Characterizing the recruitment nature of weed species

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The core goal of my research program is to determine how and why weeds emerge when they do. The timing of seedling emergence is a prime determinant of species success and for weeds, the transition from seed to seedling represents a transition from the least to the most vulnerable stage in a plant’s lifecycle. The relative timing (versus crop plants) and the success of weed seedling emergence also determines the competitiveness of weed infestations, the potential for weeds to escape management, and the quantity and quality of weed seeds left to form persistent seed banks. In addition, emergence timing is also a key determinant of the geographic range of species and their invasive potential. Finally, time of emergence greatly impacts the ability of weed species (including escaped crop plants) to survive in unmanaged habitats including roadsides. This has implications for gene flow at the landscape scale and the effective segregation and coexistence of genetically modified (GM) from non-GM crops. Despite its fundamental importance, our understanding of why weeds emerge when they do remains poor. To-date in my program we have been working to document weed emergence timing and to gain deeper insight into the mechanics of emergence timing. Most recently we have shown that timing of flowering and seed shed can play a very significant role in determining what conditions seeds experience (including whether and to what extent they are buried) and that this, in turn, can determine timing of emergence. We use facultative winter annuals (FWA) as model species for this work and with the FWA, Canada fleabane, we were the first to document the effects of these factors (flowering and seed shed timing, and seed depth) on emergence timing. What is not clear is the extent to which observations on one weed species apply to other weed species and to what extent these effects increase fitness of certain individuals thereby impacting population performance (and weediness) in future generations. Our approach over the next 5 years will be to look forward in the life cycle of weeds (flowering timing and seed shed) in order to gain insight looking backward in the life cycle (recruitment and emergence timing) using facultative winter annual weeds as test species. This research will lead to a better understanding of the mechanics of weed emergence timing which in turn will aid weed management, weed risk assessment and the coexistence of GM and non-GM crops.