Progressive effects of shading on experimental wetland communities over three years

To investigate how the composition of wetland communities changes over time in response to altered light regimes, experimental communities of five Carex and four grass species were subjected to artificial shading (continuous or seasonal) in a three-year field experiment. Shoot number and size was measured after six weeks, and shoot biomass was harvested five times during the experiment. Communities were initially dominated by three grass species in all treatments, but subsequently, the Carex species increased and reached dominance in the control plots, whereas grasses remained dominant in the shaded plots. Shading had no effect on the biomass of communities or of single species in the first year. In the second year, community biomass was still unaffected, but shading reduced the biomass of three Carex species and also reduced species diversity. In the third year, shading reduced community biomass and all Carex species, but not species diversity. The greater shade tolerance of the grasses could not be explained by differences in morphological plasticity: after six weeks of growth all species had increased shoot height in response to shade by 40-70%. Grasses were hardly more plastic than Carex species. We propose that the long-term success of the Carex species in full light was due to a high allocation of biomass to belowground parts, which may have reduced losses caused by repeated harvesting of shoots (a simulation of management in productive wet meadows). Shading probably caused the Carex plants to change their allocation pattern, and thus prevented their progressive increas

Herausforderung alpiner Renaturierungen : markante Unterschiede in Vegetation, Bakterien und Boden

Die Schweiz weist mit ihrer abwechslungsreichen Topografie eine hohe Artenvielfalt auf. Die heterogene Landschaft und insbesondere die mächtigen Gebirgszüge tragen dabei zur besonderen Verantwortung gegenüber dem Schutz und Erhalt der Biodiversität bei. Bautätigkeiten und Eingriffe in die Landschaft ausserhalb der Bauzonen werden daher häufig von Renaturierungsmassnahmen begleitet. Jonathan Blank-Pachlatko untersuchte in seiner Masterarbeit am Corvatsch im Engadin, welche ökologischen Unterschiede sich dabei kurz nach der Ausführung im Vergleich zu unberührten Flächen feststellen liessen

Progressive effects of shading on experimental wetland communities over three years

ISSN:1385-0237ISSN:1573-505

Differences in vegetation composition, bacterial community and soil properties after restoration of construction sites on alpine grasslands

Vegetation surveys and soil samples were taken within two former construction sites and near them in undisturbed areas at 2500 m, above the tree line in circular 10 m2 plots at the Curtinella ski lift on the Corvatsch mountain range (Canton Graubünden, Switzerland) in 2021. The sites were re-vegetated in 2015 (seeding and turf) and 2020 (turf). The areas from 2015 are used as ski slopes with artificial snow. Vegetation cover per species recorded as well as ground cover (stones, gravel, fine soil) was estimated and the soil depth, pH and electrical conductivity were measured. The nutrient content (C, H, N) as well as the content of active microorganisms of the soil samples were analysed. In addition, the bacterial community was analysed via 16S rRNA-sequencing. The plots of the sown construction site from 2015 show a decrease in the number of species and Shannon Index compared to the undisturbed plots, the plots of the construction site with turf from 2020 show a decrease in the vegetation cover and Shannon Index. Both former construction sites show a significant decrease in soil depth and nutrients and an increase of pH. In addition, a significant decrease in soil microbial activity could be detected. The bacterial communities differ between the former construction sites and the undisturbed area. Despite the successful revegetation for this altitude, the results show a considerable loss of topsoil and species diversity of the investigated species groups and speak for a considerate approach for future construction sites in alpine regions

Differences in vegetation composition, bacterial community and soil properties after restoration of construction sites on alpine grasslands

