Mathieu Lévesque

Last Name

Lévesque

First Name

Mathieu

ORCID

0000-0003-0273-510X

Organisational unit

08701 - Gruppe Waldbau / Group Silviculture

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Publications 1 - 10 of 44

Potential alternative tree species to Fraxinus excelsior in European forests
Lévesque, Mathieu; Bustamante Eduardo, José Ignacio; Queloz, Valentin (2023)
Frontiers in Forests and Global Change
Common ash (Fraxinus excelsior L.) is a keystone tree species in Europe. However, since the 1990s, this species has been experiencing widespread decline and mortality due to ash dieback [Hymenoscyphus fraxineus (T. Kowalski) Baral, Queloz and Hosoya]. Besides H. fraxineus, emerald ash borer (Agrilus planipennis Fairmaire), an invasive alien pest already devastating ash trees in western Russia, is spreading westward and becoming an emerging threat to the remaining European ash populations. While efforts to control ash dieback continue to be a priority, it is becoming crucial to compensate for the loss of ash and its ecosystem services by elaborating restoration strategies, including the search for alternative native and non-native tree species. This review summarizes available knowledge on potential alternative tree species to common ash to help forest managers to cope with ash dieback. Although using natural regeneration and promoting tree species diversity can reduce the impacts of ash dieback in European forests, our review indicates that no native species alone or in combination can fully replace the ecological niche of common ash and its associated ecosystem services (e.g., biodiversity and timber). To fill this gap, forest managers have considered using non-native ash species that are tolerant to both H. fraxineus and A. planipennis and have similar ecological and forestry values as common ash. Of the 43 ash species reviewed, few non-native ash species (e.g., Fraxinus mandshurica Rupr. and Fraxinus platypoda Oliv.) have similar ecological characteristics to common ash and are tolerant to H. fraxineus and A. planipennis. However, the performance of non-native ash species in European forests, their invasiveness potential, and the risk of hybridization with native ash species are still unknown. With the current state of knowledge, it is thus too early to recommend the use of non-native ash species as a suitable option to deal with ash dieback. The priority should be the conservation, regeneration, and breeding of tolerant common ash populations to H. fraxineus, as well as the use of the natural regeneration of other native tree species. Our review highlights the need for controlled experimental plantations to better understand the regeneration ecology and invasiveness potential of non-native ash species prior to their utilization in natural forests.
Understanding physiological mechanisms of European beech dieback responses to climate using a triple isotope approach in northern Switzerland
Neycken, Anna; Lehmann, Marco M.; Saurer, Matthias; et al. (2025)
Dendrochronologia
To investigate which physiological predispositions led to the drought-induced vitality decline in beech (Fagus sylvatica L.) following the severe 2018 drought, we studied trees with premature leaf discoloration and shedding (early-browning trees) and trees showing no symptoms (vital trees) in a forest in northern Switzerland. We analyzed annual tree-ring width (TRW) and applied a triple isotope approach (i.e., carbon (δ13C), oxygen (δ18O), and hydrogen (δ2H) isotopes) in tree-ring cellulose for the period 1960–2020. To retrieve tree physiological responses, we normalized the tree-ring δ values to temporal isotopic variations in CO2 or precipitation (Δ). Δ13C and Δ18O values suggest that the early-browning trees had a more conservative water-use strategy and lower stomatal conductance than the vital trees in the initial decades of the measurement period. However, several decades before the onset of crown dieback in 2018, the early-browning trees showed a decrease in TRW and an increase in Δ2H, suggesting a higher use of carbon reserves for the early-browning trees. These long-term trends may be the first signs of a progressive deterioration of the physiology of the early-browning trees. During and after the 2018 drought, changes in Δ2H suggested high carbon investments into drought damage repair for the early-browning trees. Moreover, a higher TRW and isotope sensitivity to previous year's summer climate in early-browning than vital trees suggests stronger negative carry-over effects. Our findings highlight that the early-browning trees may have already been weakened before the 2018 drought, eventually pushing them beyond their physiological tipping points and inducing dieback.
No Future Growth Enhancement Expected at the Northern Edge for European Beech due to Continued Water Limitation
Klesse, Stefan; Peters, Richard L.; Alfaro-Sánchez, Raquel; et al. (2024)
Global Change Biology
With ongoing global warming, increasing water deficits promote physiological stress on forest ecosystems with negative impacts on tree growth, vitality, and survival. How individual tree species will react to increased drought stress is therefore a key research question to address for carbon accounting and the development of climate change mitigation strategies. Recent tree-ring studies have shown that trees at higher latitudes will benefit from warmer temperatures, yet this is likely highly species-dependent and less well-known for more temperate tree species. Using a unique pan-European tree-ring network of 26,430 European beech (Fagus sylvatica L.) trees from 2118 sites, we applied a linear mixed-effects modeling framework to (i) explain variation in climate-dependent growth and (ii) project growth for the near future (2021–2050) across the entire distribution of beech. We modeled the spatial pattern of radial growth responses to annually varying climate as a