Throughout evolutionary history plant communities have adapted to seasonal forest fires, however human interaction and fire suppression has left forest communities susceptible to major burns. The Horseshoe II fire in the Chiricahua Mountains of southeastern Arizona was one such event, burning over 90,000 hectares in June and July 2011. In summer 2019, we studied how riparian vegetation varied in the Chiricahua Mountains across a range of burn intensities. We hypothesized that changes in stream vegetation would be correlated to the intensity of the burn because of the change in competition following the fire. We predicted that as the burn intensity increased, we would see an increase in angiosperm richness and grass density with a decrease in canopy cover and tree density. Four 100-meter stream sites were subdivided into ten 64 square meter plots within Pinery Canyon, North Fork Cave Creek, and East Turkey Creek. We had five points of canopy cover and four points of grass density within the plots. Tree density and species composition were recorded with angiosperm richness across all four sites.
Results/Conclusions
Angiosperm (i.e. flowering plants) richness was positively correlated with burn intensity (P=0.017). We observed trends of declining canopy cover and tree density, and increasing grass density, with increasing burn intensity, but these patterns were not statistically significant (p> 0.15). Most tree species were found across the gradient of burn intensity, but Gambel’s oak (Quercus gambelii) was a much more prominent member of the forest in the highest burn intensity sites. In summary, even 9 years after severe wildfire, we observed significant lingering effects of fire on flowering plant richness in riparian areas, with more flowering plants in more heavily burned areas, and at least some shifts in tree species composition. Future research should include larger sample sizes to increase statistical power and to better test the trends we saw between fire intensity and canopy cover, tree density, and grass density. Additionally, future research should examine how these impacts of wildfire on vegetation scale up to affect higher trophic levels.