Long-term plant community responses to resource objective wildfires in montane coniferous forests of Grand Canyon National Park, USA

Interest in use of naturally ignited wildland fires managed to meet multiple resource objectives (resource objective wildfire) is increasing among U.S. public forest managers; however, only a limited number of studies have examined this approach for conserving or restoring understory plant diversity, productivity, and community structure. We analyzed understory community changes two and twelve years after resource objective fire, using permanent sample plots in three montane contrasting forest types in Grand Canyon National Park, AZ. Our findings indicated that species composition in the pine-oak forest rebounded to be similar to that observed before the fire, but plant cover did not recover to pre-fire levels by the twelfth year post-fire. Plant cover showed mixed results post-fire in mixed-conifer and spruce-fir forests, and species composition was still characterized by ruderal species twelve years later. Patterns observed in this study likely reflect interacting factors of burn severity, periodic drought, large ungulate herbivory, and inherent site variability. Other than cheatgrass (Bromus tectorum), we found no non-native species occurring with high frequency. Continued monitoring with increased frequency and intensity could lead to better understanding of long-term changes in these forests after resource objective fire, and enhance our understanding of important drivers of variation including interactions of climate, burn severity and herbivory by large ungulates.

Automated summary

Interest in using naturally ignited wildfires for resource objectives is increasing among U.S. public forest managers. This study found that species composition in pine-oak forests rebounded after the fire, but plant cover did not fully recover even 12 years later. Mixed-conifer and spruce-fir forests showed mixed results in plant cover and species composition. Non-native species were not found except for cheatgrass.