Here is the definition of various RDDs.

The relative deer density associated with a sus-
tained yield of deer for harvest (RDD I/, where the
subscript refers to the maximumsustained yield of deer for
harvest) is consistently higher than that associated
with a sustained yield of timber (RDDT, where the
subscript refers to sustained yield of timber).. The
relative deer density associated with sustaining bio-
logical diversity (RDDs, where the subscript refers to
sustaining all resources) is yet lower.-