Tree growth sensitivity to climate is temporally variable.

Despite a long history of discussion of 'non-stationarity' in dendrochronology, researchers and modellers in diverse fields commonly rely on the implicit assumption that tree growth responds to climate drivers in the same way at any given time. Synthesising recent work on drought legacies and other climate-related phenomena, we show tree growth responses to climate are temporally variable, and that abrupt variability is commonly observed in response to diverse events. Thus, we put forth a 'growth-climate sensitivity' framework for understanding temporal variability (including non-stationarity) in the sensitivity of tree growth to climate. We argue that temporal variability is ubiquitous, illustrating limits to the ways in which tree growth is often conceptualised. We present two conceptual hypotheses (homoeostatic sensitivity and dynamic sensitivity) for how tree growth sensitivity to climate varies, and evaluate the evidence for each. In doing so, we hope to motivate increased investigation of the temporal variability in tree growth through innovative disturbance or drought experiments, particularly via the inclusion of recovery treatments. Focusing on growth-climate sensitivity and its temporal variability can improve prediction of the future states and functioning of trees under climate change, and has the potential to be incorporable into predictive dynamic vegetation models.