Decline of Euphorbia Garberi, a Federally Listed Threatened Species, and Shifts in a Coastal Plant Community at Northwest Cape, Everglades National Park, USA

A plant community's response to disturbance is often unpredictable, particularly when compounding environmental changes are involved. Similarly, an altered disturbance regime can be a significant driver of plant community shifts, including rare plant loss. In February 2020, we resampled plots on Northwest Cape (Everglades National Park, USA) originally established in 2007 to assess the status of a disturbance-dependent, federally listed species, Garber's spurge (Euphorbia garberi), as well as compositional shifts in its coastal grassland habitat. The survey occurred 2.5 y after Hurricane Irma (2017) and almost 20 y after the last known fire event (2004). We encountered a significant (86.5%) decrease in E. garberi individuals since 2007, corresponding with an overall increase in cover of all plant functional groups examined, notably trees and shrubs. A nonmetric multidimensional scaling ordination and SIMPER analysis determined a shift in species composition since the last survey, especially with the grasses Dactyloctenium aegyptium (a nonnative; dominant in 2007) and Schizachyrium sanguineum (a native; dominant in 2020) and woody plants. Notable among the latter are the native hardwood tree Piscidia piscipula and the invasive shrub Brazilian pepper (Schinus terebinthifolia), both of which threaten to accelerate successional trajectories and alter responses to future disturbances. We posit that in the absence of management intervention, the habitat will continue to deviate from grassland conditions that support E. garberi. Future activities to conserve this threatened species and its habitat should include frequent monitoring, increased prescribed fires, seed banking, and invasive species management.