Specification of a Regional-National Recursive Model for IIASA/FAP's Iowa Task 2 Case Study

The major objectives of the Food and Agriculture Program (FAP) of the International Institute for Applied Systems Analysis are to evaluate the nature and dimensions of the world food situation, to identify factors affecting it, and to suggest policy alternatives at the national, regional, and global levels to alleviate current food problems and to prevent future ones. The present shortrun problems of policy are explored in FAP's Task 1, "Strategies: National Policy Models for Food and Agriculture" by means of a set of descriptive, general-equilibrium, price-endogenous national models of various countries linked in a consistent international framework. From a longer term perspective the food problem acquires added dimensions; and questions of availability of resources to produce adequate food, efficiency of techniques, and environmental consequences become important. These questions are addressed by FAP's Task 2 "Technological Transformations in Agriculture: Resource Limitations and Environmental Consequences". Quantitative knowledge of the interactions between agriculture and the environment requires a great deal of detailed information on the site-specific nature of resource inputs and on alternative land use practices. A general-equilibrium approach to such types of investigation is not empirically feasible. The research methodology of Task 2 is to formulate a series of region-specific case studies within a general recursive programming framework. The regional-national recursive model specified in this paper represents the intermediate stage of development of the Iowa Case Study. The Iowa model has been specified by a team of researchers including Dr. Earl 0. Heady, James Langley, Andrew Morton, and Burton English of the Center for Agricultural and Rural Development, Iowa State University, and Wen-yuan Huang and Klaus Alt of the Natural Resources Economics Division, U.S. Department of Agriculture. Work is continuing on the specification of various components of the Iowa model along with preliminary applications in accordance with the framework of FAP's Task 2

Virus infection and grazing exert counteracting influences on survivorship of native bunchgrass seedlings competing with invasive exotics

1.  Invasive annual grasses introduced by European settlers have largely displaced native grassland vegetation in California and now form dense stands that constrain the establishment of native perennial bunchgrass seedlings. Bunchgrass seedlings face additional pressures from both livestock grazing and barley and cereal yellow dwarf viruses (B/CYDVs), which infect both young and established grasses throughout the state. 2.  Previous work suggested that B/CYDVs could mediate apparent competition between invasive exotic grasses and native bunchgrasses in California. 3.  To investigate the potential significance of virus-mediated mortality for early survivorship of bunchgrass seedlings, we compared the separate and combined effects of virus infection, competition and simulated grazing in a field experiment. We infected two species of young bunchgrasses that show different sensitivity to B/CYDV infection, subjected them to competition with three different densities of exotic annuals crossed with two clipping treatments, and monitored their growth and first-year survivorship. 4.  Although virus infection alone did not reduce first-year survivorship, it halved the survivorship of bunchgrasses competing with exotics. Within an environment in which competition strongly reduces seedling survivorship (as in natural grasslands), virus infection therefore has the power to cause additional seedling mortality and alter patterns of establishment. 5.  Surprisingly, clipping did not reduce bunchgrass survivorship further, but rather doubled it and disproportionately increased survivorship of infected bunchgrasses. 6.  Together with previous work, these findings show that B/CYDVs can be potentially powerful elements influencing species interactions in natural grasslands. 7.  More generally, our findings demonstrate the potential significance of multitrophic interactions in virus ecology. Although sometimes treated collectively as plant ‘predators’, viruses and herbivores may exert influences that are distinctly different, even counteracting