Survival Islands Chronicles
In the heart of Düsseldorf, the city's Deichwiesen meadows stand as some of its most ecologically valuable green spaces. Recently, the city's wastewater management department, in collaboration with landscape and ecological planning offices, has been reconsidering the mowing practices in these meadows.
The primary goal of mowing remains the same - to protect citizens from flooding, just as it does for river banks. However, the approach to mowing flower strips has undergone a change. Previously, these strips were mowed twice a year, in June and September, with the grass clippings removed. This year, some flower strips on the Löricker Deich and the Lohauser Deich will be mowed only once.
The new mowing method, known as tray mowing, is being employed by the city's wastewater management department. This technique, which protects insects more than previous methods, results in meadows being mowed only once a year, as opposed to twice. The ecological planning office is closely monitoring both the positive and potential negative impacts on the grass sward due to this new method.
The tray mowing technique does not alter the fact that certain types of grass for dike protection still need to be mowed. Mowing grass stabilises the dike soil during high water levels and prevents soil erosion. However, the decision to mow flower strips once a year was made with the aim of preserving the habitat for insects.
Studies have shown that reducing mowing frequency can have a significant positive impact on biodiversity. Mowing has a detectable negative impact on some invertebrate communities such as snails. Research indicates that snail abundance and species richness decline significantly in mowed areas, even though diversity indices like evenness sometimes appear to increase due to changes in species dominance patterns.
Moreover, mowing removes substantial aboveground biomass compared to grazing, which can reduce food sources and habitat structures for various meadow species, making ecosystems more sensitive to frequent mowing events. A meta-analysis comparing extensive grazing and mowing versus abandonment across European grasslands indicated that mowing can reduce biodiversity relative to less intensive or more natural management regimes.
Urban green management projects, not specific to Düsseldorf but relevant in principle, transitioning from high-frequency mowing to mosaic or no-mow zones have resulted in increased biodiversity, including higher pollinator species richness. Such findings support recommendations to reduce mowing frequency or create heterogeneous mowing regimes (mosaic mowing) in urban and ecologically valuable meadows.
While specific studies on Düsseldorf’s Deichwiesen itself were not found, applying these broader findings suggests that reducing mowing frequency in Deichwiesen would likely benefit biodiversity. This could be achieved by allowing more species (including snails and pollinators) to persist and thrive, increasing structural habitat complexity, and supporting higher abundances and richness of meadow plants and invertebrates.
Therefore, mowing less often or adopting a mosaic mowing pattern—where some areas are left unmowed for longer periods—would be an ecologically sound strategy for maintaining and enhancing biodiversity in these valuable meadow ecosystems.
In the context of the changed mowing practices, the city's wastewater management department is implementing the tray mowing technique in some environmental-science focused flower strips, which is a method that protects insects more than previous methods, and allows the meadows to be mowed only once a year. This approach to mowing, aimed at preserving the habitat for insects and promoting biodiversity, has the potential to increase the diversity of plants and invertebrates in home-and-garden environments like the Deichwiesen meadows.
