Keeping Up with Conservation: Protecting Savannas Mint

Savannas Mint (Dicerandra immaculata var. savannarum) was historically known from one small natural population on private property in a housing subdivision in south St. Lucie County. Following construction of a house, the population was extirpated and the only natural population of this species no longer existed. However, several years ago the Rare Plant Conservation Program (RPCP) partnered with biologists at Savannas Preserve State Park to begin introducing protected populations of Savannas Mint into the park. These are now the only plants that exist outside of a small number of curated plants in the National Collection beds at the Gardens. Each spring, the plants at the park are tracked for survival and size, and new seedlings are counted. This work has helped us understand its average life span, growth rate, reproductive output, and other demographic factors that reflect a self-sustaining population of Savannas Mint.

We have also learned much about its habitat requirements. As a gap specialist, Savannas Mint requires a canopy to provide filtered sunlight to full sun, and requires about 60% bare sand in order for its seeds to germinate. An overgrowth of pines or oaks will result in too little sunlight for the plant to adequately grow, and too much leaf litter for seedlings to germinate and survive. Typically, the ideal conditions for Savannas mint and other species in its scrub habitat would be maintained by periodic wildfire, and a prescribed fire will soon be needed where the plants are currently growing, but the effect of fire on the plants is unknown.

The RPCP began a project in 2022, funded by the Florida Forest Service, to study just that. Through this project, an overabundance of sand pines were removed and fire breaks installed. Half of the population has been delineated to be part of an upcoming burn, and half of the population will be excluded. Plants in the ‘burn’ and ‘burn exclusion’ areas were counted and their size measured. Once the burn is performed, the population will be revisited to record survival, and next spring, seedling recruitment and size will be compared for both areas. Through this new project, not only is the habitat being improved but much-needed data on the response of this species to fire is being collected.

Article written by the Cheryl Peterson, Rare Plant Conservation Program Manager.