moyenne des arbres échantillonnés et l’altitude. La hauteur moyenne des arbres diminue avec l’altitude (R= 0,89).
URL http://geomorphologie.revues.org/docannexe/image/7895/img-7.jpg
Fichier image/jpeg, 92k
Titre Fig. 8 – Average ecesis of Norway spruces and Larches in the Forni Glacier forefield. Fig. 8 – L’ecesis moyen des Picea abies L. Karst et des Larix decidua Mil. échantillonnés dans la zone proglaciaire du Glacier des Forni.
Légende 1 : Norway spruces (Picea abies L. Karst) ; 2 : larches (Larix decidua Mill.).1 : épinettes de Norvège (Picea abies L. Karst) ; 2 : mélèzes (Larix decidua Mill.).
URL http://geomorphologie.revues.org/docannexe/image/7895/img-8.jpg
Fichier image/jpeg, 120k
Titre Fig. 9 – Minimum ecesis of Norway spruces and Larches in the Forni Glacier forefield. Fig. 9 – L’ecesis minimum des Picea abies L. Karst et des Larix decidua Mil. échantillonnés dans la zone proglaciaire du Glacier des Forni.
Légende 1 : Norway spruces (Picea abies L. Karst) ; 2 : larches (Larix decidua Mill.).1 : épinettes de Norvège (Picea abies L. Karst) ; 2 : mélèzes (Larix decidua Mill.).
URL http://geomorphologie.revues.org/docannexe/image/7895/img-9.jpg
Fichier image/jpeg, 123k
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Référence papier

Valentina Garavaglia, Manuela Pelfini et Irene Bollati, « The influence of climate change on glacier geomorphosites: the case of two Italian glaciers (Miage Glacier, Forni Glacier)investigated through dendrochronology », Géomorphologie : relief, processus, environnement, vol. 16 - n° 2 | 2010, 153-164.

Référence électronique

Valentina Garavaglia, Manuela Pelfini et Irene Bollati, « The influence of climate change on glacier geomorphosites: the case of two Italian glaciers (Miage Glacier, Forni Glacier)investigated through dendrochronology », Géomorphologie : relief, processus, environnement [En ligne], vol. 16 - n° 2 | 2010, mis en ligne le 01 juillet 2012, consulté le 20 août 2017. URL : http://geomorphologie.revues.org/7895 ; DOI : 10.4000/geomorphologie.7895

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Auteurs

Valentina Garavaglia

Dipartimento di Scienze della Terra A. Desio - Università degli Studi di Milano - Via Mangiagalli 34 - 20133 Milan - Italy (valentina.garavaglia@unimi.it)

Manuela Pelfini

Dipartimento di Scienze della Terra A. Desio - Università degli Studi di Milano - Via Mangiagalli 34 - 20133 Milan - Italy

Irene Bollati

Dipartimento di Scienze della Terra A. Desio - Università degli Studi di Milano - Via Mangiagalli 34 - 20133 Milan – Italy

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