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Rebetez, Martine

Nom
Rebetez, Martine
Affiliation principale
Site web
Fonction
Professeure ordinaire
Email
martine.rebetez@unine.ch
Identifiants
https://libra.unine.ch/handle/123456789/403

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  • Publication
    Métadonnées seulement
    The upward shift in altitude of pine mistletoe (Viscum album ssp austriacum) in Switzerland - the result of climate warming?
    (2005)
    Dobbertin, Matthias
    ;
    Hilker, Nadine
    ;
    Rebetez, Martine 
    ;
    Zimmermann, Niklaus E
    ;
    Wohlgemuth, Thomas
    ;
    Rigling, Andreas
    Pine mistletoe (Viscum album ssp. austriacum) is common in natural Scots pine (Pinus sylvestris L.) forests in the alpine Rhone Valley, Switzerland. This semi-parasite, which is regarded as an indicator species for temperature, increases the drought stress on trees and may contribute to the observed pine decline in the region. We recorded mistletoes on representative plots of the Swiss National Forest Inventory ranging from 450 to 1,550 m a.s.l. We found mistletoe on 37% of the trees and on 56% of all plots. Trees infested with mistletoe had a significantly higher mortality rate than non-infested trees. We compared the current mistletoe occurrence with records from a survey in 1910. The current upper limit, 1,250 m, is roughly 200 m above the limit of 1,000-1,100 m found in the earlier survey 100 years ago. Applying a spatial model to meteorological data we obtained monthly mean temperatures for all sites. In a logistic regression mean winter temperature, pine proportion and geographic exposition significantly explained mistletoe occurrence. Using mean monthly January and July temperatures for 1961-1990, we calculated Skre's plant respiration equivalent (RE) and regressed it against elevation to obtain the RE value at the current mistletoe elevation limit. We used this RE value and temperature from 1870-1899 in the regression and found the past elevation limit to be at 1,060 m, agreeing with the 1910 survey. For the predicted temperature rise by 2030, the limit for mistletoe would increase above 1,600 m altitude.
  • Publication
    Accès libre
    Recent climate change: Rethinking drought in the context of Forest Fire Research in Ticino, South of Switzerland
    (2005)
    Reinhard, Michael
    ;
    Rebetez, Martine 
    ;
    Schlaepfer, Rodolphe
    We analyse trends over the past 32 years in drought variables in the context of forest fire research and climate change in Ticino, Southern Switzerland. January to April and in particular the month of March have become drier. This is the time of the year when forest fires are most frequent. Our results show an increasing trend in all climatic variables favourable to drought and forest fires, including the length of episodes without precipitation, sunshine duration and temperature, and a decrease in relative humidity. The only exception is the number of "foehn" days, which have not significantly increased.
  • Publication
    Accès libre
    Climate change may already threaten Scots pine stands in the Swiss Alps
    (2004)
    Rebetez, Martine 
    ;
    Dobbertin, Matthias
    Large numbers of Scots pine are dying in the dry inner-alpine valleys of the European Alps; in Switzerland, locally almost half the Scots pine (Pinus sylvestris L.) population has died since 1995. As Switzerland's temperature has increased at more than twice the global average in the 20(th) stop century and as most of this increase has occurred during the last 20 years, we investigated possible relationships between the dying Scots pine and climatic parameters. We centred our studies in the upper Rhone valley. Our results show that the strong climatic warming that has occurred in recent years may well be the indirect cause of the mortality observed in these forests. Tree mortality was highest following the dry and hot year 1998, and tree defoliation, an indicator of tree vitality, showed a strong correlation with the previous year's precipitation. While precipitation showed no clear significant trend over time, the number of warm days (mean >20degreesC, maximum >25 degreesC) and potential evapotranspiration have significantly increased over the last 20 years. Higher temperatures favour pine wood nematodes and bark beetles, both of which are found at the study site, and increasing drought stress reduces tree resistance against pathogens. As these forests have in part protective functions, there is a need to better understand the mortality through interdisciplinary research and also to find means to change the species composition in order to establish tree species that are better able to withstand warmer temperatures.
  • Publication
    Métadonnées seulement
    To what extent can oxygen isotopes in tree rings and precipitation be used to reconstruct past atmospheric temperature? A case study
    (2003)
    Rebetez, Martine 
    ;
    Saurer, Matthias
    ;
    Cherubini, Paolo
    We analyzed the relationship between air temperature and oxygen isotopes measured in tree rings of silver fir (Abies alba Mill.) from a long-term forest ecosystem research plot in the Swiss Jura mountains (LWF project). The oxygen isotope data were compared with a century-long meteorological series of air temperature data. Measurements of oxygen isotope ratios in precipitation were also used for comparison. Results show that the late-wood tree-ring series is significantly correlated with May to August temperatures. Correlations were higher for maximum (daytime) air temperature and even better for air temperature measured on rainy days only. We stress that trends in maximum temperature series for this time of the year, like trends in oxygen isotope ratios series from tree rings, are completely different from trends in yearly mean temperature. Indeed, maximum temperature trends during the vegetation period slightly decreased during the 20th century, whereas yearly means increased strongly.
  • Publication
    Accès libre
    Changes in daily and nightly day-to-day temperature variability during the twentieth century for two stations in Switzerland
    (2001)
    Rebetez, Martine 
    An analysis of day-to-day variability was performed on two century-longs daily minimum and maximum temperature series from Switzerland. Warmer temperatures during the 20(th) century have been accompanied by a reduction in day-to-day variability, particularly for minimum temperatures and for winter. There is a significant negative correlation between day-to-day variability and the skewness of the temperature distribution, particularly in winter and for minimum temperatures. Lower variability is linked to a reduced number of cold days and nights. Higher NAO index values tend to be associated not only with warmer temperatures but also with lower day-to-day variability. This paper confirms that the temperature warming during the 20(th) century has happened mainly through the loss of the coldest part of the series, not only in the 24-hour or yearly cycle, but also through the loss of the coldest episodes in each month.