We analyzed the structure and spatial temporal changes of a population of Echinacea pallida in the Tall Grass
Prairie Preserve of Oklahoma. Plants were classified into different categories based on total leaf length and transition
probabilities for three periods (1997-1998, 1998-1999, 1999-2000) and were used to determine temporal changes.
The analysis of transition probabilities among different size classes for the three periods allowed us to discriminate the
transition probabilities matrices. A univariate spatial analysis of individuals showed significant aggregation for most
distances greater than 40 cm; from 0 to 40 cm the spatial distribution of stems did not differ (p>0.05) from a random
distribution. Aggregation increased from year 1 to year 4 of the study period, which seems to be related to an increase in
density.Although we did not have a control site, results for both years with previous burning strongly suggest the effect of
fire in the population dynamic.