Using a comparative approach, the presented study explores the ecology of ten species of native New Zealand broom, Carmichaelia, and their vulnerability to competition and herbivory, with the aim of gaining a better understanding of the significance of introduced species as a threat to rare indigenous plants in New Zealand. In particular, the study focuses on the relationship between characteristics of the Carmichaelia species and their vulnerability, as well as on other factors influencing the significance of introduced species as a threat. To gain a better understanding of the ecology of the Carmichaelia species, their current habitats and associated plant communities were investigated using quantitative-descriptive methods in the field. The effect of competition with introduced plants was studied in two glasshouse experiments, differentiating above ground competition for light from below ground competition for nutrients and water. The experiments focussed on the early life-stage of seedling establishment of the Carmichaelia species. The impact of herbivory by introduced mammals was studied in four field-based exclosure trials, focussing on the effects on survival and reproductive activity of adult Carmichaelia plants. The results showed that the effects of competition and herbivory vary between the different species. Furthermore, they provided a set of species characteristics that can be used as indicators to predict the vulnerability of Carmichaelia to the impact of introduced species. These indicators provide a useful tool for threatened species management, as they allow the identification of the most vulnerable species as well as the most significant threat to each species. Furthermore, the indicators can be used to group species, combining those with similar vulnerability profiles, and therefore, likely similar management needs. However, the example of the Carmichaelia species also illustrated that the use of indicators for the vulnerability of threatened species is limited and needs to be combined with case-by-case studies to verify the actual significance of threats for each population of concern. The vulnerability profiles derived from species’ characteristics can be used to guide such site specific studies, ensuring they focus on the most relevant threat factors. This combination of the understanding of general patterns in the vulnerability of species with targeted species and site-specific studies will lead to increased efficiency in the conservation management of threatened plant species.