Atmospheric Deposition on Swiss Long-Term Forest Ecosystem Research (LWF) Plots

Atmospheric deposition of the major elements was estimated from throughfall and bulk deposition measurements on 13 plots of the Swiss Long-Term Forest Ecosystem Research (LWF) between 1995 and 2001. Independent estimates of the wet and dry deposition of nitrogen (N) and sulfur (S) on these same plots were gained from combined simplified models. The highest deposition fluxes were measured at Novaggio (Southern Switzerland), exposed to heavy air pollution originating from the Po Plain, with throughfall fluxes averaging 29 kg ha−1 a−1 for N and 15 kg ha−1 a−1 for S. Low deposition fluxes were measured on the plots above 1800 m, with throughfall fluxes lower than 4.5 kg ha−1 a−1 for N and lower than 3 kg ha−1 a−1 for S. The wet deposition of N and S derived from bulk deposition was close to the modeled wet deposition, but the dry deposition derived from throughfall was significantly lower than the modeled dry deposition for both compounds. However, both the throughfall method and the model yielded total deposition estimates of N which exceeded the critical loads calculated on the basis of long-term mass balance considerations. These estimates were within or above the range of empirical critical loads except above 1800

Species turnover reveals hidden effects of decreasing nitrogen deposition in mountain hay meadows

Nitrogen (N) deposition is a major threat to biodiversity in many habitats. The recent introduction of cleaner technologies in Switzerland has led to a reduction in the emissions of nitrogen oxides, with a consequent decrease in N deposition. We examined different drivers of plant community change, that is, N deposition, climate warming, and land-use change, in Swiss mountain hay meadows, using data from the Swiss biodiversity monitoring program. We compared indicator values of species that disappeared from or colonized a site (species turnover) with the indicator values of randomly chosen species from the same site. While oligotrophic plant species were more likely to colonize, compared to random expectation, we found only weak shifts in plant community composition. In particular, the average nutrient value of plant communities remained stable over time (2003-2017). We found the largest deviations from random expectation in the nutrient values of colonizing species, suggesting that N deposition or other factors that change the nutrient content of soils were important drivers of the species composition change over the last 15 years in Swiss mountain hay meadows. In addition, we observed an overall replacement of species with lower indicator values for temperature with species with higher values. Apparently, the community effects of the replacement of eutrophic species with oligotrophic species was outweighed by climate warming. Our results add to the increasing evidence that plant communities in changing environments may be relatively stable regarding average species richness or average indicator values, but that this apparent stability is often accompanied by a marked turnover of species

Nitrogen deposition is negatively related to species richness and species composition of vascular plants and bryophytes in Swiss mountain grassland

Nitrogen (N) deposition is a major threat to biodiversity of many habitats in the lowlands. In mountain habitats, however, the effect of N deposition on biodiversity is not well understood. Here, data from the biodiversity monitoring of Switzerland were used to investigate whether high N deposition is negatively related to species richness and community uniqueness of vascular plants and bryophytes in mountain grassland. The total species diversity, as well as the diversity of three subsets of species (i.e. oligotrophic species, eutrophic species and targeted grassland species according to conservation objectives of the Swiss authorities) were analyzed. Overall, the empirical data from the present study indicate that the currently expert-based range of the critical load of N deposition below which harmful effects on sensitive ecosystems should not occur (upper bound is currently at 20 kg N ha−1 yr−1) is set too large for mountain hay meadows. Negative relations between N deposition and species richness and community uniqueness in mountain grassland were found already at 10–15 kg N ha−1 yr−1. The results suggest that the negative effect of N deposition on plant diversity is mainly due to a decrease of oligotrophic plant species and to a lesser extent to an increase in eutrophic plant species. While for bryophytes, the decrease of community uniqueness is related to changes in both oligotrophic and eutrophic species. Furthermore, because plant species richness of target species for conservation was negatively related to N deposition, airborne N deposition is likely to defeat conservation efforts in mountain grassland

Nitrogen deposition and multi-dimensional plant diversity at the landscape scale

Estimating effects of nitrogen (N) deposition is essential for understanding human impacts on biodiversity. However, studies relating atmospheric N deposition to plant diversity are usually restricted to small plots of high conservation value. Here, we used data on 381 randomly selected 1 km(2) plots covering most habitat types of Central Europe and an elevational range of 2900 m. We found that high atmospheric N deposition was associated with low values of six measures of plant diversity. The weakest negative relation to N deposition was found in the traditionally measured total species richness. The strongest relation to N deposition was in phylogenetic diversity, with an estimated loss of 19% due to atmospheric N deposition as compared with a homogeneously distributed historic N deposition without human influence, or of 11% as compared with a spatially varying N deposition for the year 1880, during industrialization in Europe. Because phylogenetic plant diversity is often related to ecosystem functioning, we suggest that atmospheric N deposition threatens functioning of ecosystems at the landscape scale

