Mowing meadows and pastures apparently harms insects and spiders more than expected – and thereby endangers the biodiversity. Two studies now show what this is and what measures the useful small animals could protect. However, the researchers emphasize that the insects and spiders also need small unused islands as retreat.
Wiesen and pastures offer many animals a habitat. The grassland used in agriculture thus contributes significantly to biodiversity and healthy ecosystems. However, some meadow residents, especially insects and spiders, are at risk from regular mowing. Because with the MAHD and the subsequent processing of the green cut, up to 80 percent of insects are killed, as can be seen from previous studies. Since the pastures are mowed up to five times a year, this can lead to a massive decline in the insects and spiders living therein. In addition, the young insect – for example butterfly caterpillars, beetle larvae or young grasshoppers – dries up if the shade -giving green lacks in summer. The lack of privacy screen also makes it easier to find and eat by birds.
Mowing techniques in comparison
Researchers around Lea von Berg from the University of Tübingen have therefore searched for how farmers can mow their grassland as gently as possible. To do this, they compared the damage over two years that different mowing machines do: tractor-powered beam mower with double-moving double meters and conventional rotary disc mower with rotating blades. The test fields of the University of Hohenheim were mowed twice a year and the occurrence of eight groups of animals was determined before and then. A total of almost 50,000 small people were included in the rehearsals.
The evaluation showed that the choice of the mowing machine hardly makes a difference. “We could not find any significant differences between the two most common mowing techniques,” reports co-author Johannes Steidle from the University of Hohenheim. “In practice, we could not find any indication that the bar mower, which is often classified as the more environmentally friendly alternative, is gentler for insects and spiders than the disc mower.” The rotating blades obviously do not generate a strong as often as it was assumed. Such rotation mower and tractor -powered beam mower damaged the insects and spiders on meadows and pastures in the test: “Compared to the unexpected controls, we found 34 percent fewer individuals in the parcels, which are mowed with the beam mower and 36 percent less in the surfaces mowed with the disk mower,” reports from Berg.
Spiders and caterpillars died above average: their number decreased by up to 55 percent. On the other hand, grasshoppers and beetles that are more mobile and have thicker skin or tank were less decimated, only by 20 to 30 percent. “A jump can often flee and escape the mower quickly by jumping, while many beetles apparently let themselves go on the floor instead of leaving the area,” explains von Berg. The beetles were at least well protected from the beam mower, but less from the disc mower.
What can help?
The team therefore compared alternative measures in a second study that should keep the consequences of mowing as low as possible. “A promising approach for biodiversity-friendly mowing is various framework devices that are installed in front of the mower,” explains co-author Stefan Böttinger from the University of Hohenheim. “They should persuade the animals to flee or drop them and thus protect them from injuries or death.” The researchers compared to three techniques on their test fields for three years: a truck tarpaulin mounted on a metal bracket, which brushes the grass, a kind of calculation in which droping metal tines are led through the grass, as well as a blower. All three devices were attached directly in front of the mower or in front of the tractor and gave the meadow residents to flee so much time.
The practical test showed that these framework techniques can actually partially reduce the loss of insects and spiders when mowing. However, their success depended on several factors: “At a low driving speed of five kilometers per hour, insect shields from truck tarpaulin proved to be very effective. At higher speeds of twelve kilometers per hour, which are common practice, this device was ineffective,” reports Von Berg. “Here, more robust models such as the rake with metal tines or the powerful blower showed better results.” It also showed that the truck tarpaulin is only available for poets and high vegetation and then scares the animals worse. The more stable metal tines, on the other hand, penetrate even density meadows and drive the insects more effectively.
The blower turned out to be particularly effective in all cases. In contrast to the other techniques, it not only failed a few, but almost all of the animal groups examined from the mown area. Living beings that can fly or bounce actively fled to the blower. Crawling and creeping animals that are slower were passively blown away by the strong air flow. “Only with spiders could we not have an effect of the blower,” said co-author Jonas Frank from the University of Hohenheim. “This is probably due to the fact that mainly networking species live on the meadows that cling to their nets in strong winds.”
Unexpected islands as retreats
The researchers conclude from the fact that scam techniques can help protect biodiversity on meadows and pastures when mowing and make agriculture more sustainable. This does not have to be expensive: Even cost-effective solutions such as the stripping devices from truck tarpaulin can be successful if they are used correctly, the team emphasizes. However, the purchase of blower slays is associated with higher costs, but then enables faster driving speeds.
In addition to these techniques, Berg and her colleagues recommend that not to mow the green areas completely, but to maintain small unexpected surfaces. The frightened insects and spiders can withdraw there, are protected from harvesting and drying up and can later colonize the mown surfaces. “It is enough to leave small islands or (side) stripes unexpected,” emphasizes co-author Oliver Betz from the University of Tübingen. However, the researchers not only address their recommendations to farmers, but also to municipalities, the green spaces along streets and paths. These meadows also offer habitats important for insects and spiders.
Sources: University of Hohenheim; Specialist articles: Journal of Applied Ecology, Doi: 10.1111/1365-2664.14852 and Insect Conservation to Diversity, DOI: 10.1111/iCAD.12854
