We analyzed the chronologies of cellulose stable isotopes ( delta 13C and delta 18O) and tree-ring widths from European larch (Larix decidua) in a high-altitude site (2190ma.s.l.) at the bottom of a ...glacial valley in the Italian Alps, and investigated their dependence on monthly meteorological variables and delta 18O precipitation values. The delta 18O of tree-ring cellulose appears to be strongly driven by the delta 18O of winter snowfall (November to March), which suggests that larch trees mostly use the snow-melt water of the previous winter during the growing season. This water, which also comes from the slope streams and from the underground flow of nearby steep slopes, infiltrates the soil in the valley bottom. The tree-ring cellulose delta 18O values were also found to be influenced by the August precipitation delta 18O and mean temperature. The associated regression model shows that the delta 18O chronology from the tree rings explains up to 34% of the variance in the winter precipitation delta 18O record, demonstrating the potential for reconstructing the delta 18O isotopic composition of past winter precipitation in the study region. Unlike most other tree-ring studies that focus on growing season signals, in our study the summer signal was small and the winter signal dominant due to the special conditions of the glacial valley. Site topography, geomorphology and soil characteristics in particular influence the stable isotope signal in tree-ring cellulose.
In this study, a barely used method to measure delta 13C values from lignin methoxyl groups ( delta 13Cmethoxyl) of tree-rings is applied to high alpine larch trees to test their potential as a ...climate proxy. Thirty-seven larch trees (Larix decidua Mill.) were sampled at a tree line site near Simplon Village in the Valais/Switzerland. Samples were used to measure tree-ring width, and from five individuals, delta 13Cmethoxyl was determined at annual resolution from 1971 to 2009, and at pentadal resolution from 1747 to 2009. The physiological tree responses to increasing atmospheric CO2 concentration since 1850 and the corresponding decrease in delta 13C (Suess effect) were corrected using a range of published discrimination factors and approaches. One of these approaches considers a flexible correction factor, which minimizes the residuals with target climate data. Testing the response of the new delta 13Cmethoxyl proxy to climate revealed significant correlations with June to August temperatures, ranging from r =0.56 to 0.75 for annually and from r =0.41 to 0.87 for pentadally resolved data depending on the correction methods. Tree-ring width also shows significant correlations with June to August temperature. These results demonstrate the potential of delta 13Cmethoxyl to serve as a summer temperature proxy in high-elevation alpine environments.
Although numerous species distribution models have been developed, most were based on insufficient distribution data or used older climate change scenarios. We aimed to quantify changes in projected ...ranges and threat level by the years 2061–2080, for 12 European forest tree species under three climate change scenarios. We combined tree distribution data from the Global Biodiversity Information Facility, EUFORGEN, and forest inventories, and we developed species distribution models using MaxEnt and 19 bioclimatic variables. Models were developed for three climate change scenarios—optimistic (RCP2.6), moderate (RCP4.5), and pessimistic (RPC8.5)—using three General Circulation Models, for the period 2061–2080. Our study revealed different responses of tree species to projected climate change. The species may be divided into three groups: “winners”—mostly late‐successional species: Abies alba, Fagus sylvatica, Fraxinus excelsior, Quercus robur, and Quercus petraea; “losers”—mostly pioneer species: Betula pendula, Larix decidua, Picea abies, and Pinus sylvestris; and alien species—Pseudotsuga menziesii, Quercus rubra, and Robinia pseudoacacia, which may be also considered as “winners.” Assuming limited migration, most of the species studied would face a significant decrease in suitable habitat area. The threat level was highest for species that currently have the northernmost distribution centers. Ecological consequences of the projected range contractions would be serious for both forest management and nature conservation.
We quantified changes in projected ranges and threat level by the years 2061–2080 for 12 European forest tree species under three climate change scenarios and three Global Circulation Models using MaxEnt model. Due to different responses of tree species to projected climate change, species may be divided into “winners” – mostly late‐successional species, “losers” – mostly pioneer species, and alien species. Assuming limited migration, most of the species studied would face significant decrease of suitable habitat area, especially species that currently have the northernmost distribution centers.
