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Ecosystems services such as biomass production are essential for humans. However, these services depend on basic ecosystem functions which are shaped by natural conditions like climate and species composition, and human interventions. A large international research team, led by the Max Planck Institute for Biogeochemistry (MPI BGC), Jena and the German Centre for Integrative Biodiversity Research (iDiv), has identified three key indicators that together summarize the integrative function of terrestrial ecosystems: 1) the capacity to maximize primary productivity; 2) the efficiency of using water; and 3) the efficiency of using carbon. The sole monitoring of these key factors will allow a description of ecosystem behaviour and an understanding of its responsiveness to climatic and environmental changes. The monitoring of these key indicators will allow a description of ecosystem function that shapes the ability to adapt, survive and thrive in response to climatic and environmental changes. The study was recently published in “Nature”.

Ecosystems on the earth’s land surface support multiple functions and services that are critical for society, like biomass production, vegetation’s efficiency of using sunlight and water, water retention and climate regulation, and ultimately food security. Climate and environmental changes as well as anthropogenic impacts are continuously threatening the provision of these functions. To understand how terrestrial ecosystems will respond to this threat, it is crucial to know which functions are essential to obtain a good representation of the ecosystems’ overall well-being and behaviour. This is particularly difficult since ecosystems are rather complex in terms of their structure and their responses to environmental changes.

 

A large international network of researchers, led by Dr Mirco Migliavacca from the MPI BGC and iDiv, tackled this question by combining multiple data streams and methods. The scientists used environmental data from global networks of ecosystem stations, combined with satellite observations, mathematical models, and statistical and causal discovery methods. The result is strikingly simple: “We were able to identify three key dimensions that allow us to summarise how ecosystems behave: the maximum realized productivity, the efficiency of using water, and the efficiency of using carbon,” says Dr Migliavacca, first author of the recent publication. This surprising finding made the team reflect on how complex ecosystems are ultimately driven by a small set of major factors just like was found, for instance, for leaf photosynthesis based on a handful of leaf traits.

“Using only these three major factors, we can explain almost 72 per cent of the variability within ecosystem functions,” he adds. “With water-use efficiency being the second major factor, our results emphasize the importance of water availability for ecosystems’ performance. This will be crucial for climate change impact considerations,” says senior author Professor Markus Reichstein, director of the Department of Biochemical Integration at the MPI BGC and iDiv.

The researchers inspected the exchange rates of carbon dioxide, water vapour, and energy at 203 monitoring stations around the world that cover a large variety of climate zones and vegetation types. For each site they calculated a set of the ecosystems’ functional properties, and further included calculations on average climate and soil water variables as well as vegetation characteristics and satellite data on vegetation biomass. “The study is also a wonderful example of how global data, when analysed across disciplines and using the latest statistical methods, can lead to new insights,” says Professor Miguel Mahecha, from the Remote Sensing Centre for Earth System Research at Leipzig University, who helped design the study.  

The three identified function groups critically depend on the structure of vegetation, that is vegetation greenness, nitrogen content of leaves, vegetation height, and biomass. This also underlines the importance of ecosystem structure, which can be shaped by disturbances and forest management in controlling ecosystem behaviour. At the same time, the water and carbon use efficiency also critically depend on climate and partly on aridity, which points at the critical role of climate change for future ecosystem functioning. “Our exploratory analysis serves as a crucial step towards developing indicators for ecosystem behaviour and ecosystem health,” summarises Professor Markus Reichstein, “adding to a comprehensive assessment of the world’s ecosystems response to climate and environmental changes.”

Original title of the publication in Nature:

“The three major axes of terrestrial ecosystem function”, DOI 10.1038/s41586-021-03939-9

www.nature.com/articles/s41586-021-03939-9