Loss of herbivory and nutrient enrichment decrease plant diversity via increased competition for light 

Anthropogenic nutrient enrichment and loss of herbivory are two major causes for diversity loss in plant communities. Increased competition for light is one of the most often suggested forces linking the impacts of nutrients and herbivory on diversity. However, empirical tests of the role of light in natural systems are based on indirect evidence and have contributed to strong debates over the last 40 years.

Researchers from Finland, Germany, and the Netherlands used a novel experimental manipulation - addition of supplementary light with modern LED-lamps to understory plants in a natural grassland – and crossed this treatment with fertilization and exclusion of sheep herbivory. They provide the first direct experimental evidence in natural communities that competition for light is a major mechanism of plant diversity loss under eutrophication and loss of herbivory.

These findings have implications for grassland management and conservation policy. “Our results highlight the importance to preserve native herbivores, to use sustainable livestock grazing as a management strategy, and to employ rewilding (i.e. returning herbivores to areas from where they have been extirpated) as a tool to revert lost plant diversity”, says Anu Eskelinen, the lead author and associate professor at the University of Oulu . “The key is that we now know one important mechanism, alleviation of light competition, by which herbivores protect plant diversity”.

The study was conducted in Germany, at Global Change Experimental Facility (GCEF), belonging to Helmholtz Centre for Environmental Research UFZ. The main funder of the study are Finnish Academy and UFZ. The researcher team includes Yann Hautier, an associate professor from Utrecht University, Stan Harpole, a professor from Helmholtz Centre for Environmental Research (UFZ) and German Centre for Integrative Biodiversity Research (iDiv), Maria-Theresa Jessen, a postdoctoral researcher from UFZ and iDiv, and Risto Virtanen, a senior researcher from the Botanical Museum at the University of Oulu.

Link to the publication: Eskelinen, A., Harpole, W.S., Jessen, MT. et al. Light competition drives herbivore and nutrient effects on plant diversity. Nature (2022).

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• Ecology and genetics research at the University of Oulu
• This study is part of ‘eDiValo’ (ecological effects of light on diversity) research project led by Anu Eskelinen and part of Eskelinen’s research related to global changes and biotic interactions.
• Arctic Interactions research at the University of Oulu