In this study I assessed the potentials of selected, established perennial grasses to maintain site occupancy in the foothills ecosystem of the Rogue River Valley of southwest Oregon which is currently dominated by a variety of annual plants. The first evaluation compared growth curves of the perennial grasses and contrasted them to growth patterns of residual annual plants. Periods of growth varied among the perennial grasses studied. Of the perennial grasses, Idaho fescue (Festuca idahoensis), a native, and Berber orchardgrass (Dactylis glomerata var. 'Berber'), introduced, most closely emulated the growth patterns of the majority of the annual plants. Relative to the other perenial grasses tested, they initiated growth earlier, continued some growth through the winter and matured earlier. Once established, they should be able to effectively compete with the resident annuals for resources and maintain their populatiOhs. To assess the potential for competition for available moisture, the second evaluation considered timing and extent of soil moisture extraction by the perennial grasses and the resident annual community through the periods of active growth. This verified growth analysis results. Idaho fescue and Berber orchardgrass extracted moisture earlier than the other perennial grasses. Perennial grass plots and plots dominated by yellow starthistle (Centaurea solstitialis) end of season residual soil moisture levels were similar. Resident annual grasses left considerably more soil moisture. In years with an early summer drought, the earlier growing perennial grasses should be able to satisfy growth requirements and persist. An assessment was also made of the abilities of several selected established perennial grasses to resist reinvasion by resident annual plants. Earlier growing perennial grasses such as Berber orchardgrass and Idaho fescue suppressed the annuals more effectively than the later growing perennial grasses. Of the perennial grasses studied, those emulating the growth patterns of the annuals have been the Most competitive and have maintained the most vigorous stands. / Graduation date: 1990