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Levesque M.,Lamont Doherty Earth Observatory | Rigling A.,Institute Federal Of Recherches Sur La Foret | Brang P.,Institute Federal Of Recherches Sur La Foret
Schweizerische Zeitschrift fur Forstwesen | Year: 2015

The sensitivity to drought of five conifers was studied along a climatic gradient covering the northern flank of the Swiss Alps, the Swiss Plateau, the Jura foothills and the central Alps. Three native species, i.e., Norway spruce, Scots pine and European larch, and two non-native species, i.e., Douglas fir and black pine, were analyzed. A total of 770 trees on 14 sites were sampled. To assess the sensitivity of conifers to drought, dendroecological analyses were performed for the period 1941-2006. On dry sites in the central Alps, spring water deficits sharply reduce growth, while on mesic sites located on the Swiss Plateau and the Jura foothills summer droughts significantly restrict growth. Spruce, larch and Scots pine are, depending on the site conditions, the most vulnerable species to extreme droughts, which implies that their long-term performance and survival may be compromised if the climate becomes warmer and drier. Conversely, black pine and Douglas fir were less drought-sensitive and grew faster than native species along the gradient. Selecting species with different but complementary strategies regarding drought could secure the productivity and efficiency of water use of forest stands and increase their resistance to climate change. Source


Thimonier A.,Institute Federal Of Recherches Sur La Foret | Pannatier E.G.,Institute Federal Of Recherches Sur La Foret | Schmitt M.,Institute Federal Of Recherches Sur La Foret | Waldner P.,Institute Federal Of Recherches Sur La Foret | And 2 more authors.
Schweizerische Zeitschrift fur Forstwesen | Year: 2012

Emissions of nitrogenous pollutants reached a peak in the mid-1980s and have decreased since then, but they remain at a high level. Long-term observation sites were established between 1984 and 1995 within three networks in Switzerland (IAP, LWF and NITREX), following growing concern that the vitality of forests might be affected by air pollution. Here we assess the nitrogen status of selected sites and its changes over the last 15 to 25 years. Nitrogen deposition at the sites was either obtained from models (IAP) or from throughfall measurements (LWF and NITREX). Indicators of the nitrogen status of a site included nitrate leaching from the rooting zone (43 sites), tree foliar concentrations of nitrogen and other nutrients (>100 sites), and the species composition of ground vegetation (59 sites). Nitrogen deposition has significantly decreased on eight out of twelve sites during the last 15 years. However, except in the Alps, deposition remains within or above the range of empirical critical loads, which correspond to the deposition levels above which the ecosystem might be negatively affected. Nitrate leaching can be locally high, depending on deposition rates, but also on other factors such as soil properties. Tree foliar concentrations in nitrogen and phosphorus have tended to decrease during the last 15 to 25 years. The comparison of vegetation surveys, first carried out in 1984, then repeated in 2003/2004, indicated an increase in nitrophilous species (IAP), but on a more recent and shorter period (1994/1998-2011), on a smaller number of sites (LWF), we found no significant changes. Source


Levesque M.,Institute Federal Of Recherches Sur La Foret | Levesque M.,Lamont Doherty Earth Observatory | Rigling A.,Institute Federal Of Recherches Sur La Foret | Brang P.,Institute Federal Of Recherches Sur La Foret
Revue Forestiere Francaise | Year: 2015

The sensitivity to drought of five conifers was studied along a climatic gradient covering the north of the Swiss Alps, the Swiss Plateau, the Jura foothills and the central Alps. Three native species, i.e., Norway spruce, Scots pine and European larch, and two non-native species, i.e., Douglas-fir and black pine were analysed. A total of 770 trees on 14 sites were sampled. To assess the sensitivity of conifers to drought, tree-rings formed in the period 1941-2006 were analysed. On dry sites in the Central Alps, spring water deficits sharply reduce growth while on mesic sites located on the Swiss Plateau and the Jura foothills summer droughts significantly restrict growth. Spruce, larch and Scots pine are the most vulnerable species to extreme droughts, which implies that their long-term performance and survival may be compromised if the climate becomes warmer and drier. Conversely, black pine and Douglas-fir were less drought sensitive and grew faster than native species along the gradient. Selecting species with different but complementary strategies regarding drought could secure the productivity and efficiency of water use of forest stands and increase their resistance to climate change. © AgroParisTech, 2015. Source


Graf E.,Institute Federal Of Recherches Sur La Foret | Thimonier A.,Institute Federal Of Recherches Sur La Foret | Schmitt M.,Institute Federal Of Recherches Sur La Foret | Waldner P.,Institute Federal Of Recherches Sur La Foret | Walthert L.,Institute Federal Of Recherches Sur La Foret
Schweizerische Zeitschrift fur Forstwesen | Year: 2012

After a massive input of acidifying components on the environment in the middle of the 20th century, atmospheric acid deposition has decreased as a result of sulphur emission reduction. The continuous acid input might affect the chemistry of soils and drainage waters and accelerate soil acidification. In the framework of the Swiss Long-Term Forest Ecosystem Research (LWF), we examined whether acid deposition has continued to decline in the last ten years in different forest ecosystems and how the chemistry of soil water reacted to the improvement in air quality. Acid deposition decreased significantly at only three out of the nine study sites. Sulphur deposition declined at all sites, but due to the relatively low sulphur load compared to nitrogen deposition, it did not contribute to decrease acid deposition. Chemistry of soil solution remained quite constant since the beginning of the measurements about ten years ago. We did not observe any acidification of soil solution in six out of eight sites. In contrast, changes in soil solution chemistry at two sites showed a rapid acidification. At three sites, the deeper soil layer released large amount of sulphate coupled with base cations, which likely contributed to deplete the soil in nutrients. The analysis of the base saturation in 1039 soil profiles across Switzerland shows a high risk of relatively fast acidification of soil solution in almost 20% of sites. Source

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