  Whereas most plants are flexible structures that undergo large deformations
under flow, another process can occur when the plant is broken by heavy
fluid-loading. We investigate here the mechanism of such possible breakage,
focusing on the flow-induced pruning that can be observed in plants or aquatic
vegetation when parts of the structure break under flow. By computation on an
actual tree geometry, a 20-yr-old walnut tree (Juglans Regia L.) and comparison
with simple models, we analyze the influence of geometrical and physical
parameters on the occurrence of branch breakage and on the successive breaking
events occurring in a tree-like structure when the flow velocity is increased.
We show that both the branching pattern and the slenderness exponent, defining
the branch taper, play a major role in the breakage scenario. We identify a
criterion for branch breakage to occur before breakage of the trunk. In that
case, we show that the successive breakage of peripheral branches allows the
plant to sustain higher flow forces. This mechanism is therefore similar to
elastic reconfiguration, and can be seen as a second strategy to overcome
critical events, possibly a widespread solution in plants and benthic
organisms.
