Global processes ask for regional solutions (essay) In this essay we discuss the impact of import... more Global processes ask for regional solutions (essay) In this essay we discuss the impact of important global processes on the Swiss forests, such as 1) climate change, 2) the nuclear reactor disaster of Fukushima with the consequence of a pull-out from nuclear energy, 3) the globalization of the international commodity trading and the resulting increase of introduced pests, 4) the deforestation of the tropical rainforests and 5) the increasing demand on further forest services in addition to wood production. Even if the Swiss forests are increasingly impacted and steered by global processes one should be aware that solutions and management concepts need to be effective on a local scale. Hence, an important task of the Swiss Federal Institute for Forest, Snow and Landscape Research WSL is to engage in international networks, to observe international trends in the state of the environment and research, to bring in the Swiss particularities and to contribute to the development of region...
Summary Higher atmospheric CO2 concentrations (ca) can under certain conditions increase tree gro... more Summary Higher atmospheric CO2 concentrations (ca) can under certain conditions increase tree growth by enhancing photosynthesis, resulting in an increase of intrinsic water‐use efficiency (iWUE) in trees. However, the magnitude of these effects and their interactions with changing climatic conditions are still poorly understood under xeric and mesic conditions. We combined radial growth analysis with intra‐ and interannual δ13C and δ18O measurements to investigate growth and physiological responses of Larix decidua, Picea abies, Pinus sylvestris, Pinus nigra and Pseudotsuga menziesii in relation to rising ca and changing climate at a xeric site in the dry inner Alps and at a mesic site in the Swiss lowlands. iWUE increased significantly over the last 50 yr by 8–29% and varied depending on species, site water availability, and seasons. Regardless of species and increased iWUE, radial growth has significantly declined under xeric conditions, whereas growth has not increased as expect...
Question: Lower montane treeline ecotones such as the inner Alpine dry valleys are regarded as se... more Question: Lower montane treeline ecotones such as the inner Alpine dry valleys are regarded as sensitive to climate change. In the dry Valais valley (Switzerland) the composition of the widespread, low altitude Pinus forests is shifting towards a mixed deciduous state. The sub‐boreal P. sylvestris shows high mortality rates, whereas the deciduous sub‐mediterranean Quercus pubescens is spreading. These species may act as early indicators of climate change. We evaluate this hypothesis by focusing on their differences in drought tolerance, which are hardly known, but are likely to be crucial in the current forest shift and also for future forest development.Methods: We used dendroecological methods to detect species‐specific patterns in the growth response to drought. The relationship between radial growth of 401 trees from 15 mixed stands and drought was analysed by calculating response functions using yearly tree‐ring indices and monthly drought indices. PCA was applied to the respon...
Pine mistletoe (Viscum album ssp. austriacum) is common in natural Scots pine (Pinus sylvestris L... more 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
Tree-species change in the Scots pine forests of Valais The Valais is among the most extreme inne... more Tree-species change in the Scots pine forests of Valais The Valais is among the most extreme inner-Alpine dry regions. The distinct temperature increase of the recent years results in increasing drought stress for plants during dry years. In Valais forest vegetation is presently in change: mortality processes in Scots pine (Pinus sylvestris L.) go along with an increase of broadleaved trees, mostly downy oak (Quercus pubescens Willd.). A combined approach (assessment of forest structures on a regular grid, intensive monitoring and experimental plots, and analysis of past forest management) was applied to analyze the shift in tree-species composition and to keep apart the impact of changes in climate and land-use. The shift from pine to oak was most pronounced on dry sites, where pine mortality was highest and oak regeneration most frequently. Pine mortality was highest after dry years, whereas oak was less affected. Although oak regeneration seems to profit from the dryer climate, the changes of the land-use regime during the past decades was identified as the main driver for the increased spread of oak.
