Pre- and post-dam shifts in vegetation throughout the Grand Canyon: What do novel systems mean for management?

Gabrielle N. Bohlman

Abstract: Prior to the installation of the Glen Canyon dam, the Grand Canyon experienced relatively frequent, high intensity flooding that acted to scour away vegetation, creating a dynamic plant community along the riparian corridor. Current post-dam flows are heavily regulated, virtually eliminating the canyon’s natural disturbance regime. While post-dam high flow experiments have been implemented over the years for a variety of reasons, they have yet to reach the historical severity of pre-dam flood events and are too infrequent to have the same effect on vegetation as the historical flood regime. The lack of regular disturbance has led to the stabilization of substrate along the river banks and, thus, the creation of new habitats. Both native and non-native riparian vegetation have appeared to benefit from this novel system however some could argue that the lack of disturbance has favored invasive, non-native species such as Tamarix spp. over native species in the area. Pre- and post-dam vegetation communities throughout the Grand Canyon are discussed here, along with the shifting dynamic between native and non-native species, and how this dynamic, along with a newly introduced biocontrol agent is impacting current and future management of the canyon’s vegetation.