The Eck Memorial Natural Area is the largest old-growth shortleaf pine (Pinus echinata Mill.) forest in Missouri, USA. The objectives of this study were to characterize vegetation, examine historic and contemporary disturbances, and describe potential vegetation changes for this natural area. Shortleaf pine was the most important tree species at the site and had the highest single species basal area (8.1 m2 ha-1). Old-growth shortleaf pines averaged 230 years in age and ranged from approximately 120 to 325 years. Canopy gaps ( 6 years old) constituted 4% of the total area, and average expanded and actual gap sizes were 421 m2 and 210 m2, respectively. The uneven-aged structure of shortleaf pine suggests that the species has continually regenerated and recruited to the overstory despite the relatively low fire frequency of 44 years. Results of this study suggest that although canopy gaps are important in allowing understory trees to recruit to overstory positions, they are not likely the sole reason for the uneven-aged shortleaf pine structure. During the past century, pine regeneration and recruitment have decreased, possibly as a result of fire suppression. Without major changes in disturbance type and frequency, future forest composition probably will be dominated by hardwoods such as black oak (Quercus velutina Lam.), white oak (Quercus alba L.), and hickories (Carya Nutt. spp.) - species that were most successful in gap-phase replacement and regeneration. ©Natural Areas Association. Abstract reproduced by permission.