On the mechanism of thermal self-regulation of trees: a kind of homeothermic observation

TL;DR

This paper investigates how trees regulate their temperature through mechanisms involving both canopies and trunks, highlighting the importance of trunk regulation and groundwater uptake in urban thermal management.

Contribution

It introduces new quantitative measurements of tree trunk temperature regulation and suggests a self-regulatory mechanism involving groundwater uptake, expanding understanding beyond canopy shading.

Findings

Tree trunks contribute to thermal regulation alongside canopies.

Groundwater uptake may be a self-regulatory mechanism for trees.

Tree thermal regulation has implications for urban planning.

Abstract

What is certain is that surface temperatures around the globe vary considerably, regardless of the time scales or underlying causes. Since 1850, we have observed an average increase in global surface temperature anomalies of 1.2$^{\circ}$ and a median increase of 0.7$^{\circ}$: this overall difference masks significant regional differences. Nearly 60\% of the world's population now lives in urban areas, where vegetation cover has been significantly reduced, despite the paradoxical fact that vegetation plays an important role in regulating the thermal environment (\textit{eg} through the shading provided by tree canopies). Continuous electrical and thermal measurements of trees in a Parisian grove (France) show and quantify that canopies are not the only protectors against heat waves; we must also consider the role of tree trunks. It is clear that these trunks probably regulate themselves, possibly by modulating the uptake of groundwater, whose geothermal stability is well established at a depth of just one meter. This quantitative observation should not be overlooked in the urban planning of our cities.