-En Valais (Suisse), deux types de pin sylvestre (Pinus sylvestris L.) se distinguent morphologiq... more -En Valais (Suisse), deux types de pin sylvestre (Pinus sylvestris L.) se distinguent morphologiquement et écologiquement : un pin de plaine et un pin d'altitude. Les pinèdes de plaine présentent des signes de dépérissement depuis le début des années 1990. Quatre paires de populations ont été choisies dans cette vallée et deux autres dans deux autres régions alpines à climat continental. La différenciation génétique entre les deux types et entre deux classes de vitalité a été étudiée à l'aide d'amplification aléatoire d'ADN polymorphe (RAPD). La croissance en diamètre et la quantité d'aubier des deux types ont été mesurées. À l'exception d'une paire de populations, les deux types se distinguent génétiquement, mais faiblement (Φ ST = 4, 2% à 5,8 %). Une sélection différenciée avec l'altitude, la recolonisation à partir de différents refuges glaciaires, un isolement phénologique et les vents dominants sont les facteurs de différenciation envisagés. Aucune raison génétique au dépérissement n'a été trouvée. Les différences de croissance et dans la quantité d'aubier soutiennent une adaptation aux régimes hydriques locaux. écotypes / RAPD / cernes de croissance / dépérissement forestier / variation génétique Abstract-Random amplified polymorphic DNA (RAPD) patterns show weak genetic differentiation between low-and high-elevation types of Scots pine (Pinus sylvestris L.) in dry continental valleys in the Alps. Two types of Scots pine (Pinus sylvestris L.), found either in the lowland or in the subalpine zone, are morphologically distinguished in the central-Alpine Valais (Switzerland), a dry continental valley. The low-elevation pine forests show signs of die-back since the early 1990s. We selected four elevational population pairs in the area, and two additional pairs in two other central-Alpine regions. Genetic differentiation between the two pine types, i.e. between elevations, and between two classes of vitality were studied using random amplified polymorphic DNA (RAPD). Growth in diameter and sapwood proportion was further assessed. Population pairs, with one exception, showed weak, but significant genetic differentiation (Φ ST = 4.2%-5.8%). On the other hand, there was no correlation between genetic data and the die-back observed. We consider disruptive evolution, postglacial migration, phenological separation or wind directions as possible explanations. Differences in growth and sapwood proportions supported the assumption of adaptation to local hydrological regimes. ecotypes / RAPD / growth rings / forest die-back / genetic variation
The ongoing climatic changes potentially affect plant growth and the functioning of temperature-l... more The ongoing climatic changes potentially affect plant growth and the functioning of temperature-limited high-altitude and high-latitude ecosystems; the rate and magnitude of these biotic changes are, however, uncertain. The aim of this study was to reconstruct stand structure and growth forms of Larix sibirica (Ledeb.) in undisturbed forest-tundra ecotones of the remote Polar Urals on a centennial time scale. Comparisons of the current ecotone with historic photographs from the 1960s clearly document that forests have significantly expanded since then. Similarly, the analysis of forest age structure based on more than 300 trees sampled along three altitudinal gradients reaching from forests in the valleys to the tundra indicate that more than 70% of the currently upright-growing trees are o80 years old. Because thousands of more than 500-year-old subfossil trees occur in the same area but tree remnants of the 15-19th century are lacking almost entirely, we conclude that the forest has been expanding upwards into the formerly tree-free tundra during the last century by about 20-60 m in altitude. This upward shift of forests was accompanied by significant changes in tree growth forms: while 36% of the few trees that are more than 100 years old were multi-stem tree clusters, 90% of the trees emerging after 1950 were single-stemmed. Tree-ring analysis of horizontal and vertical stems of multistemmed larch trees showed that these trees had been growing in a creeping form since the 15th century. In the early 20th century, they started to grow upright with 5-20 stems per tree individual. The incipient vertical growth led to an abrupt tripling in radial growth and thus, in biomass production. Based on above-and belowground biomass measurements of 33 trees that were dug out and the mapping of tree height and diameter, we estimated that forest expansion led to a biomass increase by 40-75 t ha À1 and a carbon accumulation of approximately 20-40 g C m À2 yr À1 during the last century. The forest expansion and change in growth forms coincided with significant summer warming by 0.9 1C and a doubling of winter precipitation during the 20th century. In summary, our results indicate that the ongoing climatic changes are already leaving a fingerprint on the appearance, structure, and productivity of the treeline ecotone in the Polar Urals.
Please cite this article in press as: Allen, C.D., et al., A global overview of drought and heat-... more Please cite this article in press as: Allen, C.D., et al., A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests.
