ABSTRACT
An understanding of successional processes is essential to land reconstruction, which can also be viewed as an attempt to hasten the rate of succession to a late seral stage. Where restoration, or a return to the predisturbance ecosystem is the goal, promoting succession may be especially important.
The assumption is usually made that natural succession will result in a predisturbance state. Three pictoral models are presented to illustrate that succession may result in different rates, patterns, and trajectories, depending on the initial as well as later seral conditions. These are illustrated with examples from the literature and from my research in sagebrush grassland. According to the models, different rates and patterns will eventually result in a predisturbance vegetation, while a different trajectory will result in a system with different species composition. The discussion will focus on different trajectories that are caused by loss of topsoil, introduction of nonindigenous plant species, and absence of mycorrhizal fungi. Where initial conditions alter the trajectory of succession restoration of the predisturbance system may not be possible, although reclamation or rehabilitation may be viable goals.
Because successional studies are always time-limited, it is often not possible to determine whether a site conforms to the model of rate, pattern or succession. For the purposes of restoration, a site that shows deviation from the desired course of succession, whether because of 90rate, pattern, or especially trajectory, will require special effort to establish and maintain a desirable community.
