University of Bern
Dr. Jean-Yves Humbert
Institute of Ecology and Evolution
Phone: +41 31 631 31 73
Jean-Yves did his PhD thesis between March 2007 and March 2010. Now he is working as a research and teaching assistant for Prof. Raphaël Arlettaz, Institute of Ecology and Evolution, Division Conservation Biology, University of Bern. Link
An important element of the on-farm activities that directly impacts biodiversity, specifically grassland fauna community, is the harvesting process itself. As yet the direct effects, such as the mechanical impacts, of the cutting process on arthropods have rarely been differentiated from the indirect effects, such as changes in habitat.
The thesis assessed the direct impacts of the grass harvesting process on field invertebrates. It showed that different mowing practices, using different types of machinery, are remarkably different in terms of their impacts. Hand bar mowers are slightly less damaging than rotary mowers, and adding a conditioner to a rotary mower increases impacts two to three folds. Furthermore, post-mowing harvesting interventions (i.e. tedding, raking and baling) proved to have also considerable impacts, especially on less mobile species such as Orthoptera where about 60% of the individuals that survived mowing were subsequently killed. Indeed, any benefits gained in terms of reduced grasshopper mortality by using a tractor-powered bar mower over a rotary mower were mostly lost by the cumulative impact of the subsequent harvesting stages. Finally, we demonstrated that leaving uncut grass refuges is a simple yet effective measure to mitigate the direct negative impact of the harvesting process.
Given the strong negative impacts on field fauna of harvesting practices we recommend, where conservation of field fauna is an objective, a reduction in the number of harvests per year to the strict minimum required to maintain the plant community (one or at most two). When harvesting the grass, no conditioner should be used and uncut refuges should be left for the fauna. The use of hand motor bar mowers is recommended over tractor-powered mowers. For field vertebrates, such as amphibians, a cutting height of 10 cm is recommended.
The project was initiated on a large interest from the stakeholders and was supported by local authorities (13 out of 26 Swiss cantons). It was supervised by Thomas Walter (Agroscope Reckenholz-Tänikon Research Station ART) and Prof. Jaboury Ghazoul (ETH Zürich).
Complete list of publications here
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