function of mean climate conditions (mean annual temperature, mean annual climatic water balance, and continentality). Over the calibration period (1952–2011), the model yielded high regional explanatory power (R² = 0.38–0.72). Considering a moderate climate change scenario (CMIP6 SSP2-4.5), beech growth is projected to decrease in the future across most of its distribution range. In particular, projected growth decreases by 12%–18% (interquartile range) in northwestern Central Europe and by 11%–21% in the Mediterranean region. In contrast, climate-driven growth increases are limited to around 13% of the current occurrence, where the historical mean annual temperature was below ~6°C. More specifically, the model predicts a 3%–24% growth increase in the high-elevation clusters of the Alps and Carpathian Arc. Notably, we find little potential for future growth increases (−10 to +2%) at the poleward leading edge in southern Scandinavia. Because in this region beech growth is found to be primarily water-limited, a northward shift in its distributional range will be constrained by water availability.
Tree-ring cellulose δ18O records similar large-scale climate influences as precipitation δ18O in the Northwest Territories of Canada
Field, Robert D.; Andreu-Hayles, Laia; D'Arrigo, Rosanne D.; et al. (2022)
Climate Dynamics
Stable oxygen isotopes measured in tree rings are useful for reconstructing climate variability and explaining changes in physiological processes occurring in forests, complementing other tree-ring parameters such as ring width. Here, we analyzed the relationships between different climate parameters and annually resolved tree-ring delta O-18 records (delta O-18(TR)) from white spruce (Picea glauca [Moench]Voss) trees located near Tungsten (Northwest Territories, Canada) and used the NASA GISS ModelE2 isotopically-equipped general circulation model (GCM) to better interpret the observed relationships. We found that the delta O-18(TR) series were primarily related to temperature variations in spring and summer, likely through temperature effects on the precipitation delta O-18 in spring, and evaporative enrichment at leaf level in summer. The GCM simulations showed significant positive relationships between modelled precipitation delta O-18 over the study region and surface temperature and geopotential height over northwestern North America, but of stronger magnitudes during fall-winter than during spring-summer. The modelled precipitation delta O-18 was only significantly associated with moisture transport during the fall-winter season. The delta O-18(TR) showed similar correlation patterns to modelled precipitation delta O-18 only during spring-summer when water matters more for trees, with significant positive correlations with surface temperature and geopotential height, but no correlations with moisture transport. Overall, the delta O-18(TR) records for northwestern Canada reflect the same significant large-scale climate patterns as precipitation delta O-18 for spring-summer, and therefore have potential for reconstructing past atmospheric dynamics in addition to temperature variability in the region.
From seedlings to trees: Using ontogenetic models of growth and survivorship to assess long-term (>100 years) dynamics of a neotropical dry forest
McLaren, Kurt P.; Lévesque, Mathieu; Sharma, Chait; et al. (2011)
Forest Ecology and Management
Climate change impacts on tree species, forest properties, and ecosystem services
Bugmann, H.; Brang, P.; Elkin, C.; et al. (2014)
CH2014-impacts : toward quantitative scenarios of climate change impacts in Switzerland
Changes in tree-ring wood density of European beech (Fagus sylvatica L.), silver fir (Abies alba Mill.), and Norway spruce (Picea abies (L.) H. Karst.) in European mountain forests between 1901 and 2016
Torresan, Chiara; Hilmers, Torben; Avdagić, Admir; et al. (2024)
Annals of Forest Science
Key message We found a significant increase in the latewood density of European beech, and a decrease in the latewood and mean wood density of silver fir and Norway spruce in European mountain forests over the period 1901–2016. In the past century, drought did not directly influence the wood density trend of the three studied species. However, for both fir and spruce, drought indirectly affected the mean wood density via changes in the latewood to earlywood ratio, i.e., in the case of extreme drought, trees with high values of latewood to earlywood ratio experienced a slight attenuation in the declining trend of their mean wood density. Context Century-long wood density measurements can provide novel information on tree response to climate change and the carbon sequestration potential of forest ecosystems. Still, the knowledge about long-term changes in wood density of European beech (Fagus sylvatica L.), silver fir (Abies alba Mill.), and Norway spruce (Picea abies (L.) H.Karst.) in European mountain forests needs to be further explored. Aims We assessed long-term changes in tree-ring mean wood density, earlywood density, and latewood density in trees of the three species between 1901 and 2016. We investigated the influence of endogenous factors (i.e., tree-ring width, current tree diameter, and latewood to earlywood ratio) and drought events on wood density. Methods In total, 150 tree cores were sampled from mountain forests in Bulgaria, Bosnia and Herzegovina, Slovenia, Switzerland, and Germany. The mean, early, and latewood density of these samples were measured with the LIGNOSTATION™ system. To address our research aims, we applied a linear mixed-effect modelling approach using the data from 101 correctly cross-dated cores that spanned the entire period of analysis. Results In the absence of drought, the latewood density of European beech increased by 7.1%, the late and mean wood density of silver fir decreased by 16.8% and 11.0%, respectively, and the late and mean