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Second Otay Watershed Project Moves Ahead

Invasive Weed Removal at the Lawrence and Barbara Daley Preserve

Thanks to funding from SANDAG’s Transnet program, phase I of a habitat restoration project on the Daley Preserve along upper Dulzura Creek, located in the eastern portion of the Otay River watershed, will begin in early spring. In partnership with San Diego County Department of Parks & Recreation, River Partners will remove invasive plant infestations of giant reed (Arundo donax), tamarisk (Tamarix parviflora), and castor bean (Ricinus communis) on 55 acres and develop a native plant design and site management plan for the future habitat restoration work. The Daley Preserve Restoration site is located north of SR 94, east of Honey Springs Road, just west of Dulzura.

“This is an area that has been impacted heavily by wildfire. It took out a lot of native vegetation which provided an opportunity for arundo and tamarisk to take over,” says Greg Treber, River Partners’ regional director. “As a result of this infestation, the wildlife corridor that runs along the creek is now fragmented. This phase I weed control is critical for helping this area. We can now get the weeds under control while we seek funding for the native plant restoration phase.”

The California Invasive Plant Council has rated both giant reed and tamarisk as having severe ecological impacts on ecosystems, plant and animal communities, and vegetational structure. Giant reed is a vigorous, invasive perennial plant that displaces native plants and associated wildlife due to the immense stands it forms, competing with native plant species by monopolizing soil moisture and shading. Giant reed is estimated to use three times the volume of water used by native vegetation; thus, its presence in a stream or river deters both growth of native vegetation as well as water conservation efforts. The result is a reduction in habitat and food supply to wildlife, which adversely affects special status aquatic and riparian species. Giant reed is also suspected of altering hydrological regimes, reducing groundwater availability, altering channel morphology, and increasing fire hazards.

Tamarisk is associated with dramatic changes in geomorphology, groundwater availability, soil chemistry, fire frequency, and plant community composition. This species can result in the lowering of groundwater tables and an increase in soil salinities which inhibits the growth and germination of native riparian plant species. High amounts of leaf litter can increase the frequency of fire where tamarisk is dominant in cover; moreover, this species re-sprouts vigorously following fires. These effects on the ecosystem from the presence of tamarisk can result in this species dominating riparian communities.

Wildlife movement surveys of the corridors leading to and from the project site have shown that Duluzura Creek, including the tributary along Hollenbeck Canyon, is an important movement corridor for a variety of medium- and large-sized mammals. By addressing these infestations, River Partners is taking the first steps in improving ecosystem values for this reach of the Otay watershed.

The above article originally appeared in the March 2011 issue of the River Partners Journal.