WEED SUCCESSION UNDER CONSERVATION TILLAGE - A HIERARCHICAL FRAMEWORKFOR RESEARCH AND MANAGEMENT

The awareness and adoption of conservation tillage is one of the most important changes taking place in agriculture today. There are, howeve r, concerns regarding weed species shifts under conservation tillage. Under conservation tillage, shifts toward grass, perennial, wind-disse minated weeds and volunteer crop plants have been observed. Shifts in weed species composition may either represent long-term ecological suc cession or temporary fluctuations in species composition; few long-ter m studies have examined the ecology of these shifts in detail. Further studies are needed to identify mechanisms driving these shifts to det ermine whether they are fluctuational or successional and to develop m ore sophisticated management strategies. In this paper, we present a r esearch approach for studying ecological processes such as competition within a hierarchical framework of all possible causes, processes, an d defining factors related to weed succession under conservation tilla ge. Succession management strategies can be developed to act at the ca usal level in the successional hierarchy. Three primary causes are sit e availability, colonization, and species performance. Site availabili ty may be controlled through ''designed disturbance'', while different ial species availability may be regulated through ''controlled coloniz ation'' 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 resea rch, within the hierarchical framework outlined here, would identify p otential problems and enable management strategies to account for the numerous factors that may be influencing fluctuations and succession o f weeds under conservation tillage.