Invasive Plant Impacts, Monitoring, and Restoration 2

Friday, October 21 at 3:00-4:40 pm, Fir Room

*note alternate instance of this session – Thursday at 1pm

Session Description: Invasive plants are a major threat to native plant biodiversity in California. This session highlights cutting-edge ecological research on invasive plants and shares reports on habitat restoration projects incorporating invasive plant control.

Session Chairs: Jutta Burger and Doug Johnson (California Invasive Plant Council, Berkeley, CA, USA) 

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27.1    Planning large-scale horticultural restoration of riparian woodlands along the Alamo River in the Imperial Valley

Emma Havstad (River Partners, San Diego, CA, USA), Francis Ulep (River Partners, San Diego, CA, USA), Erin Hagen (River Partners, San Diego, CA, USA)

Located approximately 12 miles upstream of the Salton Sea, the Finney-Ramer Unit of the Imperial Wildlife Area encompasses 1,500 acres on both sides of the Alamo River in Imperial County. The primary inputs to the Alamo River are tailwater, drainwater, and spill water from the surrounding agricultural lands, with careful regulation that limits flooding and natural river processes. Saline soils, high temperatures, and low natural rainfall make recruitment and establishment of native plant communities challenging. Under these conditions, invasive salt cedar has proliferated, creating a flammable corridor in the riparian zone and promoting the further spread of monotypic stands. After thoroughly analyzing soils, hydrology, wildlife, vegetation, and water quality, River Partners has developed a restoration plan to re-establish diverse native riparian forests and mesquite bosque terraces. The future restoration will create valuable wildlife habitat, sequester carbon, and create local opportunities for recreation and employment. The project design is based on lessons learned from re-visiting a successful pilot project ten years after maintenance activities were completed and includes an adaptive management approach incorporating field trials in each project stage. This project aims to serve as a model for broad regional replication to re-establish native plant communities that are essential for wildlife recovery and have been largely lost from the region.

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27.2    Community dynamics and adaptive management in a restored coastal prairie

Eric Wrubel (Golden Gate National Recreation Area, San Francisco, CA, USA)

In 2016, the Golden Gate National Recreation Area initiated a project at Rancho Corral de Tierra in San Mateo County, to restore 5.5 acres of native coastal prairie habitat in an old field dominated by a monoculture of invasive Harding grass (Phalaris aquatica), which was encroaching on one of the last remaining populations of federally endangered Hickman’s potentilla (Potentilla hickmanii). Harding grass removal was achieved by a sequence of mowing and chemical treatments, followed by phased revegetation by container planting and direct seeding. Harding grass was reduced to maintenance levels within the first two years. However, secondary invasions of non-native annual grasses rapidly increased as Harding grass diminished. Native grass seeding was most successful in the first year, and was hampered by competition from annual grasses and bird predation in subsequent years. Adaptive methods such as shallow tilling and use of row covers increased grass establishment. Transect-based monitoring was initially used to evaluate Harding grass control across the site. We shifted to point-grid vegetation monitoring in 2019 to better detect patchy invasive grass hotspots, and map the evolving plant communities. Despite unanticipated outcomes, abundance and richness of native grasses and forbs has steadily increased each year over the course of this project as we evaluated and revised our approach.

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27.3    The removal of invasive plant species restores ectomycorrhizal fungi for native willow habitat

David C. Banuelas (University of California, Irvine, Irvine, CA, USA)

In southern California, the establishment of invasive species are responsible for the displacement of indigenous plant species. In 2020, 10 acres of invasive woodland (Schinus terebinthifolius – Brazilian pepper tree) was removed from the Big Canyon Nature Park to restore the riparian corridor with native willow habitat (Salix lasiolepis – Arroyo Willow). The goal of our research was to characterize the fungal community associated with Schinus terebinthifolius and Salix lasiolepis prior to and following restoration efforts. DNA sequencing was used to identify fungal taxa from roots and soils. For saprotrophic (decomposers) and pathogenic fungi, no significant differences were found between Schinus terebinthifolius and Salix lasiolepis. However, the relative abundance of symbiotic fungi, consisting mostly of ectomycorrhizal fungi, increased by 12% in soils that had previously been occupied by Schinus terebinthifolius. The Geopora genus was the most prevalent ectomycorrhizal species, occurring in 33% of Salix lasiolepis roots. Our results suggest the removal of Schinus terebinthifolius benefitted Salix lasiolepis by increasing the presence of ectomycorrhizal fungi in soils. Moreover, the rare ectomycorrhizal species Geopora sepulta was abundant in Salix lasiolepis roots and soils. Prior to our research, G. sepulta has only been observed on San Nicolas Island. Thus, characterizing the fungal community using DNA sequencing can reveal rare taxa that may play a crucial role in responding to restoration efforts, warranting further investigation.

