Up and at ‘em: germination timing can be a key ingredient in invasion resistance.
Buonaiuto, D. M., & Wolkovich, E. M. (2023). Contrasting responses to climate variability generate seasonal priority effects between native and invasive forest herbs. Journal of Ecology, 111, 1711–1721. PDF.
Summary
Invasive plants are often characterized by rapid seed germination. Early germination may provide invaders with competitive advantage over slower germinating natives by giving them a “head start” in the race for resources (e.g., Wolkovich & Cleland 2014). However, the relative contribution of rapid germination vs. other intrinsic competitive traits to the success of invaders is poorly understood. Buonaiuto and Wolkovich (2023) investigated the link between temperature variation, germination timing and competitive interactions using two forest understory species of Eastern North America: the invasive Dame’s Rocket (Hesperis matronalis) and native Honewort (Cryptotaenia canadensis). They found that when the species germinated at roughly the same time the native honewort was the stronger competitor, but when Dame’s Rocket had a phenological head start of just 2-3 days, it was enough to secure its competitive dominance at the seedling stage.
Honewort seeds—and many native species—require cold stratification, or exposure to cool (0-5 C) temperatures, to germinate while Dame’s Rocket seeds—and many invasives—germinate rapidly under a wide variety of temperature conditions. By experimentally manipulating cold stratification levels, the authors were able to substantially alter the differences in germination timing between the species in their study, and consequently their competitive outcomes.
Because of these contrasting physiological requirements for cold stratification, climate change will likely exacerbate differences in germination timing between native and invasive species, increasingly causing delays for native germination in regions where warming reduces cold stratification.
Take home points
Rapid germination is a key trait that enhances the competitive ability of Dame’s Rocket, and likely other fast-germinating invasive species.
Reduced cold stratification due to climate warming leads to larger differences in germination timing between native and invasive species, while increased cold stratification, which is also a potential consequence of warming in some regions, leads to smaller differences in germination timing.
This climate-mediate difference in germination timing was the main factor influencing which species was the better competitor in this experiment.
Management implications
Increasing phenological diversity in native plant communities could build invasion resistance for restoration projects, especially natives that can germinate early in the growing season.
Keywords
Competition, Invasive Plant, Phenology (Shifting Seasons)