Nearly 40,000 acres of land preserved on the historic Irvine Ranch have been designated as a Natural Landmark. This land contains important natural habitats, sensitive species, such as the California Gnatcatcher and Coastal Cactus Wren, and unusual geological formations. It is home to countless plants and animals as well as rocks and fossils, chronicling back nearly 80 million years.
However, many natural areas in our modern world need management to keep them wild and beautiful. In southern California in particular, threats such as increased fire frequency, invasive species, overuse, and a large surrounding urban population have all impacted our Natural Landmarks. As a result, over 18,000 acres of land are considered highly degraded and in need of restoration.
IRC takes a landscape-scale approach to habitat restoration, recognizing the interconnected nature of the various habitats. The goal is always to create a highly functional, diverse and resilient ecosystem, rather than an isolated project that is not valuable to the surrounding ecosystems. The combination of successful habitat restoration implementation and long-term maintenance should ideally result in improved habitat connectivity, biodiversity, and resilience to disturbance throughout the preserve areas. Let’s take a look back at some area-specific restoration efforts that occurred throughout 2018.
City of Irvine: Bommer Canyon
Bommer Canyon in the City of Irvine currently has 14 acres of active habitat restoration, including the 1.5-acre East Fork Restoration Site which was planted with a variety of shrub species in January 2018. Within these restoration sites IRC staff focus on irrigation and the removal of invasive plants, such as Russian thistle (Salsola tragus), to provide conditions that will allow for the ecological restoration of natural habitat.
Work also began on a new 2.4-acre passive restoration site near the East Fork Restoration Site in 2018. Thatch was removed from the vicinity of existing shrubs, which should provide space for new seedling recruitment.
As part of the Conservancy’s ongoing compliance with the City of Irvine’s Integrated Pest Management (IPM) policy, experimental plots were established adjacent to the East Fork Restoration Site in July to study the effect of a site preparation technique called “solarization,” which involves irrigating the soil and covering it with clear plastic for six to eight weeks. Theoretically, the combination of high temperatures and humidity in the top soil layer is lethal to weed seeds. However, there are concerns with this approach, including the fact that it is labor and resource intensive. Scaling it to the landscape scale may be challenging and expensive, and it may kill native plants and animals in addition to the targeted invasive weed seeds. The Conservancy will monitor the effectiveness and impacts of this approach.
IRC staff has begun hosting monthly Bommer Canyon habitat restoration stewardship programming. These community programs seek to harness the public interest in habitat restoration work at Bommer Canyon and will provide an opportunity for participants to learn more about ecological restoration and its role in management of the City of Irvine’s Open Space Preserve.
City of Newport Beach: Water-Wise Habitat Restoration Buck Gully
In 2013, 1.5 acres of non-native ice plant was removed from a portion of the Buck Gully Reserve and the site is being restored with native vegetation. IRC has continued maintaining the site over the past year by removing non-native weeds, including Russian thistle (Salsola tragus), from within and around the project area. Plant species to be planted this winter were started in the nursery at our Native Seed Farm, and First Friday public stewardships continued to be dedicated to the habitat restoration site as well as to adjacent habitat.
OC Parks: West Loma Ridge
In partnership with OC Parks, the Irvine Ranch Conservancy conducts habitat restoration and enhancement activities on a consistent minimum of 30 acres (for sites less than five years old) and 20 acres (for sites older than five years) within the West Loma Ridge habitat restoration area. This area has an ongoing weed control program. In north-facing habitat restoration sites there has been a focus on removing Russian thistle. Conservancy staff also conducted a survey sweep of all active habitat restoration sites for a limited set of targeted invasive plants. Horehound (Marrubium vulgare) was the only targeted invasive species found (and subsequently controlled) in this survey.
Field crews water planted areas in the habitat restoration sites using the Conservancy’s specialized watering equipment. Grass and shrub plugs planted in January 2018 are successfully establishing in these areas.
Planning and pre-project implementation are currently underway for the new 9.6-acre ridgeline habitat restoration site on the east side of the 241-toll road. This site will be mowed and raked clean in advance of two years of continued site preparation. Weed control will continue in restoration areas west of the 241-toll road.
