Large cities are typically characterized by a mosaic of green spaces that hold a remarkable variety of native and “exotic” plants. Urban beekeeping has gained increasing popularity. In order to characterize the “urban” in the honey, pollen diversity in 50 honey samples from 18 apiary locations in Vienna, Austria, was microscopically analyzed. The relative abundances of each plant taxon were determined by counting out 500 individual pollen grains per sample. In total, 202 taxa could be identified, with a median of 46 per sample. Taxa richness and diversity differed significantly across three years but did not so between urban and suburban apiaries. Despite trees comprising only roughly a quarter of all taxa, the amount of tree pollen was disproportionally high. The invasive Ailanthus altissima was predominant in 15 out of 50 samples. Other important non-native and/or ornamental trees included Sophora japonica, Gleditsia triacanthos, Castanea sativa, Koelreuteria paniculata, and Liriodendron tulipifera. Urban honey from Central Europe may typically comprise pollen taxa from Europe, East Asia, and North America alike. The results of this study show that intentionally planted, managed urban green spaces can support stable foraging resources for pollinators in cities.

Pollen monitoring is an integral part of aerobiology. The analysis of pollen content in the air, which is its core routine work, requires reliable devices. The continuous evolution of technology prompted us to give an update on current techniques used in pollen monitoring to provide a historical overview and an outlook into the future. Standard works in aerobiology and the most important literature were incorporated to summarize the development of pollen monitoring technology. We span a range from the first description of pollen monitoring in the 1870s, the invention of simple devices by early researchers, onwards to the development of the first volumetric samplers, such as the Rotorod- or Hirst-type traps. While volumetric devices are widely used in the USA and in Europe today, automatic and near-real-time pollen monitoring play an increasing role and offer new possibilities. In contrast to volumetric methods, most of these still require validation and standardization. Other methods, like the analysis of environmental DNA (eDNA) and the modeling of historical pollen data for pollination forecasts, are outlined. Aerobiology and pollen monitoring will continue to benefit from technological advances and be re-shaped in the next decades.

Ailanthus altissima (tree of heaven) is among the most abundant and widespread neophytic plants in Austria. The pollen season of Ailanthus usually ranges from the beginning of June until the mid of July, showing one peak period around the mid of June in Vienna (Austria). Over a span of 48 years (1976–2023), pollen data of Ailanthus was gathered from aerobiological samples and assessed for a temporal trend. In addition, weather data from Vienna (temperature, precipitation, relative humidity and sun hours) was incorporated to find possible associations with Ailanthus pollen indices. The change in the pollen season for Ailanthus described in this study has already manifested and is ongoing. Temperature and sunshine hours have a direct impact on the flowering of urban trees, indicating that global climate change may be a major driver towards more intense pollen and allergy seasons.