  A forest is a generalization of a tree, and here we consider the Aronszajn
and Suslin properties for forests. We focus on those forests satisfying
coherence, a local smallness property. We show that coherent Aronszajn forests
can be constructed within ZFC. We give several ways of obtaining coherent
Suslin forests by forcing, one of which generalizes the well-known argument of
Todor\v{c}evi\'{c} that a Cohen real adds a Suslin tree. Another uses a strong
combinatorial principle that plays a similar role to diamond. We show that,
starting from a large cardinal, this principle can be obtained by a forcing
that is small relative to the forest it constructs.