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27.4    Habitat restoration at Hidden Valley Wildlife Area following long-term Arundo management

Christiana Conser (HANA Resources, Inc., Lake Forest, CA, USA)

Riverside County Regional Park & Open-Space District and HANA Resources will restore 608 acres of native habitat and remove invasive plants on 1,170 acres at the Hidden Valley Wildlife Area (HVWA). The project goals are to reduce the cover of giant reed and other invasive plants, increase native riparian and upland vegetation habitat for special-status species, decrease cowbird parasitism, and increase community stewardship. The project will benefit and improve habitat for special-status species including cactus wren (Campylorhynchus brunneicapillus), coastal California gnatcatcher (Polioptila californica californica), least Bell’s vireo (Vireo bellii pusillus), southwestern willow flycatcher (Empidonax traillii extimus), yellow warbler (Setophaga petechia), and western yellow-breasted chat (Icteria virens). The project was developed in partnership with the San Bernardino Valley Municipal Water District and Santa Ana Watershed Association. The project will be executed in five phases. Phase 1, funded by the Wildlife Conservation Board, will be completed in 2022. Phase 1 tasks include environmental compliance and development of a habitat restoration plan (HRP). Project implementation will occur in Phases 2–5. Each implementation phase will be five years in duration and the entire project will be completed within 20 years. Phase 2 is projected to start in 2022 and will consist of 207 acres of giant reed biomass removal followed by planting Mulefat Scrub. Phase 3 consists of 126 acres of Willow Riparian and Southern Cottonwood/Willow Forest planting. Phase 4 will consist of 157 acres of Riparian Scrub and Riversidean Alluvial Fan Sage Scrub planting. Phase 5 includes 120 acres of Coastal Sage Scrub/Cactus planting. Management of giant reed resprouts and seedlings will be performed throughout all phases. Targeted management of high-priority invasive plants will be performed in the restoration areas within each phase.

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27.5    Invasive species removal and habitat restoration in the lower San Dieguito River Valley

Caitlin Kreutz (Rancho Santa Fe Association, Rancho Santa Fe, CA, USA), Jonathan Appelbaum (San Dieguito River Valley Conservancy, San Diego, CA, USA), Bob Byrnes (California Native Plant Society San Diego Chapter, San Diego, CA, USA)

The San Dieguito Restoration program’s primary goal is to enhance and reestablish ecological function in the lower San Dieguito River Valley in Rancho Santa Fe, California. Invasive non-native plants are displacing native vegetation, modifying hydrologic functions including sediment transport, water use, and flood regimes. In addition to these impacts, non-native plants, particularly Eucalyptus and Arundo donax, create extreme fire-prone conditions within a riparian habitat. The goals of the project are to reduce fire risk and restore riparian habitat in the San Dieguito River Watershed through the control of invasive non-native plants and the planting of native species. The invasive plant control program conducts treatments of target plants, which include Arundo, Tamarisk, Eucalyptus, Acacia, and palms in a phased manner. This project will continue over the next 5 to 10 years depending on funding availability. This program utilizes avoidance measures and methods that have been developed with U.S. Fish and Wildlife Service on several other large watershed eradication programs. The primary method is to avoid habitat areas during active breeding of wildlife, March 15-September 15. Since the program began in 2015, approximately 140 acres of the Lower San Dieguito River have been cleared of invasive species and returned to native riparian habitat via cuttings, tree planting, and natural recruitment. What is unique here is that this part of the river is almost entirely privately owned. Through public and private partnerships we have developed relationships with landowners to gain access to their properties to accomplish this restoration project. Also, we have been extremely fortunate to have the volunteer project management for this project from dedicated CNPS volunteers, a service that would have cost thousands of dollars. Since 2015, volunteers have spent over 5,000 hours removing and treating invasive vegetation.