Hydrological regime and climate interactively shape riparian vegetation composition along the Colorado River, Grand Canyon

Abstract

Questions: How closely do riparian plant communities track hydrological and climatic variation in space, and how do interactions among hydrological and climatic filters influence success of flow management strategies? Location: Grand Canyon, Arizona, USA. Methods:Multi-year vegetation surveys were conducted across three hydrological zones-active channel, active flood-plain and inactive flood-plain-within each of 42 sandbars that vary geographically in temperature and precipitation along a 400-km river segment. Ecological niche models were used to estimate locally optimal conditions of maximum inundation duration, elevation above daily peak flow, mean annual precipitation and mean maximum and minimum temperature for 16 of the most abundant woody and 58 of the most abundant herbaceous plant species. These estimates were used to calculate CWM environmental preferences, which were used to determine how closely vegetation preferences tracked local variation in environmental factors, and to assess interactive responses of species and communities to variation in hydrology and climate.Results: Communities closely tracked hydrological variation across zones, but less so within zones. Communities tracked variation in minimum temperature more closely than maximum temperature or precipitation. At the species level, woody plants that were more abundant in wetter hydrological conditions were also more abundant in wetter climatic conditions, and vice versa. This relationship was even stronger at the community level, where there were significant negative relationships between CWM preferences of inundation duration and temperature for both woody and herbaceous vegetation. Conclusions:The climate-hydrology linkages found in this system suggest that increasing temperatures and drought are likely to reduce the inundation tolerance of riparian vegetation within the Grand Canyon. Increasing the duration of high-flow events would likely reduce the abundance of encroaching woody vegetation but could also reduce the resilience of remaining vegetation to heatwaves and drought.The reinforcing effects of climatic and hydrological filters are likely to generally result in greater sensitivity of species composition to environmental change than if those environmental filters acted independently. These results have implications for

Associations between riparian plant morphological guilds and fluvial sediment dynamics along the regulated Colorado River in Grand Canyon

“…While the argument can be made that response–effect linkages are likely to be strong in riparian plant communities (Corenblit et al, ; Diehl et al, ), these linkages may be disrupted in environments with artificial flow regimes. Species within each of the effect guilds in this system do differ substantially in their responses to hydrology and climate (Butterfield, Palmquist, & Ralston, ), which may support a more individualistic approach to assessing response–effect relationships with respect to biotic feedbacks on sand deposition. Controlled experiments that follow vegetation responses through time would provide a more mechanistic understanding of linkages between flow responses and sedimentation effects of vegetation to complement the correlative patterns found here.…”

Fine‐grained sediment deposition alters the response of plant CSR strategies on the gravel bars of a highly regulated river

“…These modifications to disturbance and stress intensities over a large scale may further interact with local-scale gradients and exacerbate the related environmental changes, for example, by increasing the intensity of stress along the elevation gradient in riparian zones located in warm climates. As such, it has been shown that riparian plant communities respond consistently to local-scale hydrologic changes and broad-scale climatic changes (Butterfield et al 2018). This finding suggests that environmental changes related to human activity at different scales may have cumulative effects on the structure and dynamics of plant communities.…”

Flood regime alters the abiotic correlates of riparian vegetation

“…Flood events, which promote recruitment for many riparian plants (Kehr et al, 2014), can increase plant species richness and diversity relative to adjacent woodlands and forests that do not flood (Stromberg et al, 2012; Muldavin et al, 2017). However, additional factors that include both climate and groundwater dynamics also influence riparian plant species composition (Stromberg et al, 1996; Hingee et al, 2017; Butterfield et al, 2018).…”

“…Specifically, during the last several decades, potential drivers of plant composition in riparian corridors may have switched from the key historical driver of the flood regime to modern drivers that include groundwater, climate, and both land and water management (Osterkamp & Hupp, 2010; Butterfield et al, 2018; Palmquist et al, 2018). River regulation and groundwater usage has caused declines in the groundwater table in many regions (Margat & Van Der Gun, 2013).…”