Laura Sutcliffe discusses her latest study where, alongside colleagues, she investigated the spatial distribution of vascular plant species richness and their contribution to the food web via biomass and flower units in conventional and agri-environment cereal fields.
The study: Arable plants
Arable plants are usually simply referred to as weeds, reflecting their low status in society and also in biodiversity research. Whilst there is a wealth of literature dedicated to how to get rid of them, the biodiversity value of the several hundred species of arable-adapted plants in Europe is a relatively niche subject. Through agricultural intensification a large proportion of arable plant species are now threatened or extinct, and those that remain are mostly limited to the outermost metre or so of a field. This is a group that is both metaphorically and literally close to the edge.
But arable plants are also the base of the agricultural food web, and closely linked to declines in e.g. insects and birds. We looked at the spatial distribution of wild plants in cereal fields in Germany, and how this varies with different agri-environment schemes. In this way we wanted to demonstrate what these measures are capable of providing in terms of diversity and food-web resources (flower units and plant biomass) at the field level. We also wanted to contribute further evidence to the discussion on whether landscape configuration (i.e. field size) or management is more effective to promote biodiversity.
Findings
In contrast to conventional cereals, “extensive” management (lower sowing density, no synthetic pesticides or fertilizers) maintains arable weed populations into the field interior. This means a much higher resource provision at the field level: extrapolating to a 1ha field results in 127,000 flower units in extensive management compared to 1900 flower units in conventional management. The concentration of wild plants at the field edge means that smaller field sizes in conventional agriculture do increase in-field arable plant populations at a landscape scale.
But, it may be more practical for the farmer and better for the yield to instead incorporate extensive buffer strips around the outside of larger conventional fields. This may also help to reduce spray-drift and fertilizer run-off, and has long been recommended as a measure in nature conservation practice. An important consideration in this recommendation is that we are focusing on arable plants, and not on species that mainly use the habitats between the fields like hedgerows or ditches. As always in conservation, the best intervention depends very much on the specific landscape and the organism group you want to promote.
Why is this important?
This study is part of a wider project looking at the real-world effects of conservation measures in conventional farmland. Whilst organic farming is most often recommended as the best way to promote biodiversity, the reality is that the vast majority of farmland (around 90% in the EU) is conventional. Much of this area has very low levels of even generalist species in the landscape, reducing resilience to pests and fragmenting populations.
Within the FR.A.N.Z. project, ten farmers from across Germany agreed to test out different conservation measures over ten years, providing access for ecological and economic research and demonstrating the results to colleagues. In this way, they hope to inspire other farmers to integrate more nature conservation into their farming practice and give a boost to biodiversity in the landscape.
Read the full article “Close to the edge: Spatial variation in plant diversity, biomass and floral resources in conventional and agri-environment cereal fields” in Journal of Applied Ecology.