Alpine and subalpine areas in the mountainous region of Switzerland have long been inhabited by humans and used for grazing by cows or sheep and represent a living cultural landscape. Abandonment and forestation are leading to a decline in these alpine meadows and pastures, which represent a third of all agricultural land in Switzerland. In addition, the brisk construction activity of recent years is exerting additional pressure on the agricultural land, especially in areas used for recreation and tourism. Since the 1990s, the number of transport infrastructure (in particular drag lifts, number of cable cars remained stable) in the mountains has decreased slightly (status 2020: 2,433 installations), but the extent of snow making infrastructure has increased substantially. Of the 22,500 ha of pistes in Switzerland, 11,975 ha now have artificial snow (in 2020: 53 %). Typically, these structural interventions (e.g. pipe trenches) and anthropogenic soil movements affect easily accessible subalpine and alpine nutrient-poor grassland, which have very slow regeneration times due to temperature and the short vegetation period. Today, the high-altitude revegetation shows a pleasing success with regard to the important erosion protection and the achieved coverage of the vascular plants. From a phytosociological perspective however, it represents insufficient restoration, which contradicts the conservation of alpine biodiversity in Switzerland. Therefore, several success controls of high-altitude revegetation have already been carried out in recent years. However, with the advent of genetic analyses for species identification, revegetation can now be evaluated not only on the surface, but statements can be made about the entire biocenosis. The present work on the differences in disturbed and undisturbed alpine pastures is a start by applying these same methods on a small geographical scale to the well-studied species group of soil bacteria, combined with phytosociological surveys and soil chemical analyses. Vegetation surveys and soil samples were taken within two former construction sites and near them in undisturbed areas at 2500 m a. s. l., above the tree line in circular 10 m2 plots at the Curtinella ski lift on the Corvatsch mountain range (Canton Graubünden, Switzerland) in 2021. The construction sites were re-vegetated in 2017 (seeding and turf) and 2020 (turf). The areas from 2017 are used as ski slopes with artificial snow. The vegetation cover of the species was recorded, the soil cover (stones, gravel, fine soil) estimated and the soil depth, pH and electrical conductivity measured. The nutrient content (C, H, N) as well as the content of active microorganisms of the soil samples were analysed. In addition, the bacterial community was analysed via 16S rRNA-sequencing. The Shannon index was used as a measure of Biodiversity of species community, which was compared in pairs between the different types of sites investigated. The plots of the sown construction site from 2017 show a decrease in the number of species and Shannon index compared to the undisturbed plots, the plots of the construction site with turf from 2020 show a decrease in the vegetation cover and Shannon index. Soil chemical and biological parameters correlated strongly with soil depth and the proportion of gravel fraction of the topsoil as well as the cover of the herb layer. Both former construction sites show a significant decrease in soil depth and nutrients and an increase of pH. In addition, a significant decrease in soil microbial activity could be detected, as well as a general decrease in bacterial abundance. The Shannon index of the bacterial communities, however, was higher in the disturbed areas. In general, the composition of the bacteria differed and the undisturbed areas could be clearly distinguished. This resulted in eight common taxa of bacteria at the genus level, which in turn will serve as indicators for undisturbed alpine soils in the study area. Despite the rather successful revegetation for this altitude, the results of this small-scale study in construction sites after one to four years, show a considerable loss of plant species diversity and topsoil quantity, which has a direct impact on the nutrients available in the soil as well as on the bacterial abundance and its composition. With the claim of maintaining biodiversity in high elevation revegetation, this methodology can be applied in a larger scale study to include additional species groups and describe a more holistic biocenosis. Given the slow regeneration time of soils and habitats at this altitude as well as the current high soil losses worldwide, the results speak also for a considerate approach to future construction sites in alpine regions

Richtlinien Hochlagenbegrünung

Ökosysteme in Hochlagen sind empfindliche und schützenswerte Lebensräume. Baumassnahmen, unsachgemässe landwirtschaftliche Nutzung und der Wintersport können Narben hinterlassen, welche durch angepasste Begrünungsmassnahmen zu beheben sind. Neben dem Schutz des Bodens vor Erosion sollen Begrünungen nicht nur die landschaftliche Attraktivität, sondern auch die reiche, perfekt an die alpinen Verhältnisse angepasste Artenvielfalt erhalten. Bei Beeinträchtigungen von schutzwürdigen Lebensräumen mit seltenen oder gefährdeten Arten wird die Wiederherstellung auch vom Gesetzgeber vorgeschrieben. Die Standortbedingungen der alpinen und subalpinen Höhenstufen lassen biologische und chemische Prozesse nur langsam ablaufen. Tiefe Temperaturen, Wind oder Bodenerosion führen zu sehr langsamer Bodenbildung. Die dadurch geringe Wasserspeicherkapazität und Nährstoffverfügbarkeit erschweren das Pflanzenwachstum. Die Entwicklung und Etablierung der heutigen Vegetationsdecke ist das Resultat von sehr lang andauernden Prozessen. Nach einer Störung durch bauliche Eingriffe oder durch natürliche Ereignisse erholt sich die Vegetation in Hochlagen nur sehr zögerlich. Zudem breiten sich die meisten Pflanzenarten in dieser Höhenlage vorwiegend vegetativ und weniger über Samen aus. Es ist äusserst wichtig, die bestehende Vegetation zu schützen und bestmöglich wiederanzulegen. Ein weiterer bedeutsamer Punkt ist der Aspekt des Bodenschutzes: Nur bewachsener Boden ist gegen Einflüsse wie Erosion und Auswaschung optimal geschützt. In den letzten Jahren haben Verfahren zur Wiederherstellung einer standortgerechten Vegetation im Alpenraum weiter an Bedeutung gewonnen. Bestmögliche Resultate erzielt man mit der direkten Wiederverwendung der intakten Pflanzendecke in Form von Soden, wenn nötig mit Zwischenlagerung. Aussaaten sind unumgänglich, wenn keine oder zu wenig Soden abgeschält werden können. Das Saatgut kann nass oder trocken aufgebracht werden. Die Samenmischung sollte regional sein, dem Standort angepasst und keine gebietsfremden Arten enthalten. Zusatzstoffe wie Kleber oder Mulch helfen bei der Keimung und Etablierung der Saat. Häufig werden Aussaaten im Spätherbst als Schlafsaat ausgebracht, damit sie im Frühjahr bei optimalen Bedingungen keimen. Um langfristig ökologischen und auch wirtschaftlichen Schaden zu vermeiden, lohnt es sich, qualitativ hochstehende Begrünungen zu realisieren, welche einen guten Erosionsschutz bieten und die Anliegen von Natur- und Landschaftsschutz grösstmöglich berücksichtigen. Diese müssen bei der Projektplanung bereits vorgesehen werden