Root turnover is fastest in the finest roots of the root system (first root order). Additionally, tissue chemistry varies among even the finest root orders and between white roots and older, ...pigmented roots. Yet the effects of pigmentation and order on root decomposition have rarely been examined. We separated the first four root orders (all <1 mm) of four temperate tree species into three classes: white first- and second-order roots; pigmented first- and second-order roots; and pigmented third- and fourth-order roots. Roots were enclosed in litterbags and buried under their own and under a common species canopy in a 34-year-old common garden in Poland. When comparing decomposition of different root orders over 36 months, pigmented third- and fourth-order roots with a higher C:N ratio decomposed more rapidly, losing 20-–40%% of their mass, than pigmented first- and second-order roots, which lost no more than 20%%. When comparing decomposition of roots of different levels of pigmentation within the same root order over 14 months, pigmented (older) first- and second-order roots lost ∼∼10%% of their mass, while white (younger) first- and second-order roots lost ∼∼30%%. In contrast to root mass loss, root N content declined more rapidly in the first- and second-order roots than in third- and fourth-order roots. In higher-order roots, N increased in the first 10 months from ∼∼110%% to nearly 150%% of initial N content, depending on species; by the end of the study N content had returned to initial levels. These findings suggest that, in plant communities where root mortality is primarily of pigmented first- and second-order roots, microbial decomposition may be slower than estimates derived from bulk fine-root litterbag experiments, which typically contain at least four root orders. Thus, a more mechanistic understanding of root decomposition and its contribution to ecosystem carbon and nutrient dynamics requires a fundamental shift in experimental methods that stratifies root samples for decomposition along more functionally based criteria such as root order and pigmentation, which parallel the markedly different longevities of these different root classes.
• Efforts to develop mechanistic tree growth models are hindered by the uncertainty of whether and when tree growth responses to environmental factors are driven by carbon assimilation or by ...biophysical limitations of wood formation.
• In this study, we used multiannual weekly wood-formation monitoring of two conifer species (Larix decidua and Picea abies) along a 900m elevational gradient in the Swiss Alps to assess the biophysical effect of temperature and water potential on wood formation. To this end, we developed a model that simulates the effect of water potential on turgor-driven cambial division, modulated by the effect of temperature on enzymatic activity.
• The model reproduced the observed phenology of tracheid production, as well as intra- and interannual tracheid production dynamics of both species along the elevational gradient, although interannual model performance was lower. We found that temperature alone explains the onset of tracheid production, yet water potential appears necessary to predict the ending and the total amount of tracheids produced annually.
• We conclude that intra-annual cambial activity is strongly constrained by both temperature and water potential at all elevations, independently of carbon assimilation. At the interannual scale, biophysical constraints likely interact with other factors.
Tree growth is an indicator of tree vitality and its temporal variability is linked to species resilience to environmental changes. Second‐order statistics that quantify the cross‐scale temporal ...variability of ecophysiological time series (statistical memory) could provide novel insights into species resilience. Species with high statistical memory in their tree growth may be more affected by disturbances, resulting in lower overall resilience and higher vulnerability to environmental changes. Here, we assessed the statistical memory, as quantified with the decay in standard deviation with increasing time scale, in tree water use and growth of co‐occurring European larch Larix decidua and Norway spruce Picea abies along an elevational gradient in the Swiss Alps using measurements of stem radius changes, sap flow and tree‐ring widths. Local‐scale interspecific differences between the two conifers were further explored at the European scale using data from the International Tree‐Ring Data Bank. Across the analysed elevational gradient, tree water use showed steeper variability decay with increasing time scale than tree growth, with no significant interspecific differences, highlighting stronger statistical memory in tree growth processes. Moreover, Norway spruce displayed slower decay in growth variability with increasing time scale (higher statistical memory) than European larch; a pattern that was also consistent at the European scale. The higher statistical memory in tree growth of Norway spruce in comparison to European larch is indicative of lower resilience of the former in comparison to the latter, and could potentially explain the occurrence of European larch at higher elevations at the Alpine treeline. Single metrics of resilience cannot often summarize the multifaceted aspects of ecosystem functioning, thus, second‐order statistics that quantify the strength of statistical memory in ecophysiological time series could complement existing resilience indicators, facilitating the assessment of how environmental changes impact forest growth trajectories and ecosystem services.
