Light and grazing herbivores important for grassland diversity

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The light experiment at the Global Change Experimental Facility (GCEF) of the UFZ research station in Bad Lauchstädt. © Anu Eskelinen / University of Oulu

A European study on the importance of light for plant diversity on grassland suggests that grazing herbivores are a dominant factor controlling competition for light and plant diversity.

Plants need light to grow, but due to excess nutrients and/or lack of herbivores, less light can reach deeper layers of vegetation in grasslands. Consequently, fast-growing species dominate and plant diversity decreases. So far, this connection has been made indirectly through experiments, but never directly through experimentally adding light in the field.

This has now been achieved by an international research team with scientists from the Helmholtz Center for Environmental Research (UFZ), the Martin Luther University Halle-Wittenberg (MLU) and the German Center for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig experimentally prove for the first time the dominant role of light competition. The results were published in the journal Nature.

The team around Professor Dr. Anu Eskelinen from the University of Oulu in Finland used the Global Change Experimental Facility (GCEF) at the UFZ research station in Bad Lauchstädt for his experiments. Scientists from UFZ, iDiv and various universities use the GCEF platform to study the influence of different climate models and land use intensities on the structure of plant communities – in particular food webs and interactions between species.

Eskelinen took a new experimental approach: the team directly illuminated the low-growing plants in the grassland with LED lamps, increasing the amount of light. In addition to this treatment, fertilizer was applied to some plots and sheep grazing was used on others.

The experiment showed a sharp decline in species richness and biodiversity due to artificial fertilization if the areas were not grazed at the same time. When the researchers added LED lights, the loss in biodiversity was mitigated. Later, researchers excluded sheep from half of the plots, reducing species richness and diversity. At the same time, total non-grazing vegetation cover increased, which in turn reduced the light available to plants. Importantly, adding light to the undergrowth plants mitigated this loss in diversity.

“These results suggest that herbivores are a dominant factor controlling competition for light and plant diversity,” Eskelinen said.

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 underscore the importance of conserving native herbivores and using sustainable grazing as a management measure.”

professor dr Stan Harpole, co-author and head of the Department of Physiological Diversity at the UFZ and iDiv, said: “This study underscores the value of carefully designed manipulative field experiments, which we need to comprehensively test the causes of diversity loss. ”

The study was mainly funded by the Academy of Finland and the UFZ.

Eskelinen, A., Harpole, WS, Jessen, MT, Virtanen, R., & Hautier, Y. Light competition drives herbivores and nutrient effects on plant diversity. Nature; DOI: 10.1038/s41586-022-05383-9.

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