Assessing fire impacts to a spring-fed riparian ecosystem during a dry climate cycle in Grand Canyon National Park, USA

Recent threats to long term functionality of springs and their dependent ecosystems throughout the Grand Canyon ecoregion have surfaced as the current climate cycle continues to shift seasonal regimes to hotter and dryer conditions. Increasing fire disturbance is an emerging consequence. This study assessed ecosystem resilience to ongoing climate stressors, scouring disturbance, and novel fire disturbance throughout ~20,000 meters² of a burned spring-fed riparian ecosystem in Grand Canyon National Park for one year following the fire. Findings highlighted complex internal relationships between parameters of hydrology, geology, geomorphology, and vegetation composition that influenced ecosystem recovery to disturbances and climate stressors on a reach-scale basis. Temporally dry stream reaches were less resilient to changing hydrologic regimes induced by climate change and displayed low rates of vegetation regrowth during recovery from fire. Temporally wet reaches displayed higher rates of vegetation regrowth following fire, suggesting reaches more resilient to climate stressors were able to sustain higher rates vegetation recovery following novel fire disturbance. Scouring and significant alluvial erosion were identified as disturbances that caused ecosystem composition and structure changes that may increase in frequency following fire removal of channel-stabilizing root systems. Seasonal flooding regimes were identified as a critical disturbance required for Fremont cottonwood (Populus fremontii) sapling establishment, however flood intervals and climate impact to flood regimes were not quantified in this study. Overarching ecosystem changes to composition and structure were identified by the short-term removal of Fremont cottonwood from the system, the previously dominant phreatic species. Recommendations were made to better constrain long-term fire influences on resilience, and to rehabilitate heavily impacted ecosystem reaches. As fire in spring ecosystems is likely to increase throughout semi-arid regions, an interdisciplinary monitoring and response plan should be refined to guide management plans