This archived Paleoclimatology Study is available from the NOAA National Centers for Environmenta... more This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Switzerland, Western Europe. The time period coverage is from 134 to -59 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data.
In 2018, Central Europe experienced one of the most severe and long-lasting summer drought and he... more In 2018, Central Europe experienced one of the most severe and long-lasting summer drought and heat wave ever recorded. Before 2018, the 2003 millennial drought was often invoked as the example of a "hotter drought", and was classified as the most severe event in Europe for the last 500 years. First insights now confirm that the 2018 drought event was climatically more extreme and had a greater impact on forest ecosystems of Austria, Germany and Switzerland than the 2003 drought. Across this region, mean growing season air temperature from April to October was more than 3.3°C above the long-term average, and 1.2°C warmer than in 2003. Here, we present a first impact assessment of the severe 2018 summer drought and heatwave on Central European forests. In response to the 2018 event, most ecologically and economically important tree species in temperate forests of Austria, Germany and Switzerland showed severe signs of drought stress. These symptoms included exceptionally low foliar water potentials crossing the threshold for xylem hydraulic failure in many species and observations of widespread leaf discoloration and premature leaf shedding. As a result of the extreme drought stress, the 2018 event caused unprecedented drought-induced tree mortality in many species throughout the region. Moreover, unexpectedly strong drought-legacy effects were detected in 2019. This implies that the physiological recovery of trees was impaired after the 2018 drought event, leaving them highly vulnerable to secondary drought impacts such as insect or fungal pathogen attacks. As a consequence, mortality of trees triggered by the 2018 events is likely to continue for several years. Our assessment indicates that many common temperate European forest tree species are more vulnerable to extreme summer drought and heat waves than previously thought. As drought and heat events are likely to occur more frequently with the progression of climate change, temperate European forests might approach the point for a substantial ecological and economic transition. Our assessment also highlights the urgent need for a pan-European ground-based monitoring network suited to track individual tree mortality, supported by remote sensing products with high spatial and temporal resolution to track, analyse and forecast these transitions.
Global processes ask for regional solutions (essay) In this essay we discuss the impact of import... more Global processes ask for regional solutions (essay) In this essay we discuss the impact of important global processes on the Swiss forests, such as 1) climate change, 2) the nuclear reactor disaster of Fukushima with the consequence of a pull-out from nuclear energy, 3) the globalization of the international commodity trading and the resulting increase of introduced pests, 4) the deforestation of the tropical rainforests and 5) the increasing demand on further forest services in addition to wood production. Even if the Swiss forests are increasingly impacted and steered by global processes one should be aware that solutions and management concepts need to be effective on a local scale. Hence, an important task of the Swiss Federal Institute for Forest, Snow and Landscape Research WSL is to engage in international networks, to observe international trends in the state of the environment and research, to bring in the Swiss particularities and to contribute to the development of region...
Summary Higher atmospheric CO2 concentrations (ca) can under certain conditions increase tree gro... more Summary Higher atmospheric CO2 concentrations (ca) can under certain conditions increase tree growth by enhancing photosynthesis, resulting in an increase of intrinsic water‐use efficiency (iWUE) in trees. However, the magnitude of these effects and their interactions with changing climatic conditions are still poorly understood under xeric and mesic conditions. We combined radial growth analysis with intra‐ and interannual δ13C and δ18O measurements to investigate growth and physiological responses of Larix decidua, Picea abies, Pinus sylvestris, Pinus nigra and Pseudotsuga menziesii in relation to rising ca and changing climate at a xeric site in the dry inner Alps and at a mesic site in the Swiss lowlands. iWUE increased significantly over the last 50 yr by 8–29% and varied depending on species, site water availability, and seasons. Regardless of species and increased iWUE, radial growth has significantly declined under xeric conditions, whereas growth has not increased as expect...
Question: Lower montane treeline ecotones such as the inner Alpine dry valleys are regarded as se... more Question: Lower montane treeline ecotones such as the inner Alpine dry valleys are regarded as sensitive to climate change. In the dry Valais valley (Switzerland) the composition of the widespread, low altitude Pinus forests is shifting towards a mixed deciduous state. The sub‐boreal P. sylvestris shows high mortality rates, whereas the deciduous sub‐mediterranean Quercus pubescens is spreading. These species may act as early indicators of climate change. We evaluate this hypothesis by focusing on their differences in drought tolerance, which are hardly known, but are likely to be crucial in the current forest shift and also for future forest development.Methods: We used dendroecological methods to detect species‐specific patterns in the growth response to drought. The relationship between radial growth of 401 trees from 15 mixed stands and drought was analysed by calculating response functions using yearly tree‐ring indices and monthly drought indices. PCA was applied to the respon...
