DIRECTIONALITY, CONVERGENCE, AND RATE OF CHANGE DURING EARLY SUCCESSION IN THE INLAND PAMPA, ARGENTINA

Abstract. We tested the following hypotheses forthe first five years of a grassland succession: (a) community changes are mainly directional and related to time after disturbance ratherthanto environmental fluctuations; (b) rates of succession decrease over time, and (c) plant communities in different plots converge on a similar composition within five years of succession. We tested those hypotheses using a Principal Components Analysis applied to data from four successional plots established in successive y ears in a large cropland in the Inland Pampa, Argentina. Community changes were correlated to the age of the plots, and unrelated to rainfall variability, a major environmental variable in grasslands. Successional rates were constant over the five years, probably because of the continued dominance of different annuals; we conclude that successional rates depend on the life history of the dominant species rather than on any emergent community property. We found no evidence of convergence ordivergence; we concluded that the results of successional studies may depend on the temporal and spatial scale of observation. 1990 IAVS ‐ the International Association of Vegetation Science