Using long-term population monitoring data to prioritize conservation action among rare plant species

The decline and extinction of native plant species is a global conservation crisis, and there is a need for rapid prioritization of our conservation efforts. In the USA, the two main systems used to identify at-risk species, Threatened and Endangered (T&E) status and conservation status ranks by NatureServe (G- and S-ranks), are categorical and typically assessed with large-scale criteria, thus are not ideal to aid practitioners in developing priorities at smaller scales. Our goal was to develop a continuous risk assignment for plant species using monitoring data collected at a smaller scale so that limited conservation resources can be better prioritized among at-risk species. To do this, we modified a count-based population viability analysis to produce two regional, species-level viability metrics: a regional growth rate and a regional 50-y probability of extinction. Our validation exercises confirmed these metrics could reliability place 24 rare forb species along a continuous scale of viability. We identified nine species (37.5% of those analyzed) in need of conservation effort in northern Illinois. The challenges we faced developing these metrics and our solutions are discussed more generally to improve rare plant species monitoring practices. Overall, this method is an innovative expansion of the use of population size monitoring data to inform conservation beyond the population.