ABSTRACT
The goal of this chapter is to provide an overview of the basic physical principles and phenomena that influence the mechanical behavior of trees. This overview revolves around eight biomechanical features that hold true for all trees, regardless of their habitat:
trees sustain two general categories of mechanical forces (static loads and dynamic loads);
these forces are additive (stresses as well as strains are additive);
static loads increase slowly over time as trees increase in size (therefore, tree growth patterns can compensate for these increasing loads);
dynamic loads can change dramatically over short periods of time (these loads are unpredictable and therefore potentially dangerous);
trees generally fail as a result of dynamic loads;
plant tissues resist bending more than twisting (eccentric loadings are potentially dangerous);
the young parts of woody plants (leaves and first-year twigs) are more flexible than older parts; and
belowground growth generally does not keep pace with aboveground growth (which reduces a tree’s safety factor as overall size increases).
