AbstractKey messageRadial growth in a group ofPinus radiataD. Don. trees varies in magnitude around the circumference and follows synchronous but arrhythmic dynamics.ContextEccentric and irregular girth growth is typically associated to specific growth responses, but it is generally assumed to be small or absent during normal development. The dynamics by which excess growth is formed are unclear.AimsThe objective of this study is to determine if growth anisotropy is a commonly occurring phenomenon without apparent mechanical imbalance of the tree and to document the temporality of differential radial growth.MethodsSix mature P. radiata trees were equipped with point dendrometers at different circumferential positions. Growth rates and periods of activity were monitored over 4 months.ResultsThe highest growth differential on a single tree exceeded a factor of two. The direction of the highest growth varied between trees. In one case, that direction switched over time. The amount of anisotropy was explained by differences in the number of growing days and growth rate entropy.ConclusionTree stem formation in fast-growing softwoods is a biological process characterized by high spatial heterogeneity and intermittent temporal activity.