Invasive plant species are a major threat to biodiversity. Predicting which species will become invasive, however, has proven to be difficult. There are few common characteristics among species that become invasive, or the habitats that become invaded. The role of plant phenology may be essential to understanding the success of invasive plant species, and its effects on competition between species requires more study. Temporal niche segregation has been shown in plant communities, and several studies have shown examples of how temporal separation of growth is important in the interactions between alien and native species.
In this field experiment I will assess the importance of growth and flowering phenology on competition between native and invasive species. The experiment consists of a target-neighbor design with native plant species (all herbaceous perennials of similar size) surrounding the target individual, which is an invasive species of early (Hesperis matronalis) or late (Nepeta cataria) flowering phenology. The natives surrounding the target are planted in different combinations so that they are all early-season, all late-season, or a mixture of both. Also, the natives in each experimental treatment are always members of the same four genera: Asclepias, Liatris, Helenium, and Coreopsis, as each genera was selected because it had both early- and late-flowering species. Phenologically-based functional groups in previous research often include species of varying life histories and growth forms. Since groups were based only on one shared characteristic (their phenology), there were large differences in characteristics among species in the same group. I have attempted to correct this issue with my rigorous species selection criteria.
Results/Conclusions
Frequent measurements (height, cover, number of leaves, flowers, and reproductive units) over the course of the 2008 and 2009 growing seasons will provide information regarding competition over time, and a subset of plants will be harvested at the end of both seasons to measure biomass. Since flowering time is correlated with resource uptake, species with similar phenologies would be expected to compete more intensely, and I expect biomass and fruit set will be lower than in an individual growing with natives of a different phenology. The frequent growth measurements will also reveal whether differences in growth among treatments are realized only when resource uptake is the greatest, or whether the competitive effects are more gradual. Already, the early-season natives are growing faster than their late-season counterparts, and their varying effects on the target invasive should be interesting.
