Project Number: 6206-11220-004-00
Project Type: Appropriated

Start Date: Oct 14, 2004
End Date: Oct 13, 2009

Objective:
Determine how two manifestations of global change, atmospheric carbon dioxide (CO2) enrichment and reduced precipitation during summer, interact with regionally important differences in soil type to affect plant production and other components of the carbon (C) cycle on tallgrass prairie. Determine how history of cultivation and density and biomass of invasive woody plants affects the vertical distribution and sizes of pools of organic C in mesic grasslands. Determine whether climate change (temperature, precipitation) effects on net ecosystem exchange of C (NEE) from western rangelands may creditably be predicted from the response of NEE to seasonal and inter-annual variation in temperature and precipitation. Develop classical biological control agents for non-native weeds that have invaded western rangelands as directed by NPS. Continue research on saltcedar (Tamarix spp.) to develop the leaf beetle, Diorhabda elongata from the Mediterranean area, to control effectively saltcedars in the U.S. south of the 37th parallel, to include release methodologies, reducing mortality from biotic and abiotic factors, determining rate of spread and degree of control obtained in different ecosystems, and the need for and testing of additional agents from the Old World, and the improvement of native plant and wildlife communities and water supplies. Begin discovery, testing and release of natural enemies from the Old World for control of Russian olive (Elaeagnus angustifolia), giant reed (Arundo donax), African rue (Peganum harmala), camelthorn (Alhagi), and other invasive weeds as directed by NPS.

Approach:
Expose vegetated monoliths of three soil types to a continuous gradient in atmospheric carbon dioxide ranging from low levels of the pre-industrial period to elevated concentrations predicted within the century. Measure plant carbon and changes in soil organic carbon content on never-plowed tallgrass prairie and on four previously cultivated grassland sites following 15 years with different densities of the shrub honey mesquite. Use continuous measurements of carbon dioxide fluxes at each of eight rangeland sites in the western U.S. to quantify relationships between net ecosystem exchange of carbon and precipitation and temperature at seasonal and inter-annual scales. Identify and evaluate candidate biological control agents in Europe and Asia through exploration in collaboration with ARS foreign labs in Montpellier and Beijing and cooperators in Israel, Turkmenistan, Kazakhstan, Turkey, and China; conduct host-range and biological testing at foreign locations and in quarantine at Temple, TX. Develop methodologies for efficient releases and establishment in the field, and for determining and avoiding or mediating the factors that limit control; monitor effectiveness of approved foreign insects in cooperation with colleagues in western states; assess long-term impacts of declining weed densities on population dynamics of native riparian and rangeland communities.