PARENT SESSION
Oral Session #85: Ecosystem Restoration in the Grand Canyon.
Presiding: S. Gloss and B. Gold
Thursday, August 8. 1:00 PM to 3:45 PM. Mohave Meeting Room, TCC.

Near-shore vegetation responses to two flow regimes on the Colorado River in Grand Canyon, National Park.

Porter, Marianne^*,1, Kearsley, Mike¹, ¹ Northern Arizona University, Flagstaff, AZ

ABSTRACT- Most large rivers in the world are regulated and 60% are fragmented for irrigation. In the American southwest riparian areas make up only 3% of the total landscape and are migration corridors known for having high biodiversity. In this study we examined the responses of near-shore native and exotic vegetation to two flow regimes (experimental steady flows in 2000 and a summer of low fluctuating flows in 2001) on the Colorado River through Grand Canyon. The 2000 experimental low steady flows were designed to create habitat and increase the food base for native endangered fishes such as humpback chub (Gila cypha). In 2001 low fluctuating flows occurred due to a low water year. Native plant colonization of newly exposed beach area increased throughout the duration of these two flow regimes, but significant mortality of extant Equisetum occurred early in the experimental flows. In addition to increased native vegetation, Tamarix seedling establishment also increased significantly. However, a four-day spike flow resulted in 60% mortality of Tamarix seedlings while having no negative effect on the densities of the newly established native vegetation. Throughout the low steady 2000 flows Tamarix established prolifically, while the low fluctuating flows of 2001 showed a reversal in dominance between Tamarix and the native vegetation. We suggest the need to manage regulated ecosystems for multiple years rather than the shorter time spans often utilized in management regimes.

KEY WORDS: experimental flow, Tamarix, Equisetum, seedling establishment