#11

Substrate Enhancements and Botanical Diversity for Successful Oak Habitat Creation

Richard B. Lewis III, Psomas

Los Angeles County Public Works (Public Works) is creating 8 acres of oak woodland and sage scrub on a formerly unvegetated sediment placement site (SPS) in the San Gabriel Mountains foothills. The Santa Anita Oak Woodland Project (SAOWP) rapidly naturalized a newly graded landform as mitigation associated with reservoir sediment removal. Intensive resource inputs included 114 species of locally-harvested (subwatershed) plants/seeds, tons of salvaged coarse woody debris and placed natural snags (oak), and boulder assemblages—initiating decay/regeneration processes that would not otherwise occur for many years. The palette included hundreds of oaks of four species (two rare) via acorn planting with excellent growth/survival, and several fern species that were strategically situated in niches amongst placed debris. A total of 149 native plant species have been established including volunteer recruitment. A total of 111 native vertebrate species, 15 nesting bird species, and numerous invertebrates have been observed to date. Acorn woodpeckers have created cavities and nested in the placed snags for multiple years.

Technical studies (compaction, drainage, soils analyses) were performed to ensure site suitability for oak woodland creation. Public Works-designed spiraling drainages convey off-site inflows across the SPS to optimize storm water distribution/percolation. The soils were conditioned by incorporating a large volume of native mulch to a minimum depth of two feet via heavy machinery. Irrigation (discontinued 2018) was sparingly applied to foster drought hardiness. At the 6.5-year mark, the SAOWP has met several of the 10-year performance standards of the California Department of Fish and Wildlife.

Psomas prepared the habitat mitigation plan for Public Works; performs long-term vegetation/wildlife studies; and leads a team of landscape architects, restoration contractors, seed collectors, and plant nurseries. The SAOWP received awards from the American Council of Engineering Companies and the American Society of Civil Engineers. Project documentation is on Public Works’ website: https://dpw.lacounty.gov/wrd/Projects/SAHMP/index.cfm.