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Das Abschmelzen der Gletscher in den europäischen Alpen seit dem Ende der Kleinen Eiszeit (LIA) um die Mitte des 19. Jahrhunderts, das durch den Klimawandel noch verstärkt wurde, hat seitdem zur Entstehung großflächiger proglazialer Bereiche geführt. Diese unterliegen zum Teil einer lang anhaltenden und intensiven Morphodynamik.
Trotz vieler Forschungsanstrengungen bestehen nach wie vor einige Wissenslücken über die sich verändernde Morphodynamik. Für quantitative Langzeitanalysen dieser wurden in einigen Studien historische Luftbilder verwendet. Da diese aber erst ab Mitte des 20. Jahrhunderts zur Verfügung stehen, ergibt sich bis zum Ende des LIA eine zeitliche Lücke von ca. 100 Jahren, für die die Reaktion der Flächen auf die Eisfreisetzung kaum bekannt ist. Um entsprechende Aussagen treffen zu können, sind daher weitere Daten und Untersuchungen erforderlich. Inwieweit sich das Erosionsmuster der geomorphologisch aktiven Flächen über die letzten Jahrzehnte hinweg verändert hat, ist ebenfalls nicht bekannt. Auch der Einfluss sich ändernder externer Faktoren, wie Temperatur und Niederschlag auf geomorphologische Hangprozesse und der Einfluss der sich klimawandelbedingt ändernden Naturraumausstattung proglazialer Flächen auf Erosions- und Akkumulationsflächen, sind unzureichend untersucht. Um den Fortschritt der paraglazialen Hanganpassung beurteilen zu können, fehlen zudem jahrzehntelange Vergleichswerte der Erosionsraten der LIA-Lateralmoränen mit denen außerhalb dieser Flächen, z.B. auf würmzeitlichen proglazialen Flächen. Ziel dieser Arbeit ist es daher, die genannten Forschungslücken zu adressieren und entsprechende Ergebnisse mit bestehenden Studien zu diskutieren.
Um einen ausreichend langen Untersuchungszeitraum zu gewährleisten, wurden verschiedene topographische Datengrundlagen aus unterschiedlichen Zeiträumen, basierend auf unterschiedlichen Fernerkundungsdaten, verwendet und miteinander kombiniert. Dazu gehören historische und aktuelle Luftbilder ab Mitte des 20. Jahrhunderts sowie aktuelle Light Detection and Ranging-Daten ab Mitte der 2000er Jahre, die entsprechend zu Orthofotos für flächenhafte Analysen bzw. zu digitalen Geländemodellen für volumetrische Analysen aufbereitet wurden. Um den Analysezeitraum in die zweite Hälfte des 19. und die erste Hälfte des 20. Jahrhunderts auszudehnen, wurden einerseits historische terrestrische Schrägaufnahmen mittels digitalem Monoplotting ausgewertet und andererseits historische topographische Karten zu digitalen Geländemodellen prozessiert. Neben den topographischen Datensätzen wurden zudem naturräumliche Informationen wie meteorologische, hydrologische und vegetationskundliche Daten analysiert.
Die Ergebnisse der Arbeit zeigen, dass die beiden hier vorgestellten Ansätze geeignet sind, den Zeitraum für quantitative Analysen der Morphodynamik auf LIA-Lateralmoränen und damit die Untersuchung paraglazialer Hanganpassungsprozesse zeitlich bis in die zweite Hälfte des 19. und die erste Hälfte des 20. Jahrhunderts zu erweitern. Die flächenhafte Analyse der Veränderung geomorphologisch aktiver Flächen auf Basis georeferenzierter Orthofotos zeigt eine nahezu kontinuierliche Flächenzunahme der (initialen) Runsensysteme eines LIA-Lateralmoränenabschnittes im Zeitraum zwischen 1890 und 2020. Seit der Mitte des 20. Jahrhunderts zeigen die volumetrischen Analysen, die am gleichen Hang durchgeführt wurden, allerdings eine Abnahme der geomorphologischen Aktivität. Ein Differenzgeländemodell, das aus karten- und luftbildbasierten digitalen Geländemodellen berechnet wurde, ermöglichte es zudem, eine Rutschung mit entsprechend höherer Magnitude zu erkennen, welche sich zwischen 1922 und 1953 ereignete.
