WWA-03. Ecological succession in emerging tributaries to Glen and Cataract Canyons

Abstract
Megadrought in the southwestern United States since 2000 caused precipitous declines in the amount of water stored in Lake Powell, the second largest reservoir in the nation. By late winter 2023, Lake Powell elevations dropped to their lowest levels on since the construction of Glen Canyon dam, 180 feet below full-pool elevation. Over 100,000 acres of land once inundated by Lake Powell is not a terrestrial landscape and riparian and desert ecosystems are re-establishing. From 2019 to 2022, plant surveys were conducted in areas of the lower Cataract Canyon on the Colorado River and in Glen Canyon that were once submerged by Lake Powell and terrestrial landscape age varied from 1 to 22 years. Twelve sites in three tributary canyons of Cataract Canyon were surveyed for plant species composition and cover in 2019, 2020 and 2021 and 44 sites in 10 tributary canyons were surveyed in central Glen Canyon in 2022. Sites above an elevation of 3700 feet that were not flooded by Lake Powell had greater coverage of plants, higher species richness and greater coverage of native plants compared to sites below 3700 feet that were previously flooded. Sites that were uncovered for a shorter period of time (< 3 years) generally had less cover of plants and a greater coverage of non-native plants compared to sites that were uncovered from Lake Powell for a longer period of time (5-22 years). Unique hanging garden ecosystems that grow on shaded canyon walls near seeps established in as little as five years.