Flower strips, conservation field margins and fallows promote the arable flora in intensively farmed landscapes: Results of a 4-year study

Agri-environment measures to support biodiversity in intensively used agricultural landscapes have been implemented in many European countries, but the large-scale downward trend in many species groups continues. The arable flora is one of the species groups that suffered the steepest declines in European cultural landscapes. Despite their fundamental importance in agroecosystems as the basis of the food web, few studies have tested the effectiveness of different agri-environment measures on the arable flora in replicated field trials over several consecutive years. In a four-year participative project with the farmers, we recorded the effects of four agrienvironment measures, namely conservation field margins (CFM), annual fallow strips (fallows), alternately managed biennial flower strips (AFS), and perennial flower strips (PFS), on the species richness, plant cover and composition of the non-crop vegetation in 67 intensively managed arable fields in Northwest Germany. Compared to conventionally managed field edges, all measures led to a large increase in total plant cover (median values across measures and years: 68.5 vs. 9.5 %) and doubling of species richness (21 vs. 9 species per plot), promoting not only generalist species but also the typical arable flora (17 vs. 7 species, 56.5 vs. 8 % cover). Of the 207 plant species recorded during sampling, 43 (including 16 typical arable species) were solely found in measures. All measures promoted forbs more than graminoids, while annual species benefited especially from CFM and fallows. The overall effects on diversity and cover remained stable over the 3-yr implementation period but were significantly influenced by interannual weather fluctuation. Spillover effects of the measures into adjacent conventionally managed crops were not detectable. We conclude that, if well-managed, all tested measures can have a positive effect on the native arable flora even in long-term intensively farmed landscapes. However, especially CFM and the annual fallows are particularly effective in naturally restoring and maintaining arable plant diversity. The limited occurrence of 1/4 of typical arable plant species on less than four fields indicates severely impoverished soil seed banks in intensive farmland. Therefore, the re-introduction of native, rare arable plant species through seed mixtures should be considered in order to promote local diversity and save local populations of these species.