Many of today’s fires in ponderosa pine dominated forests are burning more severely than historical ones, generating concern that understory plant communities will not recover without intervention. There are also concerns that fires will facilitate the establishment and spread of non-native species. In 2002, Colorado’s Hayman Fire burned pre-existing understory vegetation plots and provided an opportunity to address these concerns.
We remeasured these pre-existing understory vegetation plots annually from 2003 to 2007, one to five years post-fire, and again in 2012, ten years post-fire.
We found that understory vegetation communities were quite dynamic over the decade following the fire. For all fire severities, total post-fire richness (that is, the number of species in a plot) was comparable to pre-fire values during early post-fire years, and then increased. This pattern was driven by a high rate of return of pre-fire species and by the recruitment of new species, particularly native forbs. In contrast, total cover declined in the first post-fire year for all fire severities; this decline was rapidly reversed in following years as the post-fire cover of forbs and graminoids met or exceeded pre-fire levels. Burning increased non-native plant richness and cover relative to pre-fire conditions, but non-natives always comprised <11% of total richness and cover, even in plots that experienced severe fire.