Abstract Background/Aims The European larch is a pioneer tree and a valuable economic resource in subalpine ecosystems, thus playing crucial roles to ecosystem services and human activities. However, ...their ectomycorrhizal fungal community remains unknown in high altitudinal natural habitats. Here, we explore the mycobiont diversity of Larix decidua var. decidua between naturally rejuvenated and adult trees, compare ectomycorrhizal colonization patterns in geographically disjunct areas within the Alps of South Tyrol, Italy, characterized by distinct climatic conditions, and explore turnover rates across various seasons. Methods Our approach combines morphotyping of mycorrhized root tips with molecular analysis. Particular effort was given to monitor both ectomycorrhizal host-specialist and -generalist fungi. Results Both adult and young trees show a 100% mycorrhization rate, with a total diversity of 68 ectomycorrhizal species. The ectomycorrhizal composition is dominated by typical host specialists of larch trees (e.g., Lactarius porninsis , Russula laricina , Suillus cavipes , S. grevillei , S. viscidus ), which are widely distributed across sites. A rich diversity of host generalists was also detected. The composition of rare species within a habitat was comparatively consistent during one sampling campaign, but exhibited significant differences among individual sampling campaigns. The ectomycorrhizal compositions were only weakly correlated with distinct climatic conditions and tree ages. However, species richness and diversity, particularly of generalist fungi, was consistently higher in warmer, drier sites compared to cooler, more humid ones. Conclusions This study suggests potential mycobiont community shifts across climatic conditions with significant implications for the adaptability and resilience of subalpine forests in the face of climate change.
Trees play a key role in the global hydrological cycle and measurements performed with the thermal dissipation method (TDM) have been crucial in providing whole-tree water-use estimates. Yet, ...different data processing to calculate whole-tree water use encapsulates uncertainties that have not been systematically assessed.
We quantified uncertainties in conifer sap flux density (F
d) and stand water use caused by commonly applied methods for deriving zero-flow conditions, dampening and sensor calibration. Their contribution has been assessed using a stem segment calibration experiment and 4 yr of TDM measurements in Picea abies and Larix decidua growing in contrasting environments. Uncertainties were then projected on TDM data from different conifers across the northern hemisphere.
Commonly applied methods mostly underestimated absolute F
d. Lacking a site- and species-specific calibrations reduced our stand water-use measurements by 37% and induced uncertainty in northern hemisphere F
d. Additionally, although the interdaily variability was maintained, disregarding dampening and/or applying zero-flow conditions that ignored night-time water use reduced the correlation between environment and F
d.
The presented ensemble of calibration curves and proposed dampening correction, together with the systematic quantification of data-processing uncertainties, provide crucial steps in improving whole-tree water-use estimates across spatial and temporal scales.
•Drought and frost induce abrupt growth decreases prior to tree death.•Trees respond with growth reduction during and after drought.•Trees experience instantaneous growth reduction after frost.
Tree ...mortality as a crucial element of natural forest dynamics is still a poorly understood process. Abrupt growth decreases are known to occur several years or decades before complete cessation of growth. Hence, identifying and linking these growth decreases to potential inciting factors such as drought and frost will improve our understanding of mortality processes. We analyzed nine Central European tree species including six coniferous species (Abies alba, Picea abies, Larix decidua, Pinus sylvestris, Pinus cembra, Pinus montana) and three broadleaved species (Fagus sylvatica, Quercus spp., Acer pseudoplatanus). Tree-ring data from 848 standing dead trees from 14 forest reserves all over Switzerland were sampled. We applied distributed lag non-linear models to relate abrupt growth decreases to drought and frost. The results indicate for many species that both drought and frost have a moderate to major impact on abrupt growth decreases prior to tree death. While late frost in spring may instantaneously result in sustained abrupt growth decreases in most species except Scots pine and mountain pine, severe drought over several months in spring may either show an immediate negative impact on growth, such as in beech, or feature negative reactions that are lagged by several years, such as in oak and Scots pine. Thus, extreme climatic conditions have an essential influence on abrupt growth decreases that finally result in tree death, although variability of the reactions within and among species is high.
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