Karin Hansen

Precipitation manipulation experiments: challenges and recommendations for the future

Climatic changes, including altered precipitation regimes, will affect key ecosystem processes, such as plant productivity and biodiversity for many terrestrial ecosystems. Past and ongoing precipitation experiments have been conducted to quantify these potential changes. An analysis of these experiments indicates that they have provided important information on how water regulates ecosystem processes. However, they do not adequately represent global biomes nor forecasted precipitation scenarios and their potential contribution to advance our understanding of ecosystem responses to precipitation changes is therefore limited, as is their potential value for the development and testing of ecosystem models. This highlights the need for new precipitation experiments in biomes and ambient climatic conditions hitherto poorly studied applying relevant complex scenarios including changes in precipitation frequency and amplitude, seasonality, extremity and interactions with other global change drivers. A systematic and holistic approach to investigate how soil and plant community characteristics change with altered precipitation regimes and the consequent effects on ecosystem processes and functioning within these experiments will greatly increase their value to the climate change and ecosystem research communities. Experiments should specifically test how changes in precipitation leading to exceedance of biological thresholds affect ecosystem resilience and acclimation.

Tree mineral nutrition is deteriorating in Europe

The response of forest ecosystems to increased atmospheric CO2 is 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 CO2 emissions by increasing use of wood biomass for bioenergy, it is crucial that nutrient limitations for forest growth are considered.

Exceedance of critical loads and of critical limits impacts tree nutrition across Europe

Key messageExceedance of critical limits in soil solution samples was more frequent in intensively monitored forest plots across Europe with critical loads for acidity and eutrophication exceeded compared to other plots from the same network. Elevated inorganic nitrogen concentrations in soil solution tended to be related to less favourable nutritional status.ContextForests have been exposed to elevated atmospheric deposition of acidifying and eutrophying sulphur and nitrogen compounds for decades. Critical loads have been identified, below which damage due to acidification and eutrophication are not expected to occur.AimsWe explored the relationship between the exceedance of critical loads and inorganic nitrogen concentration, the base cation to aluminium ratio in soil solutions, as well as the nutritional status of trees.MethodsWe used recent data describing deposition, elemental concentrations in soil solution and foliage, as well as the level of damage to foliage recorded at forest plots of the ICP Forests intensive monitoring network across Europe.ResultsCritical loads for inorganic nitrogen deposition were exceeded on about a third to half of the forest plots. Elevated inorganic nitrogen concentrations in soil solution occurred more frequently among these plots. Indications of nutrient imbalances, such as low magnesium concentration in foliage or discolouration of needles and leaves, were seldom but appeared more frequently on plots where the critical limits for soil solution were exceeded.ConclusionThe findings support the hypothesis that elevated nitrogen and sulphur deposition can lead to imbalances in tree nutrition.

Bioenergy in the Nordic-Baltic-NW Russian Region : Status, barriers and future

The status of use of bioenergy, the current barriers for increased use and the future use of bioenergy in the Nordic-Baltic-NW Russian region is described in this report. In this region, forests ar ...

Variables related to nitrogen deposition improve defoliation models for European forests

Key messageAtmospheric deposition of nitrogen compounds and soil and foliar variables related to N deposition resulted important factors accounting for the variability of defoliation in European forest plots.ContextNitrogen (N) deposition has increased in the northern hemisphere because of anthropogenic-related emission of N compounds. Increased N availability may have an adverse impact on forest sustainability.AimsThis study aims to test the importance of throughfall N (Nthr) deposition in explaining the variability of the frequency of trees with defoliation >25xa0% (F25), an indicator of forest condition.MethodsA pan-European data set (71 plots) with enhanced quality control was considered. The additive effect of Nthr-related predictors (identified conceptually and by rank correlation) in explaining F25 was investigated by partial least square regression in comparison with a reference model based on site, stand, management and climate data. Reported damage to foliage, Nthr deposition, foliar N ratios and mineral top-soil variables were added stepwise to the reference model.ResultsN-related variables improved defoliation models. Higher Nthr deposition led to higher F25 for beech and Norway spruce, while the effect was opposite for Scots pine. Higher foliar N ratios led to higher F25 for all species.ConclusionNthr deposition, damage to foliage, foliar N/P, N/Ca, N/Mg, N/K, top-soil pH, C/N and exchangeable base cation resulted important factors (although with possible diverse effect) in explaining the variability of F25 among plots.

Environment and host as large-scale controls of ectomycorrhizal fungi

Explaining the large-scale diversity of soil organisms that drive biogeochemical processes—and their responses to environmental change—is critical. However, identifying consistent drivers of belowground diversity and abundance for some soil organisms at large spatial scales remains problematic. Here we investigate a major guild, the ectomycorrhizal fungi, across European forests at a spatial scale and resolution that is—to our knowledge—unprecedented, to explore key biotic and abiotic predictors of ectomycorrhizal diversity and to identify dominant responses and thresholds for change across complex environmental gradients. We show the effect of 38 host, environment, climate and geographical variables on ectomycorrhizal diversity, and define thresholds of community change for key variables. We quantify host specificity and reveal plasticity in functional traits involved in soil foraging across gradients. We conclude that environmental and host factors explain most of the variation in ectomycorrhizal diversity, that the environmental thresholds used as major ecosystem assessment tools need adjustment and that the importance of belowground specificity and plasticity has previously been underappreciated.Analyses of data from 137 forest plots across 20 European countries show that ectomycorrhizal fungal diversity is strongly influenced by environmental and host species factors and provide thresholds to inform ecosystem assessment tools

Integrating ecosystem services in Swedish environmental assessments: an empirical analysis

Abstract Given the growing number of policies and laws that encourage inclusion of ecosystem services (ES) in processes, we have investigated environmental impact assessments (EIA) and strategic environmental assessments (SEA) conducted in Sweden in order to analyse whether ES may be integrated to enhance and improve environmental assessment of today. Representative Swedish environmental projects were reviewed. Three cases with different geographic and environmental settings were selected to allow us to study consideration of a wide range of different ES. We investigated the processes and discussions taking place using documentation from the cases. We formalized and labelled the expected impacts into an ES framework. Summarizing each case, we described conformities and divergences in explicit and implicit prioritizations between the actors. We discussed the benefits of integrating ES into current practices and possible improvements in the processes and methodologies. When ES could be integrated into EIAs and SEAs more aspects would be visualized and a larger stakeholder engagement stimulated leading to improved support for decision-making.

The response of soil solution chemistry in European forests to decreasing acid 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 10xa0years of observations from the ICP Forests monitoring network were used. Trends were assessed for the upper mineral soil (10-20xa0cm, 104 plots) and subsoil (40-80xa0cm, 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 10-20xa0cm and 40% at 40-80xa0cm. Nitrate was unchanged at 10-20xa0cm but decreased at 40-80xa0cm. 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 (Bcxa0=xa0Ca2+ xa0+xa0Mg2+ xa0+xa0K+ ) and Altot over the entire dataset. The response of soil solution acidity was nonuniform. At 10-20xa0cm, ANC increased in acid-sensitive soils (base saturation ≤10%) indicating a recovery, but ANC decreased in soils with base saturation >10%. At 40-80xa0cm, ANC remained unchanged in acid-sensitive soils (base saturation ≤20%, pHCaCl2xa0≤xa04.5) and decreased in better-buffered soils (base saturation >20%, pHCaCl2xa0>xa04.5). 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.