Pine mistletoe (Viscum album ssp. austriacum) is common in natural Scots pine (Pinus sylvestris L... more 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
Tree-species change in the Scots pine forests of Valais The Valais is among the most extreme inne... more Tree-species change in the Scots pine forests of Valais The Valais is among the most extreme inner-Alpine dry regions. The distinct temperature increase of the recent years results in increasing drought stress for plants during dry years. In Valais forest vegetation is presently in change: mortality processes in Scots pine (Pinus sylvestris L.) go along with an increase of broadleaved trees, mostly downy oak (Quercus pubescens Willd.). A combined approach (assessment of forest structures on a regular grid, intensive monitoring and experimental plots, and analysis of past forest management) was applied to analyze the shift in tree-species composition and to keep apart the impact of changes in climate and land-use. The shift from pine to oak was most pronounced on dry sites, where pine mortality was highest and oak regeneration most frequently. Pine mortality was highest after dry years, whereas oak was less affected. Although oak regeneration seems to profit from the dryer climate, the changes of the land-use regime during the past decades was identified as the main driver for the increased spread of oak.
-En Valais (Suisse), deux types de pin sylvestre (Pinus sylvestris L.) se distinguent morphologiq... more -En Valais (Suisse), deux types de pin sylvestre (Pinus sylvestris L.) se distinguent morphologiquement et écologiquement : un pin de plaine et un pin d'altitude. Les pinèdes de plaine présentent des signes de dépérissement depuis le début des années 1990. Quatre paires de populations ont été choisies dans cette vallée et deux autres dans deux autres régions alpines à climat continental. La différenciation génétique entre les deux types et entre deux classes de vitalité a été étudiée à l'aide d'amplification aléatoire d'ADN polymorphe (RAPD). La croissance en diamètre et la quantité d'aubier des deux types ont été mesurées. À l'exception d'une paire de populations, les deux types se distinguent génétiquement, mais faiblement (Φ ST = 4, 2% à 5,8 %). Une sélection différenciée avec l'altitude, la recolonisation à partir de différents refuges glaciaires, un isolement phénologique et les vents dominants sont les facteurs de différenciation envisagés. Aucune raison génétique au dépérissement n'a été trouvée. Les différences de croissance et dans la quantité d'aubier soutiennent une adaptation aux régimes hydriques locaux. écotypes / RAPD / cernes de croissance / dépérissement forestier / variation génétique Abstract-Random amplified polymorphic DNA (RAPD) patterns show weak genetic differentiation between low-and high-elevation types of Scots pine (Pinus sylvestris L.) in dry continental valleys in the Alps. Two types of Scots pine (Pinus sylvestris L.), found either in the lowland or in the subalpine zone, are morphologically distinguished in the central-Alpine Valais (Switzerland), a dry continental valley. The low-elevation pine forests show signs of die-back since the early 1990s. We selected four elevational population pairs in the area, and two additional pairs in two other central-Alpine regions. Genetic differentiation between the two pine types, i.e. between elevations, and between two classes of vitality were studied using random amplified polymorphic DNA (RAPD). Growth in diameter and sapwood proportion was further assessed. Population pairs, with one exception, showed weak, but significant genetic differentiation (Φ ST = 4.2%-5.8%). On the other hand, there was no correlation between genetic data and the die-back observed. We consider disruptive evolution, postglacial migration, phenological separation or wind directions as possible explanations. Differences in growth and sapwood proportions supported the assumption of adaptation to local hydrological regimes. ecotypes / RAPD / growth rings / forest die-back / genetic variation
The ongoing climatic changes potentially affect plant growth and the functioning of temperature-l... more The ongoing climatic changes potentially affect plant growth and the functioning of temperature-limited high-altitude and high-latitude ecosystems; the rate and magnitude of these biotic changes are, however, uncertain. The aim of this study was to reconstruct stand structure and growth forms of Larix sibirica (Ledeb.) in undisturbed forest-tundra ecotones of the remote Polar Urals on a centennial time scale. Comparisons of the current ecotone with historic photographs from the 1960s clearly document that forests have significantly expanded since then. Similarly, the analysis of forest age structure based on more than 300 trees sampled along three altitudinal gradients reaching from forests in the valleys to the tundra indicate that more than 70% of the