MSc data: Urban agriculture – A chance for insect diversity and food security? Pollination exclusion experiment using Sinapis alba in urban allotment gardens in Göttingen, Germany

Data and manuscript of the master thesis of Jan-Lorenz Fohrmann entitled: Urban agriculture – A chance for insect diversity and food security? Pollination exclusion experiment using Sinapis alba in urban allotment gardens in Göttingen, Germany. The thesis was supervised by Prof. Catrin Westphal and Dr. Arne Wenzel from the Functional Agrobiodiversity of the University of Göttingen. Abstract: Globally, biodiversity is in decline. This is particularly alarming for insects, with reported losses of up to 75% of the biomass. At the same time, insects provide important ecosystem services, for example as pollinators. Among the discussed drivers of diversity decline is urbanization. Currently, half of the world’s population live in or near cities, which keep expanding with no indication of an end. Besides their role as living and working space, cities are also a place of food production. Urban agriculture is growing in importance, especially in developing regions, which are also the hotspots of urbanization and, in many cases, biodiversity. Still, urban agriculture can also reduce the environmental footprint of food production in developed regions. There is no clear consensus on the role urbanization plays for the abundance and diversity of pollinating insects. Alongside negative, neutral and even positive responses have been reported. Therefore, for my master thesis, I conducted a pollination exclusion experiment in eight garden allotments around the city of Göttingen, Germany, to evaluate how the surrounding land-use and grade of urbanization affects the pollinator community. For this, I cultivated Sinapis alba-plants in the green house until they induced flowering, and then transported them to the study sites. While some plants were given access to pollinators, others were excluded with a net. I then observed the insects visiting the study plants and those that were overall present in the gardens before the plants were brought back to the greenhouse and harvested to get an impression of their reproductive success. Additionally, I derived the surrounding land-use from satellite imagery using QGIS, and assessed local characteristics of each garden, such as flower abundance and nesting resources. The results point out that well managed urban green spaces can attract a large and healthy pollinator community. At least 72 taxa of flower-visiting insects were observed on my study plants, and the plants’ reproductive output did not seem to be impaired. However, while the number of visitors was even increasing with urbanization, their richness was negatively affected, indicating a dominant role of fewer generalist species in highly urbanized areas. Also, unlike suggested by several other studies, local effects such as flowering and nesting resources did not seem to overshadow the effect of larger-scale landscape characteristics, as both types of models showed similar amounts of significant relationships. Still, abundant floral resources and a high proportion of open soil seemed to positively affect pollinator activity. Urban pollinators put high-priority and high-impact biodiversity conservation within reach of a large proportion of the human population. Allotment gardens have shown to be a highly attractive habitat for insect pollinators, as they provide continuous floral resources and various nesting opportunities, and the observed pollinator communities included large, attractive species like Andrena agilissima and Xylocopa violacea. Insect conservation is of great popularity and can be achieved with relatively little effort, by providing adequate floral and nesting resources. The allotment gardeners I worked with showed great awareness and knowledge of this and often considered themselves agents of insect conservation. Therefore, for future research in the field of urban pollinators, citizen science can be a very promising approach.