Benefits of agri-environment wildflower areas vary according to the surrounding landscape

Recent research assessed non-pollinator invertebrates (spiders and beetles) using a focus on landscape characteristics to broaden the perspective on this debate. The researchers report that the presence of different semi-natural habitats in the surrounding area can influence the effects on arthropod communities. They recommend that landscape characteristics be considered in the design of such schemes.

The establishment of wildflower areas in cultivated landscapes is a popular agri-environment intervention. However, studies on the biodiversity benefits of such schemes have produced conflicting evidence. Studies have typically focused on pollinators as the key target group, often within a limited timeframe, and rarely considered wider landscape characteristics. This study aimed to provide a wider context for interpreting existing ambiguous findings.

Fieldwork was conducted in Schleswig-Holstein, northern Germany, between May and July from 2017 to 2019. In 2016 a provincial agri-environment scheme promoted the sowing of wildflower areas, and the researchers selected ten of these as sample sites. Then they paired each wildflower area with a nearby winter cereal field as an additional site. They sampled all sites with pitfall traps to collect ground-dwelling arthropods, a non-target invertebrate group. Three types of arthropod were counted and identified to species or genus level – carabid beetles, rove beetles and spiders. The researchers used these records to produce indices of density and species richness for each arthropod group.

The researchers also evaluated the landscape in a 750-metre radius of each wildflower site to establish the proportion of land area occupied by wildflower sites and by permanent semi-natural habitats such as hedges, trees and ponds. The proportion of wildflower areas varied between 0.4% and 14.2% across the study sites while the level of semi-natural habitat ranged from 0.3% to 7%.

The researchers report that over the three field seasons they collected 86 445 specimens representing 334 species. They say that the results did not indicate a steady increase in arthropod density or diversity over the three-year period. However, they note that the middle year experienced an extremely hot and dry summer which could have disrupted the results.

Both density and richness of arthropods was lowest in cleared landscapes (with very low proportions of semi-natural habitat), according to the researchers, and increased as this habitat proportion rose. However, these measures peaked in relatively simple landscapes with moderate amounts of semi-natural habitats and declined again as the landscape became more complex, with higher proportions of these habitats, say the researchers. They interpret this finding in the light of the ‘intermediate landscape-complexity hypothesis’¹ – which suggests that conservation interventions have minimal impact in cleared landscapes with negligible natural areas, which lack the species pool to colonise new habitat areas. However, the hypothesis proposes that the impact of interventions also decreases in relatively complex landscapes with higher biodiversity, where minor enhancements make a minimal additional contribution. Hence conservation actions have the greatest impact in landscapes with an intermediate level of complexity, according to the hypothesis.

In contrast, the researchers say that an increased proportion of wildflower areas generally led to a steady increase in arthropod density and richness. They say that this was most pronounced in the case of rove beetles in landscapes with low levels of semi-natural habitat. Here the increasing proportions of wildflower areas led to marked increases in species richness, they say. They note that in these very simple landscapes the wildflower areas made a greater contribution to overall habitat complexity.

The researchers highlight the significance of landscape characteristics in determining the impact of newly-established wildflower areas. They suggest that agri-environment schemes should consider complementarity between habitat types in their design, for example with reference to the intermediate landscape complexity hypothesis. They also highlight the potential impact of extreme weather events on arthropod communities and argue that the effect of climate change needs to be incorporated into agri-environmental planning. They suggest that further research could consider different landscape features and multi-year studies to build on these results.

Footnotes:

1. For more information see: Tscharntke, T., Tylianakis, J. M., Rand, T. A., Didham, R. K.,

Fahrig, L., Batary, P., et al. (2012) Landscape moderation of biodiversity patterns and processes - eight hypotheses. Biological Reviews, 87: 661–685.

Source:

Hoffmann, H., Peter, F., Donath, T. W., and Diekötter, T. (2022) Landscape- and time-dependent benefits of wildflower areas to ground-dwelling arthropods. Basic and Applied Ecology 59: 44–58. Available from: https://doi.org/10.1016/j.baae.2021.12.008

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“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.

Notes on content:

The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.