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. 

The major objectives addressed in this research are: (1) Can complementary growth and flowering phenology of a native community resist invasion? (2) What are the underlying mechanisms responsible for this outcome? The novel aspects of this research are first, that species phenological functional group diversity is assessed independently from species diversity (numbers of species). Second, the native and invasive species chosen were specifically selected based not only on their phenologies, flowering either early or late in the season, but the natives are congeneric pairs also selected for their similar life histories and growth forms. Third, the invasibility of a native community is examined both when the invasive is established at the same time as the native community and when invasive is introduced into a native community that is already established. I predict an invasive that has a phenology that contrasts with the native community experiences less competition for resources, giving it an advantage in resource pre-emption, which is believed to be one of the most important factors in plant competition.
Results/Conclusions

Preliminary analyses conducted on a subset of the data of several species are currently available. The invasive Nepeta cataria showed a significant effect of treatment where plants with no neighbors flowered earlier than plants surrounded by native neighbors (Pearson Chi-square, p=.0075). Thus at this early stage it appears that an invasive’s flowering time is influenced by neighboring plants. Date of first flower in the native Coreopsis lanceolata is highly variable among treatments, but not significant. These preliminary results indicate that date of first flower and subsequently flowering periods and flower number may be influenced by the identity of neighboring plants. This suggests that plant community members can affect phenology, and thus alter any outcomes or relationships related to flowering. There are implications for community composition, species coexistence, plant mutualists, and herbivores.