Auswirkungen von Stickstoff auf die Baumverjüngung in einem temperaten Bergwald auf Basis von bodenchemischen Daten und Ellenberg-Zeigerwerten

In einer Zusammenarbeit der Universität Wien mit dem Umweltbundesamt wurden im Zuge des Langzeitmonitoring (ICP-IM) Vegetationsveränderungen in Hinblick auf Luftschadstoffe untersucht. Vorrangiges Ziel dieser Arbeit ist, die unterschiedlichen Stickstoffeffekte auf die Baumverjüngung auf Basis von bodenchemischen Daten und Ellenbergs Zeigerwerten zu untersuchen. Die Erhebungen wurden an zwei Dauerflächen (IPs) an unterschiedlichen Standorten (IP1 am Plateau eines ehemaligen Fichtenforstes und IP2 am Hang eines naturnahen Bergwaldes) durchgeführt. Bodenproben des A-Horizonts wurden auf NH4+, NO3-, C/N Verhältnis, Brutto- und Nettomineralisierung und pH-Wert analysiert. Für die Abschätzung der abiotischen Verhältnisse wurden Parameter wie das Mikrorelief und die Strahlungsdurchlässigkeit auf die Waldbodenvegetation gemessen und der Sameneintrag berechnet. Die Effekte der abiotischen und bodenchemischen Faktoren auf die Baumverjüngung von Berg-Ahorn (Acer pseudoplatanus), Gewöhnlicher Esche (Fraxinus excelsior), Rot-Buche (Fagus sylvatica) und Gewöhnlicher Fichte (Picea abies) wurden mittels Regressionsanalysen (Generalized Linear Models) getestet. Vergleichsweise wurden Analysen mit den korrespondierenden Zeigerwerten nach Ellenberg durchgeführt. Unsere Ergebnisse zeigen, dass die Stickstoffverfügbarkeit einen deutlichen Effekt auf die Keimung der verschiedenen Baumarten ausübt. Die Baumarten reagieren differenziert und bevorzugen unterschiedliche Stickstoffquellen als Regenerationsnischen. In Bezug auf das Überleben der Keimlinge konnte nur für eine Baumart ein schwach signifikanter Zusammenhang mit der Stickstoffverfügbarkeit festgestellt werden. Beim Wachstum reagierte wiederum jede Baumart unterschiedlich stark auf eine Stickstoffvariable. In Bezug auf die verschiedenen Lebenszyklusstadien (Keimung, Überleben, Wachstum) erfolgte eine unterschiedliche Einnischung der jeweiligen Baumarten hinsichtlich verschiedener Stickstoffvariablen. Nur für den pH Wert und die Bruttomineralisierung konnte ein enger Zusammenhang zwischen den gemessen Werten den jeweilig korrespondierenden Zeigerwerten gefunden werden. Unter den verschiedenen Variablen, die den Stickstoffgehalt der Böden beschreiben, scheint daher die Bruttomineralisierung ein besonders guter Indikator für den für Pflanzen tatsächlich verfügbaren Stickstoff zu sein.The UNECE-ICP Integrated Monitoring site 'Zöbelboden' situated in the 'Northern Limestone Alps' national park in Austria was established to assess the impacts of air pollutants on ecosystems. This study mainly concentrates on the effects of nitrogen availability on recruitment of the four most abundant tree species (Picea abies (L.) Karst, Fagus sylvatica (L.) Karst, Fraxinus excelsior (L.) Karst, Acer pseudoplatanus (L.) Karst) on the basis of measured soil variables and indicator values. Top mineral soil was analyzed for pH-value, NH4+, NO3-, gross N and net N mineralization and C/N ratio. Additional abiotic site conditions (radiation and relief) were measured and seed input estimates were calculated. Recruitment, survival and growth rates were related to abiotic variables as well as Ellenberg indicator values, respectively, using Generalized Linear Models. Despite the relatively high correlations of Ellenberg indicator values to at least three of the measured soil variables (gross N mineralization, ammonium and pH value), results of GLMs using measured variables and Ellenberg indicator values were inconsistent in most cases. In general, measured variables captured correlations between gradients in soil characteristics and tree seedling or sapling performance more sensitively than Ellenberg indicator values. Measured nitrogen variables had a strong impact on the recruitment rates of all four study species and also affected growth rates, whereas survival was largely independent of nitrogen. Apart from this variation among vital rates, the species also differed in their sensitivity to the different variables related to nitrogen in the soil. Partitioning of regeneration niches might hence be a key factor to their co-existence in mixed mountain forests

