Transient dynamics in plant population models

Transient dynamics describe short-term responses to unstable conditions in population models. Although the theoretical potential of these short-term effects to change interpretation of model behavior has been demonstrated, it is unclear whether transient analyses will be relevant or useful in management applications. This dissertation explores the role of transient dynamics in plant populations based on long-term demographic data. Based on a survey of modeling results for plant populations in the literature, I found that theoretical indices of transient behavior greatly overemphasized the role of transient responses for the populations for which data were available. Transient indices were indicative of the variation in distance from asymptotic conditions that the models experienced; however, empirical data on long-term environmental variability was substantially closer to asymptotic conditions than theoretical measures. However, transient responses do play an important role in the variability that populations experience. Across nine perennial plant species, transient responses contributed more on average to variability in annual population growth rates than variation in vital rates alone. I also found evidence that transient responses may at times have a buffering effect on the variation that populations experience, by pushing the population in the opposite direction as demographic variation. These results demonstrate the importance of viewing transient dynamics and demographic variation as interrelated processes, with implications for both understanding population dynamics and in management applications. Finally, I explored the role of transient dynamics to assess the non-target impacts of herbicide use on population dynamics of Balsamorhiza sagittata, a native perennial forb in Montana grasslands. Using long-term monitoring data, I found that stage-specific effects of herbicide on Balsamroot demography, combined with episodic recruitment, lead to highly variable population demographic structures during the 10 year study period. My analyses suggest that timing herbicide use based on current population stage structures and mitigating changes to stage structure after spraying could help to minimize long-term impacts of herbicide use on long-lived perennial forbs like Balsamroot. More generally, my analysis demonstrated how information on current population status and specific timescales can be used to better inform management