Projects
Mojave Desert Resource Conservation District's Invasive Non-Native Weed Control Program
The Mojave Desert Resource Conservation District (MDRCD) is a Special District operating under Division 9 of the Public Resources code. The MDRCD is responsible for developing and carrying out programs for the conservation, protection, and development of soil, water, and related plant and animal resources within the district boundaries. The MDRCD recognizes that the Mojave River is a key, vital natural resource in the Mojave Desert. This river is located in the high desert region of Southern California. It flows from the San Bernardino Mountains, inland through the Mojave Desert, to its terminus at Soda Lake. The flows in alluvial reaches of the river are naturally ephemeral and flashy, but have been greatly influenced by upstream water storage and imports, a flood control basin, levee confinement, locally high rates of groundwater withdraw, and municipal waste treatment facility discharges. This altered hydrologic regime has contributed to the establishment of nonnative plants such as Arundo (Arundo donax), Russian-olive (Elaeagnus angustifolia) and Salt Cedar (Tamarix ramosissima). The high density of these nonnative species along some reaches have further impacted the geomorphology, hydrology, and ecology of the riparian community by altering stream flow patterns and restricting channel capacity, consuming relatively large amounts of groundwater, and out-competing natives.
The MDRCD secured a grant in 2005-2006 through the State Water Resources Control Board (Proposition 13) to survey (ground truth) salt cedar, arundo, and Russian-olive within the uppermost reach (50 miles) of the Mojave River. During Fiscal Year 2006-2007 the Mojave Water Agency (MWA) provided funding to continue this mapping. From this combined funding, 16,950 acres of infestation of these targeted invasive species were mapped and recorded.
In 2008, the MDRCD, in partnership with the MWA and the USDA Natural Resources Conservation Service (NRCS), embarked on a multi-phase project to remove arundo, Russian-olive and salt cedar from areas within a 50-mile long riparian corridor along the Mojave River channel. As part of project planning, resource specialists from NRCS and MDRCD evaluated the potential impacts of the proposed project on stream function and riparian ecology. The team general assessed the potential impacts of the proposed project on locally-identified resource concerns including stream bank erosion, wind erosion, wildlife habitat, water availability and use, and flooding. The planning report developed by the NRCS/MDRCD team included a map showing critical areas within the inventoried reach, technical guidelines for evaluating other reaches of the channel, and listed approved mitigation alternatives for critical areas.
The primary methods used to kill and eradicate these invasives have been mechanical extraction/grinding, and herbicide treatment utilizing cut stump, basal bark and foliar applications. The herbicides used on the project include glyphosate, imazapyr, and triclopyr, applied under varying infestation scenarios as affected by target species, landowner preference, species phenology and preferred treatment method, and site-specific objectives relative to erosion control and stream bank projection considerations.
To date, a total of 1,780 “weed acres” of a total of 10,000 bank to bank acres of these invasive weeds have been removed or controlled. Several areas have received up to 5 retreatments. Retreatments will be needed over the next 3-5 years to suppress reemerging invasive plants.
The U.S. Department of the Interior Bureau of Reclamation through a grant with MWA published a report for our project entitled “Reclamation – Managing Water in the West.” This study was conducted to provide technical information on vegetation water usage in the Mojave River floodplain, with emphasis on salt cedar. Study analyses included 2007 and 2010 classification of native and non-native vegetation, vegetation evapotranspiration (ET) modeling, lidar elevation map development, groundwater mapping, and water evapotranspiration cost calculations.
The report concluded that there was a reduction of 797 acre-feet – which equates to a savings of $8.1 million dollars over a 3 year period. One acre foot is equal to 325,858 gallons – or the size of a football field that is one foot deep. Reductions in ET cannot be directly measured as additional water available (what comes out of your faucet) as water is used in other ways in the environment such as plants taking advantage of that water, some will be held in the soil and some on bare ground will be lost due to evapotranspiration. The entire report can be viewed at http://www.usbr.gov/lc/socal/planning.html.
By removing these voluminous weeds, especially the salt cedar, the MDRCD anticipates a restoration of native riparian habitats, the rising of groundwater levels to better support native riparian plants and the ever-increasing High Desert population, far less disastrous flooding and a lesser risk of wildfire damage.