wood density of Norway spruce decreased by 16.1% and 7.2%, respectively, between 1901–2016. In the past century, drought influenced the trends of wood density through an effect mediated by changes in the latewood to earlywood ratio. Specifically, in cases of extreme drought, silver fir and Norway spruce trees with a latewood to earlywood ratio value 50% higher than the median experience a slight attenuation in the declining trend of their mean wood density, making the negative impact of drought marginally less severe. Conclusions Our findings have significant implications for the accuracy of carbon stock assessments, national greenhouse gas inventories, and the utilization of wood from the three species. Given the fact that changes in wood density follow species-specific patterns and the expectation of more frequent drought events in Europe, in the future, it is essential to build further tree-ring density time series for other species and sites to improve our understanding of how climate change alters wood density and carbon sequestration of forest ecosystems.
Lessons learned from a long‐term irrigation experiment in a dry Scots pine forest: Impacts on traits and functioning
Bose, Arun K.; Rigling, Andreas; Gessler, Arthur; et al. (2022)
Ecological Monographs
Climate change exposes ecosystems to strong and rapid changes in their environmental boundary conditions mainly due to the altered temperature and precipitation patterns. It is still poorly understood how fast interlinked ecosystem processes respond to altered environmental conditions, if these responses occur gradually or suddenly when thresholds are exceeded, and if the patterns of the responses will reach a stable state. We conducted an irrigation experiment in the Pfynwald, Switzerland from 2003–2018. A naturally dry Scots pine (Pinus sylvestris L.) forest was irrigated with amounts that doubled natural precipitation, thus releasing the forest stand from water limitation. The aim of this study was to provide a quantitative understanding on how different traits and functions of individual trees and the whole ecosystem responded to increased water availability, and how the patterns and magnitudes of these responses developed over time. We found that the response magnitude, the temporal trajectory of responses, and the length of initial lag period prior to significant response largely varied across traits. We detected rapid and stronger responses from above-ground tree traits (e.g., tree-ring width, needle length, and crown transparency) compared to below-ground tree traits (e.g., fine root biomass). The altered above-ground traits during the initial years of irrigation increased the water demand and trees adjusted by increasing root biomass during the later years of irrigation, resulting in an increased survival rate of Scots pine trees in irrigated plots. The irrigation also stimulated ecosystem-level foliar decomposition rate, fungal fruit body biomass, and regeneration abundances of broadleaved tree species. However, irrigation did not promote the regeneration of Scots pine trees which are reported to be vulnerable to extreme droughts. Our results provide extensive evidence that tree- and ecosystem-level responses were pervasive across a number of traits on long-term temporal scales. However, after reaching a peak, the magnitude of these responses either decreased or reached a new stable state, providing important insights into how resource alterations could change the system functioning and its boundary conditions.
A narrow window of summer temperatures associated with shrub growth in Arctic Alaska
Andreu-Hayles, Laia; Gaglioti, Benjamin V.; Berner, Logan T.; et al. (2020)
Environmental Research Letters
Warming in recent decades has triggered shrub expansion in Arctic and alpine tundra, which is transforming these temperature-limited ecosystems and altering carbon and nutrient cycles, fire regimes, permafrost stability, land-surface climate-feedbacks, and wildlife habitat. Where and when Arctic shrub expansion happens in the future will depend in part on how different shrub communities respond to warming air temperatures. Here, we analyze a shrub ring-width network of 18 sites consisting of Salix spp. and Alnus viridis growing across the North Slope of Alaska (68–71°N; 164–149°W) to assess shrub temperature sensitivity and compare radial growth patterns with satellite NDVI (normalized difference vegetation index) data since 1982. Regardless of site conditions and taxa, all shrubs shared a common year-to-year growth variability and had a positive response to daily maximum air temperatures (Tmax) from ca. May 31 (i.e. Tmax ~6 °C) to early July (i.e. Tmax ~12 °C), two-thirds of which were significant correlations. Thus, the month of June had the highest shrub growth-temperature sensitivity. This period coincides with the seasonal increase in temperature and phenological green up on the North Slope indicated by both field observations and the seasonal cycle of NDVI (a proxy of photosynthetic activity). Nearly all of the sampled shrubs (98%) initiated their growth after 1960, with 74% initiated since 1980. This post-1980 shrub-recruitment pulse coincided with ~2 °C warmer June temperatures compared to prior periods, as well as with positive trends in shrub basal area increments and peak summer NDVI. Significant correlations between shrub growth and peak summer NDVI indicate these radial growth patterns in shrubs reflect tundra productivity at a broader scale and that tundra vegetation on the North Slope of Alaska underwent a greening trend between 1980 and 2012.
Long-term changes in above ground biomass after disturbance in a neotropical dry forest, Hellshire Hills, Jamaica
Niño, Milena; McLaren, Kurt P.; Meilby, Henrik; et al. (2014)
Plant Ecology

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Mathieu Lévesque

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