Trabuco Creek Habitat Restoration

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OCWR Trabuco Creek Habitat Restoration Project

at O’Neill Regional Park

Background

This 51-acre restoration and habitat enhancement project is sponsored by Orange County Waste and Recycling (OCWR) and is mitigation for habitat impacts associated with the Prima Deshecha Landfill Zone 4 Expansion Project in southern Orange County. The site was selected in cooperation with Orange County Parks staff familiar with O’Neill Park and Trabuco Creek habitats. Project plans were approved by the US Army Corps of Engineers, California Department of Fish and Wildlife, and the Regional Water Quality Control Board. OCWR has contracted with the Irvine Ranch Conservancy (IRC) to implement and monitor this project for several years.

Existing habitats include sycamore - alder and willow riparian forests near the main creek. Sycamore and coast live oak woodlands and savannah occur on higher banks and terraces. The Trabuco Creek watershed has been severely invaded by giant reed (Arundo donax), a non-native, bamboo-like grass that has significantly altered the hydrology and, in many places, completely displaced native vegetation and stream flow. As part of a regional planning effort, nearly all stands of giant reed upstream of this site were previously removed.

Implementation

The project includes the following activities and timelines:

• Obtaining Plant Materials: In 2021 and 2022, seed from 48 species of native trees, shrubs, grasses, and wildflowers was collected. All these species are characteristic of riparian and near-riparian habitats of Trabuco Creek. In addition to O’Neill Park, collection sites also included Caspers Wilderness Park and Peters Canyon Regional Park. Seed of some species will be propagated in nurseries to produce the desired numbers of container plants; seed of other species will be sowed at the IRC Seed Farm in Irvine to produce the necessary bulk volume of seed.
• Removing Giant Reed: In October 2021, dense stands of giant reed were masticated in place and reduced to fine mulch. Where giant reed was intermixed with native species, crews cut the stalks by hand, and piled them outside the floodplain for mastication. Regrowth was mowed repeatedly in 2022 to weaken the plants, which were then spot sprayed with an herbicide in August 2022. In areas along trails, giant reed roots were manually grubbed from the soil.
• Managing Secondary Weeds: Other weeds that germinated in the footprint of the former giant reed groves were mowed or manually removed. Palm trees, eucalyptus, and other woody non-native trees and shrubs were cut beginning in August 2022.
• Restoring Creek Hydrology: The massive rhizomes of giant reed created an “armoring” effect on the Trabuco Creek channel, which can prevent water from reaching the floodplain during flood events. Giant reed also causes sediment to pile up along the channel edges, often blocking secondary channels of this formerly braided river system. Restoration of hydrologic function is necessary to ensure renewal of the riparian forest.  In Fall 2022, giant reed root balls will be extracted and removed from the site. Limited re-contouring will be conducted to re-connect secondary and main channels.
• Reintroducing Native Vegetation: By spring 2024 and 2025, as the abundance of non-native vegetation decreases to a manageable level, gaps in the native vegetation will be planted and seeded. Frequent maintenance will be needed for five years to ensure establishment. Over 300 sycamore trees will be planted.
• Protecting Wildlife: Project activities are timed to occur outside the nesting season whenever possible. Nesting bird surveys are conducted each spring, prior to the main surge in maintenance activity. Project staff trained in ornithological surveys re-check sites each day before commencing work.
• Creating Wetland Habitat: The project site is contiguous with a golf course that discharges water into an oak woodland habitat. These “nuisance flows” have damaged that habitat, promoting invasive weeds, and complicating road maintenance. This component of the project involves diverting flow away from oak trees and into a constructed basin, which will be planted with wetland vegetation to provide additional wildlife habitat.
• Monitoring: Project success is evaluated based on field measurements of vegetation composition, complexity of vegetation structure, and hydrologic and geomorphic indicators. OCWR submits annual reports to all regulatory agency stakeholders. Successful project completion requires concurrence from all these parties.

Long-term Management

Upon completion of this project, OCWR will provide a long-term endowment to cover all on-going maintenance needs of the restored habitat. Anticipated needs are covered in a resource agency-approved Long-Term Protection and Management Plan (LTPMP). Close coordination of the work with Orange County Parks staff ensures that all management needs are considered.

Before Giant Reed Removal

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After Giant Reed Removal

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Map of OCWR Trabuco Creek Restoration Area at O’Neill Regional Park

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