currently upright-growing trees are o80 years old. Because thousands of more than 500-year-old subfossil trees occur in the same area but tree remnants of the 15-19th century are lacking almost entirely, we conclude that the forest has been expanding upwards into the formerly tree-free tundra during the last century by about 20-60 m in altitude. This upward shift of forests was accompanied by significant changes in tree growth forms: while 36% of the few trees that are more than 100 years old were multi-stem tree clusters, 90% of the trees emerging after 1950 were single-stemmed. Tree-ring analysis of horizontal and vertical stems of multistemmed larch trees showed that these trees had been growing in a creeping form since the 15th century. In the early 20th century, they started to grow upright with 5-20 stems per tree individual. The incipient vertical growth led to an abrupt tripling in radial growth and thus, in biomass production. Based on above-and belowground biomass measurements of 33 trees that were dug out and the mapping of tree height and diameter, we estimated that forest expansion led to a biomass increase by 40-75 t ha À1 and a carbon accumulation of approximately 20-40 g C m À2 yr À1 during the last century. The forest expansion and change in growth forms coincided with significant summer warming by 0.9 1C and a doubling of winter precipitation during the 20th century. In summary, our results indicate that the ongoing climatic changes are already leaving a fingerprint on the appearance, structure, and productivity of the treeline ecotone in the Polar Urals.
Please cite this article in press as: Allen, C.D., et al., A global overview of drought and heat-... more Please cite this article in press as: Allen, C.D., et al., A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests.
This archived Paleoclimatology Study is available from the NOAA National Centers for Environmenta... more This archived Paleoclimatology Study is available from the NOAA National Centers for Environmental Information (NCEI), under the World Data Service (WDS) for Paleoclimatology. The associated NCEI study type is Tree Ring. The data include parameters of tree ring with a geographic location of Switzerland, Western Europe. The time period coverage is from 134 to -59 in calendar years before present (BP). See metadata information for parameter and study location details. Please cite this study when using the data.
In 2018, Central Europe experienced one of the most severe and long-lasting summer drought and he... more In 2018, Central Europe experienced one of the most severe and long-lasting summer drought and heat wave ever recorded. Before 2018, the 2003 millennial drought was often invoked as the example of a "hotter drought", and was classified as the most severe event in Europe for the last 500 years. First insights now confirm that the 2018 drought event was climatically more extreme and had a greater impact on forest ecosystems of Austria, Germany and Switzerland than the 2003 drought. Across this region, mean growing season air temperature from April to October was more than 3.3°C above the long-term average, and 1.2°C warmer than in 2003. Here, we present a first impact assessment of the severe 2018 summer drought and heatwave on Central European forests. In response to the 2018 event, most ecologically and economically important tree species in temperate forests of Austria, Germany and Switzerland showed severe signs of drought stress. These symptoms included exceptionally low foliar water potentials crossing the threshold for xylem hydraulic failure in many species and observations of widespread leaf discoloration and premature leaf shedding. As a result of the extreme drought stress, the 2018 event caused unprecedented drought-induced tree mortality in many species throughout the region. Moreover, unexpectedly strong drought-legacy effects were detected in 2019. This implies that the physiological recovery of trees was impaired after the 2018 drought event, leaving them highly vulnerable to secondary drought impacts such as insect or fungal pathogen attacks. As a consequence, mortality of trees triggered by the 2018 events is likely to continue for several years. Our assessment indicates that many common temperate European forest tree species are more vulnerable to extreme summer drought and heat waves than previously thought. As drought and heat events are likely to occur more frequently with the progression of climate change, temperate European forests might approach the point for a substantial ecological and economic transition. Our assessment also highlights the urgent need for a pan-European ground-based monitoring network suited to track individual tree mortality, supported by remote sensing products with high spatial and temporal resolution to track, analyse and forecast these transitions.
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