Comment on "Forest microclimate dynamics drive plant responses to warming".

Zellweger et al (Reports, 15 May 2020, p. 772) claimed that a microclimatic debt, mainly controlled by canopy buffering, evolved in European forest understories. However, their analysis is based on circularity, as they explained the sum of three components by one of these components. The response of the understory to the thermal environment is generally weak.