Test Riparian Revegetation Methods along the Virgin River, Zion National Park

Research Task: 8327CKY.2.0
Task Manager: Pat Shafroth

The North Fork of the Virgin River, which flows through Zion National Park, was channelized in the early 1900s to protect the newly built (and now historic) road and Zion Lodge situated along the river. Wire caging filled with rocks (revetments) were installed, which stabilized and heightened the river’s banks. Although the effort has been successful in preventing flooding, channelization has had ecological repercussions. Historically, cottonwood and willow forest dominated the canyon floor, providing habitat and forage to native fauna and important aesthetic values to humans. Today, the forest is composed solely of aging trees, as natural flood processes that supported phreatophyte seedling establishment no longer occur. As a result, non-native plants are invading and dominating the understory (primarily tamarisk [Tamarix ramossisima], cheatgrass [Bromus tectorum], and ripgut brome [Bromus rigidus]). The decline of native riparian forests is a concern throughout the western United States, especially in arid environments where riparian zones support a disproportionately high percentage of the overall regional biodiversity. Zion's General Management Plan prescribes revetment removal along a 2-mile stretch of river where the most enduring and extensive revetments occur. The goal is to restore natural connectivity between the river and its floodplain, thus reinvigorating ecological processes and native biota; however, more than 5,000,000 square feet of ground will be disturbed during removal and recontouring. Without active revegetation, the disturbed area will be susceptible to soil erosion and further invasion of exotic plants. Well-designed experiments are needed to test revegetation methods along the Virgin River on a small scale prior to dechannelizing efforts.

 For more information contact Pat Shafroth