IF grassland is managed intensively, biodiversity typically declines.
A new study led by plant ecologists Eric Allan and Markus Fischer at the University of Bern in Switzerland found that rare species suffer the most. These negative effects could be reduced if farmers vary the intensity of their land use between years.
Globally, the intensification of agricultural land use is considered the leading threat to biodiversity. Previous studies on the impacts of land use intensity on biodiversity have looked at only single or small groups of organisms. However, individual species can vary greatly in how they respond to different land uses, meaning that the overall impact on biodiversity is often not clear.
A research study, published in Proceedings of the National Academy of Science, found that farmers can help protect grassland biodiversity by varying management intensity over time. This reduces some of the negative effects of intensive land use, particularly for rare species.
A team of 58 scientists from Switzerland and Germany assembled a uniquely comprehensive data set on the biodiversity of up to 49 groups of organisms, including groups of bacteria, fungi, plants and animals. They used data from study sites they had established in 150 grasslands in three regions of Germany — the Biodiversity Exploratories — which varied from extensively managed and lightly grazed to intensively grazed or mown grasslands with high fertilizer input.
The scientists used these data to compile a novel index of "multidiversity," which measures total ecosystem biodiversity.
"The study showed that overall biodiversity declined very strongly with increasing land use intensity and that this was particularly true for rarer species," Allan explained. Plants, grasshoppers and butterflies had the most pronounced declines.
According to Allan, the results provide very strong evidence of the importance of extensively managed grasslands for nature conservation.
"This new index provides a single measure of biodiversity for an ecosystem and should make it easier to assess the effects of conservation measures or restoration efforts on biodiversity," he said.
The scientists also found biodiversity to be much higher in grasslands in which land use intensity had varied over the last few years.
"This suggests that varying management intensity over time could be a novel strategy to maintain biodiversity in grasslands, for instance, by altering the number of livestock or the frequency of mowing between years," Fischer explained.
The rare species in the study benefited particularly from changing land use over time: At intermediate land use intensity, the biodiversity of the rarer species was almost twice as high when land use intensity varied between years.
"This result shows that farmers could do a lot for biodiversity conservation simply by varying the intensity of their land use between years, as long as the mean intensity of management does not get too high," Allan said.