Ackerson Meadow Restoration
The purpose of this project is to protect the remaining intact wetlands, restore lost wetland ecosystem function, and re-establish self-sustaining wetland processes in the Ackerson Meadow complex. Based on stratigraphic evaluations and radiocarbon dating, the Ackerson Meadow complex was an extensive wet meadow system with a high-water table throughout most of the growing season prior to human manipulation. Land use practices over the past 150+ years have created a large gully network that has drained 90 acres of wetlands in the meadow complex and threatens another 100 acres of wetland and wet meadow habitat. Roughly 151,000 cubic yards of soil has eroded from the meadow through the gully network. The eroding gullies have lowered the groundwater table and intercepted sheet water flows in the meadow, which has led to early-season onset of dry conditions and loss of wetland habitat and vegetation.
Action is needed to lessen the effects of the gully, specifically to raise the lowered groundwater table, return overland water movement including sheetflows, protect and re-establish extensive wetland vegetation, and halt excessive erosion and soil loss. Restoration actions will reconnect meadow floodplains with seasonal groundwater regimes that support natural wetland plant communities and enhance habitats for at-risk wildlife species, including the great gray owl (Strix nebulosa), little willow flycatcher (Empidonax traillii), and western pond turtle (Actinemys marmorata). Restoration actions will also enhance ecosystem resilience to climate change and support plant resources important to local native tribes. Yosemite National Park and the Stanislaus National Forest jointly propose to implement actions to reduce erosion and restore wetland
functionality at Ackerson and South Ackerson Meadows.
1. Protect intact wetlands from advancing gullies and headcuts and re-establish hydrologic conditions dominated by sheetflow and shallow dispersed swales.
2. Restore the extent of functional wetlands in the Ackerson Meadow complex by re-establishing sustained high-water tables and an increased proportion of wetland plants.
3. Restore high-quality habitat for at-risk wildlife species.
4. Restore native wetland vegetation communities including special status plants, culturally important plants, forage for wildlife and livestock, and remove invasive species.
5. Enhance ecosystem resilience to climate change.
6. Facilitate ecological restoration by enabling tribal tending and gathering of traditional use plant materials.
7. Provide functional grazing allotments on USFS-managed lands.
8. Preserve wilderness character by limiting activities and tools to the minimum required to restore water tables, especially in designated wilderness.
Yosemite and the Stanislaus considered several options including taking no action to restore the meadow complex. Through civic engagement and analysis several options were dismissed as not feasible. The following three action alternatives were evaluated through development of the environmental assessment (EA). The Ackerson Meadow Restoration Environmental Assessment underwent public and agency review from June 2, 2021 to July 8, 2021.
• Alternative 1 (Selected Action). Completely fill the erosion gullies to the level of existing meadow terraces to restore original topography, hydrology, and vegetation. Fill material will be generated from a combination of nearby upland hillslope soil excavations and locally generated wood chips and biochar. Approximately 151,000 cubic yards of fill will be needed. This alternative will maximize the acres of protected and restored existing and former wetlands.
• Alternative 2. Encourage sediment deposition and re-direct erosive flow energy within the erosion gullies by installing more than 350 hand-built structures from natural materials. These hand-built structures include beaver dam analogs (BDA) and function to create a stair-step sequence of ponds about 4 feet deep over the length of active channels. This treatment will require hand tools and manual labor, no fill or heavy equipment will be needed. Annual long-term maintenance of structures will be required. This alternative would not fully restore the gullies to natural meadow topography, rather it would enhance the wetland and floodplains within the gully network and eventually form an inset floodplain. This alternative would protect and restore the least acres of existing wetlands and former wetlands. The park has also considered the introduction of beavers to the meadow for restoration purposes but considers that action infeasible at this time.
• Alternative 3. Apply individual prescriptions of the fill or hand-built alternatives to specific reaches of the gullies based on depth of incision to restore meadow hydrology and reconnect with the floodplain. This hybrid alternative would use soil from the same sources as the other fill alternatives in the deeper portion of the gullies and use BDAs in the areas where the gullies are less than 3-5 feet deep. This would require less fill than the full fill option and more fill than the intermittent fill option, and it would require annual long-term maintenance of the BDA structures. This alternative would protect and restore a moderate number of existing and former wetlands.
Yosemite and Stanislaus have determined alternative 1 (complete fill option) to be the Selected Action. The Selected Action best meets the purpose and need of the project while minimizing impacts to visual, operational, natural, and cultural resources. The Selected Action will maximize the acres of protected and restored wetlands and will minimize the amount of long-term maintenance needed.
Based on the information contained in the Ackerson Meadow Environmental Assessment; the comprehensive mitigation strategy to avoid and minimize impacts; and the full consideration of scoping and EA review comments received from agencies and the public; it is the determination of the NPS and the USFS that the Selected Action is not a major federal action significantly affecting the quality of the human environment. A Finding of No Significant Impacts (FONSI) and the Determination of Non-Impairment were signed by NPS on September 21, 2021.
The restoration of Ackerson Meadow may begin as early as spring 2022, depending on funding.
The Ackerson Meadow complex makes up the largest mid-elevation meadow complex in Yosemite National Park and represents one of the region's most extensive and contiguous meadow systems. The meadow complex spans onto U.S. Forest Service (USFS) lands of the Stanislaus National Forest. While they account for only about one percent of the land cover in the entire Sierra Nevada, montane meadows and associated riparian communities provide habitat for approximately 20 percent of the 400 terrestrial vertebrate species that inhabit the Sierra Nevada.