Die volumetrischen Analysen, die einen Zeitraum von mehreren Jahrzehnten (ab der Mitte des 20. Jahrhunderts) abdecken, zeigen im Allgemeinen eine Abnahme der geomorphologischen Aktivität der LIA-Lateralmoränen. In einigen Fällen kann auch ein zunehmender Trend oder ein Verbleiben der Morphodynamik auf ähnlichem Niveau nachgewiesen werden. Dies kann als Verzögerung des paraglazialen Anpassungsprozesses interpretiert werden, bzw. zeigt, dass die Systeme einer solchen Anpassung auch entgegenlaufen können. Bei der Analyse der Entwicklung der Erosionsmuster auf den Hängen konnten vor allem zwei Gruppen von geomorphologisch aktiven Flächen mit unterschiedlichen Reaktionen identifiziert werden. Auf der einen Seite zeigt eine Gruppe nicht nur einen abnehmenden Sedimentaustrag, sondern auch eine anfänglich deutlich höhere Variabilität des Erosionsmusters innerhalb der Fläche, die im Laufe der Jahrzehnte konstanter wird. Eine weitere Gruppe zeigt ebenfalls eine Abnahme des Sedimentaustrags über die Jahrzehnte, jedoch bleibt das Erosionsmuster innerhalb der Fläche über die Zeiträume hinweg konstant, so dass beide Gruppen in den letzten Jahrzehnten ein ähnliches Verhalten zeigen. Die entsprechenden Ergebnisse führten schließlich zur Entwicklung des „Sedimentaktivitätskonzepts“, welches den paraglazialen Hanganpassungsprozess der letzten Jahrzehnte zusammenfasst.
Erosionsflächen mit einer höheren mittleren und maximalen Hangneigung sowie einer größeren Hanglänge weisen generell höhere geomorphologische Aktivitäten auf als solche mit entsprechend geringeren Werten. Diese Charakteristik scheint jedoch einen größeren Einfluss auf die geomorphologische Aktivität zu haben als die Zeit der Eisfreiwerdung. Analysen sich verändernder externer Faktoren, wie der Temperatur- und Niederschlagswerte, konnten sowohl fördernde als auch hemmende Auswirkungen auf geomorphologische Hangprozesse identifizieren, sodass abschließend nicht beurteilt werden kann, inwieweit sich diese tatsächlich auf die Erosionsprozesse der letzten Jahrzehnte der LIA-Lateralmoränen ausgewirkt haben. Es ist davon auszugehen, dass der andauernde paraglaziale Anpassungsprozess, der in der Regel mit einer Abnahme der Morphodynamik proglazialer Flächen verbunden ist, hier einen deutlich größeren Einfluss hat, als die sich ändernden meteorologischen Einflüsse.
Die Langzeit-Vegetationsanalysen zwischen 1890 und 2020 haben gezeigt, dass sich die Vegetation innerhalb eines LIA-Lateralmoränenabschnitts vor allem in den Bereichen entwickelt, die geomorphologisch nicht aktiv sind. In den geomorphologisch aktiven Flächen schwankt die Vegetationsausbreitung deutlich stärker, da diese durch Erosions- und Ablagerungsprozesse regelmäßig zurückgedrängt wird. Mit zunehmendem Abfluss konnte in jüngerer Zeit beobachtet werden, dass Akkumulationsflächen seitlich erodiert werden können. Ebenso kann gezeigt werden, dass die geomorphologische Aktivität innerhalb des Vorfluters eine Verflachung im unteren Bereich der Hänge unterbindet und letztlich eine Verlandung der Erosionsbasis verhindert, was wiederum für die angrenzenden Hänge erosionsfördernd sein kann.
Der Vergleich mit den langjährigen Erosionsraten außerhalb der proglazialen Flächen zeigt, dass die Erosionsraten auf den LIA-Lateralmoränen um einige Magnituden höher liegen. Daraus kann geschlossen werden, dass sich diese noch deutlich in der Phase der paraglazialen Anpassung befinden.
The existence of the common ash (Fraxinus excelsior L.) is acutely threatened by ash dieback, caused by the fungus Hymenoscyphus fraxineus. The disease may lead to reduced pollen flow due to crown damage and tree mortality, which affects the reproductive ecology of Fraxinus excelsior L. However, sexual reproduction in forest trees plays an essential role not only in species conservation and adaptive potential, but also in natural selection and the promotion of genetic diversity. The impending risk of reduced gene flow is therefore of serious concern and threatens the conservation of this valuable tree species. Therefore, it is critical to advance research on the effects of ash dieback on (effective) pollen transport and reproductive ecology of Fraxinus excelsior L. These results can be used to support forest management, such as maintaining ash genetic diversity and promoting the development of natural resistance. Therefore, this study will conduct extensive research in two seed orchards and one floodplain forest in Southern Germany from 2018 to 2021. The main objective of this dissertation was to improve our understanding of gene flow patterns by investigating (effective) pollen dispersal, pollen production and pollen and seed quality of ash trees in relation to their health status.