Schlussbericht des Projekts Nitrate leaching risk mapping (NitLeach II): Kartierung des Risikos von erhöhtem Nitrataustrag im Forschungsprogramm Wald und Klimawandel

Auswaschung von Stickstoff (N) aus Waldflächen mit dem Sickerwasser ist in der Schweiz unter anderem im Zusammenhang mit der Gewinnung von Trinkwasser aus Grundwasservorkommen relevant. In diesem Projekt wurde der Zusammenhang zwischen der N-Auswaschung und Indikatoren für die Stickstoffsättigung anhand von Messungen auf 70 Waldflächen in der Schweiz, Deutschland, Frankreich, Belgien Italien und Irland statistisch untersucht. Wichtigste erklärende Variable war der Stickstoffeintrag, der entweder als Fracht in der Kronentraufe oder als modellierte Gesamtfracht einbezogen wurde. Ebenfalls signifikant, als erklärende Variablen jedoch weniger wichtig, waren der N-Status der Bäume (N-Konzentration in Blättern/Nadeln), der Niederschlag und der Deckungsgrad der Strauchschicht (inklusive Verjüngung Waldbaumarten). In direkten Vergleichen von Fichten- (Rottannen) und Buchenbeständen am selben Standort bestätigte sich auch für die Schweiz, dass Fichtenbestände höhere N-Auswaschungsraten aufweisen als Buchenbestände. Die N-Austräge wiesen eine hohe zeitliche Variabilität auf, die teilweise durch Holznutzung/Mortalität, teilweise durch Niederschlag erklärt werden konnte. Zur Erstellung einer Übersichtskarte mit einer generellen Einschätzung der Wahrscheinlichkeit erhöhter N-Austräge wurde der Zusammenhang zu schweizweit kartierten Variablen untersucht. Als erklärende Variablen wurden die N-Deposition, die Gründigkeit und die Vernässung des Bodens aus der Bodeneignungskarte verwendet. Die N-Auswaschung reflektiert einerseits das Muster der N-Deposition: so wurden im Mittelland und in Teilen des Juras höhere N-Austragswerte geschätzt. Andererseits kommen in der Karte auch einzelne das Austragsrisiko beeinflussende Standortfaktoren zum Ausdruck, beispielsweise die tendenziell geringeren Bodenmächtigkeiten in Teilen des Juras. Diese auf der Karte abgebildete generelle Einschätzung weist jedoch eine grosse Unsicherheit auf. Auf kleinerer Skala kann diese Unsicherheit mit dem Einbezug von weiteren Parametern in die Kartierung (Strauchschicht, Verjüngung, Nähr-stoffversorgung der Blätter) vermindert werden. Um in Gebieten mit hoher Wahrscheinlichkeit erhöhter N-Austräge das Risiko zu vermindern, ist im Sinne des Verursacherprinzips die Reduktion der N-Deposition mit entsprechenden Luftreinhaltemassnahmen angezeigt. Bei der Waldbewirtschaftung kann die Wahrscheinlichkeit erhöhter N-Austräge mit geeigneten Holzerntemethoden und günstiger Baumartenwahl ebenfalls etwas reduziert werden. Die dazu bereits bestehenden Empfehlungen wurden durch die Ergebnisse dieser Studie bestätigt

Growth losses in Swiss forests caused by ozone : epidemiological data analysis of stem increment of Fagus sylvatica L. and Picea abies Karst

The estimate of growth losses by ozone exposure of forest trees is a significant part in current C sequestration calculations and will also be important in future modeling. It is therefore important to know if the relationship between ozone flux and growth reduction of young trees, used to derive a Critical Level for ozone, is also valid for mature trees. Epidemiological analysis of stem increment data from Fagus sylvatica L. and Picea abies Karst. observed in Swiss forest plots was used to test this hypothesis. The results confirm the validity of the flux-response relationship at least for beech and therefore enable estimating forest growth losses by ozone on a country-wide scale. For Switzerland, these estimates amount to 19.5% growth reduction for deciduous forests, 6.6% for coniferous forests and 11.0% for all forested areas based on annual ozone stomatal uptake during the time period 1991-2011

Data from: Nitrogen deposition and multi-dimensional plant diversity at the landscape scale

Estimating effects of nitrogen (N) deposition is essential for understanding human impacts on biodiversity. However, studies relating atmospheric N deposition to plant diversity are usually restricted to small plots of high conservation value. Here, we used data on 381 randomly selected 1 km2 plots covering most habitat types of Central Europe and an elevational range of 2900 m. We found that high atmospheric N deposition was associated with low values of six measures of plant diversity. The weakest negative relation to N deposition was found in the traditionally measured total species richness. The strongest relation to N deposition was in phylogenetic diversity, with an estimated loss of 19% due to atmospheric N deposition as compared with a homogeneously distributed historic N deposition without human influence, or of 11% as compared with a spatially varying N deposition for the year 1880, during industrialization in Europe. Because phylogenetic plant diversity is often related to ecosystem functioning, we suggest that atmospheric N deposition threatens functioning of ecosystems at the landscape scale