Over the past few decades, a large number of Germany’s animal populations in agricultural landscapes have experienced sharp declines, both in the number of individuals and species. According to a recent study published in the Journal of Applied Ecology, fallow land – arable land left without sowing for one or more vegetative cycles – appears to be an effective method for slowing this decline and promoting bird diversity.
The experts investigated the correlation between the proportion of fallow land and the number and abundance of farmland birds during a period of nine years. They discovered that areas of fallow land have contributed to a significant increase in these birds’ populations.
Nevertheless, the benefits of fallow land were found to depend on the complexity of the surrounding landscape, measured by the density of boundary lines between fields, as well as between fields and adjacent woody structures such as hedges or forest edges.
The analysis revealed that establishing areas of fallow land is most effective in agricultural landscapes with a medium level of structural complexity, with an average density of around 65 meters per hectare of agricultural land.
“Our research enabled us to identify regions where fallow land should preferably be established in order to have the greatest effect,” said study co-author Sebastian Klimek, an expert in the conservation of biodiversity in agricultural landscapes at the Thünen Institute of Biodiversity.
“In order to stop declining populations of farmland birds nationwide, it is necessary to maintain a minimum proportion of fallow land in the agricultural landscape,” added senior author Johannes Kamp, a landscape ecologist and conservation scientist at the University of Göttingen.
The total area of fallow land in Germany is largely determined by EU’s Common Agricultural Policy (CAP). Due to changes in this policy, the amount of fallow land in Germany has decreased substantially since the early 2000s, leading to a lack of suitable breeding sites and food for a variety of bird species.
Although the “greening” of the last CAP funding period has slightly increased the area of fallow land from 2015, the current amount of such land remains far below the levels observed before 2007.
Fortunately, in the new CAP support period starting this year, farms will be obliged to set aside four percent of their arable land, which could contribute to increases in farmland bird populations. However, in order to restore their pre-2007 levels and thus enhance biodiversity in agricultural landscapes, a further increase would be required.