A resilience-based bionic interpretation of the conifer branch–stem junction integrating form, function and environmental stimulus

Branches make the tree resilient to natural hazards by building a robust, fault-tolerant structure. In conifers, branches are formed annually at the internodes, giving rise to the crown. Branches that receive sufficient sunlight contribute to photosynthesis and are maintained, whereas shaded branches under competitive conditions lose their photosynthetic function and are shed. The cellular arrangement at the branch–stem junction reflects the biological principles of growth, function, and survival strategy. The relevant literature, however, has so far tended to describe this junction as an optimised load-bearing structure designed for maximum mechanical performance, with the aim of deriving bio-inspired engineering solutions from this understanding. The authors conclude that in the observed structure, and perhaps more generally in nature, the principle at work is not optimisation but rather resilience to the environment and survival. This hypothesis is supported by the analysis of microtome images of the junction’s morphology, which has enabled an improved representation and biological understanding of the fibre arrangement of Norway spruce. This improved understanding primarily concerns the orientation and organisation of the fibres on the upper side of the branch. Through the formation of a collar and a sacrificial tissue, nature creates a structure that is mechanically below optimal performance. From this we derive that the underlying principle is not mechanical performance, but resilience and survival.