AN ABSTRACT OF THE DISSERTATION OF

Relatively recent increases in ponderosa pine abundance have effected unprecedented changes to ecosystem structure and function. Efforts to restore ponderosa pine systems are often focused on the manipulation of tree structure and the re-introduction of a more natural fire regime. Successful restoration should also incorporate understory components but information addressing changes in understory species is minimal for Pacific Northwest ponderosa pine forests. Moreover, state and transition models (STM) derived from the concepts of non-equilibrium ecology may be appropriate for characterizing ecosystem dynamics in modern ponderosa pine forests, however this approach has not previously been used. The focus of this research was to evaluate ecosystem dynamics within a hypothesized STM framework and to experimentally assess the existence of model components with particular emphasis on understanding understory species dynamics. The analyses of vegetation, soil, and environmental attributes measured in a eastern Oregon ponderosa pine forest indicated that increased ponderosa pine occupancy modified the under-canopy environment through alterations in light