Ecosystems on 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 functioning. This is particularly difficult since ecosystems are rather complex in terms of their structure and their responses to environmental changes.