Anticipating land surface change

Abstract

The interplay of human actions and natural processes over varied spatial and temporal scales can result in abrupt transitions between contrasting land surface states. Understanding these transitions is a key goal of sustainability science because they can represent abrupt losses of natural capital. This paper recognizes flickering between alternate land surface states in advance of threshold change and critical slowing down in advance of both threshold changes and noncritical transformation. The early warning signals we observe are rises in autocorrelation, variance, and skewness within millimeterresolution thickness measurements of tephra layers deposited in A. D. 2010 and A.D. 2011. These signals reflect changing patterns of surface vegetation, which are known to provide early warning signals of critical transformations. They were observed toward migrating soil erosion fronts, cryoturbation limits, and expanding deflation zones, thus providing potential early warning signals of land surface change. The record of the spatial patterning of vegetation contained in contemporary tephra layers shows how proximity to land surface change could be assessed in the widespread regions affected by shallow layers of volcanic fallout (those that can be subsumed within the existing vegetation cover). This insight shows how we could use tephra layers in the stratigraphic record to identify "near misses," close encounters with thresholds that did not lead to tipping points, and thus provide additional tools for archaeology, sustainability science, and contemporary land management.bifurcations | geomorphology | Iceland | resilience | tephrochronology

Cryptotephras: the revolution in correlation and precision dating

“…Although features of post‐depositional processes can be catastrophic for those searching for isochrons, there is also much to be gained from adopting the ‘total tephrochronology’ approach of Dugmore and Newton (). To date, this approach has been applied to visible tephras in proximal settings, giving considerable insight into landscape development, archaeological change and geomorphological processes such as cryoturbation and soil erosion (Streeter and Dugmore, ,). A multitude of stratigraphic sections, including those that are poorly developed, are required to optimize this large‐scale approach.…”

European Neolithic societies showed early warning signals of population collapse

“…Key themes include accounting for complexity and multicausality in instances of collapse, modeling, and predicting both short-and long-term environmental change and the importance of historical and archaeological case studies. Although significant progress has been made in measuring ecosystem resilience and predicting collapse (2), quantifying the resilience of human societies presents a major challenge for social science research (3,4). Further, the use of archaeological data and EWS methods to predict known periods of collapse in ancient human societies (i.e., retrodiction) (5) remains largely unexplored.…”

Impact of small-scale vegetation structure on tephra layer preservation

“…Data from the Fm site support previous research that suggested tephra layers may record ecological resilience at the time of deposition. Streeter and Dugmore surveyed the G2011 tephra in eroded and vegetated areas either side of an active erosion front and observed marked differences in the variability of layer thickness21. They interpreted these differences in tephra layer morphology as indicators of ecological resilience and posited that as an external driver (e.g.…”

“…Although a few high-resolution measurements of tephra layer morphology have been taken before21, to our knowledge, this is the first tephra layer survey to make measurements at centimetre intervals over such long distances (tens of metres). Given the large number of samples collected, we are confident that our estimates of mean thickness closely approximate the true mean.…”