  Heat propagation in quasi-one dimensional materials (Q1DMs) often appears
paradoxical. While an isolated Q1DM, such as a nanowire, carbon nanotube, or
polymer, can exhibit a high thermal conductivity \k{appa}, forests of the same
materials show a reduction in \k{appa}. Here, the complex structures of these
assemblies have hindered the emergence of a clear molecular picture of this
intriguing phenomenon. We combine multiscale (coarse-grained) simulation with
the concepts known from polymer physics and thermal transport to unveil a
generic (microscopic) picture of \k{appa} reduction in molecular forests. We
show that a delicate balance between the bond orientations, the persistence
length of the Q1DM and the flexural vibrations govern the knock-down of
\k{appa}.
