Aim: Changes in dryland ecosystem functioning are threatening the well-being of human populations worldwide, and land degradation, exacerbated by climate change, contributes to biodiversity loss and puts pressures on sustainable livelihoods. Here, abrupt changes in ecosystem functioning [so-called turning points (TPs)] were detected using time series of Earth observation data. Hotspot areas of high TP occur- rence were identified, observed changes characterized and insights gained on poten- tial drivers for these changes. Location: Arid and semi-arid regions. Time period: 1982–2015. Methods: We used a time series segmentation technique (breaks for additive sea- son and trend) to detect breakpoints in rain-use efficiency as a means of analys- ing changes in ecosystem functioning. A new typology to characterize the detected changes was proposed and evaluated, at regional to local scales, for a set of case studies. Ancillary data on population and drought were used to provide insights on potential drivers of TP occurrence. Results: Turning points in ecosystem functioning were found in 13.6% (c. 2.1 × 106 km2) of global drylands. Turning point hotspots were primarily observed in North America, the Sahel, Central Asia and Australia. In North America, the majority of TPs (62.6%) were characterized by a decreasing trend in ecosystem functioning, whereas for the other regions, a positive reversal in ecosystem functioning was prevalent. Further analysis showed that: (a) both climatic and anthropogenic pressure influenced the oc- currence of TPs in North America; (b) Sahelian grasslands were primarily character- ized by drought-induced TPs; and (c) high anthropogenic pressure coincided with the occurrence of TPs in Asia and Australia. Main conclusions: By developing a new typology targeting the categorization of abrupt and gradual changes in ecosystem functioning, we detected and characterized TPs in global drylands. This TP characterization is a first crucial step towards under- standing the drivers of change and supporting better decision-making for ecosystem conservation and management in drylands.
Global-scale characterization of turning points in arid and semi- arid ecosystem functioning
Year: 2020