The extreme flood event that occurred in August 2005 was the most costly (documented) natural hazard event in the history of Switzerland. The flood was accompanied by the mobilization of >69,000m3 of ...large wood (LW) throughout the affected area. As recognized afterward, wood played an important role in exacerbating the damages, mainly because of log jams at bridges and weirs. The present study aimed at assessing the risk posed by wood in various catchments by investigating the amount and spatial variability of recruited and transported LW. Data regarding LW quantities were obtained by field surveys, remote sensing techniques (LiDAR), and GIS analysis and was subsequently translated into a conceptual model of wood transport mass balance. Detailed wood budgets and transport diagrams were established for four study catchments of Swiss mountain streams, showing the spatial variability of LW recruitment and deposition. Despite some uncertainties with regard to parameter assumptions, the sum of reconstructed wood input and observed deposition volumes agree reasonably well. Mass wasting such as landslides and debris flows were the dominant recruitment processes in headwater streams. In contrast, LW recruitment from lateral bank erosion became significant in the lower part of mountain streams where the catchment reached a size of about 100km2. According to our analysis, ~88% of the reconstructed total wood input was fresh, i.e., coming from living trees that were recruited from adjacent areas during the event. This implies an average deadwood contribution of 12%, most of which was estimated to have been in-channel deadwood entrained during the flood event.
•Wood budgets and transport diagrams established for four study catchments•Landslides and debris flows were dominant recruitment processes in headwater streams.•Bank erosion predominated in the lower part of mountain rivers•Estimated deadwood contribution of 12%
The response of forest ecosystems to increased atmospheric CO₂is constrained by nutrient availability. It is thus crucial to account for nutrient limitation when studying the forest response to ...climate change. The objectives of this study were to describe the nutritional status of the main European tree species, to identify growth‐limiting nutrients and to assess changes in tree nutrition during the past two decades. We analysed the foliar nutrition data collected during 1992–2009 on the intensive forest monitoring plots of the ICP Forests programme. Of the 22 significant temporal trends that were observed in foliar nutrient concentrations, 20 were decreasing and two were increasing. Some of these trends were alarming, among which the foliar P concentration in F. sylvatica, Q. Petraea and P. sylvestris that significantly deteriorated during 1992–2009. In Q. Petraea and P. sylvestris, the decrease in foliar P concentration was more pronounced on plots with low foliar P status, meaning that trees with latent P deficiency could become deficient in the near future. Increased tree productivity, possibly resulting from high N deposition and from the global increase in atmospheric CO₂, has led to higher nutrient demand by trees. As the soil nutrient supply was not always sufficient to meet the demands of faster growing trees, this could partly explain the deterioration of tree mineral nutrition. The results suggest that when evaluating forest carbon storage capacity and when planning to reduce CO₂emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.
•Stand density and age were strong predictors of European forest growth.•We found direct and indirect impacts of N deposition on forest growth.•Forest growth showed a positive, but in some cases ...quadratic response to N deposition.•Beech forest growth was significantly reduced at high N deposition levels.•Climate predictors were species-specifically related to European forest growth.•There was limited evidence of an ozone impact on European forest growth.
Changing environmental conditions may substantially interact with site quality and forest stand characteristics, and impact forest growth and carbon sequestration. Understanding the impact of the various drivers of forest growth is therefore critical to predict how forest ecosystems can respond to climate change. We conducted a continental-scale analysis of recent (1995–2010) forest volume increment data (ΔVol, m3 ha−1 yr−1), obtained from ca. 100,000 coniferous and broadleaved trees in 442 even-aged, single-species stands across 23 European countries. We used multivariate statistical approaches, such as mixed effects models and structural equation modelling to investigate how European forest growth respond to changes in 11 predictors, including stand characteristics, climate conditions, air and site quality, as well as their interactions. We found that, despite the large environmental gradients encompassed by the forests examined, stand density and age were key drivers of forest growth. We further detected a positive, in some cases non-linear effect of N deposition, most pronounced for beech forests, with a tipping point at ca. 30 kg N ha−1 yr−1. With the exception of a consistent temperature signal on Norway spruce, climate-related predictors and ground-level ozone showed much less generalized relationships with ΔVol. Our results show that, together with the driving forces exerted by stand density and age, N deposition is at least as important as climate to modulate forest growth at continental scale in Europe, with a potential negative effect at sites with high N deposition.
