Changes in arable weed communities over the last 100 years

Abstract

During the last decades, agricultural practices have changed dramatically. Today, the fields are managed mechanically, and industrial fertilizer and herbicides are applied. This intensification has on one hand increased yields but on the other hand plants and animals living in the agricultural landscape were repressed or got extinct. Therefore, the introduction of agri-environmental schemes (wildflower strips, set-asides) was decided in Europe during the 1980s. These schemes were intended to promote the natural communities of arable fields. To show the changes in the arable flora in a bigger context, a meta-analysis was conducted for data across Europe. A meta-analysis compares the outcome of all traceable studies that were conducted on a specific topic. Hence, a reliable conclusion about the underlying effect can be drawn. Therefore, internet databases were searched for studies that were carried out on arable fields in Europe comparing historic and contemporary vegetation surveys. A total of 32 studies corresponded with the criteria, yielding 53 datasets. The studies compared vegetation surveys from 1939 to 2007. Averaged over these datasets the species number per plot of arable plants declined by about 20%. However, twelve of these datasets showed an increase in average species number per plot. All studies that started after 1980 showed an increasing average species number. Plant species preferring nutrient rich sites, neophytes, and monocotyledons largely increased since 1980, while species of typical arable weed communities declined. The change in species number was not influenced by crop type or study design. Furthermore, neither geographic location nor precipitation of the study region had an influence on the outcome of the meta-analysis. This temporal development of the European arable flora suggests that conservation measures, such as ecological compensation areas like unsprayed field margins or wild-flower strips, may have helped to some extent to “slow” the decline in species numbers, but not in terms of typical arable weeds like corn-cockle or cornflower. Hence, more specific measures should be taken to stop this decline, making sure that they are advantageous for rare arable species. Of course, it has to be taken into account that mainly threatened arable weeds and those plants beneficial for the farmer should be promoted. The growth of plants which bring a disadvantage for the production of agricultural goods should be prevented as much as possible.