The main research questions were:
(1) How does ash (effective) pollen transport vary with stand density, ash abundance and meteorology?
(2) Is there a link between mating success and damage to the paternal tree?
(3) Does the health of the ash trees affect pollen and seed quality, as well as pollen quantity?
To answer these questions, different methods were used in the study areas, which differed in topography and degree of stocking. Therefore, not all parameters were examined at every site and in every year, depending on the issue concerned. The health status of the ash trees was assessed every year in July using a six-level vitality score. In addition, phenological observations were made annually in spring according to the BBCH code to determine different phenological stages such as beginning of flowering, full flowering, flower wilting and end of flowering.
Aerobiological pollen measurements were carried out in the two orchards in 2019 and 2020 using self-constructed gravimetric pollen traps of the Durham type. One of the traps was placed in the center of each orchard and up to five additional traps were placed at a maximum distance of 500 m from the orchard. Five vaseline-coated slides were attached to each trap (one in each cardinal di-rection and one horizontally) to measure pollen transport (N=4) and weekly cumulative pollen position (N=1). To study the influence of meteorological parameters, a climate station was placed in each orchard. In addition, other anemometers or data loggers for air temperature and relative humidity were installed.
For paternity analyses, cambium samples were collected for genotyping from branches and stumps of 251 ash trees in a seed orchard and floodplain forest. In addition, seeds were collected from 12 parent trees per site with different health status. Genetic analyses were performed to determine paternal trees using nuclear microsatellites. Paternities were assigned using the likelihood model implemented in Cervus 3.0.7 software.
Pollen viability of ash trees with different health status were studied at all three sites. Pollen production in the two seed orchards and seed quality in one orchard and the floodplain forest. For this purpose, inflorescences of 105 ash trees (pollen production), pollen of 125 ash trees (pollen viability) and seeds of 53 ash trees (seed quality) were collected. Pollen production was estimated from flower to tree level and pollen viability was determined using the TTC (2,3,5-triphenyltetrazolium chloride) test. In addition, pollen storage experiments were carried out to investigate the influence of meteorological factors on pollen viability. Pollen were stored for various periods at different temperatures and humidity conditions and their viability was determined. Seeds were analyzed for quantity and quality (solid, hollow grains, insect damage and germination) and seed quality was determined by both stratification and the TTC test.
The results on aerobiological pollen transport showed that pollen transport is related to meteorology, phenological development and the topography of the study site. The Schorndorf orchard, located on a slope, showed higher pollen levels at the downslope traps, likely due to the transport of pollen by cold air flow. The prevailing wind direction often corresponded with the compass direction in which the highest pollen deposition was measured. When analyzing the pollen data for individual traps, the highest pollen levels were measured outside the orchards in 2019, a year with low flower development. In contrast, most pollen were collected inside the orchard in the pollen-rich year 2020. This suggests that trees outside the orchard can potentially contribute more to pollination in a poor pollen year. In Emmendingen, minor difference in pollen quantity was found between traps at 1.5 m and 5 m height, but there were temporal differences indicating vertical variation in pollen availability. Ash pollen were found to be transported over a distance of more than 400 m, with the amount of pollen decreasing with increasing distance. About 50 % less pollen were measured at a distance of 200 m, but even at a distance of 500 m more than 10 % pollen were still detected.
The studies on effective pollen transport showed similar results: the average distance between father and mother tree was 76 m in the orchard and 166 m in the floodplain forest, with pollination success decreasing considerably with increasing distance. Despite the dense tree cover, the longest distances (> 550 m) were recorded in the floodplain forest. Based on this and the fact that 66.5 % cross-pollen input was recorded in the seed orchard, it can be assumed that pollination does not only involve local sources. However, self-pollination generally did not have a substantial effect on ash reproduction. In terms of health status, both healthy and slightly damaged parent trees showed similar mating success. However, in severely damaged trees almost no flowering could be documented. In general, it was demonstrated that both healthy and slightly diseased fathers sired more offspring than severely diseased ash trees.
The effect of ash dieback on pollen production showed no significant difference between healthy and diseased ash trees, although 53 % of severely diseased male ash trees did not produce flowers. In terms of pollen viability, there was a tendency for diseased ash trees to have less viable pollen than healthy ash trees. In addition, the viability experiments revealed a strong influence of prevailing temperatures on pollen viability, which decreased more rapidly under warmer conditions. There was also no statistical difference in seed quality between ash trees of different health status. However, non-viable seeds were often heavily infested with insects.
