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Tephra layers and early warning signals for critical transitions


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Society, economy and culture
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Culture & history

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This project aims to develop early warning signals for threshold-crossing events within human-occupied landscape systems. The focus is on the tipping point between surface stability and erosion and the alternative stable states of vegetated soil cover and no soil. Threshold-crossing events are common features of complex dynamic systems ranging from financial markets and medical conditions to climate and ecological systems. It is very difficult to predict threshold-crossing before it happens, but there is good evidence that early warning signals do exist. ‘Critical slowing down’ has been identified as a key underlying phenomena that develops with proximity to a threshold change or bifurcation point. Critical slowing down describes the increased time taken to return to equilibrium following disturbance and as a result there are marked increases in auto-correlation and variance. A ‘flickering’ may also occur as a system switches between two stable states. This project considers the stability of the soils that underpin ecosystems and provide an integrated record of past land use. The aim is to use form of volcanic ash (tephra) layers to determine the surface stability of landscapes and their proximity (or otherwise) to threshold-crossing events in the time between the deposition of the tephra and its incorporation within the stratigraphic record.