Background for E054

Time is intrinsic to the concept of succession, which has often been defined as the repeatable change in community composition through time following a disturbance (e.g., Drury and Nisbet 1973). One class of models for succession assumes a simple direct effect of time on changes in species occurrence and abundance. Differences in dispersal rates and growth rates of species are thus hypothesized to be responsible for many of the successional patterns observed in old fields and in the intertidal (e.g., Egler 1954, Connell and Slatyer 1977). Other models suggest that time-dependent changes in resource availability control succession. The role of time is thus hypothesized to be indirect, with species responding directly to resources. Christensen and Feet (1984), for example, suggested that species became more restricted in their distribution with time, due to competitive displacement from areas where they were less efficient at using resources, and Tilman (1982, 1985) has suggested that changes in the relative availability of limiting resources, in particular nitrogen and light, drive changes in species composition during succession.

E054 is a study of limiting soil resources and vegetation in a chronosequence of more than 20 old fields, with time since abandonment spanning several decades. The objectives are both to document successional patterns in vegetation and soils, and to compare field age and soil nitrogen as predictors of successional changes in vegetation. The study can examine how plant species richness and species composition changes with field age over time, and whether these can be predicted.  Also, the correlation of species richness and composition with soil nitrogen can be studied.