The EuroDendro project -Snow-avalanche frequency and magnitude in European Middle Mountain unravelled by dendrogeomorphological analyses

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The EuroDendro project -Snow-avalanche frequency and magnitude in European Middle Mountain unravelled by

dendrogeomorphological analyses

Armelle Decaulne, Ó. Eggertsson, Þ. Sæmundsson, K. Laute, A.A. Beylich, Olympiu Pop, Emmanuelle Defive, Sébastien Larrue

To cite this version:

Armelle Decaulne, Ó. Eggertsson, Þ. Sæmundsson, K. Laute, A.A. Beylich, et al.. The EuroDen-

dro project -Snow-avalanche frequency and magnitude in European Middle Mountain unravelled by

dendrogeomorphological analyses. European Geoscience Union General Assembly, May 2010, Vienne,

Austria. 2010. �hal-01131041�

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Armelle Decaulne ([email protected]),

Ólafur Eggertsson, Þorsteinn Sæmundsson, Katja Laute, Achim A. Beylich, Olimpiu Pop, Emmanuelle Defive & Sébastien Larrue

The EuroDendro project - Snow-avalanche frequency & magnitude

in European Middle Mountain unravelled by dendrogeomorphological analyses

G E OLAB

SKÓGRÆKT RÍKISINS

Objectives

Investigated areas The dendromorphological approach

The dendrochronological approach Tree species

The EuroDendro project aims to detect the signal of recent snow-avalanche activity within the analyses of tree rings.

In mountain areas, even middle mountains, snow avalanches are a common process & pose serious hazards & risks in recently occupied sectors, either for residence or recreation purposes.

Where (i) geomorphological evidence of snow-avalanche occurrence are scarce, (ii) historical records are poor & (iii) trees are colonizing part of the slopes, tree-ring analyses appear as a good alternative to reveal the recent snow- avalanche history.

The dendromorphological approach consists in a survey of the investigated areas to inventory damages that affect the morphology of the tree:

tilting of the trunk,

presence of scars on the trunk, topped trees.

Such a survey enables mapping the most frequent snow- avalanche paths, helping to:

locate the maximum potential damages estimate the runout distances

appreciate the lateral dispersion of the events The EuroDendro project is very interested in:

(i) broad-leaved trees, which attracted seldom attention in dendrogeomorphology related to snow-avalanche activity:

birch (Betula pubescens) in N Iceland

birch (Betula pubescens) & alder (Alnus) in W Norway beech (Fagus sylvatica) in NE Cantal - France

(ii) coniferous trees in little explored areas where broad- leaved trees are unavailable:

spruce (Picea abies) in Central Romania

Core extractions in c &

d directions, i.e. parallel to the main flux lines, on both the uphill & the downhill sides of the tree

Core analyses on a Lintab measurement table, enabling tree-

rings counting, location & dating of growth disturbances (narrow & large rings) &

reaction wood formation.

The EuroDendro project investigates four main areas, some of them in connection with other scientific frameworks.

The investigated areas are located in:

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(A) Northern Iceland, in the Dalsmynni valley, the Ljósavatn- skarð pass & the southern Fnjóskadalur valley, (B) Western Norway, at the bottom of Nordfjord, in Erdalen &

Bødalen,

(C) Central Romania, in the Southern Carpathians, in the Bâlea valley, Făgărăş massif,

(D) Central France, in the Northeastern valleys of the Cantal massif.

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All these areas are characterised by steep slopes, harsh wintry conditions, known frequent snow-avalanche activity, a relative remotness & a tree-cover on talus & cones.

A B

C D

The Fjnóskadalur site, Iceland

© Armelle Decaulne

The Bâlea site, Romania

© Armelle Decaulne The Erdalen site,

Norway

© Armelle Decaulne

The Cantal site, France

© Emmanuelle Defive

© GoogleEarth Study sites location

Recurrent snow avalanches strongly influence the growth of the birches that develop typical tilted trunks (Ljósavatnskarð, Iceland). © Armelle Decaulne

Slow growth

Samples from the lower track & upper runout zones Broad-leaved trees => tension wood on the strained side of the trunk => asymmetrical growth

Reference growth from outside the snow-avalanche influence area isolate the role of climatic accident & insect attacks Location of the reaction wood date recurrent events over the last 80 years, with a different distribution

Young trees could indicate:

(i) recent snow-avalanche activity drop at valley level (ii) change in grazing zones

Well-defined areas of felled trees = recent major snow- avalanche events

Reference growth = average of all cores extracted in c-d directions

Samples from the lower runout zones

Bødalen: sudden drop of tree growth in 2000 = major avalanche felled the tree

Erdalen: recurrent avalanchy winters post-1995, severe from 2000 & especially in 2002 & 2006

Reference curve built from straight spruces sampled below the path

Narrow path with poor tree cover, even in the distal runout zone Most of the trees are very young (+/- 30 years)

Reaction wood formation on the downhill side = recurrent stress due to snow-avalanche activity.

Oldest trees signal several avalanchy periods, especially from 1920s to early 1950s again during the 1980s.

Spatial distribution of major impact areas affecting trees in the Bødalen valley, Norway.

Background image is © Norwegian land survey

Main dendrogeomorphological investigated paths in the Bødalen valley, Norway.

© Katja Laute Map of the tree morphology, reflecting damages due to snow-avalanche

occurrence on a colluvial cone in the Dalsmynni valley, Iceland.

Topped & tilted spruce in the distal part of

the path, Romania. © Armelle Decaulne Asymetric branch distribution on a spruce in Romania. © Armelle Decaulne Scars on the trunk & main branches in the snow-avalanche path. © Armelle Decaulne

Tilting, scars & topping Tilting & scars

Main areas of felled trees Main areas of damaged shrubs Tilting

200 m

Dalsmynni, Iceland - tree #16

Years 0

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2 2.2 2.4 2.6

1933 1935 1937 1939 1941 1943 1945 1947 1949 1951 1953 1955 1957 1959 1961 1963 1965 1967 1969 1971 1973 1975 1977 1979 1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007 2009

tree ring width (mm)

Years

Ljósavatnskarð-west, Iceland - tree #9

0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8 2

1914 1916 1918 1920 1922 1924 1926 1928 1930 1932 1934 1936 1938 1940 1942 1944 1946 1948 1950 1952 1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

reference curve

reaction wood core c (upside)

core d (downside)

Bødalen, Norway - tree #4

0 0.5 1 1.5 2 2.5 3 3.5 4

1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008

Years

tree ring width (mm) tree ring width (mm)

Years 0

0.5 1 1.5 2 2.5 3 3.5 4

1981 1983 1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005 2007

Erdalen, Norway - tree #7

Făgărăş, Romania - tree #A4

0 0.5 1 1.5 2 2.5 3 3.5 4 4.5

1914 1916 1918 1920 1922 1924 1926 1928 1930 1932 1934 1936 1938 1940 1942 1944 1946 1948 1950 1952 1954 1956 1958 1960 1962 1964 1966 1968 1970 1972 1974 1976 1978 1980 1982 1984 1986 1988 1990 1992 1994 1996 1998 2000 2002 2004 2006 2008 Years

reference curve zone

sampled zone: distal runout zone

Map of the tree morphology, reflecting damages due to snow-avalanche occurrence on a colluvial cone in the Ljósavatnskarð pass, Iceland.

200 m