Botanical Assessment of Disturbed Urban Population of Threatened Gopher Tortoise (<i>Gopherus polyphemus</i>) Habitat in SE Florida During Drought.

Abstract

Gopher tortoises (<i>Gopherus polyphemus</i>) are threatened burrowing keystone ecosystem engineers indigenous to open uplands in the Southeastern United States. Perils to the species include habitat degradation and fragmentation, anthropogenic disturbances, predation, parasites, and disease. Problems are severe in the SE Florida study area due to coastal urban sprawl, confining the tortoises in small, scattered, unnatural pockets subject to novel stresses. The annual South Florida February to ca. late May dry season became a severe drought in 2025. The present project centered on the broad question of foodplant resilience through the drought. The tortoise-grazed areas host three dominant groundcover species, in order of abundance: non-native <i>Richardia grandiflora</i>, native grass <i>Paspalum setaceum</i>, and non-native sedge <i>Fimbristylis cymosa.</i> Key findings were as follows: 1. The most abundant and most-often grazed species, <i>Richardia grandiflora</i>, when tortoises were excluded, expanded despite the drought (from 39% to 49.5% mean coverage). Under combined drought and grazing, that species cover decreased slightly (42.5% to 39.4%). Tortoise-free, <i>Paspalum setaceum</i> declined slightly during the drought (32.7% to 27.1% mean coverage), and showed mixed results with little net effect exposed to drought and to grazing. Never observed to be grazed during the study, <i>Fimbristylis cymosa</i> formed a nearly monospecific lawn in a sizeable portion of the study area. During the drought, it mostly browned, retaining green rosette centers, and tortoise exclusion showed no discernable effect. With transition to late spring, however, with increased rainfall, tortoise exclusion allowed rapid competition from grasses among the <i>Fimbristylis</i> rosettes. Adjacent unenclosed grazing, by contrast, maintained the <i>Fimbristylis</i> lawn without increase in grass coverage. Conclusions are that the two chief "fodder" species, <i>Richardia grandiflora</i> and <i>Paspalum setaceum</i>, were robust to drought and grazing. The introduced <i>Fimbristylis cymosa</i> appears to be facilitated by selective grazing-suppressing grass competitors.