In summary, the studies show that a variety of factors influence the reproductive ecology and (effective) pollen transport of ash trees. However, the fact that severely affected ash trees are linked to a reduced flower production and lower pollen quality suggests that as health deteriorates, reproductive capacity also declines. It is therefore likely that severely diseased ash trees have a limited ability to pass on their genes to the next generation. Paternity analyses also suggest that high vigor has a positive effect on reproductive success and that pollen transport can occur over long distances. As susceptibility to ash dieback can be passed on from parents to offspring, these reactions to ash dieback may make ash populations less susceptible in the future.
Background:
Pollen allergies are widespread around the world, making the study of pollen levels in and around cities a task of high importance. This is also related to the fact that an increasing number of people is living in cities and urban areas are expanding. In addition, environmental changes in the context of climate change are expected to alter plant characteristics that affect the amount of pollen in the air. In order to assess the allergy risk, information on pollen that people are exposed to is needed. Monitoring of aeroallergens in cities is often conducted using a single trap. This trap can provide information on background pollen concentration, however, it does not reflect temporal and spatial variations of pollen at street level of the heterogeneous urban environment. The amount of pollen in the air is the result of a number of processes, one of which is pollen production. Pollen production is expected to be altered by climate change and is influenced by environmental factors such as temperature or air pollutants. To further investigate variations of allergenic pollen in cities, this thesis focuses on these central research questions:
- Are there differences in the amount of airborne pollen between urban and rural locations and do pollen loads vary at different spatial and temporal scales?
- What is the influence of land use and management on pollen loads?
- Is there a difference in pollen production of allergenic species between urban and rural locations and can the influence of environmental factors be detected?
Data and Methods:
Data on airborne pollen were gathered in two study areas with various pollen traps. In Ingolstadt, Germany, background pollen concentrations of Poaceae were measured in 2019 and 2020. Additionally, a network consisting of twelve gravimetric pollen traps was set up during the grass pollen seasons of those years. For an additional sampling campaign, portable volumetric traps were used to measure pollen concentration at street level. Investigations were also conducted in Sydney, Australia, where concentrations of Poaceae, Myrtaceae and Cupressaceae pollen and Alternaria spores were measured during three pollen seasons from 2017 to 2020. In the summer of 2019/2020, additional ten gravimetric traps were set up. For both study areas, pollen season characteristics and temporal and spatial variations of pollen concentrations and pollen deposition were analysed in context with land use, land management and meteorological parameters.
Furthermore, pollen production of the allergenic species Betula pendula, Plantago lanceolata and Dactylis glomerata was investigated in the Ingolstadt study area along an urbanisation gradient, which covered different types of land use. In total, 24 individuals of B. pendula, 82 individuals of P. lanceolata and 54 individuals of D. glomerata were analysed. Pollen production was compared between urban and rural locations and the influence of air temperature and the air pollutants nitrogen dioxide (NO2) and ozone (O3) was assessed. Air temperature was measured in the field and pollutant concentrations were computed using a land use regression model.
Results and Discussion:
In Ingolstadt, grass pollen concentrations and deposition were generally higher at rural than at urban locations as documented in peak values and seasonal totals. Diurnal variations however, did not vary between urban and rural locations. Grass pollen levels were linked to local vegetation and land use but also land management, as grass cutting was reducing pollen levels in the surroundings.
In Sydney, pollen season characteristics varied between the seasons and we found significant correlations between daily pollen and spore concentrations and meteorological parameters. There were significant positive correlations with air temperature for all analysed pollen and spore types. Correlations with humidity (Myrtaceae, Cupressaceae, Alternaria) and precipitation (Myrtaceae, Cupressaceae) were negative. Spatial variations of pollen deposition were observed, but there were no correlations with land use. This could be attributable to the drought before and during this sampling campaign as well as the temporal setting of the sampling campaign.
The results from both study areas suggest that local vegetation is the main influence on the pollen amount at street level. However, when the season’s intensity decreased, other influences such as resuspension or pollen transport become more important. Analyses of pollen production revealed statistically significant differences between urban and rural locations for B. pendula and P. lanceolata. Pollen production decreased with temperature and urbanisation for all species, however, pollen production varied at small spatial distances within species. For increasing air pollutant levels, decreases were observed for B. pendula and P. lanceolata, but increases for D. glomerata. These results suggest that environmental influences seem to be species-specific.
The results from the studies contribute to the knowledge on temporal and spatial variations of airborne pollen in cities, as well as on pollen production of allergenic species. They highlight the importance of pollen monitoring at street level and at different locations in cities to assess the amount of pollen that people are exposed to. Further research in this area should investigate the influence of land management, which was identified to influence the amount of pollen in the air, and which could be a mitigation strategy for allergy-affected people. In addition, pollen production should be further examined with different kinds of experiments, as it is the major influence of ambient pollen concentration in the air.