Does delaying the first mowing date benefit biodiversity in meadowland? A meta-analysis

In Europe, extensively managed hay meadows are considered as high nature value farmlands, and this recognition makes them among the most commonly implemented agri-environmental schemes (AES). The most important management action on these grasslands is mowing, however, the time of year at which meadows should be first mown in order to maximize biological diversity remains controversial and may vary with respect to context and focal taxa. In order to provide the best available evidence for the management of this habitat, we carried out a systematic review and meta-analyses on the effects of delaying the first mowing date upon plants and invertebrates in European meadowlands.

Delayed mowing in an extensively managed meadow

We followed the review methodology of the Collaboration for Environmental Evidence partnership (CEE: http://www.environmentalevidence.org/). ISI Web of Science, Science Direct, JSTOR, Google and Google Scholar were searched. We recorded all studies that compared the species richness of plants, or the species richness or abundance of invertebrates, between grassland plots mown at a delayed date (treatment) vs plots mown earlier (control). In order to be included in the meta-analyses, compared plots had to be similar in all management respects, except the date of the first cut that was (mostly experimentally) manipulated. They were also to be located in the same meadow type. Meta-analyses applying Hedges’d statistic were performed.

Overall, the review showed that in general delaying the first mowing date in European meadowlands has either positive or neutral effects on plant and invertebrate biodiversity. Specifically, our results showed that plant species richness reacted differently with respect to the date to which mowing was postponed. Delaying mowing from spring to summer had a positive effect, while delaying either from spring to fall, or from early summer to later in the season had a negative effect. Invertebrates were expected to show a stronger response to delayed mowing than plants, due to their dependence on vegetation structure and high susceptibility to mechanized harvesting processes. However, only invertebrate species richness showed a clear overall significant positive response, while no effect was detected on invertebrate abundance. It was only after removing two studies contradicting basic meta-analysis assumptions that delaying the first mowing date was found to have a positive effect on invertebrate abundance. It is important to note that there was also strong between-study heterogeneity, pointing to other major confounding factors, the elucidation of which requires further field experiments with both larger sample sizes and a distinction between taxon-specific and meadow-type-specific responses.

Alpine meadow

While most AES have the clear objective of restoring biodiversity and ecosystem services they often bind farmers to threshold dates for agricultural operations. The date of the first mowing of meadows is usually defined as a trade-off between expected agricultural yield and supposed effects on wildlife. Given that this first mowing date is an easily changed management practice and can be applied over large scales, it is likely to provide significant environmental benefits at little economical cost. In addition to agricultural grasslands, some open nature reserves and hotspots are also mown as a management strategy. When conservation is the primary goal of such management, the date of the first possible cut should be considered carefully in the light of our results.

Reference

Jean-Yves Humbert, Jérôme Pellet, Pierrick Buri, and Raphaël Arlettaz. 2012. Does delaying the first mowing date benefit biodiversity in meadowland? Environmental Evidence 1:9.

Open Access journal: http://www.environmentalevidencejournal.org/content/1/1/9/abstract

Jean-Yves Humbert - Division of Conservation Biology, Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, 3012 Bern, Switzerland. Email: jean-yves.humbert@iee.unibe.ch

Jérôme Pellet -1) Division of Conservation Biology, Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, 3012 Bern, Switzerland; 2) A. Maibach Sàrl, CP 99, Ch. de la Poya 10, 1610 Oron-la-Ville, Switzerland

Pierrick Buri - Division of Conservation Biology, Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, 3012 Bern, Switzerland

Raphaël Arlettaz - Division of Conservation Biology, Institute of Ecology and Evolution, University of Bern, Baltzerstrasse 6, 3012 Bern, Switzerland