Changes in understory vegetation of a ponderosa pine forest in northern Arizona 30 years after a wildfire

Wildland fires can cause shifts in understory species composition and production. Many studies have examined short-term changes in understory vegetation following a wildfire; however, very few long-term studies are available. The objective of this study was to examine changes in understory (herbaceous and shrub) species composition and production since the 1972 Rattle Burn wildfire on the Coconino National Forest near Flagstaff, Arizona. Understory species composition and production were originally sampled in 1972, 1974, and 1980 and were re-sampled during July and August of 2002 and 2003 on 30 plots in each of four sites: high severity burn, low severity burn, unburned site prescribed burned in 1977, and an unburned site. Repeated measures analysis was used to test for the effects of fire and time on understory species production. The effects of fire on understory species composition were tested using multi-response permutation procedures (MRPP). A lingering effect of the Rattle Burn wildfire on the understory plant production and composition was revealed. Severely burned sites, which had the least pine basal area, may have greater understory production as compared to unburned sites up to 30 years after a wildfire. However, species composition on all sites was altered. A significant, negative relationship was found between tree basal area and understory species composition and production for 1972 and 2003.