  A generalization of the coherent-noise models [M. E. J. Newman and K.
Sneppen, Phys. Rev. E{\bf54}, 6226 (1996)] is presented where the agents in the
model are subjected to a multitude of stresses, generated in a hierarchy of
different contexts. The hierarchy is realized as a Cayley-tree. Two different
ways of stress propagation in the tree are considered. In both cases, coherence
arises in large subsystems of the tree. Clear similarities between the behavior
of the tree model and of the coherent-noise model can be observed. For one of
the two methods of stress propagation, the behavior of the tree model can be
approximated very well by an ensemble of coherent-noise models, where the sizes
$k$ of the systems in the ensemble scale as $k^{-2}$. The results are found to
be independent of the tree's structure for a large class of reasonable choices.
Additionally, it is found that power-law distributed lifetimes of agents arise
even under the complete absence of correlations between the stresses the agents
feel.
