Restoring riparian habitats along the Paria River
The world-famous Paria Canyon is threatened by the invasion of non-native tamarisk and Russian olive along its riparian corridor. We are working with the BLM and the Arizona Water Protection Fund to remove these invasive species from 18 miles of Paria Canyon and to monitor the recovery of native vegetation, the river’s channel form, and native wildlife species. Monitoring data will be used to inform removal efforts in the lower canyon and other sites, where infestation by these species is significantly greater.
The Paria River canyon winds along the eastern edge of the Kane and Two Mile Ranches, before meeting the Colorado River just a few miles below Lake Powell and Glen Canyon Dam. The Grand Canyon Trust grazing allotments on the Paria River fall within the Vermilion Cliffs National Monument, the Paria Canyon-Vermilion Cliffs Wilderness Area, and section of stream that is valued for potential Wild and Scenic River designation.
Riparian areas within this canyon are lush and diverse, but many of the terraces have become invaded by non-native tamarisk and Russian olive trees, and these species are becoming especially well established along the lower reaches of the river, near the confluence with the Colorado River. Tamarisk and Russian olive impact riparian ecosystems in several ways. Both of these species can alter soil nutrients and groundwater availability, and can displace native vegetation following disturbances such as flooding or drought. Tamarisk and Russian olive both spread by seed and can propagate from buried or submerged stems. The high competitive and reproductive success of tamarisk and Russian olive often results in dense stands where only these two plants will grow, reducing the diversity of other plants and wildlife species, increasing fire hazard, and altering stream hydrology.
Tamarisk and Russian olive were intentionally planted in the Paria River watershed in the late 19th Century to stabilize stream banks, and their spread was enabled by changes in climate, by on- and off-site grazing activities, and by their ability to outcompete native species. The stress of on-site grazing has been eliminated (grazing ceased in this allotment in 1999), and we believe that this bodes well for the restoration potential for this area. Since natural streamflow and sediment processes are relatively intact, there is a high likelihood of success in reestablishing native riparian species in places that were formerly dominated by invasives. A diverse native riparian community still exists within the allotment, particularly in the most upstream sections, and active recruitment of native species is occurring in the floodplain.
The Paria River is one of the largest, and most important tributaries of the Colorado River below Glen Canyon Dam. Removing invasive species is a critical step in maintaining the ecological integrity of the greater lower Colorado River System. The Paria River is a key source of sediment input into the Colorado River, accounting for over half of the sediment inputs into Marble Canyon, upstream of the Little Colorado River. Sediment is a critical resource for beach-building and endangered humpback chub spawning habitat in the Colorado River. In addition to its sediment contribution, the Paria River is also one of the largest sources of Russian olive seed into the Grand Canyon. Thus, the benefits of removing these non-natives may extend well beyond Paria Canyon, and into peripheral ecosystems.
Following the baseline assessment, we mapped Tamarisk and Russian olive along a 38-mile stretch of Paria Canyon, from just upstream of the Grand Canyon Trust grazing allotments to the confluence with the Colorado River. This initial effort has allowed us to assess the extent, distribution, and magnitude of invaded areas and to develop appropriate restoration plans, goals, and timelines.
In 2007, we worked with the BLM to develop an Environmental Assessment that would allow us to remove tamarisk and Russian olive from the uppermost 17-mile section of Paria River grazing allotment. In fall of 2007, the Environmental Assessment was completed and we received funding from the Arizona Water Protection Fund to initiate this first phase of tamarisk and Russian olive removal on the Paria River. This section of the Paria River contains a diverse riparian community, especially as compared to the lower sections of the stream where tamarisk and Russian olive are the dominant species. The purpose of this project is to restore and preserve natural conditions in the Paria River Canyon by decreasing the negative impacts of tamarisk and Russian olive and to enhance wildlife habitat by protecting and restoring native riparian vegetation. Additionally, we strive to engage, educate, and involve the public and volunteers in the riparian conservation and restoration issues that exist in the arid Southwest.
We anticipate that this project will require approximately 11,000 volunteer hours over the course of five years. Beginning in fall of 2008, tamarisk and Russian olive will be removed using hand tools and stumps will be treated with a selective herbicide to prevent regrowth. We have developed a comprehensive monitoring plan that will allow us to track changes in floodplain dynamics, vegetation, and wildlife habitat associated with invasive species removals. Monitoring will occur throughout the 5-year duration of the project and for 15+ years into the future.
Monitoring data will be used to inform removal efforts in the lower canyon, where infestation by these species is significantly greater. We have developed a partnership with the BLM Vermilion Cliffs National Monument to complete this work. The BLM administrates the Paria River allotment, and have facilitated NEPA clearance for the project, and will continually play a role in project implementation and monitoring.
We are continuing to pursue collaborations with the management agencies responsible for portions of the Paria River watershed that extend beyond the boundaries of the Kane Ranch in preparation for future work in these areas. We anticipate that Phase II of the project will involve removing tamarisk and Russian olive from the lowest 20 miles of the Paria River. This will be a challenging endeavor, given that these are the dominant riparian tree species in the lowest portion of the watershed. We intend to proceed with caution and use monitoring data from Phase I of the project to help inform future work in the canyon. This adaptive management approach will key in on the success of invasive species removals in Phase I, and the effects of these removals on floodplain dynamics. Natural floodplain dynamics may actually reduce riparian productivity and wildlife habitat, relative to the current state in which stabilized stream banks and wide floodplains are occupied by invasive species. The broader implications of invasive species removals to wildlife and recreation will need to be continually evaluated as restoration work proceeds.