WEED SUCCESSION UNDER CONSERVATION TILLAGE - A HIERARCHICAL FRAMEWORK FOR RESEARCH AND MANAGEMENT

The awareness and adoption of conservation tillage is one of the most important changes taking place in agriculture today. There are, however, concerns regarding weed species shifts under conservation tillage. Under conservation tillage, shifts toward grass, perennial, wind-disseminated weeds and volunteer crop plants have been observed. Shifts in weed species composition may either represent long-term ecological succession or temporary fluctuations in species composition; few long-term studies have examined the ecology of these shifts in detail. Further studies are needed to identify mechanisms driving these shifts to determine whether they are fluctuational or successional and to develop more sophisticated management strategies. In this paper, we present a research approach for studying ecological processes such as competition within a hierarchical framework of all possible causes, processes, and defining factors related to weed succession under conservation tillage. Succession management strategies can be developed to act at the causal level in the successional hierarchy. Three primary causes are site availability, colonization, and species performance. Site availability may be controlled through ''designed disturbance'', while differential species availability may be regulated through ''controlled colonization'' and species performance may be regulated through ''controlled species performance''. In general, the goals of succession management would involve reducing populations of the weed species most likely to proliferate under conservation tillage. Comprehensive ecological research, within the hierarchical framework outlined here, would identify potential problems and enable management strategies to account for the numerous factors that may be influencing fluctuations and succession of weeds under conservation tillage.