A research team headed by the Technical University of Munich (TUM) reports on two unexpected findings of the long-term study: Biodiversity influences almost half the processes in the ecosystem, and intensive grassland management does not result in higher yields than high biodiversity.
An ecosystem provides humans with natural "services", such as the fertility of the soil, the quality of the groundwater, the production of food, and pollination by insects, which is essential for many fruits. Hence, intact ecosystems are crucial for the survival of all living things. What functional significance therefore does the extinction of species have? Can the global loss of species ultimately lead to the poorer "functioning" of ecosystems?
The results of the long-term project "Jena Experiment", which is managed by the Friedrich Schiller University Jena, are published in the journal "Basic and Applied Ecology".
"One unique aspect of the Jena Experiment is the fact that we performed our experiments and analyses over 15 years", explains Prof. Weisser, the first author of the study. "Because the influence of biodiversity is only visible after a delay, we were only able to observe certain effects from 2006 or 2007 onwards - i.e. four or five years after the beginning of the project." If a habitat is destroyed due to human intervention, a species usually does not go extinct immediately, but instead some time later. According to these findings, this extinction then has a delayed effect on the material cycles.
The effects of biodiversity became correspondingly more pronounced over time in the Jena Experiment: In species-rich communities, the positive effects, such as carbon storage in the ground, microbial respiration, or the development of soil fauna only became more pronounced over time. On the other hand, the negative effects of monoculture also only became visible later on. "This means that the negative effects of current species extinctions will only become fully perceptible in a few years", warns Weisser.
Farmers are not more successful than nature
80,000 measurements were taken by interdisciplinary working groups from Germany, Austria, Switzerland, and the Netherlands. In more than 500 test plots, they planted varying numbers of plant species, from monocultures to mixtures of 60 species. In addition to plants, all other organisms occurring in the ecosystem were also examined - in and above the ground. In addition, soil scientists also investigated the material cycles for carbon, nitrogen, and nitrate, as well as the water cycle over the entire 15-year period.
"The Jena Experiment is also unique in the comprehensive study of the plants themselves in the communities of varying species richness" says UFZ scientist PD Dr. Christiane Roscher, who was still as an employee of the University of Jena the first scientific coordinator and decisively involved in the establishment of the Jena Experiment. In recent years, it becomes increasingly apparent that not species numbers alone, but the functional diversity of the plant communities is important for the positive effects of plant diversity on ecosystem processes.
Among other things, the findings led to the following conclusions:
- High-diversity meadows had a higher productivity than low-diversity meadows over the entire period of the Jena Experiment. Increased cultivation intensity via additional fertilization and more frequent mowing achieved the same effect: When a farmer promotes certain species and fertilizes, he is on average not any more successful than mother nature.
- The energy of the biomass (bioenergy content) from high-diversity meadows was significantly higher than that from low-diversity meadows, but at the same time similar to that of many of today's highly subsidized species, such as miscanthus.
- High-diversity areas achieved better carbon storage.
- The number of insects and other species was significantly higher.
- Reciprocal interactions between species such as pollination took place more frequently.
- Higher-diversity meadows transported surface water into the soil better.
- High-diversity ecosystems were more stable in the case of disruptions such as droughts or floods than low-diversity ecosystems.
Due to its breadth, the Jena Experiment proves for the very first time that a loss of biodiversity results in negative consequences for many individual components and processes in ecosystems. Hence, the loss of species worldwide not only means that a percentage of the evolutionary legacy of the earth is being irrecoverably lost, and that humans are not fulfilling their duty of care towards other creatures, but will have direct, unpleasant consequences for mankind. Among other things, the loss of species also has an effect on material cycles - which in turn have a direct influence on water supply, the source of all life.
The new spokesperson for the Jena Experiment is Professor Nico Eisenhauer from the German Centre for Integrative Biodiversity Research (iDiv) Halle-Jena-Leipzig. The expert from the Leipzig University will continue the experiment in order to investigate the underlying mechanisms of the biodiversity effects in greater detail.
Publication
Weisser WW., Roscher C., Meyer S., Ebeling A., Luo G., Allan E., Beßler H., Barnard R., Buchmann N., Buscot F., Engels C., Fischer C., Fischer M., Gessler A., Gleixner G., Halle S., Hildebrandt A., Hillebrand H., Kroon Hd., Lange M., Leimer S., Roux XL., Milcu A., Mommer L., Niklaus P., Oelmann Y., Proulx R., Roy J., Scherber C., Scherer-Lorenzen M., Scheu S., Tscharntke T., Wachendorf M., Wagg C., Weigelt A., Wilcke W., Wirth C., Schulze E-D., Schmid B. and Eisenhauer N.: Biodiversity effects on ecosystem functioning in a 15-year grassland experiment: patterns, mechanisms, and open questions, Basic and Applied Ecology 2017, Nr. 23.
DOI: https://doi.org/10.1016/j.baae.2017.06.002
Further information
Prof. Dr. Wolfgang Weisser
TUM, Chair for Terrestrial Ecology
Phone: +49 8161 71 3496
wolfgang.weisser@tum.de
PD Dr. Christiane Roscher
UFZ-Department Physiological Diversity
Phone: +49 341 9733212
christiane.roscher@ufz.de