Water Conservation and Habitat Improvement in Riparian Flood Plains: Evaluation of Integrated Management Methods for Multiple-Species, Multiple-Growth Form Invasive Plants
* Which integrated invasive species management methods are best for reducing water consumption, increasing water salvage, preventing reinvasion of weeds, and reducing erosion where herbaceous understory to salt cedar and/or Russian-olive is dominated by equally aggressive invasive species?
Reclamation proposes to study impacts of integrated biological, herbicidal, cultural, and mechanical control measures on aggressive, mixed growth form, perennial invasives (e.g., salt cedar, Russian-olive, Russian knapweed, perennial pepperweed, and/or Canada thistle) relative to effects on water salvage, site restoration potential, and site stabilization. Research will emphasize:
* Quantification of consumptive water use by these species via field techniques (Eddy Covariance) and literature review
* Development of restoration strategies and techniques on riparian infestation sites
* Evaluation of microclimatic, hydrologic, and invasive species response to integrated control techniques
Need and Benefit
Executive Order 13112 (Invasive Species) mandates Federal agencies to control and monitor invasive species, provide restoration of native species and habitat in ecosystems that have been invaded, and conduct research to develop technologies to prevent introduction and provide environmentally sound control of invasive species. Up to 1, 000, 000 acres of potential salt cedar (_Tamarix spp._) and Russian-olive (_Elaeagnus angustifolia_) control and restoration efforts across all land ownerships over the next 10 years are projected to occur. Of this cumulative amount, as much as 100, 000 acres may be directly impacted on Reclamation-owned or controlled property alone within the next 5 years (in light of probable federal funding for salt cedar / Russian-olive control within this time frame).
Many sites densely infested with salt cedar also exhibit concurrent, herbaceous understory infestations of equally aggressive riparian invasive species, particularly Russian knapweed (_Acroptilon repens_), perennial pepperweed (_Lepidium latifolium_), and Canada thistle (_Cirsium arvense_). These understory species often achieve equal densities and cover in a lower canopy layer beneath salt cedar and Russian-olive, further competing for water, nutrients, and solar energy with desirable native species. These aggressive, herbaceous species are rapidly becoming some of the most dominant and difficult-to-control invasive species in riparian systems, establishing co-existent with, or immediately following control of salt cedar and/or Russian-olive on many prominent river systems. In the absence of integrated control measures, these species rapidly fill vacant ecological niches created by control of salt cedar and Russian-olive.
These herbaceous invasives exhibit deep taproot and vegetatively spreading rootstock systems that have near equal ability with salt cedar and Russian-olive to access, penetrate, and deplete soil moisture reserves, shallow ground water, and return flows in the upper soil horizons. In practical terms, if the pretreatment condition is 100 percent cover and composition by co-dominant salt cedar and, for example, Russian knapweed, replacement of these by native stands of shrubs, forbs, and grasses exhibiting less overall cover (transpiration leaf area) and much higher water use efficiency (less water use per unit biomass or leaf area) will conserve water in the soil profile.
To date, little research has been conducted addressing:
* Consumptive water use of herbaceous (understory) invasive species, with associated water savings derived from control of these species
* Integrated control and restoration of sites dominated simultaneously by multiple invasive species exhibiting both woody and herbaceous composition--the root architecture and physiology of which cumulatively deplete moisture reserves in excess of salt cedar and/or Russian-olive alone.
These studies will provide Reclamation staff with functional methods to quantify water savings (via study site instrumentation for evapo-transpiration (ET) and ground water responses to treatment), and develop models for use in restoring Southwestern United States riparian sites following control of multiple, aggressive perennial invasive species (woody and herbaceous). Integrated control and restoration methods that will result from testing and development in this research will result in significant reductions (greater than 50 percent) of consumptive water use by dense stands of invasives (based on existing literature values for native species consumptive water use). This savings increases potential for habitat development, river return flows, and water storage and delivery capacity. This will enable broadened ecological applicability, strategic flexibility, and general acceptance of proven techniques over a wide range of invasive plant communities by land management and scientific communities.