OOS 44-9
We are not there yet: What is missing from restoration efforts targeting rare species on the Sacramento River
The Sacramento River is one of the largest on-going riparian restoration efforts in the country. Restored floodplain habitats are currently distributed over 100 river miles from Red Bluff to Colusa, CA. Early restoration efforts are approaching 25 years in age and our subsequent knowledge of successful restoration design has grown. We pay particular attention to the complexities of hydrology, fluvial geomorphology, and alluvial soils to ensure successful floodplain restoration design, which is essential to protecting regional gene pools. While restoring floodplain vegetation has created habitats for diverse species, we argue that more work is necessary to ensure long-term, sustainable restoration success. Horticultural planting designs often create specific habitats for target plant and animal species with drastically declining populations associated with habitat loss. We present two case studies of targeted restoration design for rare species with federal listing status: the Valley Elderberry Longhorn Beetle (or VELB, Desmocerus californicus dimorphus) and the Yellow-billed Cuckoo (or YBCU, Coccyzus americanus) Western DSP.
Results/Conclusions
Both species require mid-successional riparian habitat, however they have very distinct habitat requirements, thus the horticultural restoration planting designs differ accordingly. Our research suggests that the physical processes that drive succession progression and define and maintaining these species habitats are arrested as the restored habitats mature beyond the point of suitability for either species. In VELB restored sites, elderberry savannas senesce while in mixed riparian forest dense growth and canopy closure reduces elderberry bush vigor and persistence as vegetation transitions from the mid to late succession. Similar results are found with YBCU where mid-successional vegetation with complex understory structure that typifies YBCU habitat transitions to closed canopy dominated forests. Though these species have very different habitat requirements, they share the same limitation to long-term habitat sustainability and thus, to their recovery success: the lack of physical processes that perpetuate multiple stages of vegetation. Historically, river processes including overbank flooding, erosion, deposition, and channel lateral migration maintained a complex and dynamic mosaic of different vegetation successional stages. This dynamism has been removed from the system, yet without the physical processes, these mid successional species will require continual habitat maintenance for recruitment. To be successful in achieving long-term restoration success and species recovery goals, and for sustaining many other floodplain species reliant on diverse, ever-changing habitats on the middle Sacramento River, there is a compelling need for collaboration and cooperation among scientists, river managers and policy makers to restore the physical river processes.