This paper presents a vascular plant species list for two sites that are part of a long-term study exploring the effects of varying fire intervals on forest characteristics including the abundance and composition of understory vegetation. The Chimney Spring study area is on the Fort Valley Experimental Forest near Flagstaff, AZ, and the Limestone Flats study area is on the Long Valley Experimental Forest, 90 km (56 mi) southeast of Flagstaff. Since 1976 (Chimney Spring) and 1977 (Limestone Flats), three replicates of each of seven burn intervals (1, 2, 4, 6, 8, 10 years, plus unburned) have been maintained by the USFS Pacific Southwest Research Station. Each study area encompasses approximately 40 to 48 ha (99 to 119 acres) of dense ponderosa pine (Pinus ponderosa) forest. Our plant species list was generated through systematic sampling of the understory vegetation in 2006 and 2007 as well as surveys of the entire study areas for additional species. We documented a total of 147 species, with 96 species found at Chimney Spring and 123 species at Limestone Flats. There are eight introduced species on the list, with six introduced species found at Chimney Spring and seven found at Limestone Flats. All of the exotic species we found have been intentionally introduced to North America, either directly or indirectly, and are widespread throughout the United States so their presence at these sites is not surprising. This survey will serve as baseline information for these two sites when examining future floristic changes due to continued research on fuels management and prescribed fire.