Biodiversity does not enhance ecosystem productivity equally across all ecosystems under climate extremes. During years of extreme drought, drier grasslands showed the strongest positive effects of biodiversity on productivity.
When extreme drought strikes, drier grasslands receive the greatest productivity benefit from biodiversity. By contrast, forests did not show the same context-dependent pattern under drought, according to a new global synthesis of 75 biodiversity experiments. Researchers from YOKOHAMA National University published their results in Nature Ecology & Evolution on July 15.
Biodiversity has been studied long before it got its catchy name, though fully exploring all it entails is a never-ending process. Through other studies, it has already been established that biodiversity plays a significant role in an ecosystem's productivity. What is lesser known is where this biodiversity matters most when climate extremes are taking their toll.
"Our ultimate goal is to move away from a broad ecological insight to a practical basis for climate adaptation," said Takehiro Sasaki, professor of the Faculty of Environment and Information Sciences at YOKOHAMA National University and first author of the study.
With intense heat waves and droughts becoming more commonplace, this question becomes a crucial one in the space of climate science. A global synthesis of 75 biodiversity experiments sought to answer this question, along with whether these benefits persist, weaken or intensify under times of drought or extreme heat, and if the benefits of biodiversity apply equally to different ecosystems.
In more-arid grasslands, plant diversity had its strongest positive effect on productivity during years of extreme drought. This effect was driven mainly by stronger complementarity among species, consistent with species contributing in more functionally distinct and/or mutually supportive ways under water limitation. In less-arid grasslands, by contrast, drought was associated with stronger selection effects, indicating a greater contribution from a few highly productive species.
Forests did not show comparable context dependence under extreme drought, although this does not mean that biodiversity is unimportant in forests. Heat extremes likewise did not produce clear context-dependent changes in biodiversity effects across ecosystem types or aridity gradients. Across both grasslands and forests, soil nutrient conditions did not detectably modify biodiversity effects under either drought or heat extremes, suggesting that water limitation may become a more important constraint on productivity than soil nutrient supply as climatic stress intensifies.
The study synthesized data from 75 biodiversity experiments in grasslands and forests spanning broad climatic gradients, with experiment durations ranging from 2 to 23 years. These data were linked to long-term daily precipitation and maximum-temperature records, as well as site-level aridity and soil data. The analysis assessed whether aridity and soil nutrient conditions modified biodiversity effects under drought and heat extremes
Results show that biodiversity effects on productivity were strongest under extreme drought in drier grasslands, whereas forests show no comparable context dependence under the same conditions.
Further exploration to fully unpack the question of where biodiversity is going to make the biggest difference when climate extremes hit is necessary. Researchers hope to improve their forest evidence by increasing the duration of studies, improving more sensitive indicators of drought for forest ecosystems, in addition to testing whether the effects of biodiversity are slower to emerge in forests than in grasslands. Looking into the tree health indicators and the crown condition of forests years after extreme climatic anomalies might be better indicators of the ecosystem's health and the weight the biodiversity of the forest carries.
Another goal of this research is to make the science more predictive for use in geographical blind spots in biodiversity experiments. This type of insight would help prepare ecosystems to better adapt to a warming climate, and ideally make conservation efforts a top priority when it comes to preserving the varied environments present on this planet.
Takehiro Sasaki, affiliated with both the Graduate School of Environment and Information Science and the Institute for Multidisciplinary Sciences at YOKOHAMA National University, together with Yuki Iwachido of the Graduate School of Environment and Information Science and Nico Eisenhauer of the Institute for Multidisciplinary Sciences at YOKOHAMA National University, contributed to this research.
The Ministry of Education, Culture, Sports, Science and Technology of Japan, Tottori University, Deutsche Forschungsgemeinschaft, NSF Biodiversity on a Changing Planet Program and NSF Long-Term Ecological Research Prgroam, Consejo Nacional de Ciencia y Tecnologia, Swiss National Science Foundation, Margarete-von-Wrangell Fellowship of the Ministry of Science, Research and Arts Baden-Wurttemberg and the European Social Fund, NSF Awards, NSERC DG grant, EXCELLENTIA project, the German Research Foundation, Swedish Research Council Formas and the Agence Nationale de la Recherche made this research possible.
