Mixed-severity fire has long been a keystone ecological process in ponderosa pine – Douglas-fir forests of the Colorado Front Range. However, many of today’s fires in these forests are burning more severely than historical ones, and there are concerns that understory plant communities will not recover following fire without intervention. There are also concerns that fires will facilitate the establishment and spread of non-native plants.
In 2002, Colorado’s Hayman Fire burned research plots used to sample understory plant communities, providing an opportunity to address these concerns. We remeasured these plots annually from 2003 to 2007, one to five years post-fire, and again in 2012, ten years post-fire. We found that understory plant communities were quite dynamic over the decade following the fire. Burning promoted diverse and productive native understory communities, even in severely burned areas, suggesting that concerns may be unwarranted.
For all fire severities, total post-fire richness (i.e., the number of species in a plot) was comparable to total pre-fire richness 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.