Radial stem growth of trees (GRO) occurs mainly during the night. Daylight hours show systematically lower growth. The columns in the figure below indicate how much of the annual growth occurred at a specific time of the day. The vertical bars show periods with highest and lowest growth activity. The patterns are species and site-specific.
The main reason for these daily patterns are limiting conditions for the biochemical growth processes from the water relations side. High transpiration during the day induces low water potentials in the entire tree and also affect the turgor conditions in the cambium. These turgor conditions in turn are determining whether and how fast cells are able to divide and elongate.
Data in 10 min resolution from Davos, Visp and Lägeren of the year 2012, all rights reserved, © Treenet.info.