Behaviour of terrestrial ecosystems is governed by only three main factors

Ecosystems on Earth’s land surface support multiple functions and services that are critical for society, such as 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 continuously threaten 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 regarding their structure and their responses to environmental changes.

Scientists from INRAE contributed to a large international network of researchers, led by Dr. Mirco Migliavacca at Max Planck Institute for Biogeochemistry in Jena, Germany, to tackle 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 make it possible 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 in Nature. “Using only these three major factors, we can explain 71.8% of the variability within ecosystem functions”, he adds.

The researchers particularly inspected the exchange rates of carbon dioxide, water vapour, and energy at 203 world-wide monitoring stations 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 three identified function groups critically depend on the structure of vegetation, e.g. on vegetation greenness, and nitrogen content of leaves as well as vegetation height and biomass. This also underlines the importance of ecosystem structure, that 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 to the critical role of climate change for future ecosystem functioning. “Our exploratory analysis serves as a first step towards developing indicators of the whole ecosystem behaviour” says Max Planck director Prof. Markus Reichstein, “this will facilitate a more comprehensive assessment of the overall ecosystem response to climate and environmental changes.”