Acid deposition arising from sulphur (S) and nitrogen (N) emissions from fossil fuel combustion and agriculture has contributed to the acidification of terrestrial ecosystems in many regions ...globally. However, in Europe and North America, S deposition has greatly decreased in recent decades due to emissions controls. In this study, we assessed the response of soil solution chemistry in mineral horizons of European forests to these changes. Trends in pH, acid neutralizing capacity (ANC), major ions, total aluminium (Altot) and dissolved organic carbon were determined for the period 1995–2012. Plots with at least 10 years of observations from the ICP Forests monitoring network were used. Trends were assessed for the upper mineral soil (10–20 cm, 104 plots) and subsoil (40–80 cm, 162 plots). There was a large decrease in the concentration of sulphate (SO42−) in soil solution; over a 10‐year period (2000–2010), SO42− decreased by 52% at 10–20 cm and 40% at 40–80 cm. Nitrate was unchanged at 10–20 cm but decreased at 40–80 cm. The decrease in acid anions was accompanied by a large and significant decrease in the concentration of the nutrient base cations: calcium, magnesium and potassium (Bc = Ca2+ + Mg2+ + K+) and Altot over the entire dataset. The response of soil solution acidity was nonuniform. At 10–20 cm, ANC increased in acid‐sensitive soils (base saturation ≤10%) indicating a recovery, but ANC decreased in soils with base saturation >10%. At 40–80 cm, ANC remained unchanged in acid‐sensitive soils (base saturation ≤20%, pHCaCl2 ≤ 4.5) and decreased in better‐buffered soils (base saturation >20%, pHCaCl2 > 4.5). In addition, the molar ratio of Bc to Altot either did not change or decreased. The results suggest a long‐time lag between emission abatement and changes in soil solution acidity and underline the importance of long‐term monitoring in evaluating ecosystem response to decreases in deposition.
Atmospheric nitrogen (N) deposition in terrestrial ecosystems is difficult to quantify, especially in forests. In this study, we compared three approaches for determining the wet and dry deposition ...of nitrogen (total deposition) at 17 intensively monitored forest sites in Switzerland. Specifically, we considered approaches based on: 1) measurements of bulk deposition and throughfall in 2014 (throughfall method); 2) measurements of bulk deposition and measurements of air concentrations of ammonia (NH3) and nitrogen dioxide (NO2), to which deposition velocities were applied, also in 2014 (inferential method); and 3) a model developed for Switzerland at a high spatial resolution, run for the five-year period 2013–2017 (emission based model). In addition, changes over two decades were assessed using continuous measurements of throughfall and bulk deposition. Further, air concentrations of NH3 and NO2 measured in 2014 were compared with concentrations measured in 2000 at 10 of the sites. The three approaches generally yielded comparable estimates of total deposition, with some notable differences at some sites. For both the model and the inferential method, uncertainties were related to the deposition velocities that were applied to air concentrations of N compounds, especially for NH3. The throughfall method provided a minimum estimate of the total N deposition in the forest, but the fraction of the deposited N that is directly taken up by the canopy remained difficult to quantify. Nitrogen deposition has decreased since the mid-1990s at the majority of the sites. However, deposition of the reduced forms of N seems to have stagnated at the local level. Furthermore, N deposition is still too high in comparison with the range of empirical critical loads of N (CLN). The minimum deposition estimated from throughfall exceeds the lower limit of CLN at all sites except those in the Central Alps. Deposition estimated with the model and the inferential method exceeds the lower limit of CLN at all sites and even exceeds the upper limit at several locations.
•Throughfall and inferential methods and an emission based model were compared.•Deposition estimates were consistent overall but showed large local differences.•The uncertainties related to each method are difficult to reduce.•The deposition of oxidised nitrogen compounds decreased from 1995 to 2015.•Nitrogen deposition is still too high in comparison with critical loads.
Abstract
The uptake of carbon dioxide (CO
2
) from the atmosphere through photosynthesis is accompanied by an inevitable loss of water vapor through the stomata of leaves. The rate of leaf-level CO
2
...assimilation per unit stomatal conductance, i.e. intrinsic water-use efficiency (WUE
i
), is thus a key characteristic of terrestrial ecosystem functioning that is central to the global hydroclimate system. Empirical evidence and theory suggest a positive response of forest WUE to increased CO
2
levels globally. Although evidence exists for a positive effect of ecosystem nitrogen (N) inputs on WUE
i
, it is not clear how trends in atmospheric N deposition have affected WUE
i
in the past. Here we combine twentieth-century climate and nitrogen deposition with stable isotope signature in tree rings and document a WUE
i
trend reversal at two sites in Switzerland, that matches the timing of a trend reversal in atmospheric N deposition. Using generalized additive models (GAMs), we fitted observed WUE
i
time series to multiple environmental covariates. This suggested N deposition to have a significant effect on long-term WUE
i
at the site that was exposed to higher N deposition levels. The ratio of the increase in WUE
i
in response to increase in CO
2
(dWUE
i
/dCO
2
) declined by 96% after 1980 (from 0.53 to 0.02) in the beech forest and declined by 72% in the spruce forest (from 0.46 to 0.13) concurrent with a sharp decline in N deposition. Using the GAM model for two scenarios, we show that had N deposition levels not declined after 1980s, WUE
i
would have increased more strongly in response to increasing CO
2
. Although the increase in N deposition was limited to the 1950–1980 decades and the signals have declined with improvements in air quality across Europe, the role of atmospheric pollution must be reconsidered in interpretation of tree ring studies and for building environmental proxies that are pivotal to understanding future sink capacity of terrestrial ecosystems in response to climate change.