Modelling study of soil C, N and pH response to air pollution and climate change using European LTER site observations

Current climate warming is expected to continue in coming decades, whereas high N deposition may stabilize, in contrast to the clear decrease in S deposition. These pressures have distinctive regional patterns and their resulting impact on soil conditions is modified by local site characteristics. We have applied the VSD+ soil dynamic model to study impacts of deposition and climate change on soil properties, using MetHyd and GrowUp as pre-processors to provide input to VSD+. The single-layer soil model VSD+ accounts for processes of organic C and N turnover, as well as charge and mass balances of elements, cation exchange and base cation weathering. We calibrated VSD+ at 26 ecosystem study sites throughout Europe using observed conditions, and simulated key soil properties: soil solution pH (pH), soil base saturation (BS) and soil organic carbon and nitrogen ratio (C:N) under projected deposition of N and S, and climate warming until 2100. The sites are forested, located in the Mediterranean, forested alpine, Atlantic, continental and boreal regions. They represent the long-term ecological research (LTER) Europe network, including sites of the ICP Forests and ICP Integrated Monitoring (IM) programmes under the UNECE Convention on Long-range Transboundary Air Pollution (LRTAP), providing high quality long-term data on ecosystem response. Simulated future soil conditions improved under projected decrease in deposition and current climate conditions: higher pH, BS and C:N at 21, 16 and 12 of the sites, respectively. When climate change was included in the scenario analysis, the variability of the results increased. Climate warming resulted in higher simulated pH in most cases, and higher BS and C:N in roughly half of the cases. Especially the increase in C:N was more marked with climate warming. The study illustrates the value of LTER sites for applying models to predict soil responses to multiple environmental changes

Currently legislated decreases in nitrogen deposition will yield only limited plant species recovery in European forests

Atmospheric nitrogen (N) pollution is considered responsible for a substantial decline in plant species richness and for altered community structures in terrestrial habitats worldwide. Nitrogen affects habitats through direct toxicity, soil acidification, and in particular by favoring fast-growing species. Pressure from N pollution is decreasing in some areas. In Europe (EU28), overall emissions of NO x declined by more than 50% while NH3 declined by less than 30% between the years 1990 and 2015, and further decreases may be achieved. The timescale over which these improvements will affect ecosystems is uncertain. Here we use 23 European forest research sites with high quality long-term data on deposition, climate, soil recovery, and understory vegetation to assess benefits of currently legislated N deposition reductions in forest understory vegetation. A dynamic soil model coupled to a statistical plant species niche model was applied with site-based climate and deposition. We use indicators of N deposition and climate warming effects such as the change in the occurrence of oligophilic, acidophilic, and cold-tolerant plant species to compare the present with projections for 2030 and 2050. The decrease in N deposition under current legislation emission (CLE) reduction targets until 2030 is not expected to result in a release from eutrophication. Albeit the model predictions show considerable uncertainty when compared with observations, they indicate that oligophilic forest understory plant species will further decrease. This result is partially due to confounding processes related to climate effects and to major decreases in sulphur deposition and consequent recovery from soil acidification, but shows that decreases in N deposition under CLE will most likely be insufficient to allow recovery from eutrophication

How to Optimize Carbon Sinks and Biodiversity in the Conversion of Norway Spruce to Beech Forests in Austria?

Assessments of synergies and trade-offs between climate change mitigation and forest biodiversity conservation have focused on set-aside areas. We evaluated a more comprehensive portfolio of silvicultural management adaptations to climate change and conservation measures exemplary for managed European beech forests. Based on the available literature, we assessed a range of common silvicultural management and conservation measures for their effects on carbon sequestration in forest and wood products and for substituting more carbon-intensive products. We complemented this review with carbon sequestration simulations for a typical mountainous beech forest region in Austria. We propose three priority actions to enhance the synergies between climate change mitigation and biodiversity. First, actively increase the proportion of European beech in secondary Norway spruce forests, even though beech will not be unaffected by expected water supply limitations. Secondly, optimize the benefits of shelterwood systems and promote uneven-aged forestry, and thirdly, enhance mixed tree species. Targeted conservation measures (deadwood, habitat trees, and old forest patches) increase the total C storage but decrease the annual C sequestration in forests, particularly in wood products. The establishment of a beech wood market with an extended product portfolio to reduce the use of fuelwood is essential for sustainable climate change mitigation. Since there are limitations in the production of saw timber quality beech wood on low fertility sites, C accumulation, and biodiversity can be emphasized in these areas