Why trees sleep? - explanations to diurnal branch movement
Abstract Physiological processes cause movements of tree stems and branches that follow a circadian rhythm, but there is a lack of quantitative understanding of the cause-and-effect relationships. We investigated the diurnal movement of tree branches using time-series of terrestrial laser scanning measurements coupled with measurements of environmental drivers and tree water status. Our results showed that diurnal movement of branches was largely explained by leaf water status. This conclusion was supported by the significantly lower overnight branch movement in leaf-off than leaf-on conditions. Our findings conclude that alteration in leaf water status causes systematic branch movements following a diurnal rhythm. Due to lower atmospheric water demand during the nighttime, tree branches settle down analogously to sleep as the amount of water in leaves is increasing. The results indicate that quantified movement of tree branches could help us to further monitor and understand the water relations of tree communities.