•Pan-European ICP Forests evaluation of weather cues for mast years in five species.•In beech and spruce summer conditions are the main weather cues for mast years.•Spring temperatures in the mast ...year is the main weather cue for oak species.•Weather cues are consistent on different spatial scales for beech and spruce.•Resource depletion is not present in beech, the oak species, and pine.
Mast seeding, the synchronised occurrence of large amounts of fruits and seeds at irregular intervals, is a reproductive strategy in many wind-pollinated species. Although a series of studies have investigated mast year (MY) patterns in European forest tree species at the regional scale, there are few recent evaluations at a European scale on the impact of weather variables (weather cues) and resource dynamics on mast behaviour. Thus the main objective of this study is to investigate the impact of specific weather conditions, as environmental drivers for MYs, on resources in Fagus sylvatica L., Quercus petraea (Matt.)Liebl., Quercus robur L., Picea abies (L.) Karst. and Pinus sylvestris L. at a European level and to explore the robustness of the relationships in smaller regions within Europe. Data on seed production originating from the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) were analysed. Three beta regression models were applied to investigate the impact of seasonal weather variables on MY occurrence, as well as the influence of fruiting intensity levels in the years prior to MYs. Resource dynamics are analysed at three different spatial scales (continent, countries and ecoregions).
At a European scale, important weather cues for beech MYs were a cold and wet summer two years before a MY, a dry and warm summer one year before a MY and a warm spring in the MY. For spruce, a cold and dry summer two years prior to a MY and a warm and dry summer in the year before the MY showed the strongest associations with the MY. For oak, high spring temperature in the MY was the most important weather cue. For beech and spruce, and to some extent also for oak species, the best fitting models at European scale were well reflected by those found at smaller scales. For pine, best fitting models were highly diverse concerning weather cues. Fruiting levels were high in all species two years before the MY and also high one year before the MY in the oak species and in pine. In beech, fruiting levels one year before the MY were not important and in spruce, they were inconsistent depending on the region. As a consequence, evidence of resource depletion could only be seen in some regions for spruce.
Forest soils harbor hyper-diverse microbial communities which fundamentally regulate carbon and nutrient cycling across the globe. Directly testing hypotheses on how microbiome diversity is linked to ...forest carbon storage has been difficult, due to a lack of paired data on microbiome diversity and in situ observations of forest carbon accumulation and storage. Here, we investigated the relationship between soil microbiomes and forest carbon across 238 forest inventory plots spanning 15 European countries. We show that the composition and diversity of fungal, but not bacterial, species is tightly coupled to both forest biotic conditions and a seven-fold variation in tree growth rates and biomass carbon stocks when controlling for the effects of dominant tree type, climate, and other environmental factors. This linkage is particularly strong for symbiotic endophytic and ectomycorrhizal fungi known to directly facilitate tree growth. Since tree growth rates in this system are closely and positively correlated with belowground soil carbon stocks, we conclude that fungal composition is a strong predictor of overall forest carbon storage across the European continent.
Within the formalism of the one-sublattice modified quasichemical model an equation for the computation of pair fraction distributions is derived considering distinct model modifications reported in ...the literature. For generalization an equation system is presented to determine pair fraction distributions of multicomponent solutions. Consistency of the derived equation with the analogous relationship of former versions of the modified quasichemical model is demonstrated. The derived equation is applied to the Cu-Fe-S liquid solution and its binary subsystems. Pair fraction distributions calculated exemplarily at 1200 °C (1473 K) are used to interpret recently reported predictions of the high-temperature Cu-Fe-S system.
Thermodynamic modeling of the Cu-Fe-S liquid solution is carried in the framework of the modified quasichemical model. The manifold nature of Cu-Fe-S liquid solutions from highly metallic via ...sulfur-rich to pure liquid sulfur is described by one single Gibbs energy expression at 1 bar total pressure. The model predictive ability of an asymmetric versus symmetric approach is thermodynamically analyzed with respect to the extrapolation scheme from the binary subsystems into the ternary system. Without the need of adjustable ternary parameters predictions of sulfur potentials for the liquid phase are in line with experimental data available in the literature. High-temperature pyrrhotite optimized via the compound energy formalism and Cu-Fe-S alloy phases are taken into consideration to predict phase equilibria with the liquid solution. Four isothermal and four isoplethal sections demonstrate promising agreement between a large stock of experimental data and prediction.
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