Where Are the Tall Cottonwoods?
 
Melissa Stamp1*, Paula Trater2, and Maureen Wilson3
 
1Utah Reclamation Mitigation and Conservation Commission, Salt Lake City, UT, USA; mstamp@usbr.gov
2Utah Reclamation Mitigation and Conservation Commission, Salt Lake City, UT, USA; ptrater@usbr.gov
3Utah Reclamation Mitigation and Conservation Commission, Salt Lake City, UT, USA; mwilson@usbr.gov
 
 
This case study explores the challenge of establishing a mature cottonwood forest on a restored floodplain corridor below Jordanelle Dam in northern Utah. Between 1999 and 2008, the Provo River Restoration Project (PRRP) reconstructed river meanders and a broad floodplain along a 12-mile stretch of the previously diked and channelized middle Provo River. When the project was planned, it was expected that the reconstructed floodplain would experience regular overbank flooding that would result in natural cottonwood regeneration and the development of extensive riparian woodland habitat with diverse structure and a mix of age classes. However, qualitative observations by URMCC staff and partners have identified concerns regarding natural cottonwood regeneration and survival rates. A large portion of the mature cottonwood trees currently present along the middle Provo River are found along the old river channel dikes and established in the 1940s-1950s. Many of these trees have recently died, and those that remain are reaching the end of their natural lifespan. Although many cottonwood seedlings initially established along the restored river channel shortly after PRRP construction, it appears that few of these have survived to mature into tall 10 to 20-year old trees.
 
Factors affecting cottonwood recruitment success include herbivory and flooding by beavers, lack of flow releases large enough to overtop the river banks and create suitable germination sites, overly-rapid flow recession rates, competition from invasive reed canary grass, and possible lack of adequate seed sources. As an initial step in investigating the issue of cottonwood recruitment, URMCC undertook some limited monitoring work in 2017. This study describes this monitoring effort and discusses adaptive management techniques being explored to promote cottonwood tree survival.