Field margin management for promoting plant diversity—A functional approach to investigating the effects of multiple measures on plant community dynamics

Strategies to counteract the loss of arable plant diversity often target field margins. Yet there is still need for research on how arable plant diversity is impacted by the type, scale and diversity of margin management. To assess this experimentally, we combined five measures imposing different disturbance regimes (flower-strip mown twice a year, tilling in spring or autumn, adding sand as substrate, and frequent mowing as a control) at two spatial scales.

We explored how plant community dynamics are affected by both single measures and their combination. We addressed four hypotheses: H1) single measures shift community weighted mean (CWM) values of functional traits and reduce the within-measure community weighted standard deviation (CWSD) of these traits; H2) heavy disturbance (early tilling and sand) causes taxonomic and functional diversity (alpha-diversity) to increase over time; H3) combining different measures increases dissimilarity (beta-diversity) and thus gamma-diversity across measures; and H4) increased spatial heterogeneity of measures promotes all levels of diversity.

We found shifts in CWM and reduced CWSD in flower-strips (smaller seed mass, perennial lifespan) and late-tilling (later flowering-onset) whereas sand and early-tilling tended to increase CWSD (H1). Trends across measures indicate shifts towards species with competitive strategies (H1). Compared to frequently mown controls, heavy disturbance (sand and early-tilling) promoted alpha-diversity over time, despite lower initial diversity. Moderate disturbance (flower-strip, late tilling) initially promoted alpha-diversity, but diversity then did not increase further (H2). Combining different measures promoted diversity compared to single measures, but the similarity between measures increased over time (H3). Scale played a minor role in determining community-composition (H4).

Disturbance regimes imposed by different management of field margins shape the functional composition of arable plant communities. Strategies combining different measures help to balance initial benefits of moderate disturbance with the longer-term diversity gains from heavier disturbance.