The importance of light for grassland plant diversity

Experimentally restoring light to understory plants in a natural grassland mitigates the loss of plant diversity that is caused by either nutrient enrichment or the absence of mammalian herbivores, according to research by Anu Eskelinen and colleagues, published in Nature. The findings help explain how herbivory, which damages plants, also promotes biodiversity.

Anu Eskelinen, who spent several years at the UFZ and iDiv as a visiting scientist, used a new experimental approach: the team directly illuminated the low-growing plants in the grassland with LED lamps, thus increasing the amount of light. In addition to this treatment, fertilisers were applied on some plots and grazing by sheep was used on others.

The experiment showed a sharp decline in species richness and biodiversity as a result of artificial fertilisation if the areas were not grazed at the same time. When the researchers added LED lamps, the loss of species richness was mitigated. Later, the researchers excluded sheep from half of the plots, which caused species richness and diversity do decline. At the same time, the total vegetation cover increased without grazing, which, in turn, reduced the light available to plants. Importantly, adding light to the understorey plants mitigated this loss of diversity. “These results suggest that herbivory is a dominant factor controlling competition for light and plant diversity,” says first author Anu Eskelinen.

The research team believes that the results from the field trials should be taken into account for future grassland management and conservation policies. “Our results highlight the importance of conserving native herbivores and using sustainable grazing as a management measure,” Anu Eskelinen further emphasises.

Prof. Dr Stan Harpole, co-author adds: “This study highlights the value of carefully designed manipulative field experiments, which we need so we can strongly test the causes of diversity loss. We could only advance our understanding and test the theory in more realistic conditions because of the excellent infrastructure of the UFZ’s Global Change Experimental Facility and the support provided at the Bad Lauchstädt Research Station, and the cooperation with iDiv.”

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Eskelinen, A., Harpole, W.S., Jessen, M.-T., Virtanen, R. and Hautier, Y. (2022) “Light competition drives herbivore and nutrient effects on plant diversity,” Nature. Available at: https://doi.org/10.1038/s41586-022-05383-9.