OCTA Measure M2 Environmental Mitigation Program – Bee Flat Canyon
Orange County Transit Authority (OCTA) is funding 80 acres of planned and ongoing habitat restoration within the 293-acre Bee Flat Canyon sub watershed area. Conservancy staff continue ongoing efforts to prevent weeds from setting seed, including Russian thistle, the cover of which seems to be declining compared to previous years. The other priority this past year was removing excessive accumulations of invasive annual grass thatch that would suppress the growth of native bunchgrasses and prevent the establishment of native wildflowers. Raking thatch has the additional benefit of roughening the soil surface and improving the germination success of wildflower seeds.
Grasslands continued to be a focus for the restoration team. Heavy thatch is mowed to expose bare ground, then raked into windrows. Seed chaff from the Conservancy’s Native Seed Farm, which contains a significant amount of native seed, is then spread in the bare areas. This is a cost-effective way of establishing native plants.
Coastal sage scrub areas within the restoration area are surveyed for weeds, which are subsequently removed. Staff then use supplemental seeding during the rainy season to establish native plants in areas with lower native cover.
OCTA Measure M2 Environmental Mitigation Program – Silverado Creek
OCTA is also funding over 40 acres of habitat restoration within the Silverado Creek watershed. IRC staff focus on the maintenance of planted and seeded areas in the Silverado Creek habitat restoration site, as well as targeted invasive control of fountain grass (Pennisetum setaceum), summer mustard (Hirschfeldia incana), smilo grass (Stipa miliacea), Russian thistle, and horsetail (Conyza spp.). Field crews water planted areas in the habitat restoration sites using the Conservancy’s specialized watering equipment.
OCTA Measure M2 Environmental Mitigation Program – West Loma Ridge
In addition to the ongoing habitat restoration work being funded by OC Parks, OCTA is funding over 76 acres of habitat restoration in the West Loma Ridge area. Similar to other restoration sites, IRC staff have been focused on maintaining the planted and seeded areas within the West Loma Ridge habitat restoration site. This includes targeted invasive plant removal which has recently focused on populations of fennel (Foeniculum vulgare) and artichoke thistle (Cynara cardunculus). Maintenance also includes watering planted areas in the restoration sites using the Conservancy’s specialized watering equipment.
Planning and site preparation continue for 18 acres of new sites within the West Loma Ridge habitat restoration area, including mustard thatch removal. An additional 12 acres will be seeded in the coming months using either a tractor or by hand.
OC Waste and Recycling Mitigation – Agua Chinon Canyon
Orange County Waste and Recycling is funding 15 acres of habitat restoration work in the Agua Chinon Canyon area. This site is currently in the ‘maintenance’ phase of habitat restoration, focusing on invasive plant control, including Russian thistle (Salsola tragus) and summer mustard (Hirschfeldia incana), and maintaining oak tree seedlings. However, weeds are sparse in this habitat restoration area due to the successful establishment of dense and diverse native cover. Most of these weeds have appeared on the parts of the site that are directly adjacent to the road, suggesting that the seeds may be coming in from outside the area. IRC staff maintains oak tree seedlings in this area by carefully monitoring and hand watering plants affected by stress, such as extreme heat.
Conservancy staff recently removed tree tobacco (Nicotiana glauca) from several highly inaccessible canyons in the headwaters of Agua Chinon Canyon that had not previously been surveyed. The trees were cut down and stump-treated, and flowers or seeds were collected and removed, thus removing a source of seeds that were being dispersed to downstream portions of the wash. Some tamarisk trees (Tamarix sp.) were also removed.
Ecological restoration is an effective way to return native wildlife and plant species to areas degraded by increased fire frequency, invasive species, and overuse. For more details on activities offered on the Irvine Ranch Natural Landmarks, including ecological restoration and stewardship, and to learn more about how you can give back to the lands, visit www.LetsGoOutside.org. Think of the pride you will enjoy when you see native plants thriving over the coming years that you directly helped!