Mowing machinery and migratory sheep herds are complementary dispersal vectors for grassland species

Prepared by Yves P. Klinger, Rolf Lutz Eckstein, Wiebke Hansen, Till Kleinebecker, Annette Otte & Kristin Ludewig

Semi-natural grasslands are one of the most prominent remnants of the historical cultural landscapes of Central Europe. Due to their century-long land-use history, they are highly diverse ecosystems that host vast numbers of plant, insect, and bird species. Furthermore, they provide a multitude of ecosystem services, such as supporting the production of domestic animals, harboring genetic resources, and storing carbon.

The conservation of semi-natural grasslands depends on the continuation of traditional land-use practices, such as mowing and pasturing with low amounts of fertilizer application. However, traditional grassland management has ceased in many parts of Central Europe. Consequently, the area of well-preserved grasslands has decreased drastically during the last century, and the few remaining grasslands are often isolated and surrounded by intensively used landscapes. This has resulted in a loss of processes that are necessary for the long-term conservation of these ecosystems. One vital process is the transport of seeds of habitat-specific plants between grassland patches, which enhances genetic exchange between (sub)populations of grassland species and allows species that have gone locally extinct to re-immigrate from other sites. Whether the seeds of a species can be transported strongly depends on the species’ characteristics (e.g. plant height, seed size, or time of flowering). While the role of single dispersal processes has been the subject of many studies, there is little information on the interplay of different dispersal processes in grasslands.

In our study, we investigated seed dispersal by two of the most common land-use practices in semi-natural grasslands: dispersal by mowing machinery and by migratory sheep endozoochory (the dispersal of ingested seeds that pass the gut and are deposited with the feces). To this end, we took samples of plant material adherent to mowing machinery at the beginning of July, a typical mowing date in Central Europe. Over the course of three months, we weekly collected samples of sheep dung from three migratory sheep herds. The underlying assumptions were (i) that mowers or sheep dung only transport a fraction of all plant species occurring in an area and that (ii) the identity of species being transported depends on their characteristics. We analyzed the species occurring in the samples by exposing them to favorable germination conditions in the greenhouse. The species building up the regional grassland vegetation (aboveground and soil seed bank) were assessed using vegetation surveys and a greenhouse experiment. We compared mowers and sheep dung samples to the regional grassland vegetation, concerning both their composition (i.e. which species are found in which frequencies) and their characteristics.

We found that mower samples were more similar to the aboveground vegetation, and sheep dung samples were more similar to the soil seed bank. Concerning functional characteristics, species dispersed by mowers were often small-seeded species and/or high-growing grasses, whereas species dispersed via sheep dung were characterized by very small seeds and high palatability. Interestingly, we found that both dispersal vectors cover different parts of the regional vegetation. This indicates that for the long-term conservation of semi-natural grasslands, the presence of different dispersal processes is essential.

This is a plain language summary for the paper of Klinger et al. published in Applied Vegetation Science (https://doi.org/10.1111/avsc.12579).