UC Merced

Riparian floodplains and forests are simultaneously among the planet's most biodiverse and anthropogenically altered ecosystems. With 90% or more of global riparian corridors lost to development or cultivation, it is unsurprising that ecological restoration has become a multi-billion-dollar global industry. Unfortunately, many of the restoration treatment actions commonly deployed are implemented without a scientific foundation and/or lack long-term monitoring with specified success metrics. With the continued decline of global biodiversity and increasing climate volatility, a better understanding of restoration treatment outcomes is required to achieve desired long-term ecological objectives. In the absence of long-term monitoring, direct treatment comparisons, or consistent treatment methods, restoration ecologists and other decision-makers lack the fundamental tools necessary to choose the best restoration treatment. Similarly, scientists and practitioners cannot learn from failed or successful restoration treatments without long-term monitoring.In this dissertation, 40 years of restoration treatments along the Cosumnes River, CA are evaluated for a selection of ecosystem services. Chapter 1 introduces the research conducted in subsequent chapters, provides historical information about the study area, and contextualizes the objectives within a broader context. Chapter 2 assesses the geomorphic response to hydrologically reconnecting a riparian floodplain to the Cosumnes River, the largest river on the western slope of the Sierra Nevada without a major dam project. Chapter 3 details the woody species richness, diversity, and standing biomass within riparian forests. Chapter 4 documents the quantification of carbon stocks in the upper layer of soil, litter cover, and aboveground biomass in woody species across 23 different treatments, and Chapter 5 summarizes results and potential future directions. This work, conducted within the Cosumnes River Preserve, is the latest in a series of investigations that have been ongoing for more than 30 years. The dozens of restoration treatments evaluated in each chapter were consistently grouped by treatment type throughout. Treatment types include Process-based, limited intervention; Assisted, horticultural planting and other intensive restoration activities; Hybrid, a combination of process and assisted actions; and Remnant, old-growth forests that were not created with restoration actions. Results from a levee manipulation and related restoration actions in Chapter 2 include more than 25,000 m3 of sediment deposition within the original excavation site, the development of multiple sandsplays, and natural recruitment of native riparian tree species. Chapter 3 provides evidence supporting multi-benefit Process-based restoration approaches based on measurable richness and biomass following natural species establishment. Compared to the uniform species coverage of planted Assisted restoration treatment type plots, sites where flood regime reconnection has facilitated riparian floodplain functionality recruit more species and accrue more biomass. The Carbon stock quantification documented in Chapter 4 resulted in total C values of up to 1099.5 Mg ha-1 with biomass contributing the most to individual plot measurements. Biomass C stock measurements showed an average 32 Mg ha-1 increase in C present in less than a decade. Where hydrologic regimes allow, Process-based restoration approaches that restore functionality within the system allow for sediment accretion, native species recruitment, higher woody species richness, and more carbon stock accumulation. Initiatives, such as Engineering With Nature, Nature-based Solutions, and multi-benefit solutions, that utilize the ecosystem services facilitated by natural infrastructure resulting from process-based restoration can allow for disaster mitigation, ecological functionality, and resilience in surrounding communities in an increasingly volatile climate.